Advanced Silage Corn Management 2004

Advanced Silage Corn Management: A Production guide for coastal British Columbia and the Pacific Northwest.

Editors: Shabtai Bittman and C. Grant Kowalenko

Publisher: Pacific Field Corn Association,
P.O. Box 365 Agassiz, BC V0M 1A0
© 2004 Pacific Field Corn Association
ISBN: 0-9685015-1-6

Individual copies of this publication may be purchased for $50 from the Pacific Field Corn Association. Bulk rates are available.

About the Publisher:
The Pacific Field Corn Association is a non-profit society registered in BC. Its mandate is to carry out the hybrid evaluation program and to promote research and education related to production of field corn and forage crops in BC. The association membership includes representatives from the dairy and beef industries, Agriculture and Agri-Food Canada, British Columbia Ministry of Agriculture and Food, University of British Columbia (Faculty of Agricultural Sciences), Canadian seed trade, and agri-business.

For information, please write to
PFCA,
Box 365, Agassiz, BC, V0M 1A0

or contact S. Bittman (Research Co-ordinator and Editor) at
tel: 604-796-1735
email: shabtai.bittman@agr.gc.ca

Chapter 1: Why a Book about Silage Corn?

Corn is one of the great world crops. A unique, warm-season, New World cereal-grass, corn is grown on millions of hectares around the world to feed mainly monogastric and ruminant livestock. This is grain corn. Corn for silage is largely a forgotten cousin in the corn world. Compared to grain corn, it is smaller in acreage, full of water, inherently unstable and variable and almost impossible to sell or transport.

But for ruminant producers, and most notably for dairy producers, silage corn is a crop like no other. Testimony to this are the near-heroic efforts to extend the range and uses of silage corn, breeding ever more rapidly maturing hybrids with vigorous cool-weather growth and even planting the crop under plastic in cool regions such as Ireland and Newfoundland.

There are also serious ventures to use whole corn plants as winter pasture (see Section 7)! What makes corn unique as a silage crop? High energy content, high digestibility, ease of ensiling, relatively stable and consistent quality, and of course, superior yields. No other crop offers all these advantages. Cattle farmers have long known the virtues of silage corn. But silage corn as a distinct crop has emerged only in the past decade or so when plant breeders started to identify genotypes with, not only good agronomic traits and grain yields, but also attributes of special importance for whole-plant silage use. These attributes include leafiness, stay-green leaves, stovers with low fibre concentration and high fibre digestibility, soft starch, and high whole-plant yield. In Section 1, a corn breeder describes how new corn hybrids are bred while several seed companies reveal their strategies for breeding silage-corn.

The quality of silage corn has improved, not only through breeding, but thanks also to a better understanding of crop maturation (Section 6), to new harvesting techniques such as silage processing, and to storage enhancement tools such as silage additives (Section 7). As the quality has improved, farmers have been increasing the proportion of corn silage in cattle rations. The nutritional attributes of corn (fibre and fibre digestibility, protein and fats) are also described in Section 7, as are potential problems with feed rations that are high in corn silage and health risks from mycotoxins. Some large cattle operations now contract production of silage corn or purchase the crop from speciality growers; in Section 7 you will find a method of valuing the silage corn crop based on its nutritional quality.

With silage corn emerging as a major crop in its own right, concerns have grown over the possible impact on the environment of growing this crop. Growing any corn presents some environmental risks, due to long periods with little or no soil cover after harvest, tillage practices that can lead to erosion, and the use of chemicals to control pests. Added to this are special concerns of producing silage corn, namely the absence of crop residue on the soil after harvest and, oftentimes, the use of high nutrient inputs in the form of animal wastes. Paradoxically, in a whole-farm context, silage corn can improve nutrient conservation by reducing the need for importing feed by improving the balance of nutrients produced on the farm (Section 2).

The many challenges of managing nutrients on silage corn fields are discussed in Section 2. For example, there are the benefits of injecting and incorporating manure to reduce ammonia loss to weigh against risks to water quality associated with below-ground slurry application. Providing enough P during early growth is a special challenge for corn growers, who must also understand the complex chemistry of P in manure so that they can comply with standards for protection of water quality, such as the Phosphorus Index. To manage nutrients effectively and safely, it is helpful to understand the role of each nutrient in the growing crop, the complexity of soil testing, and the practical side of manure testing. Matching corn with suitable winter cover crops can help to guard against nutrient runoff and soil erosion (Section 4).

Some of the information in this book was borrowed from studies on grain corn, because of a dearth of studies on silage corn. For example, the sections on tillage practices and soil compaction (Section 3) are based largely on studies on grain corn production, which is somewhat unfortunate because of the large difference in amount of crop residue for the two crops. Most of the information on pests (diseases, nematodes and weeds) was developed for grain corn but applies well to silage corn (Section 5).

‘Advanced Silage Corn Management’ might well have been titled ‘Perspectives in Silage Corn Production’. We did not write a primer for the beginner. We have not attempted to cover all topics, target all regions, nor to answer all questions. Rather, we have assembled the insights of a wide range of experts, working in diverse corn growing regions, on subjects of special importance to silage corn producers. Our goal was to stimulate silage corn enthusiasts with a unique collection of information.

Shabtai Bittman
C. Grant Kowalenko
September 2004
Agassiz, B.C.

Chapter 2: Breeding Corn for Silage

How Corn Hybrids are Developed

Corn, a tropical plant, was first domesticated approximately 8,000 years ago in Central America. Many different types of corn evolved with the help of indigenous people who were the first corn breeders.

Today, the ultimate goal of corn breeding is to improve the adaptation of corn to temperate and early season environments. Improved adaptation means higher yield and better quality. The development of a new corn hybrid is a slow and costly process. New hybrids must possess improved yield, standability, pest resistance and tolerance to various stresses. This means that the expertise of breeders, entomologists, pathologists, physiologists and many other specialists are required. Corn grain yields have increased in North America from approximately 1.3 t/ha (0.6 T/ac) in 1930 to 8.7 t/ha (3.9 T/ac) in 1994 or approximately 0.08-0.1 t/ha per year. This steady increase is due to a combination of improved hybrids, increased use of fertilizers, better weed control and higher plant densities.

There are five major steps in the development of a commercial corn hybrid:

1) selection and development of appropriate source germplasm
2) development of superior inbreds
3) testing of inbreds in experimental hybrid combinations
4) identification of a superior hybrid combination
5) multi-location testing of the pre-commercial hybrid
Finally, extensive seed production and marketing of all new hybrids is required.

To understand how a new hybrid is developed, a basic knowledge of corn pollination and breeding processes is required. The corn plant has separate male and female flowering parts (Fig. 1). The tassel is the male flower and produces pollen; the ear is the female flower. A typical hybrid corn ear consists of several hundred kernels attached to the cob or rachis and surrounded by a group of modified leaves called the husk. Each kernel starts as an ovule and has its own silk which grows out of the husk at the top of the ear.

When the tassel is fully emerged from the upper leaf sheath, pollen-shed will begin, usually from the middle of the central spike of the tassel and then spreading out over the whole tassel. Pollen grains are produced in anthers which open up under appropriate weather conditions. Pollen, which is only viable for 18-24 hours, is very light and can be carried considerable distances by the wind. Pollen shed from the tassel usually begins 2-3 days before silk emergence and can continue for several days thereafter, but will stop when the tassel is too wet or too dry.

The silks are covered with fine, sticky hairs that catch and anchor pollen grains. Within minutes after landing on the silks, the pollen grain germinates and a pollen tube grows down the silk to fertilize the ovule or potential kernel. This usually takes 12 to 28 hours. Under good conditions, all silks will emerge and be ready for pollination within 3 to 5 days. Unfavourable environmental conditions during pollination can have a great impact on grain yield. Since there is usually more than enough pollen (a given tassel can produce up to 5 million pollen grains), problems generally occur when there is poor synchronization between silk emergence and pollen shedding.

Corn with its separate male and female flowering parts is a naturally cross-pollinating plant. This means that ovules can be pollinated by pollen from neighbouring plants. Therefore, care must be taken in a breeding program to ensure that pollen from the appropriate tassel fertilizes ovules on the appropriate ear. This is usually achieved by hand-pollinating. As soon as ear shoots are visible in the leaf axils of a plant, a small paper ‘shoot-bag’ is placed over the shoots; this allows the ear to continue growing and the silks to emerge but prevents any pollen from falling on the silks (Fig.2).

When pollen shed begins, a paper bag is placed over the tassel and stapled at the base of the tassel to trap the pollen. The next day the tassel bag containing pollen is removed and quickly placed over the silks of a covered ear after removing the protective shoot-bag (Fig. 3). The tassel bag is pulled around the stalk, stapled and shaken so that the pollen grains fall on the silks (Fig. 4). A plant is ‘selffertilized’ (also referred to as selfing or inbreeding) when the pollen from a tassel is placed on the silks of the ear of the same plant (Fig. 5). A plant is ‘crossfertilized’ or ‘crossed’ when the pollen from a tassel is placed on the silks of a different plant. Of the millions of hand pollinations made by corn breeders, only a handful result in a superior inbred that will be used in a commercial hybrid.

     
  Fig. 3 Transferring pollen from tassels of male parent
  to silks of female parent.
  Fig. 4 Maintaining inbred lines.

 

Between 1850 and 1910, North American corn breeders developed higher yielding corn varieties by open-pollination. In this procedure, plants were allowed to shed pollen without covering silks, resulting in a mix of cross and self pollinated kernels on each ear. The best plants would be selected and their ears (usually the largest ones in the field) would be kept to use as seed the next year. The resulting populations were gradually improved for agronomic traits, but were very variable in plant height, ear height, maturity, etc., due to the random cross-pollinations.

In the 1920’s, the concept of hybrid vigour (heterosis) was discovered. If corn plants are self-pollinated for six or more generations, the plants become smaller and less vigorous due to inbreeding depression, but their traits become more uniform. At every generation, selection can be made for specific traits such as pest resistance, plant or ear type, ear size, etc. This repeated inbreeding produces an ‘inbred’ line of corn. We can save breeding time by getting two generations per year using winter nurseries in warmer climates.

An inbred is genetically uniform for all traits and will always breed true to form. Hybrid vigour occurs when we crosspollinate two inbred lines from different unrelated backgrounds (Fig. 6). The offspring of such a cross will have a larger-yielding ear and will be a more robust plant. It is also uniform for most traits. There are many theories to explain hybrid vigour, but this phenomenon is still not well understood. Note that if an ear of hybrid corn is self-pollinated, the resulting progeny will be variable in yield as well as in other traits. This is why farmers must buy their hybrid corn seed each year and should not plant the seed from a field of hybrid.

Development of inbreds takes about 75% of the effort in a corn breeding program. Most of the effort is spent evaluating inbreds by crossing to another inbred, which is called a tester, to see if it will produce a desirable hybrid. The process is called evaluating the combining ability of the inbred. The cross is called a testcross. The field performance of this testcross is extensively evaluated in replicated multi-location trials. Inbreds with superior testcross performance are advanced to the next generation. If we could select at the inbred level, i.e. if the performance of the inbred on its own could predict the performance of the hybrid testcross, we could considerably reduce expenses. In fact, this can be done for some traits such as earliness, plant height and some disease resistance but, unfortunately, not for yield. It is important to note that the seed sold to farmers is produced on small inbred plants. Therefore, besides having good combining ability, an inbred line must be easy to maintain and to cross in order to keep seed costs down.

The inbred lines used for commercial hybrids must be maintained by hand-pollination, a painstaking process (Fig. 4). For production of hybrid seed, inbred seed is planted in fields isolated from other corn by at least 200 m (600 ft). Hybrid seed is produced by planting the ‘female’ and ‘male’ inbred lines together in a field (Fig. 7).

The choice of which inbred to designate female and which to designate male depends on the ear and tassel characteristics of each; usually the female has higher yield and the male has better pollen production. The ratio of female to male rows varies among seed companies. Differential planting dates can be used to ensure synchronization between male and female flowering.

Female rows are detasseled mechanically or by hand shortly after the tassels have emerged from the uppermost leaf sheath and before they begin to shed pollen (Fig 8). This ensures that all pollen is from the male parent. Commercial seed-corn fields are normally harvested by a picker-husker and the husked ears are sorted to remove off-type ears. The ears are dried and shelled and the seed is cleaned and graded by size. Finally, germination is tested and the seed is treated with a fungicide before packaging.

Today, 80% of corn seed grown in North America is single-cross hybrid as described above. The remaining 20% of hybrids are double, three-way and modified (related-line parents) crosses. Three-way cross hybrids have only one inbred parent and are somewhat cheaper to produce.

The Industry Speaks

DEKALB CORN SEED

Genomic and biotechnology research will be the key to better corn performance. Biotechnology and genetic enhancement are powerful tools Monsanto uses to improve corn. Globally, 10% of all Monsanto sales are invested in research and 80% of that research is conducted on seed and trait development. Specifically, research is focused on identifying traits for insect and disease resistance, herbicide tolerance, enhanced food characteristics and processing quality that can be used to improve crops. We’re also working within the existing genome of the corn plant to identify genes and genetic combinations that enhance yield and performance through improved drought and cold tolerance, disease resistance and yield.

Drawing from Monsanto’s elite corn germplasm, our corn breeders focus on factors that influence yield. This means only hybrids with the highest ratings for early vigour, early flowering, disease tolerance and straw strength are candidates for further testing. Monsanto’s Canadian corn breeding team will oversee the testing of 11,000 experimental corn hybrids. These hybrids are developed across Eastern Canada and North America.

Grain and silage from advanced technology crops such as Roundup Ready, YieldGard Rootworm and stacked trait hybrids require channeling – the process of marketing approved grain to approved markets. Monsanto is committed to ensuring that growers have a market for new technology. Before advanced technology crops are sold commercially, they must have full feed and food approval in Canada, the United States and Japan.

Part of Monsanto’s Technology Development is to continue to test DEKALB corn hybrids under reduced tillage practices. DEKALB brand Reduced Tillage hybrids have been developed, tested and proven to deliver higher yields on reduced till soils that are often cooler and wetter due to crop residue on the soil surface. Each of 14 RT DEKALB corn hybrids has demonstrated superior emergence, vigour and disease tolerance, which delivers excellent results in reduced tillage environments.   RT DEKALB corn hybrids have demonstrated consistent performance, excellent early season emergence for a vigorous, fast start inthe spring even in cool, moist soils and they possess a superior defensive package of disease resistance and tolerance that stands tall against yield-robbing diseases.


HYLAND SEEDS

Francis B. Glenn, Ph.D.,
President of Glenn Seed Ltd.

The development of leafy silage corn varieties was an evolution of thought and germplasm that has led to a revolution in silage corn management. The use of blends and “dual purpose” varieties for silage is in decline.

Corn is bred at the inbred (parent of hybrid) level. For silage, the parent should have: good germination and seedling vigour in both good and cool conditions; rapid spring development to close the canopy quickly; large leaves and extra leaves; big ears with disease free kernels; soft kernels with less of the hard vitreous and more soft starch; flexible, non-rigid stalks; good leaf-disease resistance to keep the plant green and productive; and early flowering with a long grain filling period.

Through experience and farmer “feedback”, we have developed an “ideotype” or ideal hybrid. We have been selecting extra leaf and normal leaf number families with these traits for about twenty generations, so we now have a “stable” of inbred lines. In leafy types, we have found that low ear placement is

associated with less stiff stalks, more photosynthetic leaf area to feed the ear, less stalk breakage and root lodging because of a low centre of gravity. Selection for stalks that bend without breaking has resulted in stalks with lower lignin content (better digestibility) than grain hybrids. Such stalks would be inferior in a grain hybrid.

Leafy hybrids have more young leaves above the ear resulting in high sugar content in the stalk and leaves at harvest. Growers have told us that the fermentation of our leafy hybrids is rapid and the silage has a sweet fragrance. Farmers say the cows’ intake and milk production increases. Selection for

softer kernels has produced kernels that break up during harvest, facilitating rapid starch conversion to sugar. Farmers often comment that kernels are not seen in manure of cows fed leafy silage.

We have selected hybrids that have long kernel-fill, good leaf health and slow drying after the black layer stage. Our leafy hybrids stay in whole-plant moisture range of 60 to 70% for a longer time than do grain hybrids, giving farmers more time to harvest. We have also selected for high grain content by choosing lines with consistently large ears. We do not recommend these hybrids for dual purpose (both silage and grain production).

We conduct our yield trials at 69,000 plants/ha (28,000 plants/ac), because our research has shown that increasing population may give more yield under best conditions, but less grain and lower stalk digestibility under more adverse growing conditions. At this population, our leafy hybrids produce

large canopies, ensuring high silage yield and quality under dry soil conditions. Although leafy plants have a large leaf area, our leafy hybrids are selected to withstand drought. We yield-test new hybrids at several locations until we determine their climatic or maturity zone, and their ability to perform under stress.

We have conducted a huge amount of silage quality analysis in testing our screening and advanced varieties. We conducted a detailed comparison of different quality tests to determine the most useful quality testing procedure for silage hybrids. Our conclusion is that all techniques give very variable

results and that no technique gives a precise enough measurement on which to base hybrid selection. Currently we do not use any quality analysis in our hybrid selection.

Leafy silage hybrids have changed farmers’ views. A revolution in corn silage is happening and leafy silage hybrids are a big part of the revolution.


MYCOGEN SEEDS FROM DOW AGROSCIENCES

For over 15 years, we’ve been offering Silage-Specific™ corn hybrids that have defined and set industry standards. Bred to deliver nutritional feed quality and high silage yields, our award-winning lineup helps producers boost dairy and beef production. In addition, our local dealers help ensure that producers get sound silage management advice.

World-class research & development drives discovery
At Dow AgroSciences, we are continuing to evolve the development of forage hybrids to even higher levels. We are one of the few companies with the dedicated resources in place to conduct Silage-Specific™ corn hybrid seed and trait research and development. Our breeding and research facilities are located throughout the North American corn-growing region. All of our facilities provide the perfect breeding ground for hybrid and trait advancements that add real value to every ration. A broad distribution of research and breeding stations allows Dow AgroSciences to test hybrids and traits in a variety of growing conditions. We are continuously advancing our hybrid genetics and nutritional knowledge to maximize animal performance.

Get Silage-Specific™ corn hybrids for unsurpassed feed advantages
Better rations mean more milk or beef. That’s why Mycogen Seeds Silage-Specific™ corn hybrids are such assets for any operation. Our exclusive lineup includes TMF™ and FullTime Forage™ hybrids bred to create better rations to maximize production of dairy or beef cattle. Our forage hybrids provide many advantages:

  • High yields
  • Greater cell wall digestibility
  • Higher dry matter intake and total nutrient intake
  • Ability to utilize higher forage diets, which results in healthier animals, reduced feed costs and increased milk and beef production.

Utilizing our Forage Quality™ Evaluation Program to ensure quality
Mycogen Seeds Silage-Specific™ corn hybrids are the industry’s finest for many reasons. Bred specifically for silage production, they’re selected based on forage quality, yield and grain characteristics. Adhering to the most stringent standards set by our Forage Quality™ Evaluation Program (FQEP), we are able to evaluate each and every Silage-Specific™ hybrid to ensure it delivers top-quality forage. Take a look at the three key points of emphasis in our FQEP process:

1) Drawing on silage evaluations and trials for nutritional data.  Working with leading universities and USDA research facilities, Dow AgroSciences conducts yearly silage evaluations on nearly 10,000 samples. Each is thoroughly analyzed to assess cell wall digestibility, lignin content, whole-plant digestibility, non-fibre carbohydrates and other characteristics. They’re also compared head-to-head against competitive forage hybrids.

2) Measuring animal performance through in-vitro testing.  For the most accurate prediction of how hybrids will perform in an nimal, we measure silage quality through “in- vitro testing”. These detailed tests provide firm data on the digestibility and nutrient value of silage yielded from our Silage-Specific™ corn hybrids. These data allows us to confidently determine how animals will perform with our silage.

3) Tonnage Evaluation Plots help us review hybrid yields.  In order to truly understand the agronomic conditions where each hybrid thrives, we plant and harvest Tonnage Evaluation Plots (TEP’s) in leading dairy regions. From these plots, we’re able to assess silage quality and see how hybrids perform in a variety of environments.

“When you’re talking leadership in silage, you’re talking Mycogen Seeds from Dow AgroSciences.”


NK SILAGE HYBRIDS

“Maximizing feed value per acre”

Selecting and growing corn for silage is different than grain. Hybrid selection is the first step but optimum harvest moisture, chop length, ensiling and ration-fit play essential roles in realizing the total silage value.

Hybrid Selection
NK brand, Syngenta Seeds selects and rates silage hybrids based on a combination of agronomic characteristics, tonnage and feed quality characteristics. Hybrids designed for maximum beef production and profitability are high in whole-plant digestibility and starch content. Hybrids recommended for dairy are high in fibre digestibility, which results in increased dry matter intake for increased milk production.

NK also utilizes a ‘Ration Fit’ rating to assist in hybrid selection for dairy operations. Our strategy is to build the optimum diet formulation for maximum animal production while minimizing potential herd health concerns from excessive starch loads. Hybrids recommended for rations containing greater than 60% corn silage should be high in NDF (Neutral Detergent Fibre) with low starch and high fibre digestibility while hybrids recommended for rations with greater than 60% alfalfa are low in NDF with high starch and fibre digestibility.

If a portfolio of hybrids is required due to crop rotation or soil adaptability, selecting hybrids of similar forage quality characteristics and ration-fit maintains a consistent level of forage quality. The net results are:

  • Silage predictability
  • Silage consistency
  • Reduced diet reformulation
  • Reduced production swings

Production Recommendations
In general, silage planting recommendations are similar to those for grain corn. Considerations should be made for soil type, tillage and crop rotation. Final plant populations should be based on soil productivity and, at most, 5,000 to 10,000 plants/ha (2,000 to 4,000 plants/ac) greater than those recommended for grain. Maintain good fertility levels and be aware of any herbicide sensitivities.

Harvest Management
Harvest timing is critical for silage quality. Wholeplant moisture between 65-70% allows for maximum dry matter accumulation with minimal impact on digestibility (see Fig. 1). Chop length should be consistent (1.3 to 2.0 cm or 0.5 to 0.75 in) for optimum packing and fibre utilization. A storage structure that is filled quickly, packed and sealed with silage at optimum moisture levels, ensiles efficiently with reduced respiration losses, heating and spoilage.

Hybrid selection and base genetics make up only 20% of the quality story. Without good crop management, harvest timing, optimum storage and ration fit, even the best hybrid can produce disappointing results. It takes genetics and the total management package from planting to ration fit to realize true silage quality value.


PICKSEED

Since grain in the silage makes the greatest contribution of energy to the animal, some argue that the best silage hybrid is tall with high grain yields. Decades ago that might have been true, before plant breeders started selecting specific traits to put into grain hybrids, such as hard stalk rind enabling plants grown at high populations to resist lodging, and hard kernels with dense starch so that the grain would have high test weight and remain intact during harvesting. To improve yields without delaying harvest, breeders developed grain hybrids that silked late but dried down rapidly.

The current idea is that we need corn hybrids dedicated to silage use. “While excellent silage hybrids with high forage yield and high quality exist, dual purpose hybrids that are excellent for both silage and grain do not. This is because characteristics that make an excellent grain hybrid such as fast rate of kernel drydown and hard kernel texture are undesirable for silage production since they reduce the digestibility of starch in the grain. Kernels in corn silage should have high moisture and be of soft kernel texture to increase digestion. (Dr. M.S. Allen, Assis. Professor, Department of Animal Science, Michigan State University “Selection of Corn Hybrids for Silage- A nutritionist’s perspective.”)

It is important to think of silage corn in terms of forage and not grain production, and assess it in terms of high dry matter yields, palatability, and nutritive quality. At Pickseed, we believe that there should be “different horses for different courses” so we set out to develop distinctive grain and silage varieties. In the late eighties we began working with the “leafy” gene to develop silage hybrids with comparably high grain yields and plant size but more total leaves than traditional grain hybrids. The silage hybrids would also have high whole-plant dry matter yields at lower plant populations than conventional hybrids as well as soft starched grain. Our experience and observations are as follows:

  • The leafy types continue to initiate leaves in later growth stages and these younger leaves are higher in protein than older leaves.
  • The younger, healthier leaves produce extra carbohydrate, which is not stored in the grain (useless for a grain hybrid) but remains as soluble sugars in the stalk, to produce more palatable silage.
  • The leafy hybrids are huge and produce high dry matter yields with corresponding grain content, at populations of 59,000 to 69,000 plants/ha (24,000 to 28,000 plants/ ac).
  • Similar yields can be achieved by planting a conventional grain hybrid at higher plant populations but this would reduce the digestibility and crude protein of the silage while increasing the NDF and ADF. It is also an inefficient use of resources since sunlight, water and soil nutrients are employed to support non-productive portions of corn plants (e.g. additional roots would be needed in dry years) not to mention added seed cost.
  • The softer and larger kernels of the leafy hybrids fracture more readily during harvest and chewing, to reduce fecal starch.
  • The leafy silage hybrids although genetically early, tend to silk late since silking cannot occur until all the leaves have been initiated and these hybrids produce on average 3 to 4 more leaves than non-leafy hybrids of similar maturity. Although the grain moisture of leafy hybrids is high, wholeplant moisture is low, which is ideal for silage varieties.


PIONEER HYBRID

Dave Harwood, Research Coordinator, Johnston IA

Pioneer Hi-bred has been conducting specific research and development of corn hybrids for use as silage for the past 25 years. The result is a product line-up that leads the industry in bite for bite feed value and feed value per acre. In addition to having excellent nutritional characteristics, these hybrids have agronomic stability.

Pioneer’s dedicated effort to develop new silage products represents the industry’s largest such program. Conventional hybrid development continues with extensive multi-location evaluation for silage yield and quality. New techniques, however, are being deployed with the objective of increasing genetic gain for silage performance. These approaches include: improved nutritional characterization, associative breeding and transgenics.

The ability to make genetic gain for any characteristic is to a great degree a function of the ability one has to measure it. In the case of silage performance, a measurement is only valuable to the extent that it accurately and with adequate precision, predicts the way an animal will respond when fed the feed. Pioneer continues to address this important issue by continually refining the methods used to measure nutritional quality of corn silage at its world-class Livestock Nutrition Center in Iowa. This is done by staying abreast of the latest industry trends such as the use of the University of Wisconsin Milk 2000 equation for predicting nutritional value per ton and per acre. At the recent 2002 Cornell Nutrition Conference, Pioneer scientists introduced the next wave of nutritional evaluation that takes into account the site, rate and extent of forage digestion. Adopting this approach will further enhance Pioneer’s ability to make genetic gain for silage performance as realized by enhanced animal performance.

Associative breeding is a relatively new term that describes the concept of identifying the specific genetic components of a plant that contribute to specific characteristics. If one can make these sorts of associations, one can use the genetic information to identify desirable plants without having to grow and measure the plant at many locations. Pioneer is developing this technique to improve traits like the digestibility of the corn plant’s fibre. This approach can increase the rate of genetic gain for silage performance by greatly increasing the amount of genetic material that can be evaluated and the accuracy of the evaluation.

Transgenic technology is commonplace in North American corn production. The value of the application of transgenic technology to deliver traits from other species, like resistance to European corn borer and resistance to herbicides, is well understood. Perhaps less well recognized is the opportunity to use this technology to manipulate the expression of genes from within the target species. Pioneer researchers are investigating the isolation of genes native to corn that are responsible for characteristics valuable in silage hybrids. Through this approach it is hoped that the expression of these genes can be optimized to result in genetic gain for feed value of the wholeplant corn crop.

Advancing corn genetics for silage performance remains a high priority for Pioneer, recognizing the importance of corn for silage in the key corn production areas around the world. Pioneer is dedicated to delivering value to corn growers world-wide through improved plant genetics.

Chapter 3: Nutrient Management

Nutrient Management

Whole-Farm Nutrient Management

J. Oenema and J. Verloop
Plant Research International, Wageningen, the Netherlands

In the Netherlands, inputs of nutrients on dairy farms via fertilizers, legumes and purchased feed by far exceed the outputs in milk and meat. Eventually, the excess nutrients are emitted to the environment, a problem which is especially acute in sandy regions. Government policy aims at reducing these losses to ‘acceptable’ levels. Research is being carried out in a model dairy farm called ‘De Marke’, located in the eastern sandy area of the Netherlands, to generate information and explore opportunities for reducing losses. The objective of the ‘De Marke’ project is to design and operate an economically viable dairy farming system that meets strict environmental standards, taking into account societal objectives with respect to animal welfare, nature and landscape.

Dairy farming is characterized by the combination of plant and animal production within one farming system. In animal production, part of the nutrients from feed is ‘transformed’ into dairy and meat products while the remainder is excreted in manure. The manure is applied to the field as an input for crop production. The harvested crops are used as feed for the animals, thus closing the cycle. Improved nutrient management through the cycle is characterized by a higher proportion of the nutrients being transferred to products and lower losses to the environment.

Photo 1 ‘De Marke’ farm in the Netherlands (Wageningen UR).

Photo 2 Sampling corn silage at ‘De Marke’ farm in the Netherlands
(Wageningen UR).

Farming System

In order to design a suitable farming system for ‘De Marke’, first input-output relations were quantified, combining process knowledge and expert judgment. For the animal component of the system, this included the relation between milk production and feed requirements (both quantity and quality); for the plant component the relation between crop production on the one hand and nutrient (fertilizer) and water requirements on the other. On the basis of these relations various farm configurations were considered. The most interesting design from the research point of view was implemented in 1992 in the ‘De Marke’ farm. The farming systems on ‘De Marke’ are under continuous development (Table 1).

Table 1.  Characteristics of crops, animals and farm plan of experimental farm 'De Marke'.

 

1993

1996

1999

2002

Average '93-'02

Milking Cows #

82

77

77

77

78

Young Stock #

66

58

62

53

57

Stock density AU/ha (Au/ac)

1.9(0.8)

1.7(0.7)

2.0(0.8)

1.7(0.8)

1.8(0.7)

Milk Yield / cow (kg)

8005

8791

9175

8752

8632

Milk Yield / cow (lb)

17,611

19,340

20,185

19,254

18,990

Milk fat content %

4.39

4.31

4.05

4.33

4.3

Milk protein content %

3.49

3.47

3.44

3.35

3.4

Land Area ha (ac)

Grass

30.6(76)

29.2(72)

31.9(79)

31.9(79)

31.2(77)

Silage corn

13.1(32)

20.2(50)

14.9(36.8)

9.9(24)

13.5(33)

Ground ear corn silage

5.8(14)

7.1(18)

5.1(12.6)

4.7(11.6)

6.8(17)

Fodder beet

6.1(15)

0

0

0

1.5(4)

Triticale silage

0

0

0

8.4(21)

2.2(5)

Farm area

55.6(137)

56.5(140)

51.9(128)

54.9(136)

55.1(136)

*animal unit:milking cow = 1AU; young cow >1 year old = 0.439 AU; young cow

 

Land Use

The 55 ha (136 ac) of land comprise three parcel types:

• 11 ha (27 ac) of grassland (permanent pasture), located close to the farm buildings

• 30 ha (74 ac) (home parcel) – alternating three years of grassland with three years of corn

• 14 ha (35 ac) (field parcel) – alternating three years of grassland with five years of corn.

The parcels near the barns can be irrigated whereas the field parcel which is farther away from the farm buildings cannot be irrigated. Consequently, grazing intensity is higher on the permanent pasture and the home parcel than on the field parcel. There are several advantages for grass-corn rotation over continuous corn: soil organic matter content is maintained at a higher level than under continuous corn, with positive effects on moisture retention capacity and rooting; fertilizer strategy can be targeted to the rotation; weed problems are mitigated; and yields of corn are on average 10% higher in rotation than under continuous cropping.

Italian ryegrass planted between corn rows at ‘De Marke’
farm in the Netherlands (Wageningen UR)

A little more than half the land area is used for grassland; the remainder is now in use for corn (whole silage and ground ear-corn silage) and triticale silage. The proportion of the land used for corn and triticale is higher at ‘De Marke’ than on most commercial farms on sandy soils in the Netherlands.

Corn silage yields are consistently higher than those of grass (Figs. 1 and 2). Moreover, on the droughtsensitive soils of ‘De Marke’, less irrigation is required for corn than for grass (200 vs. 350 L of water/ kg dry matter or 12 vs. 20 gal/lb dry matter). Hence, a larger proportion of corn both reduces the usage of ground-water for irrigation and the requirements for purchase of feed. Furthermore, a high proportion of (energy-rich and low protein) corn in the feed ration results in lower nutrient contents in manure.

Figure 1. Average net yields of grass (excluding grazing- and harvest losses) and silage corn (kg dry matter per ha) at ‘De Marke’ in the period 1993-2002 (for lb/ac, multiply by 0.9)

Part of the corn crop is harvested as ground ear-corn silage, a product that has proven its value as a substitute for purchased concentrate. The ground ear-corn and the corn stover are harvested at the same time but separately with a specially designed harvester. Because corn stover contains little energy, protein and potassium, but high levels of cell walls which are partly digestible, it is an excellent component (with fall grass silage) for dry cow and pregnant heifer rations.

Since 2000, some corn was replaced with triticale (for silage) under-seeded to a grass/clover mix in the final year of both rotations (Table 1). This change was made because it was felt that triticale would lower nitrate concentration in groundwater relative to corn.

Manure and Fertilizer

Storage, handling and timing of application of manure all aim at maximizing utilization of nutrients by the crop in order to minimize use of chemical fertilizer. For phosphorus, the principle of equilibrium manure application (i.e. total nutrient application in manure should not exceed nutrient export in crops) is used. For the crop rotations, the equilibrium rate is based on a full rotation cycle.

The basic application rates for N are 250 kg/ha (230 lb/ac) for grass and 100 kg/ ha (90 lb/ac) for corn, including the inorganic N in the slurry. Fertilizer rates are determined per field, taking into account the crop, soil moisture-supplying capacity, phosphorus status of the soil and N-supply from ploughed-in sod and green manure. Slurry rates are based on crop N requirements for corn and crop P requirement for grassland. About 80% of all slurry is applied to grassland. Fertilizer application starts on March 1 for grassland and just before sowing (early May) corn.

Cover (relay) Crop

A disadvantage of corn is that its nutrient uptake virtually ceases after the beginning of August. In late summer and autumn, mineralization adds to the soil N that the crop doesn’t take up at this time. To solve this problem, a catch crop of Italian ryegrass is sown between the corn rows, about six weeks after sowing.

Following (early) corn harvest, the ryegrass continues growing and takes up the residual N. Such a catch crop is very effective in reducing environmental impact and is easy to include in farm management.

Photo 4 & 5 Harvesting corn underseeded with Italian ryegrass and growth of cover crop in fall at ‘De Marke’ farm in the Netherlands (Wageningen UR)

Yields

Yields of grass and silage corn in the period 1993-2002 were above expectation (Fig. 1) but year-to-year variation was very high (Fig. 2). Corn yields were mainly determined by soil moisture status during grain set. Drought at any other time reduces yield of grass more than corn so low annual grass yields resulting from moisture deficits can coincide with reasonable corn yields. In the years with favorable moisture supply (1993, 1997, 1999, 2000, 2001 and 2002), average grass and corn yields exceeded 10,000 kg/ha. In contrast, spring of 1998 was extremely wet, which resulted in high mineral N losses, especially in corn, and consequently low yields.

Yields of the ground ear-corn silage were higher than expected, and those of stover lower, but stover yields have increased in recent years since the performance of the harvester was improved.

Figure 2. Year-to-year variation in net yields of grass (excluding grazing- and harvest losses) and silage corn at ‘De Marke’ (for lb/ac, multiply by 0.9)

Nutrient Flows

The total nutrient cycle comprises the components herd, manure, soil and crop (roughage and pasture grass). These components can be considered the links in the cycle. The nutrient balance between components shows relative efficiency of nutrient utilization, which helps identify weakest links. Fig. 3 shows the average N cycle for ‘De Marke’ for a period of 10 years (1993 - 2002).

Figure 3. Nitrogen cycle (kg N per ha) of experimental farm ‘De Marke’ averaged over the period 1993 - 2002 (for lb/ac, multiply by 0.9).

The surplus nutrients of the farm can be partitioned into ammonia volatilization and denitrification (N only), and accumulation in soil organic matter, runoff and leaching (N and P) (Table 2). The absence of surface water at ‘De Marke’ means that runoff does not play a role. Average annual surplus over the period 1993 - 2002 was 144 kg N /ha (130 lb/ac) and 3 kg P2O5 /ha (2.5 lb/ac). Since 2000, some changes have been implemented in the design of the farming system (less grazing, lowering the fertilization level) resulting in a lower N surplus in 2002 of 117 kg /ha (105 lb/ac).

Comparison of the nutrient balance of ‘De Marke’ with that of the ‘current average’ farm (on sandy soil in the middle of the 1990s with a milk quotum equal to that of ‘De Marke’) shows that at ‘De Marke’ less fertilizer and feed were purchased. In other words, the realization of very high nutrient utilization efficiencies in animal nutrition and crop cultivation allows similar milk production at much lower input levels. This can be considered the most important aspect of the farming system ‘De Marke’.

 

Table 2. A comparison of nutrient balance (N and P2O5) of the ‘De Marke’ averaged over the period 1993 - 2002, and for the year 2002, with the nutrient balance of the average farm in the Netherlands (see text for explanation) in the middle of the 1990s (for lb/ha, multiply by 0.9).

Nitrogen (kg N/ha)kkk

Phosphate (kg P2O5/ha)

De Marke

Average

De Marke

Average

 

93-02

2002

Dutch Farm

93-02

2002

Dutch Farm

INPUT

 

 

 

 

 

 

Concentrates

86

87

125

28

29

49

Roughage

8

0

20

3

0

2

Chemical fertilizer

64

35

242

1

0

41

Organic manure

0

0

50

0

0

29

Biological N fixation

11

27

0

 

 

 

Animals

0

0

0

0

0

 

Deposition

49

49

49

2

2

2

Miscellaneous

5

5

0

0

1

0

Total

223

203

486

34

32

124

 

 

 

 

 

 

 

OUTPUT

 

 

 

 

 

 

Milk

66

64

64

24

23

24

Animals

9

8

14

6

5

9

Roughage

1

0

0

0

0

0

Organic Manure

1

0

0

0

0

0

Total

77

72

78

30

28

34

Changes in Stocks

2

14

0

1

1

0

Surplus

144

117

408

3

3

90

 

Essential Elements in Corn

A.M. JOHNSTON¹  and R. DOWBENKO²

¹ Potash & Phosphate Institute of Canada, Saskatoon, Saskatchewan; ² Agrium Inc., Calgary, Alberta.

Plants require 16 nutrient elements for their growth. Three of the nutrient elements (carbon, hydrogen and oxygen) are derived from air and water. The other 13 are normally obtained by the plant from the soil or applied as amendments (fertilizer, manure, etc.) if they are inadequate or unavailable in the soil. Nitrogen (N), phosphorus (P) and potassium (K) are required by plants in relatively large quantities and are most frequently required as soil amendments for maximum crop growth. In fact, the first three numbers on fertilizer products (e.g., 18-18-18) are the percentages of N, P (expressed in oxide form as P2O5) and K (also expressed as an oxide as K2O). For this discussion, these three nutrients are grouped as “primary” nutrients. Sulphur (S), calcium (Ca) and magnesium (Mg) are required by the plant in moderate quantities and are grouped as “secondary” nutrients. The remaining seven nutrients are grouped as “micronutrients” as they are required in small quantities or applied to crops less frequently. Comparative amounts of these nutrients are shown in Table 1 for a corn crop yielding 18.7 t/ha dry matter. This constitutes the amounts of these nutrients that would be removed from the field if the corn is used as silage.

Table 1.  Comparison of Quantities of 13 Essential Nutrients typically found in a Corn Crop Yielding 18.7 t/ha dry matter (9 T/ac; for lb/ac multiply by 0.9)

Nutrient

kg/ha

Nutrient

kg/ha

Nitrogen (N)

240

Chlorine (Cl)

110

Phosphorus (P)

44

Iron (Fe)

3

Potassium (K)

200

Manganese (Mn)

0.6

 

 

Zinc (Zn)

0.6

Sulphur (S)

34

Copper (Cu)

0.2

Calcium (Ca)

45

Boron (B)

0.1

Magnesium (Mg)

56

Molybdenum (Mo)

> 0.1

Primary Nutrients

Nitrogen (N)
Nitrogen is necessary for making chlorophyll and is directly involved in photosynthesis.  Each molecule of chlorophyll contains four N atoms surrounding a magnesium (Mg) atom at the core.  All proteins and enzymes contain N in the form of amino acids. Nitrogen is also a component of vitamins.  Increasing N supply enhances plant production of carotene (a precursor to vitamin A), the B vitamins (riboflavin, thiamin, and nicotinic acid), and cytokinin (a plant growth hormone).

Nitrogen deficiency in young corn reduces chlorophyll production and causes the entire plant to be pale and yellowish green, with spindly stalks. Later, V-shaped yellowing may appear on the tips of leaves. Since N is mobile within the plant, yellowing begins on the older lower leaves and progresses up the plant as the N is moved up to the newer growing tissues.  When N is deficient, the production of chlorophyll and enzymes for photosynthesis is limited, slowing the supply of energy and reducing plant vigour.  Also, the root system becomes less prolific, slowing uptake of other nutrients (Table 2).  Note the small increase in K concentration.  Nitrogen tends to increase K uptake, but only when soil K levels are high.  When soil K is low, added N stimulates growth dilution of the K in the plant.

Corn takes up N as inorganic nitrate (NO3 -) and ammonium (NH4+) ions.  Ammonium is rapidly converted to nitrate in most soils, therefore, most N uptake is in the nitrate form.  However, certain corn hybrids prefer ammonium. Taking up N as ammonium saves the plant a great deal of energy which is required to convert nitrate to ammonium before it is used for protein synthesis. Too much ammonium can be toxic to plants.

 

Table 2.  Example of how nitrogen application can increase the
concentrations of other nutrients in ear leaf at silking or anthesis
(adapted from Illinios and Ontario university data)

Nutrient

Zero N

With N

Increase

Nitrogen (%)

2.45

3.20

31%

Phosphorus (%)

0.22

0.29

30%

Potassium (%)

1.93

1.96

2%

Calcium (%)

0.88

0.90

2%

Magnesium (%)

0.43

0.48

12%

Zinc (ppm)

20

29

45%

Boron (ppm)

9

12

34%

Copper (ppm)

8

12

44%

Grain Yield, kg/ha*

5707

7212

1505 (26%)

Phosphorus (P)
Although P is not present in the plant in large quantities, it is involved in many critical metabolic functions that occur in the plant’s cells. It influences the activity of many enzymes, is a carrier of energy within the cell and can also store energy as in phytin. Because of the ability of inorganic P compounds to dissociate into various forms, it is an important component to buffer the pH within the cell. It is a component of a variety of organic molecules, such as phospholipids, which are involved in a range of activities and functions. Phosphorus is important for photosynthesis, maintenance and transfer of genetic code, development and growth of new plant cells, and germination and formation of seed.

Phosphorus deficiency usually appears when plants are young. Young plants develop shoots faster than roots, particularly when the air is much warmer than the soil, causing a high P demand per unit of root length (See Applying Starter Fertilizer section). Often soil solution P concentrations are inadequate to meet these high requirements, leading to buildup of carbohydrates and sugars, which causes a dark green or reddish-purple leaf color. Extreme symptoms include spindly stalks which are either barren or have twisted ears with incomplete grain fill. Inadequate P, even in seedlings, frequently delays maturity. Phosphorus enters the corn plant through root hairs, root tips, and the outermost layers of root cells. Beneficial fungi, called mycorrhizae, also enhance P uptake (see Early Phosphorus Nutrition in Corn and the Role of Mycorrhizae section).

Phosphate fertilizers typically contain soluble forms of P that are immediately available to plants. However, soluble P in soil reacts with iron (Fe), aluminum (Al), calcium (Ca), and magnesium (Mg) forming new compounds that are less plantavailable, a process called “fixation.” Maintaining the soil pH between 6 and 7 usually maximizes P availability. The fixed P may eventually become plant-available but this can take months or years. Phosphorus is also contained in soil organic matter and manure, and is gradually released as plant-available forms in a process called mineralization. The P used by a corn crop therefore comes from fertilizer and manure applied for that crop and from such materials applied in previous years.

Potassium (K)
Potassium is involved in photosynthesis, conversion of sugars into energy storage compounds such as starch, conversion of amino acids into proteins, the activation of over 60 enzyme systems, and regulation of leaf pore function. In addition to these factors increasing yield and quality of silage corn, K improves disease resistance, N use efficiency and water utilization by preventing excessive respiration. Potassium in cell water helps protein molecules keep their conformation or shape and maintain their activity.

Potassium deficiency is not always evident visually and can be masked by other crop stress symptoms. Look for leaf discoloration, with older leaf edges turning yellow then brown while the midrib stays green. Conditions that may indicate K deficiency include: thin stands due to poor seedling vigor and disease, slow growth rate and poor N response due to reduced enzyme activity, injury due to stress and leaf diseases, delay of silk emergence by up to one week, stalk lodging due to breakdown of internal stalk tissue and invasion by stalk rot, and chaffy, loose-grain ears and poor grain fill near the ear tip.

Potassium is provided both from the soil’s nutrient reservoir and from fertilizer. The amount of K needed by a corn crop is very site-specific, varying between fields and within fields. The fertilization program should consider several factors that affect availability and uptake of K: soil analysis, nutrient requirements for the target yield, previous crop management practices, cultural practices (tillage) and climatic conditions which interact with K availability and uptake by corn. Soil testing provides a measure of the soil’s K nutrient reserves and an estimate of likely crop response to applied fertilizer. Because K is relatively immobile in most soils, no more than 50 to 60% of fertilizer K can be absorbed by corn during the season of application, even when soil supplies are low and growing conditions are favorable. In the long term, K rates should be such that soil test K is built to and maintained at levels that ensure maximum economic yields.

Timing of Potassium Uptake The relative amounts of nutrients taken up at each stage of growth will differ and is best shown by uptake of major nutrients and dry matter production during 25-day periods which represent 5 different stages of growth (Table 3). Nearly 75% of the nitrogen, 65% of the P and 85% of the K used by the crop are taken up by the time the ears are tasseling, which is usually about the mid-point of the growing season.

Corn takes up very little N in the first month after planting, but once the crop reaches a height of about one foot uptake becomes very rapid (Table 3). Nitrogen supply before silking can affect the number of kernels set in the ear. Most corn hybrids take up less than 30% of their total N after silking. However, newer hybrids with “stay-green” and multileaf traits take up 40% or more of their N after silking. Removing nitrate from the soil late in the season reduces the amount left in the soil that may be lost over winter (see Post Harvest Nitrate Test section).

When does corn need K? Every day. The amount increases by growth stage until seedlings become fully mature plants. Potassium must be available early for optimum corn development because over 70% of the total K requirement must be in the plant by silking stage, or about 65 days after planting (Table 3). The peak rate of absorption per day occurs just prior to silking. Uptake is slower but not less important during the critical period of grain formation. Uptake per unit of root length is also an important expression of K requirement. Corn grows shoots faster than roots during early growth stages. Therefore, soils sometimes fail to meet the high requirement of each root segment and K deficiency results during the vegetative growth stage. For these situations, K supplemented by a side dress application prior to silking can improve crop productivity.

Balancing N and K The right balance of N with K improves grain and silage yields, boosts forage quality, improves input use efficiency and provides better protection of groundwater. For example, application of 160 kg/ha (145 lb/ac) of K improved the quality of N-fertilized corn silage by reducing fermentation losses by 5 percent, increasing the carotene content six-fold and nearly tripling total protein production. Application of K also improved N-use-efficiency, helping the corn plants capture nearly 25 percent more N (Table 4) thus lowering the risk of unused N moving down to ground water.

Table 3. Example of the Pattern of Uptake of Primary Nutrients by a Corn Crop

Growth Stage

Seedling

Rapid Vegetative

Silking

Grain Fill

Maturity

Total

(days)

(1-25)

(26-50)

(51-75)

(76-100)

(101-125)

(1-125)

Amount of growth and nutrient uptake during each growth stage (kg/ha)¹

Dry Matter

524

3,597

6,369

6,745

1,499

18,734

Nitrogen (N)

19

84

75

48

14

240

Phosphorus (P)

2

12

16

11

3

45

Potassium (K)

18

88

62

28

4

200

Proportion of uptake during each growth stage (%)

Nitrogen (N)

8

35

31

20

6

100

Phosphorus (P)

5

27

36

25

7

100

Potassium (K)

9

44

31

14

2

100

 

Table 4.  Example of the Influence of K on Corn Grain Yield and N Efficiency

K applied

Grain

N-Efficiency

N Uptake

(kg/ha)¹

(kg/ha)¹

(kg grain/kg N)

(kg/ha)¹

0

8,340

49

194

50

8,780

52

204

100

10,347

62

240

¹ For lb/ac multiply by 0.9

Secondary Nutrients

Sulphur (S)
Sulphur is required by plants for the synthesis of certain amino acids (cysteine and methionine), protein formation, and photosynthesis. Symptoms of S and N deficiency are often confused. Sulphur is immobile within the plant and does not readily move from old to new growth. Hence, with S deficiency, yellowing symptoms first appear in younger leaves, unlike N deficiency, where yellowing appears on the older leaves first. Both N and S deficiencies may appear as stunted plants, with a general yellowing of leaves.

Sulphur has been overlooked in many soil fertility programs. But recently, increased crop yields, reduced deposition of atmospheric S, increased use of high analysis fertilizers, and greater awareness are contributing to increased requirements for S fertilizer applications. Most S in the soil is bound in the organic matter and cannot be used by plants until it is converted to the soluble sulphate (SO4 2-) form by soil bacteria (mineralization). Corn growing on deep sandy soils with low organic matter and little clay in the subsoil will likely respond to applications of 10 to 20 kg/ha (9 to 18 lb/ac) SO4-S with pre-plant fertilizers, or with the first N side dressing. If elemental S is used, it may be necessary to apply more than 50 kg/ha (45 lb/ac) in autumn so that at least 10 to 20 kg/ha (9 to 18 lb/ac) of SO4-S is available by early spring.

Calcium (Ca)
Calcium activates growth-regulating enzyme systems, and is needed for cell wall formation and cell division. It improves the root absorption and translocation of other nutrients, and contributes to improved disease resistance. Calcium is taken up by plants as the divalent cation, Ca2+. Along with Mg and K, Ca helps to balance organic acids, which form during cell metabolism.

Symptoms of Ca deficiency are seen in the new growth because Ca is not readily translocated. The symptoms include slowed root development and slowed new leaf growth, with leaf tips sticking together. Calcium deficiency is not likely to occur when the soil is properly limed (See Liming for Optimum Corn Production section). In acidic soils, crop growth is restricted more by toxic concentrations of aluminum and manganese rather than a Ca shortage. Deficiencies are most commonly observed in acid, sandy soils where Ca has been leached by rain or irrigation water, or in strongly acid peat and muck soils with very low soil Ca content.

Magnesium (Mg)
Magnesium, as the central atom in the chlorophyll molecule, is needed for photosynthesis. It is also required for cell division, protein formation, P metabolism, plant respiration, and the activation of several enzyme systems. Magnesium is taken up by the plant as the divalent cation, Mg2+. It is mobile and easily translocated from older to younger tissues.

When deficiencies occur, the older leaves are affected first with a loss of color between the leaf veins, beginning at the leaf margins or tips and progressing inward. Leaves appear striped, with yellowing and browning of leaf tips and edges as symptoms progress (which may be confused with K deficiency), resulting in less photosynthesis and overall crop stunting. Small amounts of Mg can be applied to growing crops through foliar fertilization to correct or prevent developing deficiencies, but the preferred approach is to soil-apply the required amounts before planting.

Plant S, Ca and Mg diagnosis
The best way to diagnose S, Ca and Mg deficiencies is with plant tissue analysis, using specific tissues at different growth stages (Table 5).  In the case of S, ratios of total N to total S range from 7:1 to 15:1. Wider ratios may point to possible S deficiency, but should be considered along with actual S and N concentrations in making diagnostic interpretations.

Table 5. Sufficient concentrations of S, Ca and Mg in corn tissues
at different growth

Tissue Selected

S (%)

Ca (%)

Mg (%)

Whole plants less than 12 inches tall

0.15-0.50

0.30-0.70

0.15-0.45

Leaf below the whorl prior to tasseling

0.15-0.50

0.25-0.50

0.13-0.30

Ear leaf at initial silking

0.21-0.50

0.21-1.00

0.20-1.00

Micronutrients

The function of any nutrient is the origin of the symptom of its deficiency. A listing of the specific functions of each micronutrient (Table 6) helps to illustrate why the detection of a deficiency in corn is often difficult. For example, Fe, Mn and Cu are each involved with chlorophyll formation and a shortage will likely trigger a visible yellowing of plant tissue. Zinc, B, and Mo are each involved with protein formation, which is less likely to trigger a visible symptom, although leaves of zinc deficient plants tend to have yellowish interveinal striping.

Table 6.  The functions of micronutrients in plant development

Plant Growth Function

Cl

Fe

Mn

Zn

Cu

B

Mo

enzyme systems

 

X

X

X

X

 

X

protein formation

 

X

 

X

X

X

X

hormones and cell division

 

 

 

X

 

X

 

chlorophyll formation

 

X

X

 

X

 

 

disease resistance

X

 

 

 

 

 

 

photosynthesis

X

X

X

 

 

 

 

N, Fe and/or P metabolism

 

X

X

X

X

X

X

crop maturity

X

 

 

 

 

 

 

seed formation

 

 

 

X

X

X

 

sugar/starch translocation

X

 

 

X

 

X

Midwest U.S. researchers report that the sensitivity of corn to micronutrient deficiency is low for B and Mo, medium for Cu, Fe and Mn and high for Zn. Liming a strongly acidic soil to a pH level of about 6.0 to 6.5 impacts the availability of all micronutrients except Cl; Fe, Zn, Cu, B and Mn become less available to corn while Mo availability actually increases. Soils high in organic matter are often in need of Cu and B. Alkaline soils, that are also high in P, tend to be responsive to applied Zn. Sandy soils are more likely to be in need of micronutrients than soils high in clay content. Cold, wet soils often trigger Zn deficiency in young corn plants. Land leveling or removal of higher organic matter surface soils also triggers a shortage of Zn. Dry soils late in the season can lead to inadequate B absorption by corn roots.

The total concentration of a micronutrient in the soil is usually a poor indicator of its availability to the corn plant. For example, considerable Fe and Mn might exist in a soil, yet be limiting to plant growth because the nutrients are in a form unsuitable for absorption by roots. The content of B, Zn, Cu or Cl in soils might range from a few to several hundred kg/ha (lb/ac) and adversely affect plant growth as either a deficiency or toxicity. Thus, micronutrient management for high yield corn production should include consideration of the conditions regulating their availability—soil acidity, soil temperature and moisture, genetics, and interactions with other inputs.

Excess concentrations of micronutrients in plants can also be of concern for corn growers. The boundaries for deficiency and excess are close for B, Cu and Zn. Excess levels of Fe and Mn are alleviated by liming acid soils. Excess levels of B, Zn or Cu are seldom a problem in corn production. Occasionally, an excess of Cu or Mn will inhibit Fe metabolism and vice versa.

Soil Testing

Determining Nutrients Available in Soils

C.G. KOWALENKO
Agriculture and Agri-Food Canada, Agassiz, British Columbia

The amounts of nutrients that soils contribute to growing crops vary considerably, and amendments such as fertilizer or manure are usually required to obtain high yields. Soil testing is the best currently available option to predict how much and what types of nutrients need to be supplied for a specific field. Although soil test values imply a great degree of reliability, many factors influence their effectiveness for predicting nutrient application requirements. Nutrients are stored in the soil in a variety of complex organic and inorganic forms differing in availability to the crop. Soil tests involve extraction of soil samples with a chemical solution followed by a quantification of nutrients in the solution. The chemical extraction is expected to reflect the amount of nutrient that would be available to the crop. In fact, these extractions have limited ability to simulate plant available nutrients for soils of widely different characteristics and the test that is selected is a compromise for a wide range of soil, weather and crop combinations. Soil tests are based on statistical correlations rather than a defined biological relationship.

General Issues

There are three steps to effective soil testing: sampling and sample preparation, analysis of the sample, and interpretation of the analysis results.

Sampling and sample preparation

When to sample: Time of sampling depends on how the test will be used; for predicting how much nutrient should be added prior to planting, for evaluating the agronomic and environmental performance of nutrient management practices, or for diagnosing a specific crop nutrient problem.

Sampling just prior to planting is recommended for predicting how much fertilizer is required. Sufficient time must be allowed for completing the soil test and for purchasing the recommended fertilizer. Sampling earlier, such as the previous autumn, must be limited to those situations where the nutrient does not change after testing and before applying the nutrients. For example, in south coastal British Columbia where winters are wet and mild, most nutrients measured by soil tests will change over the winter, so sampling close to planting is best (1).

Post-harvest soil sampling is useful for assessing the amounts of available nutrients that were not used by the crop, which is helpful for both agronomic and environmental purposes. This information can be used to adjust management practices (feed-back information) or to monitor long-term trends of nutrients in fields.

Sampling for diagnosing specific nutrient problems is best done when the problem is first observed.

Where to sample: Natural variability of soil test values may be up to 30% in fields that appear uniform (1). Land leveling, banding fertilizers or uneven manure and differential tillage further contribute to variability. To obtain a sample that represents the average nutrient supply in a field or portion of a field, samples from numerous (15 or more) locations should be taken and blended into one sample. Fields where nutrients have been banded require even more samples (2). Unrepresentative areas that can skew results should be avoided or sampled separately.

With the recent advent of yield monitors on harvesting equipment, geographic positioning systems and variable-rate fertilizer applicators, grid sampling of fields with chemical analyses on each sample is becoming more popular (precision agriculture).

How to sample: Depth of sampling depends on mobility of the nutrient and purpose of the test. One approach is to sample to the depth of the majority of root exploration, which in most cases would be the top 15-30 cm (6-12 in). Alternatively, soils are sampled to the depth of cultivation because the soil is mixed and more uniform and most roots are in this zone. Deeper sampling may be required for mobile nutrients with successive depth samples kept separate for analyses and interpretation.

The individual samples from the field that are combined into one to represent the entire field should be the same size, as the samples obtained with using coring devices, to avoid over-representing a specific location. This will minimize bias from any of the sampling locations.

Sample handling: It is important to handle and prepare the sample properly and to avoid contamination, especially with fertilizer or manure. All containers should be clean and of inert material, especially for micronutrient testing. For example, certain paper products contain a lot of boron. Aerial contamination, such as ammonia emitted from manure, must be avoided. Microbial activity should be stopped or minimized after sampling by cooling or drying. Freezing and thawing samples alters some nutrients (3), so refrigeration is preferred for short storage. Nutrients are quite stable in air-dried soil, but drying should be done quickly and at temperatures close to ambient to avoid chemical changes. Air dried samples are easy to mix, use in the laboratory, and store for long periods.

Sample analysis

The methods used to extract and quantify nutrients are usually selected by laboratories. Some general issues related to sample analysis are given below. Details are discussed in a subsequent section.

Extraction of the nutrient from the soil: Extraction involves shaking a sample of soil in a chemical solution. Chemical solutions specific for each nutrient is ideal, but multiple element extracting solutions are popular as this increases efficiency for the laboratory. Multiple element extracting solutions employ a mixture of chemicals, which involves compromises for different soils and nutrients. Also, the soil to chemical solution ratio, and time and vigor of the shaking can influence the amount of nutrient extracted from the soil. Some laboratories scoop a volume of the soil sample for the extraction, while others weigh the sample. This should be considered for interpreting the results or when comparing values for samples analyzed in different laboratories. Some of the filter papers used for extraction contain significant quantities of the elements to be analyzed so they should be washed prior to filtering the sample (4).

Nutrient quantification: The choice of chemical analysis procedures includes consideration of operational factors in the laboratory (e.g., cost of the instrument and its operation, single or multiple analyses) and analytical factors (e.g., sensitivity, freedom from interferences). The type of analysis can have a significant influence on the result. For example, some instruments will measure the total amount of the nutrient including organic or inorganic forms, while others will measure only the inorganic forms. Even laboratories that use the same quantification method produce different results. For example, a recent comparison of 9 laboratories in the US, involving 24 soil samples from 9 states using colorimetry, reported variation from the mean of 10% for Mehlich-III, 13% for Bray-I and 22% for Olsen phosphorus tests (5).

Interpretation

Philosophy: Interpretations of soil tests for fertilizer recommendations vary because of the method used to develop the test (soil test correlation and calibration) and the philosophy for nutrient management (6). In some cases, the goal is to apply sufficient nutrients for optimum yield (referred to as the “sufficiency” approach). In other cases, the goal is to apply sufficient nutrients for the crop and to maintain a specific nutrient content in the soil (“maintenance” approach) or to enhance soil nutrient status (“build-up” approach). The sufficiency approach emphasizes short-term crop production with modest application rates whereas the maintenance and buildup approaches emphasize long-term productivity of the field with greater rates recommended. Soil testing can also be used to monitor long-term trends, but special precautions (e.g., uniform depth and locations of sampling, and method of analysis) are needed.

Units of measurement: Most laboratories use metric units, such as µg/g (µg g-1) or mg/kg (mg kg-1), for expressing their extraction values. Both units are equivalent to ‘parts per million’ or ‘ppm by weight’. These values are often translated into a field unit such a pounds per acre (lb/ac or lb ac-1) or kilograms per hectare (kg/ha or kg ha-1). These units refer to the amount of nutrient in a volume of soil, such as an acre of soil to a depth of six inches or a hectare of soil to a depth of 15 centimeters. To make this conversion, the bulk density (weight of soil in a specified volume) must be used but since these values are not usually measured, an “average” bulk density value is assumed (for mineral soils: ppm in 15 cm or 6 in of soil x 2 = kg/ha or lb/ac). This assumes that a six-inch deep acre of soil weighs two million pounds (15 cm deep ha of soil weighs about two million kg). Organic soils have densities that are less that 1 and should be given special consideration.

There is often confusion about different units used for the expression of the elements. Most laboratories express the soil sample nutrient measurement on the basis of the element itself (i.e., N, P, K, etc.). However, the units for fertilizers are expressed as %N-%P2O5-%K2O, and recommendations for fertilizer applications are often expressed in these units. Calcium and magnesium tend to be expressed on an element basis (Ca and Mg), but are also sometimes expressed as oxides (CaO and MgO). Clearly, units become more confusing for recommending manure applications.

Although nitrogen is usually expressed as N both for the laboratory analyses and for fertilizers, sometimes this element is expressed as nitrate (NO3). Most nitrogen soil test analyses used today analyze nitrate and express the value as N or NO3 -N but this may not be true of nitrates in feed or drinking water. Care should be taken regarding units of measurement.

Issues Regarding Analysis Methods

Nitrogen (N)
Nitrogen is present in the soil in a variety of forms that change from one to another (see the Nitrogen Cycle section). This has caused the limited use of soil N analyses throughout the world. Most of the N present in agricultural soils is in organic forms yet plants largely feed on inorganic N, particularly nitrate. Nitrate can be readily measured in soils, but the amount in the soil at any one time may not indicate how much is available to plants through the growing season because substantial amounts of inorganic N can be released from the organic forms (a process called mineralization). Unfortunately, the rate of release of inorganic N from the organic matter in the soil cannot be predicted by a chemical analysis at this time. Therefore, N recommendations based on nitrate analyses must take potential mineralization of organic N and losses of nitrate by leaching or as gas into consideration.

Since corn is a long season crop (see The Parable of Fast and Slow Growing Crops section), N can be successfully applied after the crop has been established. A soil test has been developed for guiding sidedress N applications after the crop is established (See Spring Nitrogen Tests section).

Post-harvest soil nitrate analyses can be used to evaluate the agronomic and environmental effectiveness of previous N management (report card) and to adjust N applications for the next season’s crop using feedback information (1) (see Post-Harvest Nitrate Test section).

Phosphorus (P)
Although most soils contain significant proportions of organic P, soil test extractions focus on inorganic P. Solution P, which is extracted by water or a weak solution of calcium chloride, is usually present in low concentrations in soils. The reason is that P is readily adsorbed or precipitated by calcium, magnesium, iron and aluminum compounds and organic matter. These forms are only sparingly soluble. Each contributes different proportions of P to plants, and soil extraction attempts to simulate plant uptake. The correlation between soil P in different extracting solutions and plant growth is affected by soil and weather conditions, hence regions use different extracting solutions (5).

The chemical compositions of some commonly used P extractants are shown in Table 1. The Bray-I extractant was originally developed specifically for P. The Mehlich and Kelowna extraction solutions, developed for multiple nutrient extractions, use some of the same chemicals present in the Bray-I solution.

Table 1. Composition of frequently used extraction solutions
for soil test P ldeterminations.

Extractant

Composition *

Bray-I

0.03 M NH4F + 0.025 M HCl

Olsen

0.5 NaHCOc (pH 8.5)

Mehlich-III

0.015 N NH4/f + 0.02 M HOAc + 0.25 M NH4NO3 + 0.013M HNO3 + 0.001 M EDTA

Kelowna-I

0.015 M NH4F + 0.25 M HOAc

Kelowna-II

0.015 M NH4F + 0.5 M HOAc + 1.0 M NH4OAc

* NH4F= ammonium fluoride; HCl = hydrochloric acid; NaHCO3 = sodium bicarbonate; HOAc = acetic acid; NH4NO3 = ammonium nitrate; HNO3 = nitric acid; EDTA = ethylenediamine tetraacetic acid (a chelating chemical largely for micronutrient extraction); NH4OAc = ammonium acetate.

The amount of P extracted by each method is often closely correlated. Some new extractants have been proposed based on correlations with previously used procedures without field correlations and calibrations (7). However, direct comparisons are a challenge. Sometimes laboratories change their methods making historic comparisons difficult. Some relationships between different soil P extractions are shown in Table 2. The regression equations help compare values between methods, however, comparisons should be considered to be region-specific. The Alaska data, which is separated into individual soil series, illustrates the variable relationships that can occur for soil types within a region. Although the overall relationships among the soil test methods are generally quite good (r2 values from 0.74 to 0.91), the actual numerical values may differ with soil type.

Table 2.  Comparison of P extract methods at various locations

Table 3 compares values derived by either crop response data (8) or by using regression equations for three different extractions equivalent to Bray-I value of 15 ppm. Values were 17-40 for Mehlich-III, 5-10 for Olsen, and 20 for Kelowna-I. This study included crop response data with which the critical value for Mehlich-III and Olsen methods were derived. It is apparent that the regression equations are crude, and using the regression equations derived for the specific region is preferable. Recent research emphasized that actual field calibration data for each method should be used for interpretations even when two methods are closely correlated (16).

Table 3.  Comparison of critical values for different extraction solutions with critical value of 15 for Bray-I extraction (derived in an Iowa study (8) determined by crop response data and by calculation using regression equations relating the different extracts).

Analytical instruments also affect P measurements. Colorimeters and ion chromatographs measure inorganic P whereas inductively coupled argon plasma spectrophotometers (ICAP) measure both organic and inorganic P. Various studies have shown that these methods of analysis will result in different P values in the same soil extracts (16, 17, 18, 19, 20, 21). Colorimetric values tend to be slightly greater than ion chromatography values, probably because the strong acids used for colorimetric methods decompose some organic forms of P. Therefore, some of the differences among methods in Table 2 may be due to the quantification method. Studies to develop a new multiple element extraction used the ICAP method for Bray-I and Kelowna-I, but colorimetric analysis for the Olsen extraction method (9). In a study of 10 Quebec soils extracted by Mehlich-III solution, P measured by colorimeter was slightly less than by ICAP (66 vs 72 ppm) but the two methods were highly correlated (12).

Potassium (K)
Some soil K is a structural component of clay minerals or “fixed” in structural voids of certain clay types. Plant available (exchangeable) K is adsorbed to negative charges on the surface of clay minerals, sesquioxides (amorphous iron and aluminum materials) and organic matter. A small amount of K is in the soil solution, which is in equilibrium with the exchangeable fraction.

Exchangeable K is typically extracted by ammonium acetate and measured by atomic emission or absorption spectroscopy. Ammonium is particularly effective in displacing K from exchange sites because both atoms are similar in charge and hydrated size. For multiple nutrient analysis with one procedure, ICAP spectrometry is usually coupled with sodium bicarbonate, Mehlich and Kelowna extractions. Results with sodium bicarbonate are somewhat different but correlated to those with ammonium acetate because most soil K is in inorganic form, unlike P. Regression equations among these extraction solutions are shown in Table 4. The nature of the relationship tends to vary with soil type, thus for calculating equivalents among the values it is best to use local data.

Table 4.  Comparison of K extracted from soils by different soil test methods.

Magnesium (Mg)
Magnesium, like K, is largely associated with the mineral portion of the soil, and the exchangeable fraction is traditionally extracted with ammonium acetate. However, much less is known about soil test methods for Mg compared to K (27). It is usually assumed that exchangeable Mg is readily available to plants so that ammonium acetate is a suitable soil extractant. The relationship of ammonium acetate with the Mehlich-III extractant is quite good (Table 5).

Table 5. Comparison of Mg extracted from soils by different soil test methods.

Sulphur (S)
Sulphur is often considered to be a “secondary” plant nutrient, required in smaller quantities than N and K but larger quantities than micronutrients such as boron or zinc. Since crop requirements for S are low and variable across regions, relatively little work has been done to develop soil tests. In some locations, sufficient quantities of S are deposited on the soil from the atmosphere (where it is a pollutant) to supply what the crops require but improvements in air quality have reduced this source of S to crops. Sulphur is a coincidental component of some fertilizers. It is chemically bound as potassium sulphate (0-0-50-18S), ammonium phosphate sulphate (16-20-0-15S) and sulphate of potash-magnesia or ‘sulpomag’ (0-0-22-22S). Sulphur is also a contaminant of superphosphate (0-18-0-12S) and triple superphosphate (0-45-0-1S) (28). As fertilizer manufacturers have reduced contaminant S, the requirement for intentional applications of S as fertilizer has increased.

Sulphur is present in the soil in both organic and inorganic forms, with organic S predominant in most soils. Organic S is unavailable to plants unless it is mineralized to inorganic oxidized sulphate (SO4 2-) form. Acidic soils (pH 7), extract S with water or a weak solution of calcium chloride which will not extract adsorbed sulphate in acidic soils. Phosphate-containing solutions are particularly effective and convenient for extraction of both adsorbed and dissolved sulphate (31). Other anions, such as hydroxide, acetate, carbonate and chloride, also displace sulphate but their displacing ability differs from phosphate.

The availability of adsorbed sulphate to plants is uncertain so other extracting solutions have been proposed. For example, hot KCl is thought to extract both solution and adsorbed inorganic sulphate, and to decompose readily plant-available organic S to inorganic sulphate (32). Unfortunately, the relationships between many proposed extractants are not well known (33, 34, 35). Adoption of multiple nutrient extractants (especially for P, K and Mg) for S testing has been constrained by insufficient field correlation data. A study in India (36) reported the following relationships between Mehlich-III (multiple nutrient extractant) and frequently used S extraction solutions:

Mehlich-III = 13.04 + 6.79 CaCl2, r2 = 0.83,
Mehlich-III = 20.82 + 0.92 Ca-PO4, r2 = 0.80, and
Mehlich-III = 13.89 + 0.73 Morgan’s, r2 = 0.87.

The solutions tested were calcium chloride (CaCl2), monocalcium phosphate (Ca-PO4) and sodium acetate plus acetic acid (Morgan’s), and sulphate was measured by a barium-based turbidimetric method. In British Columbia, the Kelowna-I multiple nutrient extractant was adopted for S soil testing after correlating with calcium chloride extraction using 40 soils from across the province (37). The relationship for the two methods is:

Kelowna-I = 2.61 + 1.79 CaCl2 r2 = 0.61.

Some data has shown that Mehlich-II (ammonium fluoride, acetic acid, ammonium chloride and hydrochloric acid) extraction cannot be generally used for determining “the S supplying” ability of soils (38).

A further complication, as for P, is that different analytical methods will measure different forms of S (31). Turbidimetric/colorimetric and ion chromatographic methods measure inorganic sulphate-S, hydriodic acid reduction method measures both organic and inorganic forms of sulphate-S whereas ICAP will measure all inorganic and organic forms of S. Hence, the turbidimetric/colorimetric methods will result in the smallest value, the hydriodic acid method will have intermediate values and ICAP will result in the largest value, depending on forms extracted from the soil.

Calcium (Ca), pH and lime
Most soils, especially those of alkaline pH, have adequate quantities of Ca for crop growth. Deficiencies may occur in acidic soils, but the application of liming materials to maintain a suitable pH (near neutrality for most crops) is assumed to provide more than adequate amounts of Ca. Since applications of liming materials is standard soil practice in most regions (except where sources are scarce), pH is widely used to indicate liming needs.

There is often confusion in interpretation of buffer and non-buffer pH values (39). Non-buffer pH values, usually a measurement of soil in water or a weak solution of Ca or K, indicates the pH of the soil as experienced by plants. Buffer pH indicates how much liming material needs to be applied to achieve a non-buffer pH value. Laboratories use different buffer solutions for this measurement and each would have a different relationship or equation to derive the lime requirement. A single-buffer method is used quite widely and the equations used to determine tonnes of limestone per hectare (for T/ac multiply by 0.45) for mineral soils that should be applied to achieve a pH of 6.5 are (40):

Quebec lime recommendation = 107.2 - 22.27 pH + 0.983 (pH2), and
Ontario lime recommendation = 291.6 - 80.99 pH + 5.64 (pH2).

While liming recommendations are based on limestone (calcium carbonate or CaCO3), other materials can also be used. The acid-neutralizing capacity of these products, expressed relative to limestone as calcium carbonate equivalent (28) are:

pure, finely ground limestone 100%
hydrated lime (calcium hydroxide or Ca(OH)2) 120-130%
burned or quick lime (calcium oxide or CaO) 150-175%
dolomite or dolomitic limestone (CaCO3.MgCO3) 110%

Both hydrated and burned/quick lime react quickly in the soil but require careful handling because of their caustic nature. Dolomite materials have relatively high Ca carbonate equivalents and supply Mg but act slowly and are usually more expensive than limestone (see Liming to Increase Cell pH section).

Micronutrients
Nutrients required by crops in very small quantities, such as boron, iron, manganese, copper, zinc, and molybdenum, are called micronutrients. Chloride is referred to as a micronutrient but required in greater quantities than true micronutrients (see Latest on Chloride Fertilizer section). Inadequate amounts of these elements will reduce crop growth and quality, and plants would respond to applications of these as fertilizer. Although soil tests have been proposed for all of these nutrients (41, 42, 43, 44), field trials to support the use of these are quite limited in most locations as is the case for British Columbia (45). These soil tests should be used only when all other nutrient problems have been resolved. Test strips in the field should be used to assess response before micronutrients are applied extensively because of both their cost and possible detrimental effects from excessive applications.

References

1. Kowalenko, C.G. 1991. Fall vs. spring soil sampling for calibrating nutrient applications on individual fields. J. Prod. Agric. 4, 322-329.

2. Zebarth, B.J., M.F. Younie, J.W. Paul, J.W. Hall and G.A. Telford 1999. Fertilizer banding influence on spatial and temporal distribution of soil inorganic nitrogen in a corn field. Soil Sci. Soc. Am. J. 63, 1924-1933.

3. Esala, M.J. 1995. Changes in the extractable ammonium- and nitrate-nitrogen contents of soil samples during freezing and thawing. Commun. Soil Sci. Plant Anal. 26, 61-68.

4. Scharf, P. and M.M. Alley 1988. Centrifugation: a solution to the problem posed by ammonium and nitrate contamination of filters in soil extract analysis. Soil Sci. Soc. Am. J. 52, 1508-1510.

5. Kleinman, P.J.A., A.N. Sharpley, K. Gartley, W.M. Jarrell, S. Kuo, R.G. Menon, R. Myers, K.R. Reddy and E.O. Skogley 2001. Interlaboratory comparison of soil phosphorus extracted by various soil test methods. Commun. Soil Sci. Plant Anal. 32, 2325-2345.

6. Brown, J.R. (ed.) 1987. Soil testing: sampling, correlation, calibration, and interpretation. Special Publication number 21. Soil Sci. Soc. Am., Madison, Wisc.

7. Fixen, P.E. and J.H. Grove 1990. Testing soils for phosphorus. Pages 141-180 IN R.L. Westerman (ed.) Soil testing and plant analysis. Third edition. Book series number 3. Soil Sci. Soc. Am., Madison, Wisc.

8. Mallarino, A.P. 1997. Interpretation of soil phosphorus tests for corn in soils with varying pH and calcium carbonate content. J. Prod. Agric. 10, 163-167.

9. van Lierop, W. 1988. Determination of available phosphorus in acid and calcerous soils with the Kelowna multiple-element extractant. Soil Sci. 146, 284-291.

10. Sabbe, W.E. and S.C. Dunham 1988. Comparison of soil phosphorus extractants as affected by fertilizer phosphorus sources, lime recommendation and time among four Arkansas soils. Commun. Soil Sci. Plant Anal. 29, 1763-1770.

11. Matejovic, I. and A. Durackova 1994. Comparison of Mehlich 1-, 2-, and 3-, calcium chloride-, Bray-, Olsen-, Enger-, and Schachtschabel-extractants for determinations of nutrient in two soil types. Commun. Soil Sci. Plant Anal. 25, 1289-1302.

12. Tran, T.S., M. Giroux, J. Guilbeault and P. Audesse 1990. Evaluation of Mehlich-III extractant to estimate the available P in Quebec soils. Commun. Soil Sci Plant Anal. 21, 1-28.

13. Michaelson, G.J., C.L. Ping and G.A. Mitchell 1987. Correlation of Mehlich 3, Bray 1, and ammonium acetate extractable P, K, Ca, and Mg for Alaska agricultural soils. Commun. Soil Sci. Plant Anal. 18, 1003-1015.

14. Schmisek, M.E., L.J. Cihacek and L.J. Swenson 1998. Relationship between the Mehlich-III soil test extraction procedure and standard soil test methods in North Dakota. Commun. Soil Sci. Plant Anal. 29, 1719-1729.

15. Qian, P., J.J. Schoenaru and R.E. Karmanos 1994. Simultaneous extraction of available phosphorus and K with a new soil test: a modification of Kelowna extraction. Commun. Soil Sci. Plant Anal. 25, 627-635.

16. Mallarino, A.P. 2003. Field calibration for corn of the Melich-3 soil phosphorus test with colorimetric and inductively coupled plasma emission spectroscopy determination methods. Soil Sci. Soc. Am. J. 68, 1928-1934.

17. Bolland, M.D.A. and I.R. Wilson 1994. Comparison of standard and total Colwell procedures for measuring soil test phosphorus. Commun. Soil Sci. Plant Anal. 25, 2395-2407.

18. Hylander, L.D., H.-I. Svensson and G. Simán 1995. Comparison of different methods for determination of phosphorus in calcium chloride extracts for prediction of availability to plants. Commun. Soil Sci. Plant Anal. 26, 913-925.

19. Hylander, L.D., H.-I. Svensson and G. Siman 1996. Different methods for determination of plant available soil phosphorus. Commun. Soil Sci. Plant Anal. 27, 1501-1512.

20. Masson, P., C. Morel, E. Martin, A. Oberson and D. Friesen 2001. Comparison of soluble P in soil water extracts determined by ion chromatography, colorimetric and inductively coupled plasma techniques in ppb range. Commun. Soil Sci. Plant Anal. 32, 2244-2253.

21. McDowell, R.W. and A.N. Sharpley 2001. Soil phosphorus fractions in solution: influence of fertilizer and manure, filtration and method of determination. Chemosphere 45, 737-748.

22. Alva, A.K. 1993. Comparison of Mehlich 3, Mehlich 1, ammonium bicarbonate-DTPA, 1.0M ammonium acetate, 0.2M ammonium chloride for extraction of calcium, magnesium, phosphorus, and potassium for a wide range of soils. Commun. Soil Sci. Plant Anal. 24, 603-612.

23. Tran, T.S. and M. Giroux 1989. Évaluation de la méthode Mehlich-III pour déterminer les éléments nutritifs (P, K, Ca, Mg, Na) des sols du Quebéc. Agrosol 2, 27-33.

24. Hanlon, E.A. and G.V. Johnson 1984. Bray/Kurtz, Mehlich III, AB/D and ammonium acetate extractions of P, K and Mg in four Oklahoma soils. Commun. Soil Sci. Plant Anal. 15, 277-294.

25. van Lierop, W. and N.A. Gough 1989. Extraction of potassium and sodium from acid and calcareous soils with the Kelowna multiple element extractant. Can. J. Soil Sci. 69, 235-242.

26. Ashworth, J. and K. Mrazek 1995. “Modified Kelowna” test for available phosphorus and potassium in soil. Commun. Soil Sci. Plant Anal. 26, 731-739.

27. Habey, V.A., M.P. Russelle and E.O. Skogley 1990. Testing soils for potassium, calcium, and magnesium. Pages 181-227 IN R.L. Westerman (ed.) Soil testing and plant analysis. Third edition. Book series number 3. Soil Sci. Soc. Am., Madison, Wisc.

28. Soil Improvement Committee California Fertilizer Association 1980. Western Fertilizer Handbook. The Interstate Printers and Publishers, Inc., Danville, Ill.

29. Tabatabai, M.A. 1982. Sulfur. Pages 501-538 IN A.L. Page, R.H. Miller and D.R. Keeney (eds.) Methods of soil analysis. Part 2. Chemical and microbiological properties. 2nd ed. Agonomy No. 9. Am. Soc. Agron., Madison, Wisc.

30. Kowalenko, C.G. 1996. Interpretation of autumn soil tests for hazelnuts. Can. J. Soil Sci. 76, 195-202.

31. Kowalenko, C.G. 1993. Extraction of available sulfur. Pages 65-74 IN M.R. Carter (ed.) Soil sampling and methods of analysis. Lewis Publ., Boca Raton.

32. Anderson, G.C., G.J. Blair and R.D.B. Lefroy 1998. Soil-extractable sulfur and pasture response to applied sulfur 2. Seasonal variation in soil sulfur tests and sulfur response by pastures under field conditions. Australian J. Experimental Agric. 38, 575-582.

33. Alewell, C and E. Matzner 1996. Water, NaHCO3-, NaH2PO4- and NaClextractable SO4 2- in acid forest soils. Zeitschrift Für Pflanzenernahrung und Bodenkunde 159, 235-240.

34. Prietzel, J. and C. Hirsch 2000. Ammonium fluoride extraction for determining inorganic sulphur in acid forest soils. European J. Soil Sci. 51, 323-333.

35. Schmalz, V., T. Grischek, G. Gerstäcker and E. Eckard 2001. Comparison of different extractants for the determination of inorganic sulphate in gypsumfree agricultural soils. J. Plant Nutr. Soil Sci. 164, 577-578.

36. Rao, T.N. and P.K. Sharma 1997. Evaluation of Mehlich III as an extractant for available sulphur. Commun. Soil Sci. Plant Anal. 28, 1033-1046.

37. Kowalenko, C.G. 1993. Sulphur. Pages 33-37 IN C.G. Kowalenko (ed.) Soil test analysis methods for British Columbia agricultural crops. Proceedings of a workshop of the British Columbia Soil and Tissue Testing Council, meeting 24 November 1992. B.C. Min. Agric., Fisheries and Food, Victoria.

38. Matula, J. 1999. Use of multinutrient soil tests for sulphur determination. Commun. Soil Sci. Plant Anal. 30, 1733-1746.

39. van Lierop, W. 1990. Soil pH and lime requirement. Pages 73-126 IN R.L. Westerman (ed.) Soil testing and plant analysis. Third edition. Book series number 3, Soil Sci. Soc. Am., Madison, Wisc.

40. Tran, T.S. and W. van Lierop 1993. Lime reqirement. Pages 109-113 IN M.R. Carter (ed.) Soil sampling and methods of analysis. Lewis Publ., Boca Raton, Florida.

41. Liang, J. and R.E. Karmanos 1993. DTPA-extractable Fe, Mn, Cu, and Zn. Pages 87-90 IN M.R. Carter (ed.) Soil sampling and methods of analysis. Lewis Publ., Boca Raton, Florida.

42. Gupta, U.C. 1993. Boron, molybdenum, and selenium. Pages 91-99 IN M.R. Carter (ed.) Soil sampling and methods of analysis. Lewis Publ., Boca Raton, Florida.

43. Martens, D.C. and W.L. Lindsay 1990. Testing soils for copper, iron, manganese, and zinc. Pages 229-264 IN R.L. Westerman (ed.) Soil testing and plant analysis. Third edition. Book series number 3, Soil Sci. Soc. Am., Madison, Wisc.

44. Johnson, G.V. and P.E. Fixen 1990. Testing soils for sulphur, boron, molybdenum, and chlorine. Pages 265-273 IN R.L. Westerman (ed.) Soil testing and plant analysis. Third edition. Book series number 3, Soil Sci. Soc. Am., Madison, Wisc.

45. Kowalenko, C.G. and G.H. Neilsen 1992. Assessment of the need for micronutrient applications for agricultural crop production in British Columbia. Agric. Canada Res. Branch Tech. Bull, 1992-5E.

The Nitrogen Cycle

C.G. KOWALENKO

Agriculture and Agri-Food Canada, Agassiz, BC

 

One of the fundamentals of nature is that matter is not spontaneously created or destroyed, but can be changed from one form to another. This is true of nitrogen (N), which cycles through every part of the ecosystem in well known but exceedingly complex flows.

 

To understand the N cycle, it is best to recognize that N is present in various forms and names have been given to the processes that convert it from one form to another (Fig. 1). The forms that contain the majority of N in nature, N gas (N2 constitutes 80% of the atmosphere) and soil organic N, are not directly available to plants. Inorganic N in the form of ammonium or nitrate is available to plants.

 

Conversion of N gas to a plant available (inorganic) form is called fixation, and it is accomplished naturally in the atmosphere, biologically and industrially (Fig. 1). Fixation of N gas occurs in the atmosphere during lightning events.  Ammonium in the atmosphere can be deposited directly to plants and soil or via precipitation. Biological fixation is carried out by N-fixing bacteria living symbiotically with many species of legumes, by free-living bacteria and by blue-green algae. Fertilizer N is manufactured (fixed) industrially using the very energy demanding Haber-Bosch process invented prior to World War I. This single industrial process provides most of the N fertilizer needed to feed the human population.  It should be the goal of every farmer to conserve valuable fixed N.

 

Organic N accumulates in soil by additions of plant and animal wastes or residues. Conversion of soil organic N to inorganic N is called mineralization whereas the conversion of inorganic N to organic N is called immobilization. The first inorganic N product of mineralization is ammonium. Ammonium is usually converted quickly to nitrate by a process called nitrification, hence, nitrate is the dominant inorganic N form available to plants. Ammonium is lost from the soil to the atmosphere by volatilization and nitrate by denitrification.  Nitrate does not adhere to soil particles and, hence, is vulnerable to leaching out of the root zone as water percolates through the soil. Soil organic and inorganic N can be lost to surface water by erosion and run-off.

 

Nitrogen in the Environment

 

The biological or non-biological processes that convert N from one form to another respond to climatic, soil and environmental conditions differently. An understanding of the forms and factors that influence conversion is necessary for efficiently managing N on farms.

 

Although N is an essential nutrient for all plants and animals, it can have detrimental environmental effects on air, water and natural ecosystems. Ammonia, which volatilizes from manures and fertilizer into the atmosphere, has a strong odour. At high concentrations, it can be an irritant or even directly toxic to humans. Ammonia in the atmosphere may be deposited near (1 km or 0.6 mi) the source in significant quantities. Ammonia that is not immediately deposited can combine in the air with nitrate and sulphate from factories and automobiles to form fine particulates which reduce air quality (white haze) and can be detrimental to human health.  High levels of fine particulates have been recorded in the confined valleys of the lower Fraser River (BC) and San Joaquin Valley (CA). Atmospheric ammonia deposited on the earth or surface water bodies via precipitation can be toxic to some aquatic organisms, stimulate excessive biological growth in water (eutrophication), accelerate acidification of soils or cause changes to natural aquatic and terrestrial ecosystems that may degrade species diversity. In contrast to ammonia, nitrate is not volatile but contributes to atmospheric contamination during denitrification, which occurs most often in wet soils. The main product of denitrification is innocuous atmospheric N gas (N2), but nitric oxide (NO) and nitrous oxide (N2O), are formed in small quantities as intermediates. These are potent greenhouse gases which contribute to global warming.  Small amounts of nitrous oxide are also formed during nitrification.

 

Nitrogen in the soil during corn production is subject to nutrient loss by  leaching, erosion and runoff, particularly before planting and after harvest when there is little cover over the soil. Erosion and runoff (Fig. 1) of N (both organic and inorganic) contribute to eutrophication of surface waters and ammonium in surface water is very toxic to many aquatic organisms such as fish. Nitrate leached from soils into groundwater is a widely recognized environmental and health concern, particularly due to the potential death of infants from “blue baby” syndrome.

 

 

 

 

 

Click here for Nitrogen Cycle diagram in pdf format.

 

Spring Nitrogen Tests

B.J. ZEBARTH
Agriculture and Agri-Food Canada, Fredericton, New Brunswick

Most of the N in soils is organic and must be converted to nitrate or ammonium (mineralization) before it is available to plants (see The Nitrogen Cycle section); nitrate is the predominant inorganic form in most soils. Nitrate can be high in early spring in some fields as a result of the carry-over from the previous growing season. The amount of carry-over varies with the amount of soil nitrate present in fall and the losses over the fall and winter. In some locations, such as coastal regions of the Pacific Northwest which are mild and wet, carry-over is minimal. In locations where winters are cold and dry, carry-over can be considerable. When the amounts of carry-over nitrate plus mineralized N is less than the crop requires, application of N as fertilizer or manure is required.

The amount of soil inorganic N that will be mineralized during the growing season cannot currently be predicted with a chemical analysis (see Determining Nutrients Available in Soils section), therefore, soil N testing is limited to measuring inorganic N. In south coastal British Columbia, where soil N fertility on dairy farms is high due to a history of manure use, net soil N mineralization is commonly greater than 100 kg N/ha, with some fields exceeding 200 kg N/ha. In locations where carry-over nitrate is leached below the root zone over winter, a pre-plant test has limited value for determining fertilizer requirements. Since corn is a long-season crop (see Parable of the Fast and Slow Growing Crops section), soil nitrate testing can be delayed to just prior to sidedress fertilizer time in order to detect as much soil nitrate as possible from mineralization and nitrification.

Two Soil N Tests: PPNT and PSNT

The two most common soil N tests used for determining nitrogen available for corn are the pre-plant soil nitrate test (PPNT) and the pre-sidedress soil nitrate test (PSNT). The PPNT is based on the soil nitrate concentration to 60-cm depth measured before planting (Fig.1). This test measures mainly the amount of soil nitrate carried over from the previous growing season plus early-season soil N mineralization. This test works best in dry or cold climates where carry-over of nitrate from the previous year contributes a major proportion of the total soil N supply. Disadvantages of the PPNT are that the sample is taken prior to most growing season mineralization and nitrification of soil organic matter and spring applied manure N. The PPNT might be improved in some fields by including a measure of soil ammonium concentration.

The PSNT is based on the soil nitrate concentration to 30-cm depth measured at the six-leaf stage, just prior to the period of rapid crop N uptake (Fig. 1). The PSNT works best when no more than 20-30 kg N/ha (18-27 lb/ac) is banded at planting. Based on studies in coastal British Columbia, soil nitrate measured at this time includes little carry-over from the previous growing season, about 50% of the soil N mineralization which will occur throughout the growing season, and most of the available N from spring-applied liquid dairy manure (1). Usually, most nitrification of soil and manure ammonium is complete by the time the PSNT sample is taken, so measurement of soil ammonium is not required. However, where corn was planted after plough-down of forage grass in early May (i.e. after first cut), more than half of the plant available N in the soil was still in ammonium form when the PSNT sample was taken.

Thanks to the delayed sampling, the PSNT is more sensitive to soil N ineralization and spring manure application than the PPNT, and, except where carry-over is substantial, should provide better estimates of fertilizer N requirement than the PPNT. In cases where carry-over N is significant, it may be helpful to use the PPNT to choose an appropriate spring manure application rate, and to use the PSNT to choose an appropriate sidedress fertilizer N rate.

How to use pre-sidedress soil nitrate tests (PSNT)

It should be part of a nitrogen management system:

  • Manage manure according to local environmental guidelines; in some years, liquid manure alone may supply enough N for your crop.
  • Do not broadcast N before planting. Corn requires little N early in the growing season.
  • Apply a low rate of N (20-30 kg/ha or lb/ac) with the planter. Nitrogen applied by the planter is not measured by the PSNT.
  •  Use the PSNT to decide how much, if any, fertilizer N to apply at sidedress.

Sampling protocol:

  • Sample to 30-cm (1-ft) depth midway between corn rows to avoid fertilizer banded with the planter.
  • Take at least 10 cores per field when the corn is at the 6-leaf stage or 15-30 cm (6 - 12") tall.
  • Keep the sample cool or frozen until it reaches the lab — a picnic cooler is handy; warm samples will release nitrate and give a fertilizer recommendation which is too low.
  • Have the sample analysed for nitrate-N concentration in ppm.

Interpreting results:

  • Corn will likely not respond to sidedress N in fields with PSNT values greater than the critical PSNT value. Critical PSNT values vary somewhat with region so use local information. The most common critical PSNT values in North America are 20-25 ppm. 
  • For PSNT test values less than the critical PSNT value, use local information to predict the fertilizer N requirement at sidedress. Table 1 shows values for coastal Pacific Northwest (1).
  • Field measurements have shown that where corn was planted following a late-spring plough-down of forage grass, more than half of the plant available nitrogen in the soil was still in ammonium form when the PSNT sample was taken. In this case, PSNT will over-predict N needs.

Future technology: plant chlorophyll N tests

There is growing interest in estimating plant-N status based on leaf colour for making fertilizer N recommendations (2). This approach can be used rapidly in the field and does not require laboratory analyses. Also, the plant itself provides an indication of its N status, in contrast to soil tests which focus on soil N supply and cannot readily account for variation in crop N demand. The primary disadvantage of this approach is that factors other than crop N status can influence measurements.

Perhaps the most studied field-test method measures ‘leaf greenness’ because of the direct relation with chlorophyll concentration and N status. A hand-held device called ‘SPAD-502’ (Minolta Corp.) measures chlorophyll concentration of a leaf by shining a small beam of light through the leaf. SPAD measurements are quick and repeatable but readings are very sensitive to other factors such as the position of the leaf where the reading is taken, which leaf is tested, growth stage of the plant, and to corn cultivar due to differences in leaf thickness.

Used at the six-leaf stage, the SPAD meter has been found to be useful for identifying corn fields likely to respond to a sidedress N application. Some studies have found the SPAD meter to be as reliable as the PSNT in making a ‘yes/no’ decision on fertilization. However, the SPAD meter has not proved reliable for determining how much sidedress N to apply. Some studies have employed reference plots that receive abundant N fertilizer before planting, and used the ratio of SPAD readings from the field and the reference plots, but the advantage of this approach is not well proven. The SPAD meter might best be used as a preliminary screening tool to decide which fields require a PSNT test sample to be taken.

Readings with the SPAD meter taken after the six-leaf stage have been used successfully for making fertilizer N recommendations in irrigated corn fields. For these fields, N fertilization is done when the ratio of the SPAD readings taken from the field and from the reference plots drops below a threshold value, commonly 90 to 95%.

New instruments which measure light reflected from the crop canopy are being developed for indicating corn N status. None of these instruments are in common use at this time. However, one instrument which appears to be promising is the ‘Hydro N Sensor’. This instrument uses four tractormounted sensors, to measure light reflected from the canopy surrounding the tractor, to measure crop N status in real time. With suitable calibration, it may be possible in future to use such an instrument to perform real-time variable-rate fertilizerN applications.

 

References
1. Zebarth, B.J., J.W. Paul, M. Younie and S. Bittman 2001. Fertilizer nitrogen recommendations for silage corn in high-fertility environment based on presidedress soil nitrate test. Commun. Soil Sci. Plant Anal. 32, 2721-2739.
2. Zebarth, B.J. J.W. Paul, M. Younie and S. Bittman 2002. Evaluation of leaf chlorophyll index for making fertilizer nitrogen recommendations for silage corn in a high fertility environment. Commun. Soil Sci. Plant Anal. 33, 665-684.

Post-Harvest Nitrate Test

D.M. SULLIVAN1 AND C.G. COGGER2
Oregon State University1, Corvallis, Oregon and Washington State University2, Puyallup, Washington

Nitrate can pollute groundwater if there is a substantial quantity present in the soil when leaching potential is high, usually in winter when precipitation exceeds evapotranspiration. Potential for leaching will increase after harvesting corn since the plant won’t be utilizing water and nitrogen (N). The post-harvest nitrate test (PHNT) measures soil nitrate after crop harvest. This test indicates potential for pollution since it measures soil nitrate not used by the crop and the test helps to evaluate the efficiency of N management.

How to do a PHNT

  • Sample to 30 cm (12 in) depth.
  • Sample before water moves nitrate below sampling depth. For medium to fine textured soils (loam - clay), sample prior to 13 cm (5 in) of cumulative fall rainfall. Coarse textured soils (sand - sandy loam) have low water-holding capacity and should be sampled prior to 8 cm (3 in) of cumulative fall rainfall. Table 1 shows the average calendar dates when cumulative fall rainfall (after Sept 1) reaches 8-18 cm (3-7 in) at a variety of locations in the wet coastal area of the Pacific Northwest.
  •  A sufficient number of samples (15-30 cores per field) should be collected to adequately represent the field. Avoid sampling a field that has had manure application within the last thirty days.

Interpreting PHNT

  • The PHNT looks backward in time. It evaluates the balance between N supply and crop uptake for the crops produced during the summer. 
  • Soil nitrate concentrations are typically high, regardless of overall management, after a perennial grass sod is ploughed down, therefore, it is difficult to attain low PHNT values for corn seeded after grass.
  • Low PHNT does not necessarily indicate that too little N had been applied. Continued mineralization of nitrogen can provide enough plant available N for the crop without accumulation of nitrate in the soil under some circumstances. 
  • It is difficult to achieve low PHNT when using manure. First, the timing and rate of application of organic sources is less flexible than for fertilizer. Second, environmental processes that control the quantity and timing of N mineralization from organic sources is difficult to manage. Nitrogen mineralization can continue after crop harvest. Research with silage corn in Whatcom County, WA shows that PHNT values generally increase with pre-sidedress soil nitrate test (PSNT) values when no fertilizer was sidedressed (Fig. 1).

Figure 1. Relationship between pre-sidedress nitrate-N test (PSNT) and amount of N present in soil after corn silage harvest (PHNT) when no sidedress N fertilizer was applied in Whatcom County (Washington) in 1995-96. Each data point represents one point in one year. (Unpublished data, Craig Cogger, Washington State University-Puyallup).

How to reduce PHNT values

  • Reduced N fertilizer and manure application rates.
  • Plant a relay or post-harvest cover crop that will maximize N removal in late summer and fall.
  •  Avoid N applications late in the growing season (after August 1).

 

Interpreting Soil N Tests With the Help of Computer Simulation

C. CLARK1, D. HUNT2 and S. BITTMAN2
Whatcom Conservation District, Lynden, Washington1and Agriculture and Agri-Food Canada, Agassiz, British Columbia2

The climate in Whatcom County, located west of the Cascade Mountains in Washington state, has mild, wet winters, and relatively dry summers. A long growing season from late April to mid-October is followed by over 60 cm (24 in) of wintertime rainfall. Land is expensive and dairy farmers are challenged to develop progressive management strategies to remain financially successful and limit their impact on the environment. A primary environmental concern for production of silage corn is wintertime nutrient leaching. The Conservation District, USDA-NRCS and Washington State University are working with Agriculture and Agri-Food Canada, BC Ministry of Agriculture, Fisheries and Food, and Environment Canada to help farmers on both sides of the border manage their nutrients, especially nitrogen. Management of N requires effective soil testing tools and a good understanding of N transformations and movements in the soil as affected by environmental conditions.

Our soil test tools include the pre-sidedress nitrogen test (PSNT) and post harvest nitrogen test (PHNT), formerly called the ‘fall report card test’ (see preceeding chapters). Our work involves evaluating and improving these tools. The PSNT in early summer guides (sidedress) fertilizer use to meet crop needs for the remainder of the season. The PHNT, conducted in early fall, measures the residual soil nitrate after corn harvest that will, if there is no winter cover crop, be lost by leaching and denitrification after the return of fall rains. The PHNT provides feedback on the success of the previous nutrient management.

Figures 1 and 2 show the seasonal patterns of nitrate in the soil, N-uptake by silage corn, and mineralization of N (from soil and manure) on two commercial corn fields in Whatcom County in 2001 and 2003, respectively. The graphs, based on farm-specific data, were produced by mathematical simulation of N processes in response to climate and crops using the computer model NLOS (1), which stands for ‘NLEAP On Stella®’. The soil-N simulation model, NLEAP, was developed by USDA-ARS in Fort Collins, CO; the NLOS version of NLEAP developed by Agriculture and Agri-Food Canada uses a graphical interface (STELLA®) that enables examination of all N flows in the NLEAP model.

Explanation of numbers:
1. Mineralization rate is slow until soils warm.
2. Manure is applied.
3. Pre-sidedress nitrogen test (PSNT) measurement (timing critical).
4. Post harvest nitrogen test (PHNT) measurement (timing critical).
5. Nitrate-N is lost from field by the end of the year.

Figure 1. Graph showing simulated soil-N processes with NLOS model (see text) for the year 2001 in a silage corn field in western Washington. The field has inherently large amounts of soil N.

 

Explanation of numbers:
1. Mineralization rate is slow until soils warm.
2. Manure is applied.
3. Pre-sidedress nitrogen test (PSNT) measurement (timing critical).
4. Post harvest nitrogen test (PHNT) measurement (timing critical).
5. Nitrate-N is lost from field by the end of the year.

 

Figure 2. Actual PSNT and PHNT measurements plotted on a year of simulated soil N processes in a silage corn field in western WA. The soil had moderate levels of N and received moderate manure and fertilizer applications

 The field sampled in 2001 contained considerable soil N (Fig.1). The simulation graph shows the important contribution to soil nitrate concentrations by seasonlong mineralization of organic N from soil and manure. The accumulating soil nitrate was due to conversion (nitrification) of ammonia from manure to nitrate. A PSNT sampling on June 21 showed that this field already contained 267 kg/ha (243 lb/ac) NO3-N in the surface 30 cm (12 in) of soil. This is more N than required by the crop, so most of the N mineralized through the summer and fall is excess and will likely be lost in winter. This is evident from the PHNT of 200 kg/ha (180 lb/ac) of NO3-N remaining in the soil on October 4 which is lost by the autumn rain, as shown by the simulation.

In this field, the manure application rate (250kg NH4-N/ha or 230 lb/acre) was almost double the recommended rate for nitrogen. The PSNT (81 ppm) was considered and no additional sidedress fertilizer was used; in mineral soils this concentration equals approximately 230 kg N/ha (or lb/ac). The PHNT (57 ppm) was evaluated and the manure application rate was reduced in the following year.

The data from this field underscores the need for a catch crop such as a relay crop or a fall cover crop to help take up residual nitrate in the fall. The relay or cover crop must be grazed or harvested in spring, not ploughed-under, otherwise much of the N taken up by the cover crop will be added to the pool of soil nitrate in the following season.

In Fig. 2, the model shows the behavior of soil nitrate-N in a commercial corn field that has been managed successfully with both mineral fertilizer and manure. Manure was applied at 110 kg/ NH4-N per ha (100 lb NH4-N/acre) and fertilizer N was added at planting at 50 kg/ha (44 lb/ac). The PSNT at 16 ppm (approx. 64 kg N/ha or lb/ac) indicated additional fertilizer could be utilized, so at about 9-leaves another 53 kg/ha (48 lb/ac) of N fertilizer was applied and a relay crop (see Cover and Relay Crop section) was seeded to utilize residual NO3 in the soil in fall.

The importance of timing for both the PSNT and the PHNT in Western Washington is shown in Figs. 1 and 2. Soil nitrate accumulates between early April and mid-June. Most N-uptake occurs between mid-June and late August. Release of N from organic matter continues through summer and autumn.  Delaying the PHNT after mid-October would have missed much of the soil N. We believe that mis-timing the fall soil sampling is a major source of error and has reduced the value of the PHNT in our region.

The increase of nitrate nitrogen in the fall during the PHNT test window (August 15 - October 15) is due to the mineralization of organic nitrogen (from the soil and historic manure applications) when soils have favourable temperature and moisture for microbial activity.

The results from these field studies show that NLOS simulates the complexity of the nitrogen cycle, the reactions to weather events and the variations in management practices sufficiently well for practical field use. The simulation results help us interpret the PSNT and PHNT measurements and validates our understanding of the behavior patterns of N so that we can manage nutrients effectively.

1. Bittman, S., D.E. Hunt and M.J. Shaffer 2001. NLOS (NLEAP On STELLA®) – A nitrogen cycling model with graphical interface: implications for model developers and users. In M.J. Shaffer et al. (eds) Modeling Carbon and Nitrogen Dynamics for Soil Management. Lewis Publishers, Boca Raton.

The Phosphorus Index to Minimize Water Contamination

J. LEMUNYON
United States Department of Agriculture-Natural Resource Conservation Service, Fort Worth, Texas

The Phosphorus (P) Index is a tool for risk-based management of P that considers the potential for P movement. It was developed in the USA in the early 1990s by a group of national and international scientists from USDA, universities, extension, private and state agencies, and industry called the P Index Core Team (PICT). This group recognized the need for a simple, field-based index using readily available information that could be used to assess sites for potential vulnerability to cause P movement to water bodies. The Index was based on soil, landform and management posing various degrees of risk of detrimental impacts on water quality because of P contamination. As the Index evolved, more research and field data was added to enhance science and methodology of the procedure. Subsequent validations of the Index have shown that the concept is sound and science-based.

The Index ranks sites according to risk of P movement. When analyzing each parameter of the Index, it becomes apparent which of the site conditions and parameters may be imposing greatest influence on the Index. These identified parameters can be the basis for planning and implementing activities to correct the situation. This approach provides producers with the greatest range of P management options while providing for environmental protection.

Transport of P from a field is influenced by rainfall, soil erosion, runoff, and wind. High soil-test P levels and various forms of P applied to fields may increase the amount of P moved from the field. The rate, timing, form, and method of application, along with the site location on the landscape affect the likelihood of P movement and environmental impact. Therefore, relative risk of P to be moved from the landscape will be determined by source and transport factors (below), plus location of the field.

The P Index is designed to identify the vulnerability of agricultural fields to P loss by ranking and rating transport and source factors controlling P loss in surface runoff. The Index is more comprehensive than a simple soil-test P indicator because the Index integrates soil, climate, and field characteristics that influence possible movement of P to surface water. In practice, the P Index value is determined by selecting the rating value for each site characteristic, or factor, multiplying that value by the appropriate weighting coefficient, and summing the weighted products of all factors (Fig.1). Some site characteristics are determined from observations made in the field while additional information comes from land use history and soil surveys. Site characteristics are weighted based on their influence on P movement. In this way, the assessment at all sites is performed in a systematic and consistent way.

Figure 1. The original P Index was an 8 by 5 matrix listing the site characteristics down the left column and their individual P loss rating value along the top. A specific site assessment was made by adding up the rating values for each site characteristic and comparing the sum to an interpretation table.

Since its inception in 1993, three major changes have been made to the P Index:

1. Source and transport factors are now related in a multiplicative rather than previous additive fashion, in order to better represent actual site vulnerability. For example, if surface runoff does not occur at a particular site, its vulnerability should be low regardless of soil P content. Similarly, a site with high potential for erosion, surface runoff or subsurface flow, but with low soil P, is not a risk for P loss until mineral fertilizer or manure is applied to the field. In the original P Index, a site could be ranked as high risk based on site management factors even though there was no risk of surface runoff or erosion. Catastrophic events, like floods or storms, can over-power the safeguards and carry away any and all stored P.

2. The new Index incorporates an additional transport factor reflecting the distance between field and water body. The new distance categories are based on hydrologic analysis that considers the risk that a rainfall event of a given magnitude will result in surface runoff toward the stream.

3. The new Index uses continuous, open-ended parameterscaling for erosion, soil test P values and P application rates (both fertilizer and manure). This enables indices to better address the effects of very high erosion and soil test P values of the original P Index on P loss potential, and avoid having to subjectively quantify these categories. The open-ended scaling avoids the unrealistic situation where a one or two unit parameter increase could dramatically alter the P Index rating and its interpretation.

General interpretations and management guidance for the P Index ratings:

LOW - Low potential for P loss. If current farming practices are maintained, there is a low risk of adverse impacts on surface waters.

MEDIUM - Medium potential for P loss. The chance for adverse impacts on surface waters exist, and some remediation should be taken to minimize the risk of P loss.

HIGH - High potential for P loss and adverse impacts on surface waters. Soil and water conservation measures and P management plans are needed to minimize the risk of P loss.

VERY HIGH - Very high potential for P loss and adverse impacts on surface waters. All necessary soil and water conservation measures and a P management plan must be implemented to minimize the P loss.

The P Index is used by farm advisors in consultation with the producer to assess the relative potential for leaving the land site and reaching a water body. The Index can thus be used to identify the critical parameters that most strongly influence the Index. Based on the Index, management practices can be applied to the landscape that would decrease the site’s vulnerability to P loss.

Fertilizer Use

Early Phosphorus Nutrition in Corn and the Role of Mycorrhizae

S. BITTMAN, D. HUNT, C.G. KOWALENKO, X. WU and T. FORGE
Agriculture and Agri-Food Canada, Agassiz, British Columbia

Importance of Early Phosphorus Nutrition for Corn

Growers in temperate regions are accustomed to observing corn plants with a purple tinge early in the growing season, especially while the soils are cool. The purpling appears to be characteristic of phosphorus deficiency, and it is well known that the roots of juvenile corn plants have difficulty absorbing sufficient amounts of phosphorus, especially from cold soils. Corn hybrids that produce high levels of the pigment anthocyanin are most likely to take on a purple hue.

The use of starter phosphorus fertilizer is often recommended to corn producers to help ensure high yields. The most common method of supplying starter phosphorus is to apply a band about 5 cm (2 in) below and to the side of the seed furrow (see Applying Starter Fertilizer section). Most corn planters are now equipped with sidebanding attachments. This method of application ensures close proximity of phosphorus to emerging roots, reduces fixation of phosphorus by the soil and reduces risk of loss of phosphorus by erosion or runoff. Under no-till, bands of elevated phosphorus remain intact until the next year.

The benefit of starter phosphorus is greater on low than on high phosphorus soils (1). However, starter phosphorus may be beneficial even on high fertility soils if the soils are cool at planting time (2). Typically, soils are cooler under conservation than conventional tillage systems. The visible response by corn to starter phosphorus, especially on cool, wet, compacted, fine textured soils, encourages farmers to use starter phosphorus fertilizer. While early growth is often improved with starter phosphorus, the effect does not always produce higher yield. Averaged over 22 trials in Ontario, starter phosphorus (and K) increased yield of 36-day-old corn by 36% but harvest yield was increased by less than 3% (3). It was concluded that high fertility rates would be required before starter P would be required. Farmers growing silage corn in northerly regions, such as Vermont, often sideband 25-30 kg/ha (22 -27 lb/ac) of starter P, even on soils with moderate to high levels of P from many years of manure application (4) (see Applying Starter Fertilizer section). However, few studies have been conducted to examine the benefits of starter P on silage corn grown on high P soils receiving manure.

In cool, moist coastal British Columbia, almost all silage corn is sidebanded at approximately 30 kg P/ha (27 lb/ac) even though most of the corn receives manure and is grown on soils testing medium to high in soil P. In a study on 24 BC dairy farms, we found that starter P had little effect on whole plant yield and grain yield on all but a few farms (Fig. 1). However, starter P did seem to produce a general increase in dry matter content at harvest, which may be related to improved early growth. Increasing dry matter content at harvest suggests a more mature crop and is economically important to producers.

Figure 1. Effect of applying starter P (30 kg /ha or 27 lb/ac) on whole-plant yield, grain yield and whole-plant dry matter percent of silage corn grown on 24 dairy farms in coastal BC in 2001.

The importance of early P uptake (6-leaf stage) for grain yield was shown in a controlled field trial in BC (Fig. 2). Early P uptake also improved crop maturity as indicated by dry matter content at harvest. In contrast, there was very little effect of early P uptake on the amount of P ultimately taken up in the mature crop. Deficiency of P in juvenile plants reduces grain yield potential of corn by reducing the number of kernels formed (5). This study showed that grain yield is reduced by early P deficiency even if ample P is supplied later. In these studies, maximum yield was achieved when concentration of P at the 6-leaf stage was at least 0.5%. Because P concentrations in commercial corn crops are almost always lower than this value (our values are usually under 0.4%, Table 1), one would expect that corn crops will respond to starter P in most cases. But the amount of P taken up at this growth stage is less than 1kg/ha (0.9 lb/ac) while typical application rates exceed the 20-25 kg/ha (18-23 lb/ac) taken up by the whole crop at harvest. Therefore new strategies are needed to enhance levels of P in the plant at the 6-leaf stage with the minimum amount of fertilizer P. This is especially true for soils testing high in P and those that receive ample amounts of manure. Applying excessive starter P on such soils is particularly problematic because it poses a risk of P contamination of surface waterways.

Figure 2. The effect of P-uptake at 6-leaf stage on % grain at harvest in coastal BC (2002)

Role of Mycorrhizae in Early P Nutrition

There is a considerable body of information that a contributing cause of early P deficiency in juvenile corn is inadequate root colonization by a group of fungi referred to as arbuscular mycorrhizae. For example, the phenomenon of P deficiency in juvenile plants of many mycorrhizae-dependent crops growing on previously fallowed soils is related to poor colonization by mycorrhizae (6, 7). Figure 3 shows relatively well-colonized and uncolonized roots of corn. Mycorrhizae filaments extend from the roots into the soil, reaching several times beyond the root hairs. In this way the mycorrhizae increases the zone of P absorption around the roots, effectively increasing the absorbing surface area of the root and assisting the host plants to access nutrients (esp. P, zinc and copper) that are relatively immobile in the soil.

Figure 3. Photomicrograph (approx. 60 X magnification) of corn roots colonized by fungi called arbuscular mycorrhizae (top). The slide on the bottom shows uncolonized corn roots. The mycorrhizae are stained blue and the corn root tissue appears tan.

Although spores of mycorrhizae are very persistent and almost ubiquitous in agricultural soils, they require time to germinate and attach to growing roots, particularly in cold soils (8). Therefore, the new roots of young plants are more rapidly colonized if there is an established network of hyphae in the soil (9). Thus, maintaining a network of viable hyphae in the soil is desirable for early P nutrition of corn. Despite their apparent importance, direct management of mycorrhizae remains largely impractical for field crops (10). There are several reasons for this. First, testing for mycorrhizae in the soil prior to planting is technically problematic and commercially impossible at present. Also, inoculation with spores would probably be ineffective as the young plants require the established fungal networks. Finally, since most agricultural soils are rich in mycorrhizal spores, adding more inoculum may have little impact except in reclaimed soils or other special cases. Soil-test prediction of P requirements would probably be improved if colonization by mycorrhizae could be readily measured or predicted.

Previous Crop Effect on Mycorrhizae and Early P Nutrition

The importance of a previous crop on colonization of corn roots by mycorrhizae can be seen in Fig. 4 and Table 1. More mycorrhizae were found on roots of 3-leaf corn grown after corn than corn grown after either fallow or canola (canola being a crop that does not associate with mycorrhizae). Enrichment of soil P is often reported to reduce mycorrhizal colonization, but this reduction did not occur in our studies. The reason that this reduction did not occur is probably that the P concentration in 3-leaf corn is low and not greatly affected by either soil or fertilizer P. At this stage, most of the P in the corn shoots (0.03 kg/ha or lb/ac) is derived from the seed. Note that at 3- and 6-leaf stages, all corn treatments had concentrations of P of 0.3% or less. The effects of previous crop and starter P increased at the 6-leaf stage, with corn grown after fallow and canola having lower P concentrations than corn grown after corn, especially with no added P. Note that corn following fallow or canola took up much less P than corn following corn, even when ample amounts of starter P (30 kg/ha or 27 lb/ac) were supplied. In other words, the starter P applied in great excess to crop requirement did not fully alleviate the effect on P-uptake by the previous crop! A P soil test that did not take into account the previous crop would not successfully predict early uptake of P by the crop.

Figure 4. Effect of previous crop on early growth of corn at Agassiz, BC.

Table 1. Effect of previous crop and starter P (30 kg P/ha or 27 lb P/ac) on P concentration and P-uptake in shoots of corn at 3- and 6-leaf stage at Agassiz, BC (mean of 1997 and 1998).

The importance of starter P and the previous crop on growth and yield of corn is shown in Table 2. At the 6- to 9-leaf stage, starter P increased shoot weight of corn by at least 30% when corn was grown after corn, but by 50% when corn was grown after fallow or canola. As with P uptake, starter P did not fully compensate for the effect of the previous crop on yield. The effects of starter P and previous crop were apparent also at harvest but the differences were relatively smaller. Meaningful differences were also noted in the dry matter content at harvest.

Table 2. Effect of previous crop and starter P on biomass of corn at 3-, 6- and 9-leaf stage and yield and dry matter at final harvest at Agassiz, BC (mean of 1997 and 1998).

Effect of Tillage on Mycorrhizae and Early P Nutrition

Root colonization by mycorrhizae and associated effects on P are influenced by intensive tillage practices, probably because tillage disrupts the network of mycorrhizae by breaking it apart and dispersing it in the soil profile. In our studies in BC, corn grown on soil which was ploughed and cultivated according to conventional farming practices had significantly reduced early growth (Fig. 5) and root colonization by mycorrhizae than corn grown on zero-tillage or minimum tillage (aeration) systems (Table 3). Note that disking operations, which did not turn over or pulverize the soil, reduced root colonization only slightly. Intensive tillage reduced uptake of P at 6-leaf stage significantly but the effect of tillage intensity on P uptake at harvest was comparatively small and inconsistent.

Figure 5. Intensive tillage affects early growth of corn in coastal BC.

Table 3. Effect of increasing tillage intensity on colonization of corn roots by mycorrhizae and uptake of P by corn shoots in coastal BC (1999-2000). Ploughing is the conventional practice in the region. Roto-tilling is popular in gardening and vegetable production.

The effect of tillage on growth was not apparent when the corn was at 3 leaves, but by 6 leaves plants grown on minimum till were larger and had less purple coloration than plants grown with intensive tillage (Fig. 4). Intensive tillage reduced corn growth by over 30% at the 6-leaf stage, but there was no apparent effect on final whole-plant yield (Table 4). However intensive tillage did reduce whole-plant dry matter content and grain yield, indicating that the early reduction in P-uptake delayed the maturity of the crop. Delayed maturity is often the outcome of P deficiency during early growth.

Table 4. Effect of tillage on dry matter yield at different growth stages and the dry matter content and grain content at harvest of silage corn in coastal BC (1999-2000).  Ploughing is the conventional practice in the region.

Effect of Manure on Mycorrhizae and Early P Nutrition

There is a special interest in the effect of manure on early P nutrition in the production of silage corn, because silage corn usually receives ample cattle manure. In our studies, we posed two questions: will application of manure affect colonization of corn roots by mycorrhizae and is mycorrhizal colonization beneficial for corn on heavily manured soils? In these trials manure was supplied at approximately 200 kg/ha of total N and about 60 kg/ha of P.

We found that previous fallow greatly reduced mycorrhizal colonization of roots of corn at 3-leaves, and reduce growth and P-uptake at 6-leaves (Table 5). Manure application slightly increased colonization, and also increased P uptake at 6-leaves. Note that even with large doses of manure, corn after fallow with reduced mycorrhizae did not take up as much P as corn after corn at 6-leaves. There was only a slight effect of previous crop and manure treatments on P uptake at harvest, but the effects of these treatments on yield, dry matter content and grain percentage at harvest is large enough to be commercially significant.

Table 5. Effect of previous crop and application of dairy slurry or fertilizer on colonization by mycorrhizae, early growth and P uptake, and final harvest of silage corn in coastal BC (2000-2002).

Strategic Application of P-Fertilizer and the Role of Mycorrhizae and Manure

As seen above, the crop consumes only small amounts of P at the critical early growth period, which suggests that only small amounts of starter fertilizer may be needed. We set up a trial to determine if strategic placement of small amounts of P fertilizer could be used to satisfy the requirement for P under contrasting mycorrhizal and manure backgrounds.

The standard farming practice in coastal BC corresponds to 30 kg/ha (27 lb/ac) of sidebanded P applied to corn planted after corn in soil receiving a large dose of dairy slurry. As discussed in the previous section, fallow reduced mycorrhizae colonization of roots and manure and had a slight positive effect on colonization (Table 6, top). Sidebanding with 30 kg/ha of P had little effect on mycorrhizae although placement of P in the seed furrow at 7 kg/ha slightly reduced root colonization. The sidebanding P treatment increased P-uptake at 6-leaves under all preconditions, with the greatest increase on previous fallow without manure and least on previous corn with manure (Table 6, middle). Note that even with sidebanded P, concentrations of P in the shoots at 6-leaves did not surpass 0.32% (not shown), which is lower than the ideal concentration (0.5%) recommended by Barry and Miller (5). While none of the strategic fertilizer applications exceeded the standard farming practice for early P-uptake, the in-furrow application of 7 kg P/ha (6 lb P/ac) was close to the standard in all cases. The 2 kg P/ha (1.8 lb P/ac) furrow (not shown) or seed placed treatments improved P-uptake over control but to a lesser extent than the higher rates. At harvest, all applications of starter fertilizer had a similar effect on whole-crop yield (not shown). However, the harvested crop had a higher grain content from the sidebanded P than from the 7 kg P/ha (6 lb P/ac) furrow treatment (also other starter P treatments), even though there was similar initial P-uptake (Table 6, bottom). One possible explanation is the slightly reduced colonization by mycorrhizae in the 7 kg P/ha (6 lb P/ac) furrow treatment. We still need to learn more about the strategic use of starter fertilizer to reduce rates of application on high-P and manured soils.

Table 6. Strategic use of starter P fertilizer for silage corn under contrasting crop histories and manure applications in coastal BC (2000-2002). Seed: fertilizer placed next to seed; Furrow: fertilizer spread in seed furrow; Sideband: 4 cm (1.5 in) below and beside the seed furrow. Shaded cells represent standard farming practice.

Summary of Mycorrhizae and Early P Nutrition in Corn

• P-uptake in juvenile plants affected grain content, dry matter content and to a lesser extent whole-plant yield at harvest.

• P-uptake to the critical 6-leaf growth stage was less than 1 kg/ha (0.9 lb/ac)

• Root colonization by mycorrhizal fungi enhanced uptake of P in corn to 6 leaves. Colonization was not impeded by manure application or sidebanded P at 30 kg/ha (27 lb/ac)

• Root colonization and early P-uptake was impaired when corn was planted on fields previously fallowed or growing non-mycorrhizal crops such as canola.

• Treatments that reduce mycorrhizal colonization and early P-uptake also reduce grain yield, whole plant dry matter content and to a lesser extent whole plant yield.

• Intensive cultivation reduced colonization by mycorrhiza and early P-uptake.

• Sidebanded P at 30 kg/ha (27 lb/ac) and applications of manure at 60kg P/ha (54 lb/ac) improved early corn P status and harvested crop, provided some insurance against poor colonization, but could not completely overcome the effect of poor colonization of roots by mycorrhizae.

• Small amounts of P applied in the seed furrow or near the seed improved early P uptake but did not fully improve final harvest. There may have been a slight inhibition of root colonization with 7 kg/ha (6 lb/ac) of P applied in the seed furrow.

• New approaches are still needed to reduce the requirement for starter P on heavily manured soils typical of many silage-corn fields.

Conclusion

Applying P at seeding is often encouraged as a low cost insurance against early growth suppression and, by personal observation, failure to do this may lead to disappointing growth. However application of unneeded P, even as a starter fertilizer, is uneconomical and can contribute to nutrient loading of surface and perhaps ground water. This problem is most severe in intensively managed farming systems often associated with production of silage corn. It is therefore important to identify those fields that will be responsive to addition of P. While the financial savings on each farm would be small, the potential environmental benefits, resource conservation and cost savings across large geographic areas may be considerable. Perhaps most important for producers, loading of P in the soil would be reduced, allowing higher rates of manure application. It has been suggested as early as 1980 by Stribley et al. (11) that soil test correlations for P might be improved by taking mycorrhizae colonization into account. However, even recent studies showing requirement by corn for starter P on soils having moderate levels of P, often do not measure or consider the possible influence of mycorrhizae. Although farmers are sometimes warned about potential problems with P nutrition under conditions non-conducive to root colonization, there are presently no general recommendations for applying P that take colonization status into account in any crop world-wide. We believe that improved knowledge of mycorrhizae and strategic P application may reduce application rates of starter P in the future.

References

1. Barber, S.A. 1958. Relation of fertilizer placement to nutrient uptake and crop yield. I. Interaction of row phosphorus and the soil level of phosphorus. Agron. J. 50, 535-539.

2. Young, R.D., D.G. Westfall and G.W. Colliver 1985. Production, marketing and use of phosphorus fertilizer p. 323-376 in O.P. Engelstad (ed.) Fertilizer technology and use. 3rd ed. SSSA, Madison, WI.

3. Bates, T.E. 1971. Response of corn to small amounts of fertilizer placed with the seed: II Summary of 22 field trials. Agron. J. 63, 369-371.

4. Jokela, W.E. 1992. Effect of starter fertilizer on corn silage yields on medium and high fertility soils. J. Prod. Agric. 5, 233-237.

5. Barry, D.A. and M.H. Miller 1989. Phosphorus nutritional requirements of maize seedlings for maximum yield. Agron. J. 81, 95-99.

6. Vivekanandan M. and P.E. Fixen 1991. Cropping systems effects on mycorrhizal colonization, early growth, and phosphorus uptake of corn. Soil Sci. Soc. Am. J. 55, 136-140.

7. Thompson, J.P. 1991. Improving the mycorrhizal condition of the soil through cultural practices and effects on growth and phosphorus uptake by plants. pp. 117-137 in C. Johansen et al. (ed.) Phosphorus nutrition of grain legumes in the semi arid tropics. International Crop Research Institute for the Semi- Arid Tropics. Patancheru, India.

8. Zhang, F., C. Hamel, H. Kianmehr and D.L. Smith 1995. Root-zone temperature and soybean (Glycine max (L.) Merr.) vesicular arbuscular mycorrhizae: Development and interaction with the nitrogen fixing symbiosis. Environ. Exp. Bot. 35, 287-298.

9. Evans, D.G. and M.H. Miller 1990. The role of the external mycelia network in the effect of soil disturbance upon vesicular-arbuscular mycorrhizal colonization of maize. New Phytol. 114, 65-71.

10. Miller, M.H. 2000. Arbuscular mycorrhizae and the phosphorus nutrition of maize: a review of Guelph studies. Can J. Plant Sci. 80, 47-52.

11. Stribley, D.P., P.B. Tinker and R.C. Snellgrove 1980. Effect of vesicular arbuscular mycorrhizal fungi on the relations of plant growth, internal phosphorus concentration and soil phosphate analyses. Journal of Soil Science 31, 655-672.

Applying Starter Fertilizer

W.E. JOKELA
Plant and Soil Science Dept., University of Vermont, Burlington, Vermont

Starter fertilizer refers to the placement of plant nutrients in a concentrated zone near the seed with the planter — so named because it gives plants a good early season “start”. Also known as banded or row fertilizer, it refers to an application method or placement of nutrients rather than to a fertilizer type.

Starter fertilizer for corn can result in increased early season growth, increased yields, and sometimes earlier maturity compared to the same amount of nutrients applied as broadcast fertilizer before planting. The advantages of a banded starter fertilizer can be attributed to proximity of the nutrients to the seedling and to increased efficiency of fertilizer use. Early seedling growth is often limited by cool soil temperatures, which slow root growth, plant uptake, and release of N and P from soil organic matter. Hence, placement of nutrients near the roots helps the plants access nutrients, especially P and K, which are essentially immobile in the soil. Band placement also limits contact between soil and fertilizer so less of the P and sometimes K is fixed (tied-up) in the soil. This means more applied nutrients are available for plant uptake.

Crop response to starter fertilizer is most likely with low availability of nutrients and/or cool soil temperatures. As shown in Fig. 1 (top), when soil test P or K are below optimum, band placement of soluble nutrients near the seed is more critical and the probability of a yield increase is high. When soil test P and K are high, yield increases are not as likely (Fig. 1, bottom). Low soil temperatures are more common with early planting, poorly drained soils, and high-residue conservation tillage practices.

Figure 1. Good response of corn to starter fertilizer on soils testing low in P and
K (top) and slight response on soils testing high in P and K (bottom).

Soils with low pH or highly reactive aluminum tie up more of the applied phosphorus, so the advantage of band-placement increases under these conditions. The amount of fixation of K is mainly a function of the type and amount of clay in the soil.

The “starter effect” can occur even when overall soil fertility levels are optimum or higher, but only low rates are required, enough to supply 10 to 20 kg/ha (lb/acre) of N, P2O5, and/or K2O. When nutrient levels are below optimum, starter fertilizer applied at higher rates can be an efficient method to meet the fertility needs of the crop (but see precautions below).

Band placement of fertilizer, especially P, can be considered an environmental “best management practice”. Phosphorus placed in a band below the soil surface at low rates is much less susceptible to loss via surface runoff than surface-applied P and, therefore, less likely to reach streams and lakes where it could degrade water quality. Consequently, the Phosphorus Index, an indicator of potential for P runoff from a field, assigns a lower rating to P applied as a starter fertilizer than to the same amount broadcast on the surface (see The Phosphorus Index to Minimize Water Contamination section). However, even with band placement, excessive application P will enrich the soil and increase P concentrations in runoff.

Using Starter Fertilizer for Corn

Fertilizer materials
A wide range of fertilizer grades are well suited for use as a starter for corn. Phosphorus is the key element for boosting corn growth on cool early spring soils, especially if P soil test levels are low, but some nitrogen should also be included, especially under conservation tillage. Some of the N should be in the ammonium form as it enhances P uptake by the plant. Potassium should also be added if soil test is low. Examples of starter fertilizer include 10-20-20, 10-20-10, 9-23-30, 10-40-10, and 15-15-15. If potassium is not required, then monoammonium phosphate (MAP: 11-55-0) or fluid fertilizers such as ammonium polyphosphate (10-34-0 or 11-37-0) can be good choices. Diammonium phosphate (DAP: 18-46-0) can also be used but note the precautions below. On soils testing very high in P and K, nitrogen fertilizers such as ammonium sulfate can be effective. Dry and fluid fertilizers are equally effective; the choice between forms should be based on cost and convenience.

Band placement
The key to success is to place the fertilizer band close enough to the seedling to provide nutrients but far enough to avoid salt or ammonia injury. The most common placement is 5 cm (2 in) below and 5 cm (2 in) to the side of the seed row (Fig. 2), although distances vary from 3 to 8 cm (1 to 3 in). Low rates of fertilizer can also be applied directly with the corn seed, a method known as “pop-up”. Pop-up application is best suited to high testing soils where only very low rates are needed. This method doesn’t require separate fertilizer openers on the planter. However, extra care must be taken to avoid seedling injury, especially under dry soil conditions (see precautions below).

Figure 2: Typical placement of starter fertilizer band is 5 cm (2 in) to the side
and below the seed although distances can vary from 3–8 cm (1–3 in).

Application rates
The optimum starter fertilizer rate depends on field conditions and on material used. Only low rates (10 to 20 kg/ha or lb/acre of N, P2O5, and K2O) are needed to provide a starter effect. For most dry fertilizers, this means applications of about 110 kg/ha (100 lb/ac), which is a minimum rate for many planters. For example, 100 kg of a 15-15-15 fertilizer would supply 15 kg each of N, P2O5, and K2O (100 lb would supply 15 lb of each nutrient). If soil test P and K levels are high or if manure was applied, this low rate of P and K may be adequate. However, applying 100 units of a high P analysis fertilizer such as 11-55-0 or 10-40-10 may be excessive under these conditions. Under low N conditions, a starter fertilizer N rate of 30 to 50 kg/ha (27 to 45 lb/acre) can carry over the corn plants until sidedress time. This would usually require a fertilizer with a higher N:P ratio, e.g. 1:1 or even 2:1, to avoid excess P.

If soil test levels are in the low to optimum range, then a higher rate of starter fertilizer can be used to supply most or all of the P and significant portions of the N and K. A high amount of P in the starter band is not a concern, but too much N and/or K can cause seedling injury (see precautions below). For soils testing low in P or K, a combination of starter and broadcast fertilizer or manure is recommended.

Precautions with starter fertilizer
Fertilizer salts, primarily N and K compounds, can cause poor germination and seedling injury if excessive rates are applied near the seed. To prevent these problems, limit the amount of N + K2O banded with corn planter. Specific limits depend on soils and weather conditions, ranging from 40 to 100 kg/ha (36 to 90 lb/acre) for 2 x 2 placement and from 5 to 10 kg/ha (4.5 to 9 lb/acre) for seed-placement. Another concern is the release from some N-containing fertilizers of ammonia and nitrite that can cause severe seedling injury, especially in dry soil. Avoid fertilizers containing DAP or urea for seed placement and limit to low rates for 2 x 2 placement.

Farm Experience with Starter Fertilizer

Silage corn
Farmers in a Vermont study (1) applied N-P-K starter fertilizer on a total of 12 field sites at rates to supply P2O5 at high (50-60 kg/ha or lb /acre), low (25-30 kg/ha or lb/acre), and zero (no starter applied) rates. All but two sites also received dairy manure for the current season. The yield response to starter fertilizer varied with soil test P and K levels. Three of the six sites with either P or K testing medium (below optimum) showed a significant yield increase whereas only one of the six sites testing optimum in both P and K responded to starter fertilizer. The responsive site received no manure and had the highest aluminum (Al) test level. The low fertilizer rate was adequate on three of the four responsive fields; only one site showed an additional yield increase from the high rate, probably due to low soil K. On the four responding sites, the average yield increase from the low rate of starter fertilizer was over 3 t/ha (1.4 tons/acre) dry matter basis.

Starter response was also related to soil drainage. Two of the three poorly drained sites responded to starter, compared to only two of six for the somewhat poorly drained sites and none of the three well-drained sites. In this study the earliest planting dates were in mid-May and none of the fields had high-residue conservation tillage. Early planting and/or conservation tillage would probably have increased response to starter.

Grain corn
The response of grain corn to starter fertilizer (rate of 10-20-20 kg/ha or 9-18-18 lb/ac) on soils testing high or excessive in P and K was evaluated in 100 on-farm trials in Wisconsin from 1995 to 1997 (2). On average, starter fertilizer increased yield by about 240 kg/ha (4 bu/ac) compared to no starter. An economical response to starter occurred in 30 to 40% of the trials. The probability of a yield response was greater where soil test K was less than 150 ppm (still in the high range) or when long-season hybrids were planted late. The latter point suggests that starter fertilizer had a beneficial effect by hastening crop maturity. In another series of 20 onfarm trials in Wisconsin, the recommended starter rate of 10- 20-20 kg/ha (9-18-18 lb/ac) was compared to the rate used by the farmer, commonly 2-3 times higher. As in the Vermont research above, there was no yield benefit from the higher fertilizer rate.

Researchers in Pennsylvania evaluated starter fertilizer on high-P soils in 35 trials from 1999 to 2001 (3). Results showed the following: a) yield response to starter fertilizer on high P and K soils are usually modest and uneconomical unless the N component offsets some of the total N requirement; b) sometimes most response is obtained with N, K or ammonium sulfate starters, especially where K is low to optimum and N availability is low in the spring; c) pop-up fertilizer is effective where availability of P, K and N is high.

Reduced tillage increased starter response of grain corn in Minnesota and Indiana. The Minnesota trial showed twice the yield response from starter fertilizer with no-till or chisel ploughing (600 kg/ha or 10 bu/ac) compared to mouldboard ploughing (300 kg/ha or 5 bu/ac) (4). In Indiana yield increase from starter was 500 kg/ha (8 bu/ac) under no-till but only 60 kg/ha (1 bu/ac) under conventional tillage (5).

Conclusions from field trial results
Response to starter fertilizer is most likely with:

  • Below-optimum soil test P or K
  • Soils with poor or limited drainage
  • High-residue no-till or reduced tillage

If soil tests are optimum or higher:

  • Crop response to starter rates higher than about 10-20-20 units are unlikely (unless high-N starter meets part of the crop N requirement).
  • Where N or K availability is limited, more response may be obtained with N, K, or ammonium sulfate starters than from high-P fertilizers.
  • A low rate of pop-up fertilizer is a cost-effective alternative.
  • Yield response is more likely for long-season hybrids planted late.

References

1. Jokela, W.E. 1992. Effect of starter fertilizer on corn silage yields on medium and high fertility soils. J. Prod. Agric. 5, 233-237.

2. Bundy, L.G. and T.W. Andraski 1999. Site-specific factors affecting corn response to starter fertilizer. J. Prod. Agric. 12, 664-670.

3. Roth, G., D. Beegle, M. Antle, R. Bowersox and S. Heinbaugh 2002. Corn starter fertilizers for high P soils. 2002 Pennsylvania Lime, Fertilizer, and Pesticide Conference. Penn State University.

4. Randall,G.W. and J.B.Swan 1991. Conservation Tillage for Corn and Soybean Production. p.173-177. In A report on Field Research in Soils-1991. Minn. Agric. Expt. Sta. Misc. Pub.71-1991.

5. Brouder, S. 1996. Starter fertilizer for Indiana corn production. Purdue University, West Lafayette, IN. http://www.agry.purdue.edu/ext/corn/pubs/starter.htm

Latest on Chloride Fertilizer

C.A. Grant
Agriculture and Agri-Food Canada, Brandon, MB

Chloride (Cl-) is one of the 16 essential nutrients required for plant growth. In the past, deficiencies of Chloride were generally not expected to occur in the field because the amount of Chloride required by crops is considered very low while a significant quantity of Chloride is normally present in soil, rainfall and irrigation water. However, over the last 25 years, reports of increased crop yield and reduced disease incidence with applications of Chloride have been reported in a wide range of field crops in the Great Plains (Fig. 1) and the Pacific Northwest. The concentration of Chloride in the soil where these responses were observed was well above those where Chloride responses would have been expected, based on the traditional understanding of Chloride requirements in crops. In wheat, yield improvement with Chloride application has been linked to reduced disease damage, accelerated plant development, improved kernel weight, and reduced late-season lodging. Chloride application was shown to reduce leaf tissue nitrate content in wheat (Fig. 2), which could reduce crop susceptibility to disease. Some wheat cultivars appear to be prone to a form of leaf spotting which can be eliminated by application of Chloride.

Figure 1. Chloride fertilization increased grain corn yield in Kansas (1).

Figure 2. Effect of Potassium source on wheat tissue nitrate (2)

While much of the work in the Great Plains was on wheat and barley, a number of studies have shown that corn can also benefit from Cl- application. New York state research in 1958 (3) demonstrated increased corn yield and decreased stalk rot in corn treated with KCl rather than K2SO4 (Fig 3). Work at Kansas State University (1) indicated that Cl- fertilization could often increase corn and grain sorghum yields and leaf tissue Cl- concentrations, particularly on soils testing less than 22 kg Cl-/ha. Yield responses were most consistent when concentrations of Cl- in the leaves of the check treatments were below 0.10 - 0.15%. The potential for Cl- to improve corn silage quality by reducing tissue nitrate content should be evaluated.

Figure 3. Effect of K source and rate on stalk rot in New York field-grown corn.

 

References

1. Lamond, R.E., K. Rector and C.J. Olsen 2000. Chloride fertilization for corn and grain sorghum.  (http://www.ppi-ppic.org/far/farguide. nsf/926048f0196c9d4285256983005c 64de/2c9f8f29a58f729986256a16005a 3 0 f 0 / $ F I L E / A R % 2 0 K S - 2 9 F % 2 0 Lamond.doc).

2. Timm, C.A., R.J. Goos, B.E. Johnson, F.J. Sobolik and R.W. Stack 1986. Effect of potassium fertilizers on malting barley infected with common root rot. Agron. J. 78, 197-200.

3. Younts, S.E. and R.B. Musgrave 1958. Chemical composition, nutrient absorption and stalk rot incidence of corn as affected by chloride in potassium fertilizer. Agron. J. 50, 426-429.

Liming to Increase Soil pH

A.M. JOHNSTON¹  and R. DOWBENKO²
¹  Potash & Phosphate Institute of Canada, Saskatoon, Saskatchewan
²  Agrium Inc., Calgary, Alberta

The desirable pH range for optimum corn production is 6.0 to 6.5 (Fig. 1). Soils with a pH 0.2 to 0.3 units below the recommended level should be considered for liming. Liming to maintain an optimum soil pH has several benefits. It reduces the risk of toxicity from aluminum (Al) and other metals, improves the physical condition of the soil, stimulates microbial activity, increases the cation exchange capacity (CEC) in some variable charge soils, increases the availability of several nutrients such as N, P, and molybdenum (Mo), supplies Ca and Mg for plants, and improves symbiotic N fixation by legume rotation crops such as alfalfa and soybeans. Calcitic and dolomitic aglime are the most common lime sources.

Figure 1. Yield response of corn to soil pH. 
(From Lathwell and Reid. 1984. In F. Adams, ed. Soil Acidity and Liming-Agronomy
Monograph 12, 2nd Edition. American Society of Agronomy).

As the Ca (and Mg) in ‘aglime’ dissolve in soils, they displace the acidic hydrogen (H+) ions which then react with carbonate in the limestone, ultimately raising soil pH. Note that Ca and Mg do not directly neutralize soil acidity - rather it is the reaction of the H+ ions with the carbonates. This explains why gypsum (CaSO4) has no direct effect on soil pH. The efficacy of a liming material is expressed as calcium carbonate equivalence (CCE), with all liming materials rated in comparison to pure Ca carbonate (CCE=100).

The smaller the lime particle, the faster it will act in soil (Table 1). Pelletized aglime is usually made from aglime ground to pass at least a 70-mesh sieve, which is formed into 5 to 14-mesh pellets with the aid of clay or synthetic binders. Fluid aglime is a 50% mixture of aglime particles, which have been ground to pass a 200-mesh screen, plus 50% water with a small amount of clay or other suspending agent. Both pelletized lime and fluid products are equivalent to good quality aglime. The choice among good aglime, pelletized lime, and fluid lime is often based on cost, uniformity of application, and urgency of raising soil pH.

Table 1. Lime particle fineness affects acidity neutralization.

The effective neutralizing value (ECCE) of a liming material can be estimated using the formula:

ECCE = %CCE x 0.50 (% passing 8-mesh + % passing 50-mesh).

Thorough mixing in the tillage zone is also necessary for the optimum lime reaction. Aglime should be incorporated in the entire plough layer before no-till crop production is initiated. Surface liming of no-till systems about every three years, based on soil tests, should be adequate.

Manure Nutrients

On-Farm Quick Tests for Manure

D.R. CHADWICK1, S.K.E. BROOKMAN1, J. WILLIAMS2, K.A. SMITH3, B.J. CHAMBERS4, I.M. SCOTFORD5 and T.R. CUMBY5

1Institute of Grassland and Environmental Research, North Wyke Research Station, Okehampton, Devon EX20 2SB UK. 2ADAS Boxworth, Cambridge CB3 8NN UK 3ADAS Wolverhampton, Woodthorne, Wolverhampton WV6 8TQ UK. 4ADAS Gleadthorpe, Nottinghamshire NG20 9PF UK. 5Silsoe Research Institute, Wrest Park, Silsoe, Bedfordshire MK45 4HS UK.

Animal manures contain significant quantities of nutrients that, if managed carefully, can be used to sustain crops and reduce the requirement for inorganic fertilizers. However, it is evident that farmers lack confidence in the nutrient content and availability from animal manures.  In order to exploit this resource effectively, farmers and consultants need good quantitative information on nutrient supply from manures. Recent survey data has shown that UK farmers are more likely to trust information that they can gather themselves. Laboratory analyses of animal manures are relatively expensive and there is often a delay of up to 2 weeks in reporting back to the farmer. This time delay is seen as an inconvenience. For these reasons, the development of reliable, rapid and low-cost techniques for the assessment of manure nutrient supply should encourage the uptake of improved techniques for the management and utilization of manure nutrients.

Several on-farm and rapid techniques are available to quantify the nutrient content of manures, e.g. hydrometers, in-line nutrient sensors on slurry tankers, as well as near infra-red spectroscopy (NIRS) and farmer-operated test kits for analysis of the ammonium-N content of manures. In this article, we describe some recent studies assessing the accuracy and reliability of such techniques.

Quantofix meter for testing ammonium-N content in slurry manure.

Agros meter for testing ammonium-N content in slurry manure.

Ammonium-N test kits

In a comparative study of on-farm ammonium-N (NH4-N) tests, we determined the accuracy of five different techniques, namely: Agros and Quantofix nitrogen meters, reflectometers, and conductivity and selective ammonium electrodes. The techniques were tested under laboratory conditions on 40 slurry, 25 farmyard manure (FYM) and 20 poultry manure samples from commercial units. The results obtained from each method were compared with those from standard laboratory analysis techniques for measuring NH4-N concentrations. There were strong relationships (P

Figure 1. Relationship between Agros estimates of slurry NH4-N content
and l
aboratory analyses.

Figure 2. Relationship between Quantofix estimates of slurry ammonium-N (NH4-N) content and laboratory analyses.

The conductivity electrode and reflectometer generally gave good agreement with the laboratory results for NH4-N, but the strength of the relationships varied according to animal slurry type (r2 >80% for pig slurry; >60% for cattle slurry). The relationship between the ion specific electrode and laboratory analysis of NH4-N was not linear but exponential, which resulted in problems when estimating slurry NH4-N at high concentrations. The readings also tended to drift with time, which made it difficult to decide on the ‘correct’ value.

The most successful techniques in the laboratory (N meters, conductivity meter and reflectometer) were tested by 16 farmers to assess their suitability for use on-farm. The on-farm slurry tests showed that the farmers could also obtain good agreement with the laboratory NH4-N analysis results with both nitrogen meters (the Agros and Quantofix) and the conductivity meter. However, the reflectometer was assessed as ‘impractical’ for on-farm use. The robust construction, simple operation and accuracy of the nitrogen meters meant that they were very suitable for on-farm use and were available for purchase in the market place. The simple mode of operation and ‘instant’ readout provided by the conductivity meter was also popular with the farmers, but a marketable product was not available for purchase by farmers at the time.

Hydrometers

Slurry dry matter content is a useful indicator of nutrient content, particularly P content (Fig. 3). A commercially available, calibrated glass hydrometer was used to assess slurry dry matter content. In the laboratory assessments, there was a strong relationship between the hydrometer readings and laboratory measurements of slurry dry matter content (P

Figure 3. The relationship between cattle slurry dry matter content
and slurry phosphate content. * kg/m3 = 0.1%

In-line sensors

Automatic in-line nutrient sensing offers greater convenience to farmers and contractors compared with approaches based on manual sampling. For example, nutrient estimates are in realtime, and sampling errors are reduced since the method analyzes and records the nutrients in all of the slurry being spread load-by-load; thus complete mixing of stored slurry to obtain representative samples is unnecessary. Initially, this approach was developed in the UK as a small-scale prototype incorporating a combination of standard industrial sensors to measure a set of physical and chemical properties of the slurry. The measured properties of the slurry were electrical conductivity, ammonium ions, density, temperature, differential pressure, flow, pH and redox. This device was used to assess 160 different pig and cattle slurries in 4 European Countries. Each slurry was analyzed for NH4-N, total phosphorus (TP) and total potassium (TK) using conventional laboratory techniques. The output data from the individual sensors were compared with the laboratory values, and statistical correlations were identified from these data sets by linear regression analyses. Hence, algorithms were identified to relate the physical and chemical properties of the slurries to their NH4-N, total P and total K concentrations. NH4-N concentrations were related to the electrical conductivity of the slurry, P was related to slurry density and K related to ammonium ion concentrations.

Based on the promising results obtained from the smallscale prototype, a full-scale version of the in-line slurry nutrient sensing system was constructed with sensors fitted in the side of a 7 m3 (2000 gal) slurry tanker. Thus, as the slurry was mixed by recirculation in the tanker, the slurry properties could be measured and converted to nutrient concentrations in real-time by a computer using the previously derived algorithms. This system estimated the NH4-N, total P and total K to respective accuracies of +/-0.29, +/-0.29 and +/-0.79 kg/m3. The respective ranges over which these values were determined were 0.63 - 5.29 kg/m3; 0.12 - 0.71 kg/m3 and 0.81 - 6.49 kg/m3. Further developments to include global positioning systems (GPS), enhanced data management and in-line systems for solid manures are envisaged.

Solid manures

For solid manures, it would appear that analysis by near infra-red spectroscopy (NIRS) could be a promising approach to quantify several nutrients. This technique has been tested on a limited number of solid manure samples in the UK. NIR spectrophotometer calibration equations for organic matter, dry matter, total N, NH4-N and uric acid-N showed good correlations and low standard errors of calibration. Preliminary validation experiments were undertaken on further manure samples, which gave encouraging results for all the analytes, with the exception of pH, suggesting that it should be possible to develop NIRS into a routine technique. Sample introduction to the NIRS is known to be a critical factor influencing accuracy. Therefore, in a new study, a robust homogenization procedure is being developed.

A potential advantage of using NIRS over conventional laboratory techniques is the use of larger sample size. Also, the rapidity of analysis and potentially lower costs mean that a greater number of samples can be analyszed per unit cost. These advantages mean that analysis can be carried out on a more representative sample of the manure.

Robust and accurate on-farm and rapid tests are available, or are in the process of being developed. However, if the samples being analysed are not representative of the manure supply, then the farmer is not going to make most efficient use of the manure nutrients. A current study in the UK is assessing improvements to sampling protocols for slurry stores and solid manure heaps.

Hydrometers, Agros and Quantofix meters are available from:

  • Managro Harvestore, Headingly, Manitoba — dschmidt@managro.com
  • Sylvette Corp., Minneapolis, Minnesota — www.sylvette.com
  • Qualex Limited. 51 Dauntsey, Chippenham, Wiltshire SN15 4HN UK.
  • Rekord Sales (G.B.) Ltd., Manor Rd, Mancetter, Atherstone, Warwickshire. UK
  • Martin Sykes, Cwm Wyntell, Letterston, Dyfed. UK
  • Or go to: www.agros.se/representation.html

Phosphorus in Livestock Manures

K. BUCKLEY AND M. MAKORTOFF
Agriculture and Agri-Food Canada, Brandon, Manitoba

Phosphorus (P) plays a key role in growth of bones and teeth and in energy processes in livestock. Producers provide supplemental P to their stock to ensure that performance is not hindered by deficiency. The nitrogen (N) to P ratios in manures can vary widely (Table 1) and, in most cases, tend to have narrower values than the uptake ratios of plants (4.5:1 to 9:1), in part due to over-supplementation of P in livestock diets. The imbalance between the N:P ratio in manure and that in crops is made worse by losses in ammonia-N from manure, leading to excessive P in the soil if application rates of manure are based on N requirement.

Table 1. Range of ratios of N:P in different sources of manure (1).

 

The proportion of various P forms in manure is influenced by species and age of livestock, diet, bedding type and method of manure handling. Phosphorus occurs in animal manure in a combination of inorganic and organic forms. In general, 45 to 90 percent of manure P is inorganic and the rest is considered to be organic P. Much of the organic P is easily decomposable by soil microorganisms to the inorganic form. Factors such as temperature, soil moisture, and soil pH affect P mineralization rate.

Some of the inorganic P is water soluble which makes it very mobile and thus susceptible to runoff in surface waters. Although water soluble P is the most available form, labile P, which is the next most available form, is easily liberated to be taken up by the plant. This form is often referred to as the bicarbonate-extractable inorganic and organic P found in manure. The third most available form of P is the sorbed inorganic and organic P that is characterized by its solubility in sodium hydroxide solution. The most recalcitrant form of P, is acid-extractable and generally exists in a stable residual form in the soil. There have been few studies to compare the manures of different animal species in terms of extractable forms (2, 3). In one such study (2), researchers noted that the highest concentration of total P per kg of manure was in swine slurry, followed closely by poultry and then dairy which had almost ten times less total P per kg of manure (Table 2). On the other hand, dairy manure contained the greatest proportion of the inorganic water soluble form of P, relative to the other species of livestock. In poultry manure, the largest portion of P was found to be in the acid-extractable or most stable form, whereas in the swine slurry, the greatest portion of P was found to be in the inorganic hydroxide extracted P form. Since these forms have different plant availabilities, it could be inferred that dairy manure amended soil would have proportionately higher amounts of the readily available P form compared to swine manure amended soils. Likewise the labile P, which is relatively more abundant in poultry manure than other manures would be available for plant uptake. The abundance of the readily available forms of P in dairy and poultry manure should be considered when planning applications in areas where water quality may be at risk due to topographical limitations.

Table 2. Inorganic and organic P fraction concentration and percentages in dairy, poultry and swine manures (3).

Swine and poultry manure contains more acid-soluble P than cattle manure (Table 2). This is thought to occur because swine and poultry produce very little of the phytase enzyme required to utilize phytate-P in grain (2). In contrast, cattle generally produce sufficient phytase, although the amounts vary with age and health, which leads to fluctuations in acidsoluble P in the manure. Furthermore, ruminants are fed different amounts of grain depending on seasonal forage availability, whereas a non-ruminant diet consists primarily of grain. Most water-soluble organic P in manure is in the phytate form with smaller amounts as pyrophosphate (3, 4). Increasing the storage time of swine manure decreases phytate content, liberating the P to be mineralized to a more available form (5). Similarly, increasing the storage time of cattle manure also increases the ratio of inorganic to organic P, raising the concentration of water soluble-P (6).

Diet has the greatest effect on form and amount of phosphorus in manure of all classes of livestock. In cattle, excess P increases the amount of total and inorganic P excreted as well as the proportion of water-soluble P (6). Generally, most of the excreted P can be found in the feces of sows and finisher pigs. Sows, the category of swine more likely to receive this mineral in excess, may excrete 32% of ingested P as soluble P via the urine while only 10% of P intake may be excreted in the urine of finisher pigs (7).

Manure of all species can be treated with elemental salts (aluminum sulfate, aluminum choride, ferric choride, calcium sulfate, fly ash or synthetic polymers) to precipitate soluble P and reduce the risk of P runoff. There is a concern, however, that this process may cause secondary environmental pollution by raising the concentrations of chlorides and sulfates in soil.

References

1. Egball, B. 2003. Phosphorus and nitrogen based manure and compost application. http://manure.unl.edu/v2n9_96.html.

2. Barnett, G.M. 1994. Phosphorus forms in animal manure. Biores. Technol. 49, 139-147.

3. Sharpley, A.N. and B. Moyer 2000. Phosphorus forms in manure and compost and their release during simulated rainfall. J. Environ. Qual. 29, 1462-1469.

4. He, Z. and C.W. Honeycutt 2001. Enzymatic characterization of organic phosphorus in animal manure. J. Envir. Qual. 30, 1685-1692.

5. Dou, Z., K.F. Knowlton, R.A. Kohn, Z. Wu, L.D. Satter, G. Zhang, J.D. Toth and J.D. Ferguson 2002. Phosphorus characteristics of dairy feces affected by diets. J. Environ. Qual. 31, 2058-2065.

6. Joern, B.C., T.L. Provin and A.L. Sutton 1996. Retention of swine manure phosphorous compounds in soil. 1996 Research Investment Report. http:// www.nppc.org/Research/”96Reports/”96Joern-phosretention.htm

7. Poulsen, H. D., A.W. Jongbloed, P. Latimier and J.A. Fernandez 1999. Phosphorus consumption, utilisation and losses in pig production in France, The Netherlands and Denmark. Livestock Prod. Sci. 58, 251-259.

Minimizing Nutrient Movement from Injected Liquid Swine Manure

B. BALL COELHO¹  and R.C. ROY² 
Agriculture and Agri-Food Canada, ¹ London and ² Delhi, Ontario

Pros and Cons of Injecting Liquid Manure

The poor response of crops to surface-broadcast manure can be attributed to losses of nutrients by surface runoff (N and P) and volatilization (N) of nutrients and to low root activity near the soil surface when it is dry. While injection of liquid manure reduces runoff, volatilization of ammonia and odour, it requires increased horsepower and application time, and costly equipment. Injection can be difficult where there is a lot of residue and may leave soil surfaces rough for no-till planting. The disturbed surfaces left by some injection systems leaves these soils exposed to wind erosion. On some soils there is a risk that contaminants from injected manure will move directly into tile drains and surface waters.

In our trials in Ontario, yield of (grain) corn was similar whether N was supplied by inorganic fertilizer or by pre-plant injected liquid hog manure (Fig. 1). Note that we did not plant corn directly into the injection zone to avoid risk of salt injury although a separate trial showed that this was unlikely to occur. All plots received 5 kg P2O5/ha (4.5 lb P2O5/ac) in the seed furrow.

Figure 1. Corn grain yields (1999–2001) with inorganic fertilizer
(sidedressed UAN) were similar to pre-plant manure injected at 2 rates.
The fertilizer and low manure rate treatments received 40 kg N/ha (36 lb/ac)
with the planter. (lb/ac = 0.9 kg/ha)

Nitrate Leaching from Injected Manure on Coarse-Textured Soils
Since conservation tillage is often practised successfully on sandy soils, manure injection systems are needed for these fields. Since these soils are prone to leaching of nitrate, especially where the water table is shallow, special caution must be practised when injecting manure.

In Ontario, nitrate leaching occurs most commonly after the fall corn harvest and in the following spring. Fall leaching can be minimized by avoiding over-applying manure and using cover crops (see Cover Cropping to Manage Residual Nitrogen section). However, in wet years nitrate can leach into groundwater in the weeks after application, even if the manure is injected just before planting in order to synchronize nitrate availability to the demand for N by the crop. For example, continuous rains in June and July of 2000 caused leaching of nitrate from applied manure below the crop root zone (1.5 m deep). It is important to note that more leaching was observed with pre-plant injected manure than sidedressed fertilizer N (urea ammonium nitrate, UAN) (Fig. 2) because more ammonium had been converted to nitrate from manure which had been applied several weeks before the sidedressed fertilizer. Splitting manure applications between preplant and sidedress times would minimize risk of nitrate leaching on sandy soils.

Figure 2. Nitrate concentration in the soil solution below the root zone
(1.5 m or 5 ft) after injecting swine manure before planting or sidedressing
inorganic N fertilizer, in two dry and one (2000) wet year (Norfolk County, ON)

Risk of nitrate movement to groundwater is lower in loamy than in sandy soils, so pre-plant injection of manure may be done more safely on loams. When manure was injected into the tillage band (zone tillage) before planting, yield of corn was equivalent to conventional tillage with starter fertilizer. Manure injected in the fall, however, did not provide appreciable N in spring following a winter with frequent thaws but did provide some N after a colder winter with more snow cover. Note that in some regions, where over-winter leaching potential is high, applications of manure or fertilizer to bare land in the fall is not recommended or allowed. There was no evidence of salt injury from planting into the manure injection zone, but this could be a concern in some situations.

Can the PSNT be used in previously manure-injected soils?
After manure is applied prior to planting, soil nitrate concentration increases gradually as the ammonia in the manure converts to nitrate (process called nitrification), peaking typically just before sidedress time (Fig. 3). The release of N from pre-plant injected hog manure coincides fairly well with the demand of the corn crop. In our trials, the so-called ‘late PSNT’ (sampled a few days before sidedressing) correctly in-dicated that little additional N was required for manured plots whereas earlier soil testing would have incorrectly predicted a requirement of 100 to 200 kg N/ha (90 to 180 lb N/ac) (see Spring N Tests section). Over all trials on loam soils, the PSNT correctly indicated the need for sidedress N in 80% of cases in Huron County (1999) and 93, 100 and 76% of cases in Perth County (2000, 2001 and 2002, respectively). Critical values for PSNT (beyond which yields did not increase with more sidedress N) were 50 kg nitrate-N /ha (45 lb/ac) in Huron County in 1999 and 80 kg nitrate-N /ha (72 lb/ac) in Perth County in 2000.

Figure 3. Pre-plant and pre-sidress soil nitrate tests with inorganic fertilizer or
liquid swine manure at 2 rates, Norfolk County, Ontario. Average of 2 years.
Pre-plant injection was May 29, 1999 and April 27, 2000.

The location of soil samples relative to the manure injection bands is crucial. We found that if one in three ‘late PSNT’ samples was collected from within the manure injection bands and the remainder between bands, about 61-73% of the NH4-N applied in the manure was detected as NO3-N in soil (Fig. 3). We therefore conclude that carefully taken late PSNT samples are useful for soils that have received injected liquid hog manure.

Sidedressing with Liquid Swine Manure
On fine-textured soils, some corn growers find pre-plant application of manure inconvenient because the soil is too wet prior to planting to pull heavy equipment without causing compaction. On these soils, and where tile drains increase the risk of contamination of surface waters, applying some or all of the manure at sidedress may be a better strategy than applying all the manure before planting. In Ontario, sidedressing of manure can be done from 4-6 leaf stage (Fig. 4) until about the end of June (Fig. 5). Generally good corn yields have been observed with sidedressed swine manure using a a 6-row injector mounted on a tank (Nuhn Industries, Sebringville, Ontario) (Figs. 4 and 5). Even narrow-row corn can be sidedressed, for example using a tank with narrow, tandem duals and an 11- row injector.

Figure 4. Sidedressing corn with liquid swine manure, 19 June 2002,
Perth County, ON. Flow control was used to control rate of application.

Figure 5. Sidedressing corn with liquid swine manure,
June 30, 2000, Perth County, Ontario.

In-tank mixing is important for uniform nutrient delivery and flow control helps to adjust application rates at appropriate ground speed. Flow control (Green Lea Ag Centre, Mt Elgin, Ontario) can be used for accurate application rates and convenience of changing rates according to variability in soil nitrate tests, crop yield potential, field history or other factors. It is better to regulate application rates by adjusting flow control than tractor speed. Less calibration is required and optimum ground speed can be maintained. And no one likes to slow down! Coupled with GPS and appropriate software, the system can provide records for nutrient management plans and demonstration of due diligence during manure application. The digitized maps can illustrate rate of application and any set-backs from water courses, etc.

Application rates of liquid swine manure to assure 95% maximum corn yields averaged 50,000 L/ha (5,300 gal/ac) over 1999 to 2002. We tested two methods of sidedressing the manure: injection and in-lay (or topdress). We found that method had little effect on results when application was relatively late (Fig. 6). However, when corn was sidedressed earlier in dry growing seasons (2002), injection out-yielded topdress by up to 3,100 kg/ha (50 bu/ ac) (Fig.7). Also, concentration of N in the grain tended to be higher when manure was injected than when topdressed. Inconsistency in N availability from surfaceapplied  sidedress manure is due to variations in N volatilization, runoff and surface root activity due to differences in soil moisture.

Figure 6. Corn yields (grain) with different rates and methods of sidedressing
swine manure (1999: Huron County, 51 cm or 20 in-corn rows, no-till; 2000:
Perth County, 76 cm or 30 in-corn rows, conventional till).

Figure 7. Corn responds to rates and methods of sidedress manure,
Perth County, 2002. Values on treatment plots application rates in gal/ac.

Nutrient Movement to Tile Drains
Injection of manure can increase movement of contaminants into tile drains, which occurs due to ‘by-pass’ flow through cracks and channels in the soil. In a trial in Perth County, ON, movement of manure to tiles, as indicated by an increase in phosphate concentration, occurred with injection rates above 56,000 L/ha (6000 gal/ac) (Fig. 8). Note that tile water became contaminated very rapidly after manure application (inset, Fig 8). At low rates, sidedress-injected manure containing more than 0.4% N supplied sufficient nutrients for a corn crop. Although less manure is likely to flow into tiles in soils with relatively small worm (night crawler) populations, manure rates in excess of crop requirement should be avoided to minimize residual nitrate concentrations in soil (Fig. 9) since leftover nitrate will move into tile drainage water in fall and the next spring. To minimize movement of contaminants to tile drains, manure should be applied at drier times of the year when tiles are less likely to be flowing. Also, injection equipment that provides sufficient mixing should be employed (see below). In porous loams, application rates should not exceed 56,000 L/ha (6000 gal/ac) whereas in cracking clays, special caution is required at even low application rates to avoid movement of manure.

Figure 8. Phosphate concentration in tile drainage water increases following
high rates of manure application, Perth county. Average of 2 years (2001 & 2002).

Figure 9. Residual nitrate concentrations in the topsoil after corn harvest
increase with sidedress rate of swine manure. Three-yr average from
trials in Huron (1999) & Perth (2000 & 2001) Counties, Ontario.

Injection Equipment for Reduced Tillage

The Yetter Avenger injector (Yetter Farm Equipment, Colchester, Illinois) performs well in high residue fields and leaves the soil surface smooth enough for planting (Fig.10). Optional sealing discs and press wheels which are attached to the scraper blade in front of the drop tube, help to close the injection trench. At application rates exceeding 56,000 L/ha (6000 gal/ ac), ‘wings’ are needed to ensure that all the manure remains below the surface.

The Vibra Shank (Kongskilde Limited, Exeter, ON) can be used in minimum till (Fig. 11) but may leave a rough surface by throwing root clumps, particularly when injecting over old corn rows. Coulters (Ag Systems, Hutchinson, Minnesota) can be added to help manage high residue and increase soil mixing (Fig. 12). Disc hillers (Fig. 13) can be added to prevent preferential flow of rainwater down the injection slot (Nuhn row crop injector, Nuhn Industries, Sebringville, ON). This helps reduce leaching of nutrients and other contaminants, particularly in heavier soils where the injection knives tend to leave open slots. Hillers also allow shallower injection while still keeping manure covered, helping to minimize contaminant movement both to tile drains and by surface runoff. Hillers also leave a good seed bed for planting into the injection zone in conservation tillage systems (Fig. 14). The raised berm provides a good seed bed which warms more quickly in spring promoting faster germination. In contrast the trenches left by injection warm slowly. Using an aggressive injector with the disc hillers, both zone tillage and manure application can be carried out in one pass, a procedure which has come to be called ‘zone-jection’.

Figure 10. Pre-plant manure injection (Yetter Avenger) into no-till corn
residues and overseeded cereal rye cover crop.

Figure 11. Kongskilde Vibra Shank used for pre-plant manure injection (into
killed rye rotation crop) in an experiment conducted in sandy soil in 1999.

Figure 12. Kongskilde Vibra Shank equipped with coulters for residue
handling and increased soil mixing.

Figure 13. Vibra Shank equipped with coulters and hillers (Nuhn row crop
injector) to cover manure and create a berm.

Figure 14. Fall injection into wheat stubble with Nuhn row crop injector
(coulters + injector + hillers) for planting the subsequent corn crop
in the tilled zone.

To determine what type of injection tool allows the least manure to run into tile drains after application, red dye was injected through the applicators, then trenches were dug the next day to expose dye patterns. This study revealed that injected manure can seep through worm holes, bypassing the soil matrix that would otherwise filter out the contaminants (Fig. 15). Manure applied with deep injectors such as the ‘rigid tooth with 25 cm (10 in.)- sweep’ and the Yetter Avenger was prone to leaching through worm channels. In contrast, injection tools which work manure into the topsoil reduce the chance of manure intersecting with worm holes (Fig. 16). Two examples of this type of implement include the Vibra Shank plus coulter, and the Zone Tiller (developed by Agriculture and Agri-Food Canada) which consists of a DMI shank (DMI, Goodfield, Illinois), a coulter and a hiller made from an adjustable fluted coulter.

Figure 15. Movement pattern as shown by dye with injection using a 25 cm
(10")-sweep on a rigid tooth. Material is put down in layer which can intersect
worm holes and move deeper.

Figure 16. Movement pattern as shown by dye with injection using the
AAFC-Delhi Zone Tiller (consists of coulters + DMI shank + berm coulters),
illustrates more mixing of material in the topsoil.)

 

Acknowledgements:  Ontario Pork, Nuhn Industries, Green Lea Ag. Centre, A & L Laboratories, OMAF, DeKalb, Logan Tractor, Da Costa Farms, Van Raay Farms, Bloxslea Farms, T. Groenestegue, K. Otto, V. Hulsof, AAFC Technical Staff and Delhi Farm Crew.

 

Advantages of sidedressing manure include:

  • risk of not getting manure applied if May and June are rainy;
  • yield losses on headlands;
  •  matching row length to tank volume to avoid driving empty. Some growers re-orient rows to better match applicator capacity. Additional roadways and headlands may be needed for large fields.

Disadvantages of sidedressing manure include:

  • reduced movement of ammonium, phosphate, pathogens and other contaminants to surface waters via tile drains because crop roots are actively absorbing nutrients, and tiles are less likely to be flowing than earlier in the season;
  •  better N-use efficiency;
  •  reduced compaction because the soil is probably drier;
  •  PSNT can be used.

Manure Use

Using Solid Manures

T. MISSELBROOK
Institute for Grassland and Environmental Research, North Wyke, UK

Ammonia loss

Most of the readily available nitrogen (N) in solid manure from pigs and cattle (called farmyard manure or FYM) is in the ammonia form. In contrast, readily available N in poultry litter is in the uric acid form, but uric acid can be converted to ammonia fairly rapidly in the soil. The content of readily available N in solid manure will depend on factors such as animal diet, amount and type of bedding, storage period and storage method. For example, compacting and covering manure heaps reduces loss of ammonia during storage. Also, extra bedding is thought to ‘lock-up’ the available N, reducing ammonia emissions from both housing and storage (1). In contrast, actively composting FYM by turning will promote ammonia losses during storage (2) so that very little readily available N is left.

Proportions of readily available N lost as ammonia after applications on the land are typically greater for solid manures than for slurries (Fig. 1) because solid manures cannot infiltrate the soil. Since solid manures contain less available N, less ammonia is lost per unit of applied manure. The amount of ammonia loss for a given application will depend on weather conditions and manure characteristics. In the UK, losses after application averaged 70% of available N from solid cattle or pig manure and 50% of available N (ammonia-N and uric acid N) from poultry manures (3).

Figure 1. Typical cumulative ammonia emission curves for different manure types.

Losses of available N from slurry and solid manures after land application tend to occur over a longer time period from poultry manure than from other livestock manures because the N cannot be lost until uric acid is converted to ammonia (Fig. 1). Therefore, about half the available N is lost within 6-12 h after field applications of solid cattle and pig manures but not until 40 h after application for solid poultry manure.

For solid manures, the only practical measure to reduce ammonia losses after spreading is to

incorporate the manure into the soil. Since much of the emission occurs in the first few hours after spreading, rapid incorporation is essential. The abatement achieved will depend both on the method of incorporation (e.g. plough, rotary harrow, disc or tine) and the speed of incorporation. Few measurements have been made on incorporating solid manures, but Fig. 2 gives an example of the reductions that may be achieved for slurries. Note that a fast but less efficient incorporation tool, such as the tine, may give a better overall reduction in emission if it keeps pace with the spreading operation compared to a more efficient tool, such as the plough, operating several hours behind the spreader (5).

Figure 2. Reduction in ammonia emission from pig slurry applications to arable land for different incorporation methods and timing (4).

N availability from solid manures

When crop yield response is due to the readily available N content of the manure applied, methods that reduce losses from housing, storage and land application will improve availability of N for the next crop. Some of the organic N may also become available during the growing season and in subsequent seasons. The availability of the organic N for crops is related to the ratio of carbon to organic N in the manure (6), decreasing for higher carbon content materials (Fig. 3).

Figure 3. Effect of ratio of carbon to organic N on mineralization of N in manures

Typical analyses of solid manures and their availabilities to crops are given in Table 1. Stored cattle FYM has a lower available N content than that spread fresh from the house, as some N will be lost during storage through ammonia volatilization and leaching, and some available N will be immobilized. Since there will be some loss of mass during storage in addition to N loss, the concentration of total N in stored and fresh FYM will be about the same. Poultry manures have a higher proportion of available N because of the presence of uric acid in addition to ammonia. Actual analysis of solid manure from individual farms can vary greatly, depending on diet, bedding type and amount, storage method and duration, so it is recommended that a representative sample of the manure is analysed at the time of spreading.

Table 1. Nitrogen content and availability for several solid manures (7)

Manure Type

Total N

Available N

% of total N available to next crop

 

(kg/t)

(%)

Autumn application

Spring
application (surface)

Spring
application (incorporated
within 24h)

Fresh Cattle FYM

        6.0        

25

5-10

20

25

Stored Cattle FYM

6.0

10

5-10

15

20

Broiler Litter

30

40

10-20

30

45

Layer Manure

16

50

10-20

35

50

The amount of N that will be available to a crop after manure application depends on the time and method of application. For autumn applications, the majority of the available N will be lost through ammonia volatilization soon after application and by nitrate leaching over the autumn/winter period. Note that in regions where winter leaching potential is high, authorities do not recommend or even allow manure applications on bare land in fall or winter. Nitrogen available for the next crop will predominantly come from mineralization of the organic N. Following spring application, the most important N loss will be via ammonia volatilization. Therefore, incorporation of the manure within 24 h of application will increase the proportion of N available for crop uptake.

References

1. Chadwick, D.R., R. Matthews, R.J. Nicholson, B.J. Chambers and L.O. Boyles 2002. Management practices to reduce ammonia emissions from pig and cattle manure stores. IN: RAMIRAN 2002, 10th International conference J. Venglovsky and G. Greserova (eds.), Strbske Pleso, Slovak Republic, pp. 219-222.

2. Parkinson, R., P. Gibbs, S. Burchett and T. Misselbrook 2004. Effect of turning regime and seasonal weather conditions on nitrogen and phosphorus losses during aerobic composting of cattle manure. Bioresource Technology 91, 171- 178.

3. Misselbrook, T.H., D.R. Chadwick, B.J. Chambers, K.A. Smith, J. Webb, V.R. Phillips and R.W. Sneath 2002. Inventory of ammonia emissions from UK agriculture, 2001. Report to UK Department for Environment, Food and Rural Affairs.

4. Pain, B.F., V.R. Phillips, J.F.M. Huijsmans and J.V. Klarenbeek 1991. Anglo- Dutch experiments on odour and ammonia emissions following the spreading of piggery wastes on arable land. IMAG_DLO Report 91-9, Wageningen, Netherlands

5. Huijsmans, J.F.M. and R.M de Mol 1999. A model for ammonia volatilization after surface application and subsequent incorporation of manure on arable land. Journal of Agricultural Engineering Research 74, 73-82.

6. Chadwick, D.R., F. John, B.F. Pain, B.J. Chambers and J. Williams 2000. Plant uptake of nitrogen from the organic nitrogen fraction of animal manures: a laboratory experiment. Journal of Agricultural Science, Cambridge 134, 159- 168.

7. Anon 2000. Fertiliser recommendations for agricultural and horticultural crops. Ministry of Agriculture Fisheries and Food, Reference Book 209. 7th Edition. London: The Stationery Office.

Using Solid Manure: Vermont Experience

W.E. JOKELA
Plant and Soil Science Dept., University of Vermont,Burlington, Vermont

Livestock manure provides significant benefits for soil health and crop nutrient supply, however, it can also contribute to a range of environmental problems. In fact, well-managed manure can meet most, if not all, of the nitrogen (N) need of a corn crop. Many farm systems have manure that is solid or semi-solid (see Using Solid Manures section). A field study in Vermont (1), conducted on a moderately welldrained loam soil, compared the spring applications of semisolid dairy manure at 55 t/ha (25 T/ac) that was incorporated the same day by mouldboard ploughing or left on the surface without tillage (Fig. 1). Two-year aveage corn silage yields showed a 4 t/ha (1.8 T/ac) yield increase from manure incorporated with mouldboard tillage (MB+M) and no additional increase from fertilizer N. The non-manured treatment required 50 to 100 kg/ha of N to achieve top yields. Chisel plough treatments were found to be similar to the mouldboard treatments.

Figure 1. Whole-crop corn yields (dry matter basis) as affected by combinations of manure (none and manure at 55 t/ha), tillage and rates of N fertilizer in kg/ha (lb/ac). Note that all treatments received 22 kg/ha (20 lb/ac) starter N. (For T/ac, multiply t/ha by 0.45)

Conserving ammonia by timely tillage translates into increased yields. In the Vermont study (Fig. 1), dairy manure incorporated by ploughing within a few hours of application, supplied adequate N for a 20 t/ha (9 T/ac) corn silage crop. However, when the same manure rate was surface-applied in the no-till system, an additional 55 kg/ha (50 T/ac) of fertilizer N was needed.

Reference

1. Jokela, W.E., F.R. Magdoff and D.S. Ross 1989. Tillage, manure and N fertilizer effects on corn silage yield and nitrate leaching potential. P. 243. In Agronomy Abstracts, ASA, Madison, WI.

Liquid Manure: Ammonia Loss and Nitrogen Availability

W.E. JOKELA¹  and J.J. MEISINGER²
¹  Plant and Soil Science Dept., University of Vermont, Burlington, Vermont
²  USDA-ARS, Beltsville Agric. Research Center, Beltsville, Maryland

Maximizing crop utilization of manure nitrogen (N) requires careful management to minimize N losses. Manure N can be lost by several processes — nitrate leaching, denitrification, and runoff of N (see The Nitrogen Cycle section). The process that has the potential for the greatest N loss from manure — and the one most readily controlled by management — is ammonia volatilization. Besides the obviouseconomic loss requiring replacement with purchased fertilizer N, there are the environmental concerns of deposition of ammonia contributing to eutrophication of surface waters (especially marine and estuarine), accelerating soil acidification, and loss of species diversity (1). Ammonia in the atmosphere can also form fine particulates that reduce air quality (see The Nitrogen Cycle section). Further, the decreased amount of available N left in manure reduces the N:P ratio and leads to more build-up of P in the soil for a given amount of available N (see Phosphorus in Livestock Manure section).

For solid manures, direct tillage into the soil is the main avenue for incorporation, but for slurries there are various other application options for conserving ammonia. A number of equipment and management options are available for controlling ammonia loss from manure applied to cropland, most aimed at quick incorporation of manure via tillage or injection. The particular management choice will depend on the circumstances of the individual livestock producer. Adopting manure management practices that conserve ammonium-N can lower fertilizer costs and reduce odors and the likelihood of nutrient loss in runoff, thus providing both economic savings to the farmer and environmental benefits to the society

Nitrogen in Manure

Management of manure N starts with knowing the N content of manure and the relative amounts of the two main forms, urea or ammonium-N and stable organic-N. The urea-N fraction is quickly converted in the soil to plant-available ammonium (NH4 +), and so it is essentially equivalent to fertilizer N. As manure left on the soil surface dries and the pH rises, NH4 + can rapidly convert to ammonia gas (NH3), which is readily lost to the atmosphere. If manure is mixed into the soil, ammonium- N is adsorbed onto the exchange complex of the soil and retained.

The N content of manure varies greatly from farm to farm depending on animal diet, amount of bedding added, water added from rain or milk house waste, etc. For example, a random set of 30 liquid dairy manure samples from Vermont farms showed greater than four-fold range of both ammonium and total N (Fig. 1). Typically, the ammonium fraction comprises about 50% of the total N. Despite the wide range of values the average approximates typical book values. Because of the great variability in manure nutrient content, the only way to know the N content of the manure on your farm is to sample it and have it analyzed (see On-Farm Quick Tests for Manure section). Then it can be used as the basis for determining the manure rate to meet the N crop need.

Figure 1. Nitrogen content (NH4-N and organic N) of 30 random dairy manure samples analyzed by the Agricultural and Environmental Testing Lab, University of Verm

Pattern and Amount of Ammonia Volatilization

Ammonia volatilization losses vary greatly depending on environmental conditions and management. They can range from over 90% of the applied ammonium- N for surface application with optimal conditions for volatilization, to only a few percent when manure is injected or incorporated immediately into the soil. Under typical conditions, losses from dairy manure left on the soil surface range from 30 to over 50%. The ammonia loss is usually greatest during the first few hours after application as shown in Fig. 2. This emphasizes the importance of rapid incorporation of manure to prevent this loss of N. In contrast, drier poultry litter has a slower initial rate of loss than slurries, but losses extend over several days or weeks.

Factors affecting ammonia volatilization include: a) manure characteristics such as dry matter content, pH, NH4-N content, b) application management (especially incorporation and timing), c) soil factors that affect infiltration of manure into the soil (soil moisture, soil properties, plant/residue cover), and d) environmental factors such as temperature, wind speed, rainfall (3). Of these factors, application management offers the greatest potential for reducing NH3 loss and improving N utilization by the crop. Management practices designed to reduce ammonia loss from manure provide other benefits as well — reducing phosphorus runoff losses and controlling odor, which may be as important to many livestock producers as the N savings.

Manure Incorporation by Tillage

The rapid loss of ammonia from dairy slurries (Fig. 2) exemplifies the need for timely incorporation. Even a one-day delay in incorporating manure slurries can lead to loss of 50 to 90% of the ammonium-N. While all tillage methods will help to control ammonia losses from manure if done immediately after application, the more thorough and deep the incorporation, the less ammonia is lost, e.g., tilling with a mouldboard plough is more effective than with fixed tines. Research with dairy slurry in Maryland showed reductions in

NH3 loss of 90 to 98% from immediate tillage with chisel, disk (Fig. 3) or mouldboard plough (Fig. 4). In a Canadian study, disking cattle manure reduced ammonia losses by 85 to 90% (5). Cultivating before slurry application also helps to reduce ammonia emissions by increasing the rate of infiltration into the soil.

Figure 2. Rate of NH3 emission from dairy slurry surface-applied at 65,300 L/ha (17,000 gal/ac) in Williston, VT (2).

Figure 3. Incorporating liquid manure with a disk-harrow immediately after spreading.

Figure 4. Ammonia loss from dairy slurry incorporated by different tillage methods.  Beltsville, MD (4).

Injection and Other Direct Incorporation Methods

A range of equipment options are available for direct incorporation of liquid manure. Direct incorporation can be defined as methods which incorporate the manure directly into the soil without a separate tillage operation, most commonly with knives, chisels, or other tillage tools mounted in the front or rear of a tank spreader (6) (Fig. 5). Injection of manure below the soil surface is the most effective method for controlling ammonia volatilization since there is no exposure of manure to atmosphere (assuming no surfacing of slurry), but there are also other equipment systems for use in annual cropping systems. Deep injection with a knife or chisel (15–30 cm or 6–12 in) has produced large reductions in ammonia missions from slurries applied to corn in the US (7). The reduced ammonia volatilization is generally reflected in improved N utilization and increased yields. Improved N uptake and higher corn yields have been observed in Ontario from liquid cattle manure when it was injected at either pre-planting or at sidedress time compared to surface application (8). Increased corn yields from sidedress-injected dairy manure were reported also in New York (9). In recent years, a horizontal sweep injector (Fig. 6) that operates at a shallower depth (10–15 cm or 4–6 in; Fig. 5b) has become more popular because it provides more even distribution of manure, improves N availability, and requires less power (10). Increased N has been reflected in higher Pre-sidedress Nitrate Tests (PSNT) and higher corn grain yields (see Spring N Tests section).

Figure 5. Equipment options for direct incorporation of liquid manure in row crops or on bare ground (6).

Figure 6. Sweep injection incorporates manure 10 to 15 cm (4 to 6 in) below the soil surface.

A relatively new design, now available commercially from a few companies in Canada and the U.S., does not actually inject the manure but mixes and covers it with soil using either “s-tine” cultivator shanks or pairs of concave covering disks. (Figs. 5c, 5d, 7, 8, 9). Another implement recently marketed in North America bands the liquid manure over openings created with aeration tines (see Low Disturbance Manure Application section). These methods require less power than injection tools and can be operated at a faster ground speed and with fewer problems on stony soils. 

Figure 7. Direct incorporation of liquid manure with an s-tine cultivator mounted on the rear of the tank spreader.

Figure 8. Sidedress of dairy slurry between corn rows with stine cultivators. ont. (For kg/1,000 L multiply lb/1,000 gal by 0.12).

Figure 9. Shallow incorporation of liquid manure with paired-disk applicator (Livestock and Poultry Environmental Stewardship Curriculum; USDA/EPA).

In a two-year trial in Vermont we compared application of liquid dairy manure in the fall (surface-applied, sweep injection, or s-tine cultivation) and spring (s-tine cultivation). Nitrogen availability, as indicated by PSNT values (Fig. 8), was higher for the incorporated (sweep injection, and s-tine cultivation) than surface applied manure, and spring application provided more N than fall application. Manure left on the surface in the fall provided no additional available N. Corn silage yields followed similar trends as the PSNT.

Some farmers, especially in Canada, now incorporate liquid manure at sidedress time, when corn is 30– 60 cm (12–24 in) tall (Fig. 9) (see Injecting Liquid Swine Manure section). This method provides N close to the time of high N uptake by the corn, reducing the risk of early-season N loss, and it allows use of the PSNT to estimate need for N and therefore manure rate. A Quebec study showed better utilization from swine manure applied by “s-tine” incorporation than by deep injection (12). Dairy manure sidedressed with s-tine cultivation in Vermont was as effective for corn silage as fertilizer at equivalent rates of ammonium-N (13). Newer application implements (Fig. 10) are being developed to utilize liquid manure more effectively, conveniently and economically.

Figure 10. PSNT as affected by manure timing and tillage incorporation method in Sheldon, VT (11).

References

1. Asman, W.A.H., M.A. Sutton and J.K. Schjorring 1998. Ammonia: emission, atmospheric transport and deposition. New Phytol. 139, 27- 48.

2. Jokela, W.E. and J.J. Meisinger1999. Personal communication. University of Vermont and USDA-ARS.

3. Meisinger, J.J. and W.E. Jokela 2000. Ammonia volatilization from dairy and poultry manure. pp. 334-354. IN Proc from Managing nutrients and pathogens from animal agriculture. Camp Hill, PA. 28-30

Mar., 2000. NRAES-130. Ithaca, NY.

4. Thompson, R.B. and J.J. Meisinger 2002. Management factors affecting ammonia volatilization from land-applied cattle slurry in the Mid- Atlantic USA. J. Environ. Qual. 31, 1329-1338.

5. Brunke, R., P. Alvo, P. Schuepp and R. Gordon 1988. Effect of meteorological parameters on ammonia loss from manure in the field. J. Environ. Qual. 17, 431-436.

6. Jokela, W.E. and D. Côté 1994. Options for direction incorporation of liquid manure. pp. 201-215. IN Liquid manure application systems. Northeast Reg. Agr. Engin. Serv., Cornell Univ., Ithaca, NY.

7. Hoff, J.D., D.W. Nelson and A.L. Sutton 1981. Ammonia volatilization from liquid swine manure applied to cropland. J. Environ. Qual. 10, 90-94.

8. Beauchamp, E.G. 1983. Response of corn to nitrogen in preplant and sidedress applications of liquid cattle manure. Can. J. Soil Sci. 63, 377-386.

9. Klausner, S.D. and R.W. Guest 1981. Influence of NH3 conservation from dairy manure on the yield of corn. Agron. J. 73, 720- 723.

10. Schmitt, M.A., S.D. Evans and G.W. Randall 1995. Effect of liquid manure application methods on soil nitrogen and corn grain yields. J. Prod. Agric. 8, 186-189.

11. Jokela, B., S. Bosworth and J. Tricou 1999. Manure Application Methods for Corn Field Studies on Direct Incorporation of Liquid Dairy Manure for Fall, Spring, and Sidedress Application in Corn LMWQ-4. Plant and Soil Sci. Dept., Univ. of Vermont, Burlington, VT. http://pss.uvm.edu/vtcrops/NutrientMgt.html #TOP.

12. Côté, D., A. Michaud, T.S. Tran and C. Bernard 1999. Slurry sidedressing and topdressing can improve soil and water quality in the Lake Champlain Basin. Water Sci. and Applic. 1, 225-238.

13. Jokela, W.E., S. Bosworth and D. Meals 1995. Water quality and yield effects of sidedressed dairy manure on corn: first year results. IN Animal Waste and the Land-Water Interface: Poster Proceed., Arkansas Water Resources Center, Fayetteville, AR.

 

Economic Advantage of Rapid Manure Incorporation: Vermont Experience

W.E. JOKELA
Plant and Soil Science Dept., University of Vermont, Burlington, Vermont

Can incorporation help match manure application rate to crop nutrient need? Let’s look at two scenarios for managing manure in corn (see below for soil, manure and crop specifics):

Case 1- spring-applied dairy manure injected or incorporated within one hour

Case 2- spring-applied dairy manure incorporated after seven days

Immediately incorporated manure would provide approximately 2 kg per 1,000 L (15 lb per 1,000 gal) of available mineral N (fertilizer equivalent) (1). Therefore, 64,000 L/ha (6,800 gal/ac) would be required to meet the crop need of 110 kg N/ha (100 lb N/ac). Because of the greater ammonia loss with delayed incorporation, the second scenario would require 108,000 L/ha (11,500 gal/ac) to meet the same N need. If there is additional land available, the difference in application rates (44,000 L/ha or 4,700 gal/acre) would have a potential nutrient value of about $72/ha ($29/ ac) (based on a cost of $0.55/kg or $0.25/lb for N and P2O5). Both management options supply excess phosphorus, but only 31 kg/ha (28 lb/ac) in Case 1 compared to 83 kg/ ha (75 lb/ac) in Case 2.

While manure has historically been applied to meet the crop need for N, concerns about runoff of phosphorus from fields into streams has led to a need to apply manure on a P basis on some fields. How would the two scenarios compare in this regard? In both situations the manure rate required to meet the P recommendation would be the same — 37,000 L/ha (4,000 gal/ac) (assuming 100% fertilizer equivalent for manure P). In Case 1 (quick incorporation) 45 kg/ha (41 lb/ac) of additional fertilizer N would be needed. In Case 2, with delayed incorporation, 71 kg N/ha (65 lb N/ac) would be required. The difference in cost would be about $14.80/ha ($6/ac), based on a price of $0.55/kg N ($0.25/lb N).

Soil, manure and crop specifics

  • Nutrient recommendation for silage corn on well- to moderately well-drained soil (after accounting for starter fertilizer, previous crop and past manure B): 110 kg N/ha (100 lb N/ac) and 44 kg P2O5/ha (40 lb P2O5/ac).
  • Dairy manure analysis: 2.8, 1.4, and 1.3 kg/1,000 L (23, 11 and 10 lb/1000 gal) as total N, ammonium- N and P2O5, respectively, and 8% dry matter. • Fertilizer prices: $0.55/kg ($0.25/lb) for N and $0.55/kg ($0.25/lb) for P2O5.

Reference

1. Jokela, W.E., F. Magdoff, R. Bartlett, S. Bosworth and D. Ross 2004. Nutrient recommendations for field crops in Vermont. Univ. Vermont Ext. Pub., Br1390, Burlington, VT. [www.uvm/~uvmext/publications/ br1390]

A New Low Disturbance liquid Manure Applicator

S. BITTMAN, C.G. KOWALENKO, D.E. HUNT and F. BOUNAIX
Agriculture and Agri-Food Canada, Agassiz, British Columbia

Farmers require low disturbance methods for applying liquid manure that can both reduce emissions of ammonia and odour and reduce the risk of nutrient leaching. A new applicator called AERWAY™ SSD (Holland Equipment, Norwich, ON) is designed to apply slurry to reduced-till corn land with relatively little soil disturbance. The applicator bands slurry over vertical aeration slots that facilitate infiltration of the slurry and contact with the soil. Rapid infiltration of manure reduces odour, loss of ammonia and risk of surface runoff. The aeration slots (10 per sq m or 1 per sq ft) are formed with 20-cm (8 in) long ground-driven tines spaced 19-cm (7.5 in) apart (Fig. 1, left). The narrow spacing between bands means less manure per band and more contact of manure with soil. Less manure per band reduces risk of leaching while the near-ground emitter position minimizes contact with crop residues or canopies and reduces emission of ammonia and odour.

Figure 1. SSD manure applicator showing ground-driven tines and
emission hoses (above). Low disturbance manure application on
permanent grassland (below).

The size of slots are set by the depth and offset angle (0-10°) of the tines. Adjusting the offset settings affects both the degree of soil disturbance and the rate of infiltration. At limited angle, the implement can be used on winter cover crops as tests have shown that repeated use will not damage permanent grass (Fig. 1, right). At maximum angle (Fig. 2) a light tillage is accomplished but crop residue is left on the surface. Our research has shown that the SSD reduces ammonia loss from slurry applied to grass by about 50% and significantly reduced odour (1) compared to surface broadcasting. The applicator also reduces surface runoff and nutrient loss compared to surface applied manure.

Figure 2. Application of liquid manure (approx. 60,000l/ha or 6,000gal/ ac)
with Aerway SSD on conservation tillage silage corn (right) and barley (left).
The unit on left is fed by a drag-hose while the unit on right is tank-pulled.

Reference

Lau, A., S. Bittman and G. Lemus 2003. Odor measurements for manure spreading using a subsurface deposition applicator. J. Env. Sci. Health. Part B 38, 233-240

Chapter 4: Tillage

Tillage Practices for Corn Production

C.F. DRURY¹ , C.S. TAN¹ , W.D. REYNOLDS¹ , C.A. FOX¹ , N.B. MCLAUGHLIN² , and S. BITTMAN³ 
Agriculture and Agri-Food Canada ¹ Harrow, Ontario, ² Ottawa, Ontario, ³ Agassiz, British Columbia

Tillage has been used over the centuries to control weeds, to incorporate previous crop residues, and to prepare the seedbed. The optimum choice of tillage practice is determined by tillage economics and the amount and timing of precipitation, the topography of the field, soil type and crops being grown each year and in rotation. The economics of tillage selection is a balance between the additional costs of the tillage operations versus the additional revenue of the improved yield and quality of the crop. Unfortunately, tillage can also have negative environmental impacts related to increased soil erosion and surface water runoff, loss of soil organic matter, pollution of surface and ground water resources by crop chemicals and nutrients, and evolution of ammonia, greenhouse gases and odours. These negative environmental effects can in turn produce negative economic impacts, especially when large areas or long time periods are involved.

Classes of cultivation

The many methods of tillage have been classified in a variety of ways. The trend is to consider cultivation as “conventional” when there is substantial disturbance of the soil surface and crop residue. Conventional tillage mixes the residues from the previous crop throughout the top 15-25 cm (6-10 in) of the soil. Mouldboard ploughing, a traditional tillage method in many regions, lifts and inverts the top soil (Fig. 1).

Figure 1. Conventional mouldboard ploughing in southern Ontario

Disking mixes the surface of the soil and residues to varying but relatively shallow depths (7-10 cm or 3-4 in). Chisel ploughing lifts and loosens the soil but unlike mouldboard ploughing, does not invert the soil and plant residue. The chisel plough consists of 10 cm (4 in) wide twisted teeth on shanks spaced 38 cm (15 inch) apart. Ridge tillage systems form the soil into elevated ridges in the fall. The ridges dry faster in the spring so the crop can be planted early into the tops of the ridges. The ridges are reformed when the corn is at the 6-8 leaf stage, similar to hilling of potatoes.

Conservation tillage is a term introduced in the 1980’s and refers to a range of reduced tillage systems with no-till (or zero till) being the extreme. By definition, conservation tillage systems leave 30% or more crop residue cover on the soil surface (1). No-till involves minimal soil disturbance with the crop planted directly into stubble from the previous crop.

Over the past few decades, equipment manufacturers have developed a variety of implements to cultivate narrow strips for planting corn and other row crops, leaving the areas between the strips untilled. In this ‘strip’ or ‘zone’ tillage system, 20-cm (8 in) wide strips are cultivated to a 15-30 cm (6-12 in) depth, usually in the fall, with a tool consisting of a centre shank and a wave coulter on either side of the shank (Fig. 2). Corn is planted into the centre of these tilled zones in the following spring. Zone tillage and no-till leave similar amounts of crop residue on the surface on a per hectare basis, although zone tillage leaves thicker residue between the zones (2).

Figure 2. Strip or zone tillage in southern Ontario.

Effect of tillage on soil physical quality

The physical quality of a soil refers to its strength and ability to provide water and air to plant roots. Soil with good physical quality is “strong” enough to maintain good structure, hold crops upright, and resist erosion and compaction, but “weak” enough to allow unrestricted root growth and proliferation of soil flora and fauna. Soil with good physical quality also has fluid (air and water) transmission and storage characteristics that can provide the correct proportions of water, dissolved nutrients and air for both maximum crop performance and minimum environmental degradation (3).

Some useful parameters indicating soil physical quality include bulk density, air capacity, plant-available water capacity, and relative field capacity. Bulk density is an indicator of the soil’s strength and resistance to the growth of crop roots. A soil bulk density that is too high restricts root growth while a bulk density that is too low provides insufficient root-soil contact and water retention for adequate germination and seedling growth. The optimum bulk density for most soils is in the range 0.9-1.2 t/m3 (4). Root growth becomes severely impeded at bulk density values exceeding 1.3-1.6 t/m3 in loam and clay loam soils and 1.6-1.8 t/m3 in sandy soils (5). Note that bulk density of water, referred to as specific density, is 1.0 t/m3 at 4°C (or 39°F). Soil air capacity is a measure of the soil’s ability to store air essential for root respiration; minimum nearsurface air capacity should be about 0.15 m3/m3 (or 15%) (6). Lower air capacity values can result in frequent aeration deficits in the root zone. Plant-available water capacity is a measure of the soil’s ability to store water that can be taken up by crop roots. Soil susceptibility to “droughtiness” increases substantially as plant-available water capacity decreases below 0.2-0.3 m3/m3 (6, 7). The optimal balance between soil water content and soil aeration for crop growth is achieved at a relative field capacity of 0.66, which indicates that 66% of the soil pore space is water-filled and 34% is air-filled (8). This ratio also favours microbial release of plant-available nitrogen (3, 4).

How does conventional cropping (grain corn and soybean rotation) and tillage affect the physical properties of the surface soil layer? We studied temporal changes due to cropping and tillage on Brookston clay loam at Harrow, Ontario by comparing virgin soil, soil in long-term (14 yr) bluegrass (Poa spp.) sod, and soil under 1-, 2-, 3- and 14 yr (long-term) of conventional mouldboard plough tillage. Each successive year of conventional tillage after bluegrass tended to systematically increase bulk density and relative field capacity (Fig. 3). By the third year of conventional tillage, bulk density and relative field capacity had approached values similar to those of longterm conventional tillage. Values for air capacity and plantavailable water capacity followed an approximately inverse pattern to bulk density and relative field capacity (not shown). Even long-term bluegrass sod tended to decrease air capacity and plant-available water capacity below values for virgin clay loam. This study suggests that changes in cropping and tillage can produce rapid and substantial reductions in the near-surface physical quality of a clay loam soil. After only three years of conventional cropping and tillage, all soil physical quality parameters were sub-optimal and generally similar to those of long-term practices.

Figure 3. Bulk density (top) and relative field capacity (bottom) of Brookston clay
loam soil under virgin conditions, long-term bluegrass sod, and conventional till
(corn-soybean rotation) for 1, 2, 3 and 14 yr after bluegrass. The triangles
indicate standard error.

The long-term impacts of cropping and contrasting tillage systems on near-surface soil physical quality were investigated on three different soils:

  •  “structureless”, single-grain Fox sand (90% sand, 5% silt, 5% clay in top 30 cm),
  •  “structured” Guelph loam (36% sand, 48% silt, 16% clay in top 30 cm)
  •  “cracking” Brookston clay loam (28% sand, 35% silt, 37% clay in top 30 cm).

Land management consisted of long-term (14 yr) conventional tillage cropping, long-term (7 yr) no-tillage cropping, and virgin woodlot which had never been cropped or tilled. Conventional tillage consisted of mouldboard ploughing in the spring (Fox sand and Guelph loam) or fall (Brookston clay loam) and secondary tillage (disking and harrowing) immediately before planting. No-till used a standard no-till planter, the planting operation producing the only soil disturbance. The cropping sequence was corn-soybean-winter wheat on the Fox sand and Guelph loam, and corn-soybean on the Brookston clay loam.

The measured bulk density values for all three soil types fell within the optimum range for the virgin soil, but above the optimum range for both tillage systems (Table 1). Minimal impedance of root growth would be expected in the Fox sand but moderate to substantial impedance would be expected in the Guelph loam and Brookston clay loam. Tillage system did not affect bulk density of either the clay loam or sand soils, but the loam soil had a lower bulk density under no-till than conventional till.

The air capacity was greatest under virgin conditions and above the minimum for root growth in all three soils (Table 1). Air capacity was reduced by both tillage systems, but remained above minimum in the Fox sand but below the minimum in the Brookston clay loam and Guelph loam. Air capacity was similar for the tillage treatments in all three soils.

Table 1.  Impacts of long-term cropping using no-tillage and mouldboard plough tillage on soil physical quality parameters.

The plant-available water capacity was reasonably similar and near optimum for all treatments on both loam and clay loam (Table 6). However, for the sandy soil, plant-available water capacity was well below optimum for both tillage systems, and slightly below optimum for virgin conditions.

The loam and clay loam soils had near ideal relative field capacity (0.66) under virgin conditions but above-optimum values under both tillage systems (Table 1). In contrast, the sandy soil had below-optimum relative field capacity for all three management systems. Thus, only the virgin loam and the virgin clay loam had optimum soil physical conditions for microbial production of plant-available nitrogen.

This study showed that long-term production of annual crops using both no-till and conventional till reduced the near-surface physical quality of all three soil types. Under virgin conditions, these soils had bulk density, air capacity, plant-available water capacity, and relative field capacity values that are optimal or near-optimal for field crop production. Under long-term cropping, however, bulk density increased in all three soils to above-optimal values that cause moderate to severe restriction of root growth; air capacity decreased to levels where periodic aeration deficits are likely in the loam and clay loam soils; plant-available water capacity decreased to levels that cause slight droughtiness in the clay loam and severe droughtiness in the sand; and relative field capacity increased in the loam and clay loam to values that are not optimal for microbial production of plant-available nitrogen. It is also interesting to note that the negative impacts on soil physical quality were about the same regardless of whether no-till or conventional cropping was used. Therefore the effects of tillage system on near-surface soil physical quality seem to be minor relative to other factors such as soil texture and cropping in general.

Effect on water quantity and quality

Two field-scale on-farm sites at Woodslee in southern Ontario were monitored to compare the impacts of conventional tillage and no-tillage systems on tile drainage volume and losses of nitrate through the tile drains. Over a 5-yr period (1995-1999), the average annual volume of tile drainage was 48% greater for no-till than for conventional tillage (Table 2). Similar results were reported in Ottawa, where tile drains had  46% more flow under no-tillage than conventional tillage treatments (9). Greater preferential flow due to soil macropores caused by earthworms (10) (see below) and better structure (i.e. greater wet aggregate stability, Table 3) contributed to the greater tile drainage volume under no-tillage relative to conventional tillage.

Table 2.  Mean tile drainage volume, nitrate-N (N03-N) concentration (flow weighted mean), and N03-N loss (per land area) from a Brrokston clay loam soil under long-term no-till and conventional tillage in southern Ontario (1995-1999)

The average nitrate concentration over the 5-year period was 13% lower for no-tillage than for conventional tillage (Table 2). The Canadian guideline value for nitrate in drinking water (10 mg NO3-N/L or ppm) was exceeded in 70% of the tile drainage events from the conventional tillage and in 57 % of the tile drainage events from the no-tillage. The total annual loss of nitrate over a 5-yr period was 30% greater for no-tillage compared to conventional tillage (Table 2). The greater total nitrate loss for no-tillage was primarily due to the larger volumes of tile drainage water lost; the lower nitrate concentrations in the tile drainage water for no-tillage were due to dilution by the larger drainage volumes. Note that the difference in nitrate loss was smaller (30%) than the difference in tile drainage volumes (48%) between these two tillage practices. Increases in nitrate loss with increases in tile drainage volume were found in other studies as well (11, 12). For both no-till and conventional till systems, approximately 80% of tile drainage volume and total nitrate loss in drainage water occurred from November to April when no crop was present to intercept precipitation and make use of water and nitrogen.

Effect on earthworm populations

Minimal disturbance of the soil combined with consistent availability of crop residues as a food source encourages burrowing earthworms and other soil fauna to proliferate in notill systems. Earthworms benefit the soil system (13) by mixing organic materials with soil to form organic-rich aggregates. In the process of mixing soil materials, earthworms also help to redistribute necessary nutrients in the soil profile. Their burrowing activity results in a variety of channels and pores which promote water and air infiltration into the soil (14) and reduce compaction.

Where earthworms have been able to colonize because of favourable climate and soil conditions, earthworm populations are affected by management and land use practices, in particular by (13):

  • the amount and duration that crop residues or amendments (manures or composts) remain on the soil surface;
  •  the duration and intensity of mechanical disturbance from tillage operations.

For example, conventional mouldboard plough tillage decreases earthworm food source by distributing crop residues throughout the plough layer, which both reduces accessibility of the residues to earthworms and promotes more rapid consumption of the residues by soil microorganisms (15). No-till, on the other hand, maintains crop residues on the soil surface where they are highly accessible to earthworms but largely unavailable to soil microorganisms. Intense mechanical tillage, especially mouldboard ploughing, reduces earthworm populations by direct dismemberment, by destruction of burrow networks, and by burying earthworm cocoons too deeply in the soil to hatch.

Figure 4 shows the influence of type of tillage practice on earthworm population numbers. The long-term no-till site (established in 1983) had a mean population of 89 worms/m2 (approximately 89/10 ft2) (range of 43 to 170). Mean population numbers for ridge tillage (50 worms/m2 or /10 ft2) was lower than no tillage but higher than conventional tillage (14 worms/m2). In a comparison of no-tillage and conventional tillage in a paired watershed (16, 17), the no-tillage site was observed to have over 114% more earthworms (163 earthworms/ m2) than the nearby conventional tilled site (76 earth-worms/m2). Similarly earthworm biomass (weight) was greater in no-tillage vs conventional tillage sites.

Figure 4. Earthworm abundance observed on a long-term (since 1983) tillage
site at Woodslee, Ontario, showing mean and minimum and maximum
earthworm numbers/m2 (per 10 ft2) from 1997-2001 (except 2000 when
earthworms moved below sampling depth due to severe drought).

Effects on soil temperature, corn emergence and yield

In fine textured soils in humid regions, cool and wet soils in spring delay planting and crop emergence. Soils are kept moist and cool by residues from previous crops such as winter wheat, which may leave up to 5 t/ha (2.3 T/ac) of straw after harvest. Even in loam soils, residues from a previous crop such as wheat may delay emergence. Compared to bare soils, a surface mulch decreased soil temperatures in a loam soil by 2.2°C (4°F) during early corn growth which resulted in delayed corn development (18). In a clay loam soil from 1998 to 2000, no-tillage soils were 1.2°C (2.2°F) cooler at 10 cm (4 in) depth during early growth (planting to the 6- leaf stage) than conventional tillage treatments (2). The notill soils were also wetter (28.5% volumetric water content) in the top 0-30 cm (12 in) depth as compared to conventional tillage soils (24.0% volumetric water content) during this emergence period. The net result was the cooler and wetter no-till clay loam soils resulted in lower corn grain yields (5.33 t/ha or 85 bu/ac) than the corresponding con- ventional tilled soils (7.33 t/ha or 116 bu/ac). However in a sandy loam soil removing the residue in a no-till system increased soil temperature but not necessarily final yields. Hence, it appears that cooler soil temperatures are more of a problem for delayed emergence and reduced yields in fine textured clay and clay loam soils than in coarse textured sandy loam soils.

Corn emergence following winter wheat was delayed by about 3 days with no-till and was only slightly delayed with zone tillage compared to mouldboard plough tillage (Fig. 5). The plants in zone tillage production reached similar populations as the conventional mouldboard plough tillage while no-tillage populations were 28% lower (64% emergence) than with either conventional tillage (89% emergence) or zone tillage (89% emergence).

Figure 5. Corn emergence in 1998 following winter wheat; corn was either
conventionally tilled, zone tilled or planted into no-till soil.

Effect on long-term yields

The long-term effects of conventional tillage, no-tillage and ridge tillage were evaluated over 20 years on a clay loam soil in Woodslee, Ontario (Fig. 6). Note that continuous corn was grown for the first 14 years of the study, and corn soybean rotation for the last 6 years.

Figure 6. Corn grain yield as affected by conventional tillage, ridge tillage
and no-tillage treatments on a clay loam soil at Woodslee, Ontario. The crop
rotation was continuous corn from 1983 to 1996 and corn-soybean from
1996 to 2003 with each crop present each year (for bu/ac multiply t/ha by 15.9).

Averaged over 20 years in Ontario, conventional tillage corn grain yield (6,500 kg/ha or 103 bu/ac) was 5.3% greater than no-tillage and 1.4% greater than ridge tillage. Although there was profound year to year variation in yield as a result of weather conditions, there was no obvious yield trend due to the maturation of the soils under the no-tillage treatment. In general, the corn grain yields were similar across all three tillage treatments in moist years when yields were above 6,000 kg/ha (95 bu/ac). However, in 1991 and 1993 when yields were reduced by severe July and August droughts, conventional tillage substantially outperformed conservation tillage (Fig 6).

Effects on soil organic carbon and greenhouse gases

Conventional tillage mixes the residues from the previous crop throughout the top 15-25 cm (6-10 in) of the soil surface. Mixing and aeration of crop residues accelerates their decomposition. The effects of tillage systems (no-till, chisel plough and conventional mouldboard plough tillage) on soil organic carbon levels and distribution was investigated across eight soils in Eastern Canada (19). Under varying soil and climatic conditions, tillage system did not significantly affect total organic C and N storage down to a 60 cm (24 in) depth. However, the distribution of C varied with tillage system; there were high organic carbon contents in the surface layers but lower organic carbon contents at greater depths in no-till compared to conventionally tilled soils. In a long-term study in Ontario, no-tillage soils had much higher carbon contents than conventional tillage soils (3.3% vs 2.4%) in the surface 5 cm (2 in), similar carbon contents at 5-10 cm (2-4 in) layer (2.4% carbon), and considerably lower carbon contents at depths of approximately 10-50 cm (4-20 in) (Fig. 7). There was more carbon stored in the top 0 to 50 cm soil in the conventional tilled soil (160 t carbon/ha) compared to the no-till soil (152 t carbon/ha). Although organic matter decomposition is lower in no-till soils, the lower yield during stress years limits carbon inputs and sequestration in this clay loam soil. Hence, there is a desire to find a conservation tillage treatment in these clay and clay loam soils which has similar yields and plant residue inputs (roots and crop residues) but lower rates of decomposition than conventional tillage.

Figure 7. Effect of tillage on soil organic carbon content in the soil
profile in a long-term study in southern Ontario.

Ploughed soil with little or no residue cover is more susceptible to erosion by wind and water, contributing to loss of precious top soil and organic matter. It is estimated that years of cultivation have decreased organic matter in Canadian agricultural soils by 15-30% since cultivation (20).

No-tillage was found to reduce emissions of the potent greenhouse gas, nitrous oxide, by 19 per cent while zone tillage lowered emissions by 38 per cent compared to conventional tillage (Fig. 8).

Figure 8. Nitrous oxide losses from soil with conventional tillage, zone tillage
and no-tillage treatments. The emission were measured during the corn
phase of the wheat-cornsoybean rotation.

Effect on energy consumption

A six -year study (1996 - 2002) on Brookston clay at Woodslee ON compared corn grown in a 3-yr winter wheatcorn- soybean rotation on soils which were either conventionally tilled, zone tilled or were under no-tillage. The tillage treatments for corn following a crop of winter wheat consisted of fall mouldboard plough at 15 cm (6 in) depth; fall zone-till at 15 cm depth (6 in) depth and 20 cm (8 in) width. This study examined corn emergence, corn grain yields, soil physical properties, and emissions of greenhouse gas (nitrous oxide and carbon dioxide). Six-year corn yield averages were 23% lower using no-till and only 6.6% lower in zone tillage compared to the conventional mouldboard plough tillage plots (Fig. 9).

Figure 9. Corn grain yields over 6 years following winter wheat that was
either conventionally tilled, zone tilled or was planted into no-till soil
(for bu/ac multiply t/ha by 15.9).

The yield reductions in zone tillage occurred primarily in 1998 and 2001, the two years which had severe drought conditions during the growing season (2). The decrease in revenue with zone tillage from these lower yields are partially offset by the reduction in fuel consumption and reduced labour costs with zone tillage compared to conventional mouldboard plough tillage.

Conventional mouldboard plough tillage required 20.4 L/ha (2.2 gal/ac) fuel for ploughing as compared to 6.7 L/ha (0.7 gal/ac) for zone tillage (Table 4). Hence zone tillage reduced fuel consumption by 67% (20.4 to 6.7 L/ha or 2.2 to 0.7 gal/ ac) compared to conventional mouldboard plough tillage, because less soil was tilled (i.e 27% of the soil surface is cultivated with zone tillage compared to 100% with conventional mouldboard plough tillage). In terms of drawbar energy, conventional tillage required 99.4 MJ/ha (262 hp-h/ac) to perform the tillage operation whereas zone tillage only required 49.5 MJ/ha (129 hp-h/ac) or a 50% reduction in energy requirements. If the tractor and implement sizes were properly matched, the fuel savings would be approximately the same percentage as the drawbar energy. The reason we found a 67% savings in fuel, and only 50% savings in drawbar energy for zone till over conventional mouldboard plough was that the tractor was overpowered for the mouldboard plough; we should have used a larger plough or a smaller tractor. The different ratios of drawbar energy and fuel consumption for zone tillage and mouldboard plough clearly illustrate how fuel can be wasted with improper tractor-implement match, ie, tractor too large for the implement.

The fuel and energy inputs in Table 4 are only for fall tillage; energy inputs for spring cultivation were not measured. Even greater differences for fuel and energy inputs would be expected when spring operations are considered since planting is done directly into the tilled zones, while mouldboard ploughed soil usually requires two or three spring tillage operations prior to planting.

Table 4.  Fuel consumption and draw bar energy in the fall following winter wheat harvest for conventional tillage, zone tillage

 

SUMMARY

Comparison of Tillage System

Effect

Conventional

No-till

Zone or Strip Till

Improve structure moderate to poor good good
Accelerate soil drying good poor slight
increase water infiltration moderate good good
reduce erosion/runoff poor good good
increase soil temperature good poor variable
increase crop yield good variable good
incorporate residues good poor slight
reduce greenhouse gases poor good good
kill weeds good Poor (immediately) slight
reduce plant diseases good poor slight
reduce fuel & labour costs poor very poor good

References

1. Gregorich, E.G., L.W. Turchenek, M.R. Carter and D.A. Anger 2001. Soil and Environmental Science Dictionary. CRC Press, Boca Raton Florida.

2. Drury, C.F., C.S. Tan, W.D. Reynolds, T.W. Welacky, S.E. Weaver, A.S. Hamill and T.J. Vyn 2003. Impacts of zone tillage and red clover on corn performance and soil quality. Soil Sci. Soc. Am. J. 67, 867-877.

3. Reynolds, W.D., B.T. Bowman, C.F. Drury, C.S. Tan and X. Lu 2002. Indicators of good soil physical quality: density and storage parameters. Geoderma 110, 131-146

4. Olness, A., C.E. Clapp, R. Liu and A.J. Palazzo 1998. Biosolids and their effects on soil properties. P. 141-165. In: A. Wallace and R.E. Terry (eds.), Handbook of Soil Conditioners. Marcel Dekker, New York, NY.

5. Jones, C.A. 1983. Effect of soil texture on critical bulk densities for root growth. Soil Sci. Soc. Am. J. 47, 1208-1211.

6. Cockroft, B. and K.A. Olsson 1997. Case study of soil quality in south-eastern Australia: management of structure for roots in duplex soils. pp. 339-350 in E.G. Gregorich and M.R. Carter (eds.), Soil Quality for Crop Production and Ecosystem Health. Elsevier, New York, NY.

7. Verdonck, O., R. Penninck and M. De Boodt 1983. Physical properties of different horticultural substrates. Acta Hortica 150, 155-160.

8. Skopp, J., M.D. Jawson and J.W. Doran 1990. Steady-state aerobic microbial activity as a function of soil water content. Soil Sci. Soc. Am. J. 54, 1619- 1625.

9. Patni, N.K., L. Masse and P.Y. Jui 1996. Tile effluent quality and chemical losses under conventional and no tillage - Part 1: Flow and nitrate. Transactions ASAE: 39 (5), 1665-1672.

10. Ehlers, W. 1975. Observation on earthworm channels and infiltration on tilled and untilled loess soil. Soil Sci. 119, 242-248.

11. Tan, C.S., C.F. Drury, J.D. Gaynor and T.W. Welacky 1993. Integrated soil, crop and water management system to abate herbicide and nitrate contamination of the Great Lakes. Water Sci. Technol. 28, 497-507.

12. Drury, C.F., C.S. Tan, J.D. Gaynor, T.O. Oloya and T.W. Welacky 1996. Influence of controlled drainage-subirrigation on surface and tile drainage nitrate loss. J. Environ. Qual. 25, 317-324.

13. Tomlin, A. and C.A. Fox 2003. Earthworms and agricultural systems: Status of knowledge and research in Canada Can. J. Soil Sci. 83, 265-278.

14. Shipitalo, M.J. and K.R. Butt 1999. Occupancy and geometrical properties of Lumbricus terrestris L. burrows affecting infiltration. Pedobiologia 43, 782- 794.

15. Fox, C.A. 2003. Characterizing soil biota in Canadian agroecosystems: State of knowledge in relation to soil organic matter. Can. J. Soil Sci. 83, 245-257.

16. Tan, C.S., C.F. Drury, M. Soultani, I.J. van Wesenbeeck, H.Y.F. Ng, J.D. Gaynor and T.W. Welacky 1998. Effect of controlled drainage and tillage on soil structure and tile drainage nitrate loss at field scale. Water Sci. & Technology 38, 103-110.

17. Tan, C.S., C.F. Drury, W.D. Reynolds, J.D. Gaynor, T.Q. Zhang and H.Y. Ng 2002. Effect of long-term conventional tillage and no-tillage systems on soil and water quality at the field scale Water Sci. & Technology 46, 183-190.

18. Fortin, M.C. and F.J. Pierce 1990. Developmental and growth effects of crop residues on corn. Agron. J. 82, 710-715.

19. Angers, D.A., M.A. Bolinder, M.R. Carter, E.G. Gregorich, C.F. Drury, B.C. Liang, R.P. Voroney, R.R. Simard, R.G. Donald, R.P. Beyaert, and J. Martel 1997. Impact of tillage practices on organic carbon and nitrogen in cool, humid soils of Eastern Canada. Soil Tillage Res. 41, 191-201.

20. Gregorich, E.G., D.A. Angers, C.A. Campbell, M.R. Carter, C.F. Drury, B.H. Ellert, P.H. Groenvelt, D.A. Holmstrom, C.M. Monreal, H.W. Rees, R.P. Voroney and T.J. Vyn 1995. Changes in soil organic matter. pp. 41-50 in D.F. Acton and L.J. Gregorich (eds) The health of our soils: Toward sustainable agriculture in Canada. Centre for Land and Biological Resources Research, Research Branch, Agriculture and Agri-Food Canada, Ottawa, Ontario.

 

Does no-till cool silage-corn soil under high rainfall?

D.E Hunt and S. Bittman
Agriculture and Agri-Food Canada, Agassiz, British Columbia

Crop residues shade the soil and keep it moist. Tillage increases contact of soil and air and buries crop residue, thereby helping to dry and warm the soil. Since there is little crop residue in successive crops of silage corn, tillage would be expected to have less impact on soil temperature in silage than in grain corn. Frequent spring rainfalls in coastal BC repeatedly rewet the soil so that tillage may do little to dry out the soil directly. We measured soil temperature on tilled and untilled soil planted to silage corn on several farm fields in coastal BC. The soils ranged from fairly sandy to fairly clayey. We found that when the soil temperature was below 13°C (55°F), there was little difference in temperature between tilled and untilled soil. Above this temperature, tilled soil warmed about 10% faster than untilled soil. As expected, the temperature difference was greatest in rain-free periods, which were more common when the soil was warm.

Figure 1. Relationship between temperature of till and no-till soil at 5 cm (2 in)
depth for silage corn grown on 10 farm fields in coastal BC.

Keys to Success with Reduced Tillage

G. STEWART
Ontario Ministry of Agriculture and Food, Guelph, Ontario

1. Soil drainage

Successful reduced tillage systems for corn must have either good natural drainage or systematic tile drainage. Good internal drainage improves the probability that soils in a notill system will dry and allow for timely planting of corn. Drainage also lessens the risk that soils will become saturated which causes poor root growth and activity, especially early in the season. Producers often discover that no-till is difficult in fine textured soils that are not systematically tile drained.

2. Crop Rotation

The essential message is that “rotations replace tillage”. Continuous corn and narrow rotations do not lend themselves to no-till regardless of what else is done correctly. Crop rotations with a diversity of crops, especially legumes and forages, improve soil structure and help make no-till more successful (Fig. 1).

Figure 1. Reduced tillage is often more successful when crop rotations are
diversified and soil structure is enhanced.

3. Residue management

Balancing the goals of reducing tillage costs for corn, improving net profits, and enhancing the long-term health of the soil requires corn producers to make decisions about how best to handle crop residues, particularly wheat straw. To facilitate no-till or reduced tillage corn production, it is best to remove the wheat straw from the field (Table 1). Removing straw from fields, especially in high yielding wheat crops and on heavier textured soils increases the potential for no-till corn yields to equal those of mouldboard ploughing.

Table 1.  The Effect of wheat straw levels on no-till corn yields at Wyoming, Ontario in 1994-1996.  Un-cut stubble was approximately 25-30 cm (10-12 inches) high.

Where removal of straw from the previous crop is not possible, uniform spreading of the straw and chaff is critical for no-till or reduced tillage success. Even if straw is to be left in the windrow, it is important to spread the chaff as widely and uniformly as possible during combining. Straw choppers on the combine may be useful. In cool wet springs, low soil temperatures, poor growth and potential slug damage brought on by mats of decaying wheat residue often result in yield losses that might have been avoided by uniform residue spreading.

Where the risks of water and wind erosion are high, the benefits of returning all the straw to the soil might outweigh the advantages of reducing tillage. For farms with high erosion risk, reduced tillage systems, even with the need to remove some straw, are probably more sustainable. Another option is to compromise. This will require some light tillage to partially incorporate straw while leaving the soil surface largely protected.

4. Weed Control

For corn yield potential to be realized in no-till cropping systems, optimum weed control is required. Pre-plant burndown of weeds in the spring is critical to allow the crop to develop without interference during vulnerable early growth stages. Weed management will need to target perennial weeds and some new weed invaders, i.e. shift in weed population. (See Weed Control section).

5. Starter Fertilizer (P and K)

Studies in Ontario indicate that nutrient stratification (nutrients concentrated near the soil surface) may occur in long term no-till fields. Without the option to incorporate or mix dry fertilizer material in the no-till system, fertilizer placement is particularly important. Results have shown that the size of the yield response to planter-banded K in no-till often exceeds the response on mouldboard plots. Often the best money spent in setting up a corn planter for no-till is the purchase of no-till, single disk, fertilizer openers that can deliver the fertilizer in all conditions to the right depth without having to bolt on additional coulters (see Fig. 2).

Figure 2. Single disk, no-till fertilizer openers can provide excellent dry
fertilizer placement in no-till situations.

6. Early Season Nitrogen Supply

Another important factor to consider is that no-till soils are often cooler and less aerated than tilled soils. These conditions decrease nitrogen mineralization so that less N is available to the crop early in the season. Failing to apply sufficient N fertilizer at planting time when the remainder of N fertilizer is to be sidedressed may limit yield of no-till corn. A good rule of thumb is to apply 35 kg/ha (30 lbs/ac) of starter N with the no-till corn planter (Fig. 3).

Figure 3. Some no-till planting systems have been modified to deliver
some or all of the nitrogen during the planting operation.

7. Soil Compaction

Soil compaction is often cited as one of the reasons that no-till systems may yield less corn than conventional tillage systems. An option for lowering soil compaction in reduced tillage systems is to loosen some of the soil that is below the seeding depth. This can be done in autumn without disrupting much of the crop residue on the soil surface by confining the operation to zones (strips) where the corn rows will be planted (see Fig. 4). Trials conducted by University of Guelph illustrated that deep in-row loosening generally provided insufficient yield benefit (compared to strict no-till) to pay for the cost of the additional field operation (Table 2). Some growers have claimed benefits of deep ripping on poorly drained areas or in areas such as headlands where soil compaction was excessive.

Figure 4. Deep in-row ripping in the fall prior to reduced tillage
planting in the spring.

Table 2.  The effects of tillage systems on corn yields following winter wheat at Granton, Ontario (loam to clay-loam soil) and Ridgetown, Ontario (clay-loam soil) (Average of 1998-2000)

8. Strip Tillage

Confining fall tillage to narrow zones used for planting corn in the spring is a concept which has received considerable attention over the past few years. The idea is to prepare strips of soil in the fall that are loosened, cleared of residue and hopefully somewhat elevated while leaving the rest of the field covered with residue and protected (see Fig. 5). These strips are drier, less dense and more suited to single pass corn planting in the spring.

Figure 5. The effect of tillage system on soil moisture levels in the
seed zone (0-15 cm deep) in the early May period (sampling dates
ranged from May 1 - 5 May, 2002)

Our ongoing research in Ontario has allowed us to continue to study equipment and practices for fall strip tillage. We are now confident that equipment available to Ontario growers can create uniform, elevated strips in the fall with minor adjustments or additions. The enhanced performance of the strip tillage equipment continues to be reflected in superior spring seedbed conditions.

One of the motivations for strip tillage is to avoid the delay in planting that is often associated with no-till systems, par- ticularly on the medium to fine textured soils. Field scale research continues to demonstrate massive support for the idea that a properly formed berm or strip in the fall can significantly improve soil dry-down and hence planting timeliness (Fig. 6).

Figure 6. Fall strip tillage creating residue-free zones that will
improve planting timeliness the following spring.

Soil Compaction and Corn Roots

N.B. MCLAUGHLIN, D.R. LAPEN, D. KROETSCH, X. WANG, E.G. GREGORICH, B.L. MA AND Y.X. LI
Agriculture and Agri-Food Canada, Ottawa, Ontario

Good soil management creates a favorable environment for healthy root growth. High soil strength can inhibit the penetration of roots, resulting in poor plant growth. Excess soil strength can occur naturally as soil with high clay or low organic matter hardens in droughty conditions, a process called ‘age-hardening’ or ‘hard-setting’. Soil compaction also increases soil strength and impedes root penetration.

Soil compaction is the consolidation of soil particles into close proximity with each other. This not only increases soil strength but also reduces pore volume, soil aeration and natural drainage. Wheel traffic on fields compacts the soil increasing soil strength and reducing yields by 20 to 30% depending on the severity of compaction, soil texture, soil conditions at planting, and weather during the growing season. Full season crops such as corn require field operations in early spring and late fall when the soil is often wet and vulnerable to compaction so producers often face difficult management decisions.

Fine textured soils with high clay and silt content and with low organic matter are especially prone to compaction. Water films around soil particles act like a lubricant allowing the soil particles to slide by each other into a compacted state when loaded with a heavy wheel. There is an intermediate range of water content where the greatest compaction damage occurs. Road builders intentionally wet the road surface to achieve the water content where greatest degree of aggregate compaction can be achieved. Wheel traffic in very wet conditions can surface seal (crust) the soil which is an added problem.

Surface Compaction

Soil compaction is sometimes classified as surface and subsurface. Surface compaction is usually caused by high contact pressure between the wheel and the soil surface, and is related to the tire inflation pressure. Surface compaction is visually evident as a smooth shiny surface of wheel tracks due to reduced pore space, and water laying in the wheel tracks due to reduced natural drainage (Fig. 1). Large hard clods on the soil surface following tillage also indicates surface compaction. Tillage can help break up surface compaction in a conventional tillage system, but this is not an option in a no-till system. Freeze-thaw cycles in spring and fall and use of forage crops in a rotation naturally loosen compacted soil. Surface compaction can be reduced by reducing traffic, using lighter machines, using dual wheels and larger tire sizes and reducing tire inflation pressure. Modern radial tires can usually be run at lower inflation pressures than bias ply tires. Manufacturers’ recommendations should be consulted for the correct inflation pressure for a given axle weight.

Figure 1. Soil trafficked after heavy rain; despite minimal rutting, infiltration has been reduced, with some water lying in the wheel tracks. The shiny soil surface indicates reduced pore space.

Subsurface Compaction

Subsurface compaction, often called a plough pan, is usually more problematic than surface compaction since it is not easily detected and is not corrected by natural freezethaw cycles. It is caused both by tillage and by traffic with heavy field machinery. A tillage tool passing through the soil compresses the soil in a roughly spherical zone above and immediately below the leading edge of the tillage tool. This compression causes the soil to break up or fragment, which is the desired effect of tillage. However, there is little opportunity for fracture planes to develop in the zone immediately below the tillage tool, so the soil remains in a compressed or compacted state. This compressed zone is called a “plough pan” because it is located immediately below the tillage depth, and because it was first identified in mouldboard ploughed fields. Repeated tillage operations over several years can contribute to both the formation and downward extension of a plough pan.

Compressive stresses from heavy axle loads can compact the soil to depths well below normal tillage depth. While reducing tire inflation may help to reduce surface compaction, reducing subsurface compaction must take into account total axle weight. Very heavy equipment such as grain buggies and liquid manure spreaders are especially problematic; hence confining grain buggies to headlands and applying liquid manure with drag hoses can help reduce compaction. A Swedish study found that the costs of soil compaction from manure spreading may be as large as the value of the plant nutrients in the manure.

Identifying Subsurface Compaction

Subsurface soil compaction is more difficult to detect than surface compaction. Poor crop performance and water ponding due to poor drainage may indicate underlying compaction. Plant roots can be exposed and the pattern of root growth observed by carefully removing soil from the walls of a pit. Roots take the path of least resistance, traveling horizontally along the periphery of compacted zones (Fig. 2 left) compared to the vertical movement for non-compacted soil (Fig. 2 right). Sometimes, roots will follow a crack in the soil fanning out within the crack (Fig. 3), because they are unable to penetrate compacted soil and reach water and nutrients beyond the crack.

Figure 2. Corn roots in compacted (left) and non-compacted (right) heavy clay soil from an experiment in Australia. Roots were not able to penetrate the compacted layer so growth was stunted.

Figure 3. Corn roots following a crack in compacted soil; the roots have fanned out in two dimensions within the crack, but have not penetrated the hard soil on either side of the crack.

Preventing and Remediating Soil Compaction

  • Soil compaction can be best prevented by staying off wet fields. Subsurface drains and contouring promote drainage helping the soil dry out.
  • Tire inflation pressure may be lowered as this spreads the axle load over a larger surface area. Tire manufacturers literature should be consulted to determine the proper tire inflation pressure.
  • Always driving over the same tracks (tramlines) reduces overall field compaction. This is especially effective when all field implements have the same working widths (preferably large). Because the suppressed growth strips are narrow, plants growing adjacent to the compacted tramlines will have access to additional light, water and nutrients, hence produce compensatory growth.

Deep tillage is often suggested as a method of breaking up plough pans. However, this operation is expensive, not always successful and may even cause additional damage in wet soils. Deep tillage is likely to be most effective if performed when the soil is very dry in late summer after harvest of a cereal or forage crop. It may be best to try deep tillage in a small test area known to have a subsurface compaction problem.

Compaction Demonstration Experiment

A compaction experiment was conducted in 2002 and 2003 at the Central Experimental Farm (CEF) in Ottawa to examine the effects of untimely field traffic. The objective was to determine the impact of wheel traffic compaction, such as might occur as a result of early spring spreading of liquid manure on wet soil, on the germination, growth and yield of corn. After compaction, the field plots were cultivated, fertilized and planted using normal procedures for the region.

Compaction reduced corn plant establishment and plant height in both years. In 2002, compacted plots yielded 8.0 t/ ha (127 bu/ac) compared to 8.4 t/ha (134 bu/ac) for the noncompacted plots. In 2003, compaction reduced yields by 3.1 t/ha (49 bu/ac). Field plots compacted in 2002 continued to reduce yields in 2003. The non-compacted plots also responded better to fertilizer. These results clearly demonstrate the damage that can be done by driving on fields when they are too wet.

By excavating the soil and carefully exposing roots we found that roots in the compacted strip (Fig. 5 right) exhibited much less branching than those in the non-compacted strip (Fig. 5 left). As in Fig. 3 above, roots in the compacted areas tended to follow cracks, fanning out in two dimensions within the crack.

Figure 5. Corn roots in non-compacted (left) and compacted (right) soil;
note the difference in branching of the corn roots.

Testing Soil Strength

Soil strength can be measured with a cone penetrometer which measures the force required to push into the soil, a probe fitted with a standard 12.7 mm (0.5 inch) diameter, 30 degree conical tip. In a sense, the penetrometer mimics a root pushing its way into the soil. Compaction testers consisting of a probe and a dial gage to indicate penetration force are commercially available for on-farm use. A simple manual probe can be made from a one meter (40") length of 9.5 mm (3/8") stainless steel rod, fitted with a conical tip, and a T-handle (Fig. 4). The tip can be made by first building up the surface of the rod end with a weld bead, and then machining or grinding it to a conical shape. By comparing the effort required to push the probe into known compacted areas (such as headlands) to un-compacted areas (such as fence lines), one can quickly develop a “feel” for degree and extent of soil compaction.

Soil strength is measured in units of pressure: 1 Mega Pascal (MPa) = 145 lb per square in (psi). Root growth is reduced by about half at a penetration resistance of 2.0 MPa (290psi) and severely limited at 3.0 MPa (435 psi). The 2.0 MPa threshold is equivalent to a force of about 26 kg (57 lb) to push the 0.5 inch diameter probe into the soil; penetration resistance in compacted soils can be two to four times this value. Higher soil water content typically results in lower penetrometer values so assessments should be carried out at consistent soil water contents.

Figure 4. Simple probe with conical tip and T-handle for
investigating subsurface soil compaction.

Chapter 5: Cover Crops

Cover Cropping to Manage Residual Nitrogen

R.C. ROY¹  and B. BALL COELHO²  
Agriculture and Agri-Food Canada, Delhi¹  and London², Ontario

Why plant a cover crop after corn?

It is well recognized that corn responds to nitrogen (N) applications and that corn yields vary considerably from year to year. The predominant factor for the variation in yield from year to year in southern Ontario is weather, particularly the amount of rain during the growing season. The effect of rain is amplified when corn is grown on sandy soils which have limited water storage capacity. This variability in growth potential due to summer rainfall results in substantial variability for the crop to utilize N in the soil. This is shown by the low grain yield response in dry years (1993 and 1999) compared to wet years (1994 and 2000) for corn grown on a sandy soil (Fig. 1). The years when there was limited response to increasing rate of N fertilizer application there was an increase in residual nitrate in the soil. This residual soil nitrate is vulnerable to leaching into the ground-water in late autumn and early spring.

Figure 1. Variation in response by grain corn to applied N on a
sandy soil in Ontario (for bu/ac multiply kg/ha X 0.0159).

Since it is not possible to predict the weather during the growing season, it is not possible to determine how much N fertilizer should be applied to the crop to ensure optimum growth and minimum residual nitrate in the soil after the crop is harvested. A winter cover crop can be used to take up the residual soil nitrate after corn has been harvested.

What cover crop is best?

Cover crops can be used for several purposes including minimizing erosion, increasing organic matter content in the soil and conserving N. Choice of cover crop should be based on its primary purpose. Non-hardy crops such as brasssicas, oilseed radish, oats and bin-run corn grow in the autumn but will be killed by winter conditions, releasing more than 50% of their tissue N in back into the soil. The released N is vulnerable to leaching in spring. Legumes can fix N from the air, thus potentially adding N to N-deficient soils. While forage grasses (perennial ryegrass, fescues and bromegrass) are good scavengers of soil N, these crops establish rather slowly so have limited capacity to take up N when planted after corn harvest. Interseeding ryegrass into corn has been successful in heavier soils of Quebec, but not in sandy soils of Ontario which become very dry in summer. Winter cereals, such as rye, appear to be the best cover crops for capturing residual N after corn in southern Ontario. Rye establishes and grows vigorously in the fall taking up significant amounts of soil N. Also, rye resumes growth early in spring.

When is the best time to plant rye as a cover crop for corn?

Seeding rye after grain corn has been harvested does not allow much time for substantial growth and use of soil N in the autumn. However, measurements in southern Ontario showed that rye planted into standing corn took up substantial residual N from the soil, especially during the dry years when the soil N was not utilized by corn (Fig. 2). Nitrogen uptake ranged from only 10 kg/ha (9lb/ac) after favourable corn seasons up to 50 kg/ha (45 lb/ac) after the dry summer of 1999 (Figs. 1 and 2), reaching 60 kg N/ha (54 lb/ac) by the following spring.

Figure 2. N-uptake by rye N (in November) increases with fertilizer N rate
applied to corn, especially in dry years (1993 and 1999) when N uptake by
corn is low (for lb/ac multiply kg/ha by 0.9).

Overseeding into an established corn crop in August may be the optimal method for establishing a rye cover crop. The rye generally becomes well established with late-summer rains, but does not compete with the corn for water, nutrients and light (Fig.3).

Figure 3. Cereal rye overseeded in August into standing corn grown
using conventional tillage and 200 kg/ha (180lb/ac) of fertilizer N.
Photo taken 21 Dec. 2001.

Measurements over three years have shown that regular overseeding in continuous corn reduced the amount of nitrate in soil water below the root zone (1.5 m or 5 ft depth) not only during late autumn and early spring but even during the following corn crop (Fig. 4).

Figure 4. Nitrate concentration in the soil solution (at 1.5 m or 5 ft depth)
over 3 years in Norfolk County, Ontario with and without cereal rye
overseeded into standing corn.

Does overseeded rye fit with conservation tillage?

Since rye resumes its growth in the spring, it has to be killed prior to replanting corn in the second year. In conservation tillage systems, the rye can be killed by cultivation. However, in no-till systems where the rye is killed by herbicide, there will be stubble both from the previous corn and the rye cover crop. Planters are now available with trash whippers to remove the residue from the planted row (Fig. 5).

Figure 5. No-till planting into killed rye cover crop using trash whippers

Long-term effects of rye overseeding

Our research has shown that overseeding rye into grain corn can be effective in both conventional and no-till systems. On average, the N response curves shifted upward after rye relative to winter fallow under both conventional and no-till systems. The cover crop often boosted no-till yield above conventional tillage. Over a seven-year period, average corn (grain) yield was greater after overseeded rye than after winter fallow in both tillage systems, particularly when adequate fertilizer- N was provided (Fig. 6).

Figure 6. Long-term (7-year average) yield response curves for corn to N
shift up with overseeded cereal rye cover crop in conventional and no-till
(for bu/ac multiply kg/ha X 0.159).

The trend was for increased yield response to the cover crop over time. Yield advantage with long-term use of cereal rye cover crops has been reported also in Washington State and Holland. Some of the yield gain from the overseeded rye was probably due to improved soil properties, as indicated by improved wind-erodible and wet aggregate stability of the soil (Fig. 7). To avoid any potential yield depression with rye overseeding, the cover crop should be killed a week or two prior to planting, before the C:N ratio gets too wide (over 30). Early kill prevents the cover crop from tying up N, causing allelopathy or depleting soil moisture.

Figure 7. Soil wind-erodible fraction decreases and wet aggregate stability (WAS) increases with overseeded cover crop (after 5 years) under no-till.

How to overseed rye into corn

Seeding rye into a relatively mature corn field is an operational challenge. In our research trials, the rye was overseeded by hand. On a commercial scale, specialized elevated field implements, such as a Hi-boy, is one option for overseeding the rye. An alternative is to aerial seed from an airplane. As part of the Lower Big Otter Remedial project to reduce sediment loading into the Big Otter Creek and Lake Erie in Ontario, the Long Point Region Conservation Authority aerial-seeded rye into three established commercial corn fields in the watershed in the summer of 1997. Establishment of rye was generally good (Fig. 8) except where there were late-season grass escapes and spots in the field where soil pH was less than 4.

Figure 8. Cereal rye cover crop overseeded into standing corn
(16 ha field) by aircraft as part of the Lower Big Otter Remedial Project,
April 1998. Note effect of soil texture.

The overseeding did not affect corn grain yields in the year of rye seeding and corn grain yield was increased by 880 kg/ha (800 lb/ ac) in the subsequent year. The overseeded rye took up about 20 kg N/ ha (18 lb/ac) in the fall on all fields and noticeably reduced spring nitrate concentrations in the soil in two of the three fields (Fig. 9). Aerial seeding at 180 kg/ha (160lb/ac) costs about $74/ha ($30/ac), including $25/ha ($10/ac) for seed. Based on our long term experiment, overseeding costs would be paid back in 3-6 years thanks to increased yield of grain corn. There are additional benefits of cleaner drinking and surfaced waters and improved soil structure.

Figure 9. Nitrate-N in the soil profile to 0.9 m (3 ft) depth in spring as
affected by a rye cover crop on 3 Ontario farms in 1998.

Cover Crops and Relay Crops

S. BITTMAN, D.E. HUNT and C.G. KOWALENKO
Agriculture and Agri-Food Canada, Agassiz, British Columbia

Importance of maximizing the growth period for corn

There is a dilemma for producers wishing to grow silage corn with little environmental impact. The crop is usually harvested four or more weeks after most nutrient uptake has ceased. Therefore, N mineralized after mid- to late August accumulates in the soil until it is leached by late autumn rains. Figure 1 shows the accumulated uptake of N by corn hybrids of varying maturity in coastal BC. Nitrogen remaining in the soil or mineralized after mid-August will be subject to loss over winter unless a winter cover crop is grown.

Figure 1. Effect of number of growing days and harvest date on N-uptake by silage corn hybrids varying in maturity in coastal BC. Silage corn removes very little N from the soil after August 22.

Cover crops can be planted after corn harvest to capture residual soil nutrients, especially N, and to reduce runoff and erosion. Unfortunately, the goal of maximizing corn yields conflicts with that of growing robust cover crops. The problem is that yield of silage corn, especially the accumulation of grain yield, is very closely tied to the length of the growth period for the corn. Advancing harvest reduces accumulated corn heat units and reduces grain yield regardless of corn hybrid, as shown in Fig. 2.

Figure 2. Effect of increasing accumulated corn heat units by delaying harvest on grain yield of 4 silage corn hybrids varying in maturity BC over 3 years (for bu/ac multiply kg/ha X 0.159).

Similar results were obtained from a study of 27 farms in coastal BC (Fig. 3). Here we see that over a range of soils, cultivars, management practices and pests on commercial dairy farms, over 50% of difference in grain yield of silage corn among fields could be attributed to the number of growing days for the crop. The growing period had less effect on whole crop yield and dry matter content at harvest than on grain yield. Good P nutrition improved grain yield and dry matter content at all planting dates. Note that the growing periods for corn crops ranged from about 110 to 150 days. Obviously, for over 200 days each year, many of them rainy, the soil lies bare and subject to runoff and leaching if no cover crop is planted.

Figure 3. Effect of growth period from planting to harvest on grain yield of silage corn on 27 farms in coastal BC in 2002. About 56% of the variation in grain yield among all the farm

It is evident that farmers try to maximize yield by delaying corn harvest until days are short and the weather has deteriorated. Since growing conditions further decline after corn harvest, with each passing day that cover crop planting is delayed, the potential for growth and N-recovery by cover crops declines noticeably. Trials were conducted at Agassiz, BC to examine the decline in N-recovery by cover crops with delayed planting (Fig. 4). For the Aug. 22 cover-crop planting date, which is much earlier than corn is ever harvested, all crops took up 60- 95 kg/ha (lb/ac) of N (Fig. 5). By the Sept. 5 planting date, N grain corn uptake by both legumes fell off although uptake by the nonlegumes remained fairly constant. Even the non-legumes took up no more than 45 kg N/ha (lb/ac) after a Sept. 15 planting date. By Sept 20, no more than 30 kg of soil N can be recovered by the cover crop, regardless of species. These results show that planting date is a much more important factor than choice of cover crop for fall N-uptake, and that no fall-planted cover crop will remove much N from the soil when planted after late Sept. For late (after September) planting, fall rye is consistently the best performer, although this crop is rarely harvested for feed in spring by BC dairy farmers.

Figure 4. Trial at Agassiz BC testing the effect of planting dates (top) from Sept. 1 to Oct. 1 (strips) and cover crops (plots within strips) on fall N recovery and and spring growth (bottom)

Figure 5. Effect of planting date on fall N-uptake by several cover crops in coastal BC.

Relay cropping

While the long period of bare soil seems to provide an opportunity for growth of a second crop, efforts to fully exploit the growing season for production of silage corn necessarily result in less favourable conditions for the cover crop. Of the 110 -140 days that a corn crop is in the ground, there are at least 30 days in which the canopy is small and open and much of the ground exposed to sunlight. The after-planting period when the corn canopy is open represents additional time with good growing conditions to grow another crop, provided that it does not compete with the corn. This is the thinking behind the concept (see Whole Farm Nutrient Management section) of ‘relay cropping’ which developed in BC, the Netherlands, and other places. Relay cropping is currently being carried out by many of the corn growers west of the Cascades in BC, Washington and Oregon (Fig. 6).

Figure 6. Relay crop trials at Agassiz BC in the early 1990’s showing planting at 6 leaves (top left), growth between corn rows (top right) and corn harvesting with inevitable wheel damage (bottom)

Relay cropping is designed to establish the winter cover crop while the corn is very small, to take advantage of the open canopy, so that the cover crop is well established by the time the corn is harvested (Figs. 6-7). A successful relay crop must be able to persist in the shade and humidity under the closed corn canopy and withstand probable disease burden and dry soils. There must also be compatible methods for weed control, and the relay crop must be tolerant of wheel traffic during the corn harvesting 0peration. Several crops that failed to withstand prolonged periods under corn in our trials include fall rye, winter wheat, winter canola, typhon rape, hairy vetch and crimson clover. The two crops that did persist were Italian ryegrass and red clover. Of the different types of Italian ryegrasses, we found that the tetraploid biennial varieties performed better that the diploid biennials which in turn were better than the Westerwold annual types.

Figure 7. Relay-crop at Kambro Farms in Matsqui, BC on 7 Jan 2003.

After evaluating candidate crops, we performed a series of experiments to determine best cropping practices to establish the relay crop including optimum corn population density, optimum growth stage of corn for planting the ryegrass and the impact of date of corn harvest on producing a successful relay cover crop. The purpose of the relay crops was to:

  • capture the maximum amount of residual soil nitrogen in the fall
  • provide ground cover to protect against erosion and runoff
  • produce enough yield in spring to offset the cost of growing the relay crop and decrease the need for purchased feed, hence reducing importation of nutrients to the farm (Fig. 7).

Figure 8 shows that reducing corn population from the standard 75,000 per ha (30,000 per ac) to 55,000 per ha (22,000 per ac) reduced yield of corn by about 1,500 kg/ha (lb/ac). As expected, a significant yield loss was caused by advancing harvest by 2 weeks (from late Sept. 20-25 to mid Sept. 7-10). The relay crop itself had very little effect on yield of corn. Even if ryegrass was planted when the corn had only 3 leaves, there was only about 500 kg/ha (lb/ ac) reduction in corn yield compared to the planting into 6- to 9-leaf corn. The inter-planting operation seemed to slightly increase corn yield over the control, possibly due to the soil disturbance caused by the double-disk openers which might have led to release of nutrients. Red clover planted at 6 leaves also had a very slight positive effect on yield of corn.

Figure 8. Whole-crop yield of silage corn as affected by corn population, corn harvest date (mid- or late Sept) and relay crops planted at different corn growth stages (mean of 6 trials 1993-95) fields was related to length of growth period.

The amount of ryegrass growth that occurred up to corn harvest (Fig. 9) ranged from 300 to 1200 kg/ha (lb/ac) (Fig. 10). Growth of ryegrass under the corn was enhanced by low corn populations, planting the ryegrass early and harvesting the corn early. Red clover produced less than a third the biomass of ryegrass. At this time roots produced about 60 to 80% the amount of biomass as the tops. The ryegrass contained 15-25 kg/ha (lb/ac) of N in the shoots and 5-10 kg/ha (lb/ac) of N in the roots.

Figure 9. Moderately (top) and well established (bottom) Italian ryegrass relay crop in a corn stand

Figure 10. Yield (above ground) of Italian ryegrass and red clover relay crops at time of corn harvest at Agassiz, BC (mean of 6 trials 1993-95). The relay crops were planted at different corn growth stages and corn populations. Corn was harvested in late Sept. except for one ryegrass treatment (early to mid Sept).

When the corn was harvested, the ryegrass was subjected to damage from wheel traffic and, immediately after harvest, to stress from sudden exposure to full ambient light and wind. As a result, the ryegrass grew slowly for 1-2 weeks after corn harvest before resuming more rapid growth. Ryegrass growth continued well into autumn as the grass does not tend to become dormant. Similarly, uptake of N continued through the autumn so that by early to mid-November, herbage of ryegrass relay crop contained 18-61 kg/ha (lb/ac) of N (Fig. 11a) and the roots contained another 10-20 kg/ha of N (not shown). By contrast, both the fallplanted fall rye and ryegrass had taken up less than 10 kg/ha (lb/ac) of N in both tops and roots combined. The red clover relay crop took up less than half the N as the ryegrass.

Figure 11. (top) Fall N-uptake (above ground) by relay crops and fall planted cover crops and (bottom) yield of relay crops and conventional cover crops in late April after application of spring fertilizer at Agassiz, BC (mean of 6 trials 1993-1995).

The cover crops were supplied with 55-60 kg/ ha (lb/ac) of N in early spring. By the end of April, herbage yield of the cover crop ranged from 2000 to 3400 kg/ha (lb/ac) (Figure 11b). Best yields were obtained from the plots with early corn harvest and thin corn populations. Ryegrass planted into standard corn populations yielded almost 50% more when the corn had been harvested in mid Sept. Fall planted crops yielded significantly less than the relay crops. Red clover yields in late April were quite low.

Conclusion

Relay cropping has several advantages over conventional fallplanted cover crops. They take up much more N in the fall although the capacity for fall uptake does not usually exceed 80 kg/ha in tops and roots. This means that the crop helps to take up residual soil N but should not receive manure or fertilizer in the autumn, except where fall growth has been particularly prolific. The cover crop not only captures N, it provides cover against soil erosion and nutrient runoff over winter. In the Fraser River Delta, the relay crop has been shown to provide winter grazing for water fowl and to lure them away from perennial forages which they frequently damage. Yield of the ryegrass relay crop in spring is economically significant provided that the crop receives a spring application of manure or fertilizer. Red clover is less effective for fall nutrient capture and for spring forage production. The additional feed reduces need for purchased feed and the nutritional quality of the grass is excellent when harvested in April before replanting corn. Relay crops that are ploughed-under are useful for reducing runoff and erosion but do not help the overall farm nutrient balance as much as fed relay crops.

 

Cover crops may affect growth of subsequent corn crop

While the growth period of corn affects when the cover crop can be planted and even which cover crop is most suitable, the cover crop itself may affect subsequent corn crops. Cover crops will absorb nutrients from the soil in spring and these nutrients are either returned to the soil if the cover crop is ploughed down or largely removed if the cover crop is harvested. A study was conducted at Agassiz to determine how different harvested cover crops affect the response to N of subsequent corn crops. Figure 1 shows that that corn yield after most cover crops (winter wheat, fall rye and Austrian winter peas) was similar to growth after winter fallow. That N response was not different after these cover crops compared to bare soil indicates that most of the N in the bare soil was lost over winter. The exception to this pattern was Italian ryegrass. At low N rates, corn did not grow as well after Italian ryegrass as after the other three cover crops, probably because the ryegrass took up more soil N over the winter.

Figure 1. Response of whole-crop yield of silage corn to nitrogen fertilizer after
several winter cover crops in coastal BC (1993-95).

A Recipe for Relay Cropping

S. Bittman¹  and O. Schmidt²
¹ Agriculture and Agri-Food Canada, Agassiz, BC, and ² British Columbia Ministry of Agriculture, Food and Fisheries, Abbotsford, British Columbia

Planting corn
Plant corn early, in late April to early May. This will allow you to harvest the corn early, one of the most important factors for success. Early (low heat unit) corn hybrids will facilitate early harvest. Pay very close attention to heat-loving annual weeds, especially if planting after mid-May.

Use normal corn populations of 75,000 plants per ha (30,000/ac). The ryegrass will perform better where the corn population is thin, but reducing corn density to favour the ryegrass is not economical.

The ryegrass usually performs best near the perimeter of a field because of better light penetration. Relay crops around fields may serve as filter strips to reduce runoff into waterways.

Planting ryegrass
Plant ryegrass when the corn has 3-6 leaves. Ryegrass planted before 3-leaves may suppress the corn, while ryegrass planted after 6-9 leaves will be suppressed by the corn. Plant ryegrass at 25-30 kg/ha (22-27 lb/ac). Plant in strips between corn rows to save seed because little ryegrass will grow in the corn rows. Best ryegrass establishment occurs with drilling but this takes longer and is rarely done. Irrigation may help the ryegrass establish and survive.

Ryegrass varieties
Tetraploid, biennial varieties of Italian Ryegrass varieties persist more consistently under corn than diploid which in turn are better than annual Westewold varieties.

Weed control
Inter-planted Italian ryegrass will not persist in weedy corn fields. Warm-season grassy weeds will compete very aggressively with the cool season ryegrass in the heat of the summer. Non-residual herbicides are available for pre-plant and postplant control of both grassy and broadleaf weeds prior to planting the ryegrass. Inter-row cultivation at time of planting will provide some weed control (see Weed Control section).

Harvesting the corn
It is very important to harvest the corn as early as possible to provide light to the ryegrass. By advancing corn harvest by 10-14 days, fall growth of the ryegrass may be increased by over 30%.

Some tire traffic damage is inevitable, especially in the headlands, but this is minimized by driving as much as possible over the corn rows where there is usually little ryegrass.

Fertilizing the cover crop
Fertilizing the relay crop in autumn is usually unnecessary because of the residual soil N after corn harvest. A wellestablished relay crop may require spring application of manure or fertilizer for rapid spring growth and early harvest.

Winter-hardiness
Some ryegrass varieties are as winter-hardy as many winter wheat varieties, but less hardy than fall rye. Very small plants are less tolerant of low temperature, heaving and desiccation than well-rooted plants.

Flooding tolerance
Small ryegrass plants will withstand flooding for no more than 1-2 weeks.

Using the ryegrass
Italian ryegrass is reputed to be among the highest quality cool season grasses. Ryegrass is very well suited to grazing, and cows can be put out early because of its early growth in spring. Damage to the stand or compaction of wet soil is relatively unimportant since the field will usually be cultivated again for corn.

Ryegrass also makes good green-feed and silage, although it is difficult to cure. In coastal BC and the Pacific Northwest, relay ryegrass may yield 3000-5000 kg/ha (lb/ac) by mid-April, before corn would be replanted.

Late fall grazing would rarely be possible in Canada but may be an option in milder regions of the US, Europe and elsewhere.

Well-established relay ryegrass is sometimes harvested through the next summer.

Eliminating the stand in the spring
Non-selective herbicides may be used to kill the ryegrass in the spring prior to replanting corn although they may not be fully effective. Using herbicide resistant corn hybrids allows use of non-selective herbicides against surviving ryegrass after the corn is planted. Ploughing or disking, then allowing some rotting of the sod is helpful. Intense grazing prior to ploughing will reduce crop residue.

Effect on subsequent nutrient requirement of corn
Requirements for nutrients, especially N, by corn will increase substantially following a relay crop, giving greater opportunity for use of slurry manure.

Tool used to cultivate between corn rows and seed relay crops in western Washington.

Relay Crop Reduces Over-Winter Runoff from a Silage Corn Field

L.J.P. VAN VLIET¹  and B.J. ZEBARTH²
Agriculture and Agri-Food Canada, ¹ Agassiz, British Columbia, ² Fredricton, New Brunswick

Runoff from corn land during the wet fall and winter season presents a concern for surface water quality, especially if manure is applied after corn harvest. In the Lower Fraser Valley of British Columbia, about 1100 mm (43 in) precipitation falls between November and April, mostly as rain. We conducted a field study to determine if relay crops would reduce surface-runoff and nutrient loss from a corn field after surface application of liquid dairy manure in autumn.

Figure 1. Field trial at Agassiz, BC for evaluating the effect of a relay crop on reducing
nutrient runoff from surface applied liquid dairy manure.

The experiment was conducted on a 3-5% slope at the Pacific Agri-Food Research Centre in Agassiz, BC  from 1996 to1998. On half the plots, Italian ryegrass was planted as a relay crop when the corn was at the 6- to 9-leaf stage (late June to early July).  Runoff, solids, and nutrients loads from natural precipitation were measured systematically over the fall and winter period.

Without a relay crop there was a high risk to surface water quality, due to high loadings of suspended solid (7-14 t/ha or 3-7 T/ac) and the nutrients N (98 kg/ha or 90 lb/ ac), P (21 kg/ha or 19 lb/ac) and K (63 kg/ha or 55 lb/ac). The relay crop reduced the mean annual runoff by 53% and loading of suspended solids by 74% (Table 1). The relay crop also reduced N loading by 56%, P loading by 42%, and K loading by 31%.

Table 1.  Effect of relay crop in reducing over-winter runoff, solids and nutrients from a silage corn field receiving broadcast dairy slurry in fall in south coastal BC

Relay cropping is recommended as a beneficial, sustainable management practice for silage corn grown on sloping land in high rainfall areas of the Pacific Northwest. Relay crops are particularly useful in adding to buffer strips near water courses. It is helpful that the relay crop tends to grow best around the perimeter of a field, because of better light penetration, provided that traffic during harvesting is minimized.

Chapter 6: Corn Pests

Common Diseases Of Silage Corn In Canada

L.M. REID and X. ZHU
Eastern Cereal and Oilseed Research Centre, Agriculture and Agri-Food Canada, Ottawa, Ontario

Corn can be attacked by dozens of different disease-causing organisms. Fortunately, the climate of Canada is not favourable for the development of serious epidemics, however, localized outbreaks of different diseases do occur every year. With the expansion of both grain and silage corn production areas, many of these pathogenic organisms will likely adapt to our cooler climate and agronomic practices. Most of the corn diseases in Canada are caused by fungi. The body of most plantpathogenic fungi consists of a mass of numerous threadlike hyphae called mycelium (often referred to as mould). Various other structures can be formed ranging from single cells such as asexual spores to large fruiting bodies which produce sexual spores. The asexual reproductive stage is usually associated with the mycelium while the sexual stage is usually associated with fruiting bodies. Spores can be produced from both stages and are the major means by which fungi reproduce and infect plants. Spore shape and size is often used to identify fungi along with the characteristics of the mycelium and fruiting bodies.

Fungi can attack all parts of the corn plant. Some fungi remain localized in the tissue that was first infected, e.g. the ear, while other fungi are systemic and can spread throughout the plant. All of these fungi have the potential to lower silage corn yields. Leaf diseases such as northern corn leaf blight result in a loss in dry matter weight and may affect the quality of the derived feedstuffs. The plant is killed before maturity, so that ears are not filled and have small kernels with low test weights. Leaf diseases may also weaken the plant and predispose it to more serious stalk and ear infections. Stalk lodging is a major factor contributing to harvest difficulties, reduced grain yields, and reduced dry matter production in corn.  However, losses in quality can also occur when the fungi contaminate the grain or stalks with mycotoxins such as deoxynivalenol (DON, vomitoxin) or zearalenone (see Moulds and Mycotoxins section).

Leaf Diseases

Northern Leaf Blight (White Bast, Crown Stalk Rot or Stripe)

Causal Organism: Setosphaeria turcica (Luttrell) K.J. Leonard & E.G. Suggs [asexual state: Exserohilum turcicum (Pass.) K.J. Leonard & E.G. Suggs = Helminthosporium turcicum Pass.].

Symptoms consist of long, elliptical, grayish-green or tan coloured lesions appearing first on the lower leaves (Fig. 1). Lesions may be as large as 4 x 15 cm (1.5 x 6 in). When infection is severe, entire leaves die and it is difficult to see individual lesions; this is sometimes referred to as a “burning” or “scorching” of leaves. Lesions may also occur on husks. Kernels are not infected. A severely infected plant may turn grayish-green and die prematurely.

Figure 1. Typical symptoms of Northern corn leaf blight:
long, elliptical, grayish-green or tan coloured lesions.

This has historically been one of the most damaging leaf diseases of corn in Canada. The fungus overwinters on corn debris. Spores are wind-borne up to 2 km (1.2 mi) under moderate temperatures (18-25°C or 64-77°F) and can also be dispersed by rain splash. Heavy dews favour disease development. Secondary infection can rapidly spread from field to field. The initial source of infection may be from spores blowing in from the U.S.

This fungus has seven races. Hybrids resistant to a single race or to all races are available. Crop rotation and tillage help to reduce surface residues and pathogen populations. Infected plants are more susceptible to stalk rots. Fungicide applications are not economical for silage corn.

Eyespot (Brown spot)

Causal Organism: Aureobasidium zeae (Narita & Hiratsuka) J.M. Dingley (= Kabatiella zeae Narita & Hiratsuka).

Symptoms on leaves consist of round-to-oval lesions (2-5 mm or .-¼ in diameter) with a tan-to-cream coloured centre and a brown (Fig. 2) or purple (Fig. 3) margin surrounded by a yellowish halo, giving the characteristic “eyespot” appearance. These lesions are easy to recognize if the leaf is held up to a light. The lesions may fuse to form large necrotic (dead) areas. The upper leaves may wither and die prematurely. Symptoms can be confused with non-infectious physiological leaf spots or insect damage found on some corn hybrids.

Figure 2. Eyespot lesions consisting of small round to oval spots
with a tan or cream coloured centre and a brown margin. Note the
yellow halo surrounding the spots, giving the appearance of an “eye”.

Figure 3. Eyespot lesions consisting of small round to oval spots
with a tan or cream coloured centre and a purple margin.

The incidence of eyespot is increasing in Canada. The disease occurs during cool, wet weather in late August and September. The fungus overwinters in corn debris and spores are spread by rain splash and wind. Higher incidence in conservation tillage fields and when corn follows corn has been reported.

Resistant hybrids must be grown in areas with a history of eyespot. Crop rotation and clean ploughing are recommended to control this disease. Like most leaf diseases, infected plants are more susceptible to stalk rots. Fungicide applications are not economical in silage corn.

Common Rust

Causal Organism: Puccinia sorghi Schwein.

Symptoms begin as small discoloured flecks on the leaves that soon turn into small, round to elongate, reddish brown pustules full of red coloured urediniospores (Fig. 4). Pustules can be observed on both leaf surfaces as well as husks, leaf sheaths and stalks. The red spores can be rubbed off on hands or clothing. The pustules turn black as the plant matures (Fig. 5). Pustules are frequently clustered in bands around the leaves as a result of infection that took place when the leaf tissue was in the whorl. Younger leaves are more susceptible than mature leaves. When the disease is severe, leaf tissue around the pustules turns yellow, withers and dies. Some hybrids have resistance genes; these plants may develop a hypersensitive response consisting of several small (pin-prick) pale coloured lesions.

Figure 4. Common rust, the redbrown coloured pustules erupt releasing
rust coloured spores during the summer months.

Figure 5. Late stage of infection of common rust in corn. The pustules are
now more black than rust coloured and contain black teliospores.

This fungus does not overwinter in Canada (requires living plant tissue) and therefore, is dependent on spores that survive the winter in the southern U.S. and Mexico. These overwintering spores are carried by storm fronts to the corn regions of the U.S. and Canada. Rust prefers wet seasons with high humidity (above 95%) and warm temperatures (16- 25°C, 61-77°F).

For control of rust, use resistant hybrids. Early planting may allow the crop to develop to a less susceptible stage before spores are blown in. Cultural practices such as crop rotation and clean ploughing have no effect on disease incidence since the rust spores blow in from southern regions. Heavily infected plants are more susceptible to stalk rots. Fungicide treatments are not economical in silage corn.

Stalk Diseases

Gibberella Stalk Rot

Causal Organism: Fusarium graminearum Schwabe [sexual state: Gibberella zeae (Schwein.) [Petch].

Gibberella stalk rot infected plants may wilt and the leaves may change from a light to dull green colour while the lower stalk becomes dry and the pith tissue in the center of the stalk disintegrates to a shredded appearance (Fig. 6). Distinctive symptoms of gibberella stalk rot are a tan to dark brown discolouration of the lower internodes and a pink to reddish discolouration of the pith tissue. Bluish-black coloured perithecia (fungal fruiting structures that release sexual spores) or reddish-white asexual spores form on the stalk surface. Plants may lodge if the infection is severe.

Figure 6. Gibberella stalk rot of corn. The lower internodes of the stalk turn tan to dark brown in colour and the pith becomes shredded and has a characteristic red or pink colour.

This fungus is one of the more potentially damaging stalk rotting agents in Canada. The pathogen survives in soil and on crop residue; spores are produced in wet weather and dispersed by wind, rain splash and insects or birds. Infection takes place through roots or through wounds in the stalk often shortly after pollination. Like most stalk rots, occurrence is strongly linked to stress during grain filling by any conditions that reduce photosynthesis and production of sugars (leaf diseases, drought or soil saturation, insect damage, hail damage, lack of sunlight, cool weather, etc.). Many stalk rot infections can be traced back to wounding of the stalk by boring insects such as the European corn borer.

Planting resistant hybrids, clean ploughing, crop rotation, avoidance of high plant populations and balanced soil fertility are some of the methods to control this disease. Since this fungus also causes scab in wheat, corn should not be rotated with wheat or other cereals susceptible to scab if this disease is present. Control of stalk boring insects is helpful (Fig. 7). Fields should be scouted 40 days after pollination by looking for symptoms and pinching stalks. When pinched, infected stalks are easily compressed or crushed. Fields should be harvested as early as possible if more than 10-15% of the stalks have rot because rotted stalks will lodge, making harvest difficult.

Figure 7. Corn borer entry hole for stalk rot.

Fusarium Stalk Rot

Causal Organisms: There are three main species responsible for fusarium stalk rot: Fusarium verticilliodes [= Fusarium moniliforme J. Sheld. (sexual stage: Gibberella moniliformis Wineland]; F. proliferatum (T. Matsushima) Nirenberg (sexual stage: G. fujikuroi var. intermedia Kuhlmann); and F. subglutinans (Wollenweb. & Reinking) Nelson, Toussoun and Marasas (sexual stage: G. subglutinans Nelson, Toussoun and Marasas).

Symptoms of fusarium stalk rot are similar to gibberella stalk rot. Plants may wilt, the leaves change from a light to dull green, the lower stalks dry and the pith tissue disintegrates to a shredded appearance. Brown streaks appear (Fig. 8) on the lower internodes and the rotted pith tissue may be whitish pink to salmon in colour as opposed to the distinct red-pink colour of gibberella stalk rot. Infected plants may lodge (Fig. 9). Symptoms usually appear late in the season.

Figure 8. Fusarium stalk rot produces brown streaks in lower internodes.

Figure 9. Fusarium stalk rot causes lodging.

This disease is more important in the warmer, dry areas of Canada such as southern Ontario. The pathogens survive in soil and on crop residue. Spores are dispersed by wind, rain, insects and birds. This fungus may also be present in the seeds or plants but with no apparent symptoms. Infection can take place through the roots or through wounds on the leaves or stalk. Like gibberella stalk rot, occurrence is strongly linked to stress during grain filling and often can be traced back to insect wounding of the stalk.

Control strategies are the same as for gibberella stalk rot.

Diplodia Stalk Rot

Causal Organism: Diplodia maydis (Berk.) Sacc. [= Stenocarpella maydis (Berk.) Sutton].

Like most stalk rots, Diplodia rotting symptoms include a disintegration of the pith tissue causing the pith to have a shredded appearance and stalks that are easily crushed or compressed when pinched. Diplodia stalk rot is characterized by numerous black pycnidia (flask shaped fungal fruiting structures that produce asexual spores) that appear as small dots about the size of a pinhead on the lower internodes of the stalk. The pycnidia are embedded in the stalk tissue and therefore, is unlike soil which can be easily removed. If conditions are wet, a white mould may appear on the surface of the stalk.

This fungus overwinters as spores on corn debris and as pycnidia or mycelium in corn seed. Incidence of this stalk rot are increasing in minimum tillage areas especially if corn follows corn in rotation. During wet weather, pycnidia produce spores that are dispersed by splashing water and wind. These spores infect the plant through the crowns, roots, and lower nodes. Insects may also carry the spores to plants and into feeding wounds. Dry conditions early in the season, followed by wetter conditions after silking, favour disease development. Like most stalk rots, occurrence is strongly linked to stress during grain filling.

Planting resistant hybrids, clean ploughing, crop rotation, and balanced soil fertility are some of the methods to control this disease. Fields should be scouted 40 days after pollination by looking for symptoms and pinching stalks. When pinched, diseased stalks are easily compressed or crushed. Fields should be harvested as early as possible if more than 10-15% of the stalks have rot, since rotted stalks will lodge, making harvest difficult.

Anthracnose Stalk Rot and Top-Die Back

Causal Organism: Colletotrichum graminicola (Ces.) G.W. Wils. (sexual state: Glomerella graminicola Politis).

Anthracnose stalk rot is characterized by the appearance of distinctive black streaks on the lower stalk late in the season. The pith turns dark brown and has a shredded appearance (Fig. 10). Numerous, black, spiny asexual fruiting bodies (acervuli) form on the surface of the dead tissue. Like most stalk rots, the most obvious symptom is a sudden death of plants before grain maturity. Since the leaves wilt and die after infec- tion, the plant has the appearance of being “frosted”. Another common symptom is lodging. If seedlings are infected, the plants may die before flowering. Top-die back refers to symptoms after the dough stage in which the top nodes, leaves and the tassel dry out, but the bottom leaves remain green and normal (Fig. 11).

Figure 10. Anthracnose stalk rot of corn. Black streaks appear on the lower
internodes and the pith becomes shredded and dark brown in colour.

Figure 11. Anthracnose top-die back of corn. The top nodes of the stalk,
the leaves and the tassel dry out but the bottom leaves and stalk remain green.

This disease is becoming more severe in Canada. The fungus survives in corn debris, infected seed, and some weed species. For stalk rot, the fungus infects plants through the roots or by rain splash onto stalks. Spores can also infect through wounds on the stalk or leaves. Insects may also carry spores into wounds. Like most stalk rots, occurrence is strongly linked to stress during grain filling and often infections can be traced back to wounding of the stalk by boring insects.

Use resistant hybrids; resistance to both the stalk and leaf blight forms are not necessarily found in the same hybrid. Clean ploughing may reduce inoculum levels. Crop rotation is essential especially in reduced tillage areas. Balanced soil fertility is important to control this disease. Control of the corn borer will reduce entry of the pathogen through feeding sites. Fields should be scouted 40 days after pollination by looking for symptoms and pinching stalks. When pinched, infected stalks are easily compressed or crushed. Fields should be harvested as early as possible if more than 10-15% of the stalks have rot since rotted stalks will lodge, making harvest difficult.

Pythium Stalk Rot

Causal Organism: Pythium aphanidermatum (Edson) Fitzp. (= P. butleri L. Subramanian) and other Pythium species.

A typical symptom of pythium stalk rot before flowering is a decay of the first internode above the soil (Fig. 12). Infected stalks may have a strong odour. Damaged internodes may twist and plants will fall over but the plant can remain green for several weeks. After the milk stage of plant development, the roots and several lower internodes become water-soaked and decay, resulting in early plant death.

Figure 12. Pythium stalk rot.

This disease can occur any time during the season, especially when conditions are warm and wet. The fungus overwinters in the soil and plant debris as oospores that germinate and produce mycelium or mobile zoospores, both of which can infect corn plants.

Use resistant hybrids to control this disease. Stress factors such as unbalanced fertilization, high plant populations, use of unadapted hybrids, insects, weeds, poor drainage and infection by leaf diseases may increase plant susceptibility. Fields should be scouted 40 days after pollination by looking for symptoms and pinching stalks. Infected stalks are easily compressed or crushed when pinched. Fields should be harvested as early as possible if more than 10-15% of the stalks have rot since rotted stalks will lodge, making harvest difficult.

Ear Diseases

Gibberella Ear Rot (Pink Rot, Red Rot)

Causal Organism: Fusarium graminearum Schwabe [sexual state: Gibberella zeae (Schwein.) Petch].

The typical symptom of gibberella ear rot is a pink-to-reddish coloured mould, often starting at the ear tip or from an insect wound and growing down the ear (Fig. 13). Cobs can become quite spongy and husks become bleached and adhere tightly to the kernels. A powdery, cottony-pink mould may form later. Black coloured perithecia (fungal fruiting bodies that produce sexual spores) may be visible on husks.

Figure 13. Typical mould growth on an ear of corn infected with gibberella ear rot. Mould colour is usually pink to reddish and often starts from the tip of the ear and spreads downward or from an insect/bird wound.

This is one of the most economically important ear rotting agents in Canada. The pathogen survives in soil and on crop residue; spores are produced in wet weather and dispersed by wind, rain splash and insects or birds. Infection takes place through the silks or through wounds created by birds or insects. Silks are highly susceptible 2-6 days after silking; kernels are susceptible until they reach physiological maturity. Infected ears are contaminated with mycotoxins such as deoxynivalenol (DON, vomitoxin) and zearalenone, which are highly toxic to livestock, especially swine, and humans (see Moulds and Mycotoxins section). Gibberella ear rot is favoured by cool, wet weather shortly after silking.

Hybrids with acceptable resistance are not yet available. Since this fungus also causes scab in wheat, corn should not be rotated with wheat or other cereals susceptible to scab if this disease is present. Hybrids with tight husk coverage and upright ears tend to get less infection. Crop rotation and fall tillage will reduce crop debris and thus may reduce disease levels in the next season. Insect control will reduce symptoms, especially with the use of Bt hybrids. Fields should be scouted as the corn begins to dent; if mould problems are identified, these fields should be harvested as soon as possible to prevent further mould growth.

Fusarium Ear and Kernel Rot

Causal Organisms: There are three main species responsible for fusarium ear and kernel rot: Fusarium verticilliodes [= Fusarium moniliforme J. Sheld. (sexual stage: Gibberella moniliformis Wineland)]; F. proliferatum (T. Matsushima) Nirenberg (sexual stage: G. fujikuroi var. intermedia Kuhlmann); and F. subglutinans (Wollenweb. & Reinking) Nelson, Toussoun and Marasas (sexual stage: G. subglutinans Nelson, Toussoun and Marasas).

The typical symptom of fusarium kernel or ear rot is a whitish to pink coloured mould, often starting at the ear tip or butt of the ear, commonly from an insect wound. Fusarium verticilliodes symptomatic kernels tend to be randomly scattered on the ear (Fig. 14) unlike other ear rots that spread from an initial point of entry. Infected kernels may also exhibit a “starburst” symptom in which white streaks radiate from the point of silk attachment to the kernel. Husks may become bleached and adhere tightly to the kernels. Black coloured perithecia (fungal fruiting bodies that produce sexual spores) may be visible on husks.

Figure 14. Characteristic spotty mould growth associated with Fusarium
kernel rot caused by Fusarium verticilliodes. Mould colour is usually
white and randomly distributed on the ear.

This disease is more important in the warmer, dry areas of Canada such as southern Ontario. The pathogens survive in soil and on crop residue; spores are produced in wet weather and dispersed by wind, rain splash and insects or birds. Infection takes place through the silks or through wounds created by birds and/or insects. There is also evidence that F. verticilliodes can invade the ear by systemic infection from the stalk. Infected ears may be contaminated with mycotoxins such as fumonisins, which are highly toxic to livestock, especially horses, and humans.

No hybrid with acceptable level of resistance is available yet. Control strategies are similar to those for gibberella ear rot.

Diplodia Ear Rot

Causal Organism: Diplodia maydis (Berk.) Sacc. [= Stenocarpella maydis (Berk.) Sutton].

With Diplodia ear rot, infected husks become dry and bleached but the rest of the plant remains green. Eventually, the husks and kernels become covered with a white to grayish brown coloured mould (Fig. 15). Kernels appear glued to the husks and cob by white mycelium. Infected ears are light and shrunken. Black pycnidia (fungal fruiting bodies that release asexual spores) look like small raised black bumps on husks and kernels forming late in the season. If infection occurs several weeks after flowering, symptoms are much less apparent but close inspection of the ear will reveal white mycelial growth between the kernels. Symptoms are most severe if infection occurs just after silking.

Figure 15. Diplodia ear rot covers kernels with whitish/grayish mould.

This disease is not as common as gibberella or fusarium ear rot. Diplodia maydis overwinters on corn debris so the incidence is increasing with the increased use of conservation tillage. The disease is most severe when corn follows corn in rotation, especially if conditions are wet after silking. The pycnidia on the debris produce spores that are splashed onto the silks and then grow down the silks into the ear. This fungus can also penetrate the husks especially at the base of the ear. Birds and insects may also vector the disease and create wounds on the ear for easy fungal entrance. Infection is favoured by cool, wet weather during grain fill.

For control, use hybrids with some resistance. Hybrids with tight husk coverage and upright ears tend to get less infection. Crop rotation and fall tillage are important in reducing crop debris and thus disease levels in the next season. Fields should be scouted as the corn begins to dent; if mould problems are identified, these fields should be harvested as soon as possible to prevent further disease development.

Common Smut (Boil Smut, Blister Smut)

Causal Organism: Ustilago zeae (Beckm.) Unger [ = U. maydis (DC.) Corda].

Symptoms can occur on all plants parts above the ground, especially young and actively growing plant tissues. Large 2–10 cm (1–4 in) galls (swollen, distended growths) are formed on stalks (Fig. 16), tassels and ears (Fig. 17). The galls are first covered by a silvery-white membrane, which changes to a grey mass containing black powdery spores. When mature, these galls will erupt and release black spores. Galls may also form on leaves but are generally small, brown and hard (Fig. 18). Early infection may kill young plants. Plants with large galls on the lower stalks may be stunted, barren or produce small ears. Infection of ears is usually from spores germinating on the silks and mycelia growing down the silks to infect the kernels.

Figure 16. Common smut galls on the nodes of a corn stalk. Galls will
eventually erupt to reveal masses of black spores.

Figure 17. Corn ear severely infected with common smut. Galls will
eventually erupt to reveal masses of black spores.

Figure 18. Common smut galls on corn leaves and sheaths. These galls
are much smaller than those that form on stalks and ears and rarely
erupt to release spores.

Common smut is found in most corn growing regions of Canada. Black teliospores of the pathogen overwinter in soil or crop debris and can survive for several years. Initial infections occur from wind-borne or water-borne spores in the spring. Spores from galls on the plants can infect other plants. Infection can occur through unwounded tissue, but wounds caused by insects, cultivation, hail or blowing soil are important sources of fungal entry. The fungus favours high temperatures of 26–34°C (79–93°F). There is no consensus on whether smut favours humid or dry conditions. During combine harvesting, spores are spread locally by the wind. Spores can also be spread from field to field by contaminated farm equipment.

For control, use resistant hybrids and avoid mechanical injury to plants. Destruction of galled plants is useful where feasible. Crop rotation will reduce disease severity in the following season. Maintain balanced soil fertility since high nitrogen and manure applications will promote vigorous plant growth making the plant more susceptible; phosphate fertilization tends to decrease incidence. Herbicide injury will also promote infection.

Nematodes on Corn

T. FORGE
Agriculture and Agri-Food Canada, Agassiz, BC

What are plant-parasitic nematodes?

Nematodes are translucent, microscopic roundworms, typically measuring 0.25 to 1 mm (0.01 to 0.03 in) in length and only about 0.01 to 0.03 mm (0.0004 to 0.001 in) in diameter. Most nematodes are beneficial components of the soil ecosystem because they feed on bacteria, fungi and other micro- invertebrates, helping to cycle nutrients. Their abundance ranges from about 1000 per liter (4,000 per gal) of degraded or infertile soil up to 50,000 per liter (200,000 per gal) of highly fertile soil. However, over 60 nematode species parasitize corn roots and some of these species are economically important pathogens (1).

The effects of parasitic nematodes on production of grain corn have been well studied (1, 2, 3). The groups of species most likely to cause damage to corn in temperate regions of North America include: root-lesion nematodes (Pratylenchus spp.), root-knot nematodes (Meloidogyne spp.), needle nematodes (Longidorus spp.), sting nematodes (Belonolaimus spp.) and stubby-root nematodes (Paratrichodorus spp). All plantparasitic nematodes have piercing-sucking mouthparts called stylets, which they use to puncture the cell walls of fine roots and extract cellular contents (Fig. 1). The needle and sting nematodes have particularly long stylets and feed only on cells that can be reached from outside the root; these nematodes are known collectively as ectoparasites. Other groups, including the root-lesion nematodes, completely enter root tissue and move from cell to cell within the root as they feed; these nematodes are known as migratory endoparasites. The rootknot nematodes are sedentary endoparasites which establish permanent feeding sites within the root tissue, sometimes forming swellings known as galls. These nematodes will complete most of their life-cycle, including laying eggs, while feeding from only one or a few root cells.

Figure 1.

Symptoms and Damage Caused by Nematodes

Unfortunately, very little is known about the influences of plant-parasitic nematodes on production of silage corn, so most of the information in this article refers to research on grain corn production. Annual yield losses in grain corn were estimated to be as high as 4% in Iowa and 7% in Georgia (4).

Much of the crop damage caused by plant-parasitic nema todes is overlooked because the above-ground symptoms of nematode damage are non-specific and difficult to distinguish from other factors. Because high densities of nematodes usually exist in patches, nematode damage is often observed as patches of poor, sometimes chlorotic, growth within large otherwise uniform fields (1, 2, 3). Patches of high nematode population densities may be caused by other soil factors that may also affect crop growth. For example, some nematodes reach higher populations and cause more damage in coarse than in fine-textured soils. As a result, poor crop growth observed on sandy soils can be the result of low water or nutrient availability as well as nematode damage. That nematode damage does not always appear in patches further complicates interpretation of symptoms in the field.

Symptoms of nematode damage to roots are also relatively general and difficult to distinguish from those of other pathogens or even other environmental factors. The root-knot nematodes are the exception as they cause distinctive swellings on roots called galls or knots. Root-lesion nematodes cause general symptoms that range from many small lesions on young fibrous roots to abnormal darkening and complete necrosis of root tissue. The ectoparasites (needle, stubby and sting nematodes) tend to reduce root growth at the tips, causing a “stubby” appearance. The intensity of the symptoms of nematode damage may be enhanced by other factors such as secondary pathogens (i.e. fungal pathogens), which can also produce similar symptoms.

Nematicides often improve crop growth. However, it is difficult to make direct links between the benefits of nematicides and the pathogenicity of nematodes, because nematicides can affect crop growth in other ways. For example, use of nematicides on a mixed nematode community including P. brachyurus alleviated symptoms of zinc deficiency on young corn plants (5). Nevertheless, a number of detailed greenhouse (6, 7) and field studies (8) in which nematodes were manipulated independently of other potential soil pests have confirmed the pathogenicity of root-lesion nematodes to corn.

To determine if plant-parasitic nematodes are contributing to poor crop production, soil samples should be analyzed by a qualified nematology laboratory. In the U.S, most land-grant state universities or cooperative extension centres have plantdisease diagnostic clinics with nematology expertise (or can forward samples to a nematology lab). In Canada, there is limited access for producers to diagnostic labs with adequate expertise in plant-parasitic nematodes.

Sampling strategies and interpretation of the data depend on the nematode species suspected and environmental conditions, and should be developed in consultation with the diagnostic laboratory. Populations of all nematode species vary seasonally (9, 10, 11). In particular, the distribution of migratory endoparasitic nematodes between roots and soil varies with season (9, 11), necessitating analyses of sub-populations in both soil and roots. Only soil samples are required for analyses of populations of ectoparasites.

To analyse samples, first the nematodes are extracted from soil and plant tissue, then they are identified and counted. The absence of recognized nematode pathogens of corn in diagnostic samples can be used to rule out nematodes as the cause of poor crop growth. However, the presence of large populations of one or several species of recognized pathogens should not be interpreted as proof that the poor growth is due exclusively to the nematodes. Likewise, it is difficult to relate nematode population densities quantitatively to yield loss because nematodes interact strongly with other factors, particularly water and nutrient availability and other pathogens.

Nematodes of particular interest for corn production in temperate regions

Root-lesion nematodes (Pratylenchus spp.)

Globally, root-lesion nematodes are the most common nematode pests of corn and several species in this group cause significant damage (1, 2, 3). In the Midwestern corn belt of the U.S., the most important species are P. hexincisus, P. penetrans and P. scribneri while in the southeastern U.S. and other warm-temperate to subtropical regions, P. zeae and P. brachyurus are most common (3).

Fibrous roots invaded by root lesion nematodes develop several dark lesions, which may expand into one another to girdle roots and cause sloughing of cortical tissue (1, 2, 3). Symptoms in the field range from localized patches of stunted and chlorotic plants to general suppression of growth throughout a field (1, 2, 3). In Iowa, P. hexincisus populations under 1,000 per g (30,000 per oz) of dry root had no effect on yield but densities greater than 5,000 per g (150,000 per oz) of dry root significantly reduced yield (1). Application of nematicides increased yields by 26% (12). In South Dakota, yield losses of dryland corn (grain) due to P. hexincisus averaged 600 kg/ha (9.5 bu/ac) at typical mid-season populations of 3,400 per g dry root (100,000 per oz), while yield losses of irrigated corn to P. scribneri were somewhat lower at 250 kg/ ha (4 bu/ac) with mid-season populations of 8,200 per g (250,000 per oz) of dry root (13). Todd and Oakley (14) increased yield of grain corn by 1% for each 1000 root-lesion nematodes per g dry root they eliminated with a nematicide. In contrast, nematicide did not increase yield of corn grown on soils infested with P. penetrans and P. crenatus in Prince Edward Island (15).

Root-lesion nematodes appear to be particularly damaging in the southeastern U.S. P. zeae, which is limited primarily to the southeastern U.S., reduced growth of young corn plants in a greenhouse experiment by 11 to 38% depending on population densities (7). In Georgia, a root-lesion nematode population of 650 per liter of soil (2,500 per gal) measured before planting reduced yield by 1.2 t/ha (19 bu/ac) and doubling the nematode population also doubled the yield loss. In North Carolina counts in the autumn exceeding 1,000 nematodes per liter (4,000 per gal) of soil are indicative of moderate damage (3).

Root-knot nematodes: (Meloidogyne spp.)

Three root-knot nematodes, M. incognita, M. arenaria and M. javanica can cause damage to corn in warmer temperate regions, and have been the focus of much recent study in the southeastern U.S. (3). In the irrigated areas east of the Cascade mountains in the Pacific Northwest (PNW) and northern California, corn is a host for M. chitwoodi. While the effect of this species on corn is unclear, the species is a severe pathogen of potato, which limits opportunities for rotating corn with potato. M. chitwoodi has not been detected in BC or coastal areas of the PNW. Corn is not a host for M. hapla, the most ubiquitous species of Meloidogyne in northern temperate agricultural soils (16) nor M. naasi, a significant pathogen of other cereals and grasses in northern temperate regions (16).

Stubby root nematodes (Paratrichodorus spp.)

Stubby root nematodes are found almost exclusively in sandy soils where they prefer wet conditions (17, 18). As a consequence, they are often abundant and problematic in irrigated, sandy soils. The species affecting corn most widely appears to be P. minor, recognized in the southeastern U.S. for causing significant yield losses in the 1970’s and 1980’s (3). More recently, P. minor infestations have declined in the southeastern U.S., possibly due to the more widespread use of non-fumigant nematicides (3). Because P. minor is a poor competitor with other plant-parasitic nematodes, its decline in the southeastern U.S. could be due also to increased abundance of other species of nematodes (3). We have found P. minor in soils of both coastal and interior British Columbia, but in the irrigated sandy soils of the Columbia basin of eastern Washington and Oregon, the dominant species is P. allius. The stubby root nematodes are vectors of tobacco rattle virus, which causes a severe disease of potato known as corky ringspot. Therefore, as with M. chitwoodii, growth of stubby root nematode on corn where tobacco rattle virus is present may limit opportunities for rotating corn with potato.

Sting nematodes (Belonolaimus spp.)

Sting nematodes (primarily B. longicaudatus) are among the few nematodes that can cause patches of complete yield loss in severely infested fields so nematicides can increase yield by 75% or more (19). Sting nematodes are not a problem north of Nebraska, and even in the southern Midwest and southeastern states, their occurrence is limited to sandy soils.

Controlling Parasitic Nematodes

Chemical:

Despite the likelihood of widespread yield losses of corn to nematodes, relatively little effort has been devoted to chemical management of these pathogens. There is evidence that seed treatment with nematicide reduces infection of corn roots by the root-lesion nematode (20). But, because nematode damage results typically in low-level chronic losses (e.g.

Cultural practices:

Several studies have demonstrated that minimum till reduces populations of root-lesion nematodes relative to conventional tillage (3) although the opposite has also been reported (21). The mechanisms by which minimum tillage affects this nematode are not known.

Populations of plant-parasitic nematodes generally increase with crop nitrogen status. For example, Forge et al. (22) found that long-term use of both manure and N-fertilizer increased population densities of root-lesion nematodes in tall fescue. While the benefits of fertilization will likely offset any negative effect of increased nematode populations, these nematodes may diminish the efficiency of uptake of N by the crop. The overall interactions between nutrient applications, plant-parasitic nematodes, and growth of corn needs further study.

Crop resistance:

Development of corn hybrids with nematode resistance has great potential because corn is widely grown in many countries, resistant crops require less inputs of costly chemicals or equipment, and the use of resistant cultivars is best for the environment (3). Also, where corn is grown in rotation with nematode-susceptible crops (e.g. potato), resistant corn varieties can be beneficial for the entire crop rotation. Commercial lines of corn resistant to root-knot nematodes have been released (3) and corn germplasm with resistance to root lesion nematodes has been discovered. Also, inbred lines with resistance to two species of root-lesion nematodes have been released (23, 24). Nonetheless, commercial corn seed companies consider development of resistance to plant-parasitic nematodes a low priority.

Do we need more nematode research?

If nematodes do not cause sufficient yield loss to warrant expensive control measures such as nematicides - do we need further research on nematodes in corn? The impacts of plantparasitic nematodes are likely under-estimated because they are non-specific, subtle and chronic. Since nematode effects can easily be mistaken for poor nutrient availability or damage from other pests, farmers may mistakenly apply extra fertilizer or pesticides to attempt to correct the problem. Further, the expansion of nematode populations in corn crops may impact succeeding rotation crops.

 

References

1. Norton, D.C. 1983. Maize nematode problems. Plant Disease 67, 253-256.

2. Norton, D.C. 1984. Nematode parasites of corn. pp 61-94 in: Plant and insect nematodes, W.R. Nickle (ed), Marcel Dekker, New York.

3. Windham, G.L. 1998. Corn. pp 335-357 in: Plant and Nematode Interactions, Agronomy Monograph no. 36. American Society of Agronomy, Madison, WI.

4. Society of Nematologists Crop Loss Assessment Committee 1987. Bibliography of estimated crop losses in the United States due to plant-parasitic nematodes. Annals of Applied Nematology 1, 6-12.

5. Minton, N.A., M.B. Parker and D.R. Sumner 1985. Nematode control related to Fusarium wilt in soybean and root rot and zinc deficiency in corn. Journal of Nematology 17, 314-321.

6. Dickerson, O.J., H.M. Darling, and G.D. Griffin 1964. Pathogenicity and population trends of Pratylenchus penetrans on potato and corn. Phytopathology 54, 317-322.

7. Tarte, R. 1971. The relationship between pre-plant populations of Pratylenchus zeae and growth and yield of corn. Journal of Nematology 3, 330-331.

8. Olthof, T.H.A., and J.W. Potter 1973. The relationship between population densities of Pratylenchus penetrans and crop losses in summer-maturing vegetables in Ontario. Phytopathology 63, 577-582.

9. MacGuidwin, A.E. 1989. Distribution of Pratylenchus scribneri between root and soil habitats. Journal of Nematology 21, 409-415.

10. MacGuidwin, A.E. and T.A. Forge. 1991. Overwinter survival of Pratylenchus scribneri. Journal of Nematology 23, 198 204.

11. Vrain, T.C., T.A. Forge and R. DeYoung 1996. Population dynamics of Pratylenchus penetrans parasitizing raspberry. Fundamental and Applied Nematology 20, 29-36.

12. Norton, D.C., and P. Hinz 1976. Relationship of Hoplolaimus galeatus and Pratylenchus hexincisus to reduction of corn yields in sandy soils in Iowa. Plant Disease Reporter 60, 197-200.

13. Smolik, J.D., and P.D. Evenson 1987. Relationship of yields and Pratylenchus spp. populaton densities in dryland and irrigated corn. Annals of Applied Nematology 1, 71-73.

14. Todd, T.C., and T.R. Oakley 1996. Seasonal dynamics and yield relationships of Pratylenchus spp. in corn roots. Journal of Nematology 28(S), 676-681.

15. Kimpinsky, J., L.S. Thompson, R.P. White and C.B. Willis 1977. Nematodes in field corn in Prince Edward Island. Can. J. Plant Sci. 57, 323-330.

16. Rivoal, R. and R. Cook 1993. Nematode pests of cereals. pp. 259-303 in Plant-parasitic nematodes in temperate agriculture. Evans, Trudgill and Webster (eds.), CAB Int., Wallingford, UK.

17. Winfield, A.L. and D.A. Cooke 1974. The ecology of Trichodorus. Pp. 309-342 in: Nematode Vectors of Plant Viruses, Lamberti, Taylor and Seinhorst (Eds), Plenum press, London.

18. Bell, N.L. and R.N. Watson 2001. Dynamics of sympatric Paratylenchus nanus and Paratrichodorus minor populations in soil under pasture. Nematology 3, 267-275.

19. Dickson, D.W., and T.E. Hewlett 1987. Effect of two nonfumigant nematicides on corn grown in two adjacent fields infested with different nematodes. Annals of Applied Nematology 1, 89-93.

20. Chiba, M., G.J. Fulop, B.D. McGarvey and J.W. Potter 1993. Distribution and persistence of oxamyl in relation to root-lesion nematode control following seed treatment of corn. Journal of Agricultural Food Chemistry 41, 2160- 2163

21. Yeates, G.W., and K.A. Hughes 1990. Effect of three tillage regimes on plant and soil nematodes in an oats/maize rotation. Pedobiologia 34, 379-387.

22. Forge, T.A., S. Bittman and C.G. Kowalenko 2005. Impacts of sustained use of dairy manure slurry and fertilizer on populations of Pratylenchus penetrans under tall fescue. J. Nematology 37, (under review).

23. Wicks, Z.W., J.D. Smolik, M.L. Carson and G.G. Scholten 1990a. Registration of SD101 parental line of maize. Crop Science 30, 242.

24. Wicks, Z.W., J.D. Smolik, M.L. Carson and G.G. Scholten 1990b. Registration of SD102 and SD103 parental line of maize. Crop Science 30, 242-243.

Weed Control: More than Chemicals and Cultivators

M. BETTS
British Columbia Ministry of Agriculture, Food and Fisheries, Victoria, British Columbia

Effective and economical weed control requires a good knowledge of the many available weed management tools. Corn in the 3- to 8-leaf stage is very susceptible to competition and needs to be relatively free of weeds; after the 8-leaf stage, corn becomes much more competitive so there is little value in controlling new weeds after this stage. How do you get corn to the 8-leaf stage as safely as poss ible?

Tillage for Weed Control

Tillage remains an effective tool for controlling weeds, and is especially useful where herbicide resistance in weeds has developed. Cultivating to kill weeds without injuring the corn requires careful control of cultivation timing and depth.

Timing cultivation
Early cultivation is very important because as weeds develop deeper roots with more food reserves, they increasingly resist and recover from mechanical damage. Also, the longer weeds are allowed to grow, the more nutrients and water they take from the crop.

Cultivation before planting.
In early spring, planting can be delayed slightly to allow weed seeds time to germinate. A shallow cultivation immediately before planting will destroy newly germinating weeds that are not easily noticed.

Cultivation after planting.
Cultivation after planting can be very effective but requires special equipment. A light harrow can be used up to early corn emergence. A rotary hoe can be used until corn plants are 10-12 cm (4-5 in) tall (Fig. 1). After the plants are 15 cm (6 in) tall, inter-row cultivation is the only tillage option. When using the harrow or the rotary hoe, it is vital to control weeds when they are very young.

Figure 1. Rotary hoe

Cultivation Equipment

Harrow
A light harrow can be used to control newly germinating annual weeds in corn planted 2-5 cm (1-2 in) deep. Shallow harrowing is done after the corn has sprouted but before the shoot has emerged from the ground, and when weeds at the soil surface have germinated but are still very small with few roots. The harrow should be light so the teeth will not cause crop damage but will dislodge or bury most of the newly sprouted weeds. Shallow harrowing will:

  • bring few new weed seeds to the soil surface
  • result in little loss of soil moisture
  • cause little damage to corn roots
  • require low tractor power.

Rotary hoe
The rotary hoe (Fig. 1) is generally more effective than the harrow. The rotary hoe has two gangs of closely mounted spiked wheels which lift a thin surface layer of soil that contains the small weeds while the implement is pulled at high speed (generally 10-20 km/h or 6-12 mph) across the field.

The small weeds are either buried or flipped out onto the soil surface to die. For the operation to be most effective, weed seedlings must be in the ‘white sprout’ stage when they are quite difficult to see; if the field shows a green tinge from weed growth, you are likely too late to get most effective weed control. Best results are obtained on dry soils in the middle of the day when the uprooted weeds are likely to dry out; wet soils and rainfall reduce effectiveness. Corn and other large seeded crops, planted about 5 cm (2 in) deep, are not damaged by the rotary hoe until plants reach a height of about 10-12 cm (4-5 in). however, note that hoeing should be avoided when the corn spike is still underground but close to the soil surface because loose soil can damage the plant by covering it; wait until the first leaf has emerged.

A common mistake is delaying the first hoeing operation. The first pass should be made 3-5 days after the last tillage and the second pass about 5-7 days later.

Another valuable use for the rotary hoe is to break soil crusts on newly planted fields, helping the crop to emerge. Crusting may occur on silt or clay soils after heavy rainfall.

Inter-row cultivator
Inter-row cultivation is especially helpful after herbicide application, when suppressed weeds have started to regrow or new weeds have germinated. There are many styles of inter-row cultivators and most can be modified with various types of shields and sweeps. Depth wheels with precise height adjustment are necessary to maintain accurate, shallow tillage. For implements using several cultivator sweeps per row, sweeps should be spaced to provide up to 50% overlap. Success with inter-row cultivation depends on field conditions and weed stage as well as the design and quality of the cultivator and the skill of the operator in setting-up and operating the equipment. Inter-row cultivation controls weeds between rows but  may also help to control weeds in the rows. Within-row weed control can be achieved by covering the weeds with soil thrown into the row while protecting the corn with shields. For this to work, the corn must be tall enough and weeds small, criteria which are not always met. For improved effectiveness of an inter-row cultivator, consider the addition of a tractor steering guidance system. Precision steering will improve weed control and reduce damage to the corn by allowing for fine-tuning of the cultivator. It also enables higher speed of operation and minimizes stress on the operator.

Weed control in Minimum-till

Controlling weeds in no-till systems presents particular challenges and generally increases dependence on herbicides. Weed populations tend to shift because the change in tillage impacts underground parts of perennial weeds and the movement of weed seeds within the soil profile. With conventional tillage, weed seeds are moved down the soil profile where they may remain dormant for long periods thus increasing the life of seeds and prolonging some weed problems. With no-till, most weed seeds remain on the surface where they are damaged by weathering or consumed by insects, birds and rodents. Perennial weeds however, can become more problematic with no-till systems and should be controlled with pre-plant or pre-emergence burn-down treatments. Use of post-emergence herbicides may also be necessary.

Figure 2. Band sprayer mounted on corn planter

Herbicides for Weed Control

There are many herbicides and mixtures of herbicides registered for use in corn. For effective weed control with herbicides, it is essential to:

  • Identify weeds before selecting herbicides. It is useful to record weed problems and refer to records the next year when selecting pre-plant incorporated and pre-emergence herbicides.
  • Change herbicide groups (see below) frequently so you do not build up populations of herbicide tolerant weeds.
  • Read the label and follow directions — it’s the law. Reading and understanding the herbicide label, especially before you are in the field, helps to prevent costly mistakes and improves results.
  • Frequently monitor corn and weed growth stages when using post-emergence herbicides. As weeds get older, they become more resistant to herbicides. Avoid spraying postemergence herbicides after the optimum growth stage outlined on the label.
  • Consider economic thresholds. It may not be economic to control all weeds. Weed species vary in their ability to compete against corn, but generally weeds that emerge early cause greatest yield reductions. For example, redroot pigweed plants that emerged when corn was in the 3-leaf stage suppressed corn at populations of 1 plant per 2 m (2 yd) of corn row. In contrast, pigweed that emerged when the corn was at the 6-leaf stage did not cause yield reductions even at populations of 4 pigweed plants per m (yd) of row. This shows that early identification and control of weeds is important.

Herbicide Application
A major concern with herbicide application is drift onto non-target areas. Drift refers to the movement of droplets or vapours by wind or air currents. Herbicide drift results in reduced weed control, damage to neighbouring crops and pollution of the environment. Buffers (setbacks) are required to protect sensitive areas downwind of the application, such as watercourses, shelterbelts, hedges, woodlands, or wildlife habitat. Follow instructions about buffers that may be outlined on the herbicide label, and use drift reducing equipment.

Spraying Equipment

Boom sprayers
Boom sprayers are designed to uniformly and accurately spray herbicides to the ground or weeds across the full width of the boom. For effective application, the equipment must be frequently maintained, calibrated and monitored. It is not uncommon to find application equipment significantly over-applying herbicide. This will result in unnecessary expense, possible crop damage or herbicide residue buildup and potential pollution. Underapplication may force a second herbicide treatment for adequate weed control or could result in the development of herbicide resistant weeds.

Band sprayers
Although herbicides are usually applied with boom sprayers, consider banding herbicides. Banding saves time and reduces the amount of herbicide used. Band applicators can be attached either to planters or cultivators.

Planter sprayers are used for pre-emergence herbicides at planting time. Band sprayers attached to the row-crop cultivator are used to apply herbicides after the corn emerges. Spray nozzles for banding equipment must apply a uniform rate of spray across the pattern of each individual nozzle (even-spray nozzles). When banding with row-crop cultivators, it may be necessary to use nozzles that have a narrow pattern (20-30 degrees) so that the tips can be raised high over the crop. For precise control of height, nozzles may be mounted on skids. ‘Crop leaf lifters’ can help reduce herbicide contact with the corn plants while increasing the exposure of weeds.

The Peril of Herbicide Resistant Weeds
Pests are continually acquiring resistance to chemical agents such as insecticides, fungicides, antibiotics and herbicides. Herbicide resistance is the ability of a plant or population of plants to survive a normally lethal dose of the herbicide. Herbicide resistance within a weed population is relatively rare, but when it does occur, the resistant plants are able to grow and multiply. Generally, resistance is most common in annual weeds because of the massive numbers of seeds they produce. According to the Weed Science Society of America there are over 170 weed species found in 270,000 fields throughout the world that have acquired herbicide resistance. These numbers continue to grow.

How to prevent herbicide resistance
Herbicide programs should be designed to minimize risk of developing resistance. Herbicides can be grouped by their mode of action. For example, herbicides in Group 5, which include the triazines (like atrazine), work by inhibiting photosynthesis at a particular biochemical site. The commonly used herbicide 2,4-D is in Group 4, which works as a synthetic growth regulator. When herbicides in the same Group are used in the same field for a number of years, one or more weeds may survive and multiply. Seed of these resistant weeds may remain viable in the soil for many years.

Following are some tips to help reduce build up of herbicide resistant weeds:

  • use non-chemical weed control practices such as tillage.
  • use herbicides only when necessary.
  • don’t use herbicides from the same herbicide Group every year, and choose products from different Groups when mixing herbicides
  • don’t reduce application rates below label rates
  • use herbicides with a short residual life. Most cases of resistance have occurred with persistent chemicals (e.g. atrazine).
  • keep records so you know what herbicides have been used in previous years.

Some problem weeds in corn

Following are weeds that are common problems in corn production in many regions. Remember, proper identification is essential to develop an effective weed management plan.

** insert weed photos here.

 

Tips for fighting weeds

  • Walk your fields frequently; destroy patches of weeds so they cannot produce seeds that might remain viable in the soil for years. Monitor the infested area in future years.
  • Prevent weeds from arriving in your farm as seeds or vegetative propagules in manure or on equipment (your own or your custom operator’s). While complete prevention is impossible, you can dramatically reduce importation. 
  • Destroy germinating seeds and young weeds just before planting, using tillage or broad-spectrum herbicides, to give your crop a head start.
  • Correct soil nutrient deficiencies for fast early growth, and avoid fertilizing the weeds. Applying starter fertilizers in bands 5 cm (2 in) beside and below the seed targets the young corn plants while limiting access to weeds.
  • Select vigorous corn hybrids based on local information; corn hybrids vary widely in their early spring vigour. 
  • Plant early. Plantings have generally gotten earlier over the years, partly thanks to new hybrids that do well under cool climate and soil conditions. In BC, late April and early May plantings generally yield more than later plantings.
  • Pay attention to planter maintenance, adjustment and calibration. Proper operation is essential to avoid gaps between seeds, uneven emergence, poor fertilizer placement, and inaccurate seed and fertilizer rates that give weeds an opportunity to grow and reduce corn yields. Excessive planting speed can result in poor seed placement and uneven stands.
  • Rotate crops. Alternating crops reduces the build up of hard to control weeds (also disease and insects) and the risk that herbicide resistance will develop.

Leaf Stages of Corn

It is important to know the different techniques used for counting corn leaves in order to understand herbicide label directions.

1. Leaf-tip method — count all the leaves including the newest leaf tip that may have emerged from the whorl at the top of the plant.

2. Leaf-collar method — the leaf collar is a light-green band that separates the leaf blade and the leaf sheath (leaf sheath is the cylindrical part of the leaf that wraps around the corn stalk). Corn growth stages using this method are referred to as V1, V2, V3, etc., where V2 indicates a plant with 2 collars showing.

3. Leaf-over method — counts all the leaves including the last leaf that has started to arch over. This usually happens when the leaf is about 50% emerged.

Remember that as plants get older, leaves at the bottom of the plant begin to die. All counting methods include dead leaves. It helps to know that the first leaf (the one closest to the bottom of the plant) is always short and has a rounded tip. So when assessing later growth stages after some of the bottom leaves have died, always look for the leaf with the rounded tip.

 

Tips for Sprayer Use and Maintenance

1. Follow equipment and pesticide safety procedures.

2. Ensure that nozzle spacing, spray pressure, spray output and pattern are uniform and accurate across the width of the boom. The need for frequent checks of nozzle pattern (plugged nozzles), uniform spray output and correct application rate cannot be over emphasized. Nozzles varying in output by more than 5% from the average need to be replaced

3. The spray boom needs to be stable, with constant height of nozzles over the ground or weed canopy across the boom width. Nozzle height must be appropriate for the specific nozzles being used to allow for proper spray overlap and uniformity of application.

4. Ground speed needs to be constant. Soft soil or hilly fields can cause significant variation in ground speed and corresponding errors in herbicide application rate. Application rates of sprayers having a constant pressure at the nozzle are directly affected by forward speed; if forward speed is reduced by 15%, then application rate increases by 15% with possible costly outcomes. Where variable ground-speed is a problem, ground-driven speedometers can be used to regulate flow-proportioning valves to deliver constant rates. More sophisticated sprayer monitors are now available that adjust sprayer output by determining ground speed with Global Positioning Systems (GPS). Remember that you are required by law to stay within the label application rate for each herbicide.

5. Consider using specialized nozzles that reduce drift by creating fewer small ‘driftable’ spray droplets. Examples are ‘Extended Range’ and ‘Drift Guard’ nozzles that have been shown to reduce spray drift by producing larger droplets. The newer ‘Air Induction’ nozzles mix the spray liquid with air drawn through a small hole in the side of the nozzle. This produces a very coarse spray consisting of droplets that contain small air bubbles. These large droplets, which are less susceptible to drift, shatter on impact producing smaller droplets that spread over and remain on leaves instead of rolling off, as can occur with large droplets from regular spray nozzles.

6. Clean and decontaminate your sprayer after use to prevent damage to subsequent crops. Use appropriate cleaning agents and detergents, as many newer herbicides (e.g. sulfonylurea herbicides) can cause crop damage at very low rates.

Chapter 7: Growth, Maturity and Moisture

Corn Growth and Development

B.L. MA, D.W. STEWART, AND L.M. DWYER
Agriculture and Agri-Food Canada, Ottawa, Ontario

Corn Maturity and Corn Heat Units

Corn is a tropical grass and even though it has been grown in temperate regions for hundreds of years by native people, it is still more sensitive to temperature than cool season crops like small grain cereals and alfalfa. Although day-length and soil factors (moisture, nutrients) have an influence, the development of corn from emergence, through tasselling, silking, and grain filling, to physiological maturity follows closely the amount of accumulated heat. Therefore, time to maturity will depend on the date of seeding, weather during the growing season and the corn hybrid. Since the temperature during the growing season is the most important factor, it can be used to predict maturity dates of different hybrids. This is useful for both the corn breeder and the farmer.

The most common calculation for accumulated heat for corn in Canada is the ‘Ontario Crop Heat Unit’ (CHU). This calculation is based on the maximum (Tmax) and minimum (Tmin) daily temperature in degrees Celsius. This index reflects that growth rate of corn:

1. increases proportionately to minimum daily temperature (usually night-time temperature), at all temperatures above 4.4°C (40°F)

2. increases at increasing rates with maximum daily temperature (usually daytime temperature) from 10 to 30°C (50 to 86°F), then at decreasing rates to 50°C (122°F).

A hybrid rated at 3,000 CHU’s will require that many heat units from planting to formation of black layer. The black layer is a thin black line that forms at the base of each kernel at maturity. We will discuss maturity in more detail below.

In the United States, a Growing Degree Day (GDD) index is used to describe maturity of corn hybrids. It is expressed as:

GDD= ( Tmax+Tmin )/ 2 -10.0

In this system, Tmax values above 30°C (86°F) are set to 30°C while Tmax or Tmin below 10°C (50°F) are set to 10°C. Growing Degree Day units are summed from planting to maturity.

Because different assumptions are made for the two indices, they cannot be directly equated. As an approximation, 3,000 CHU’s corresponds to about 1,265 GDD units.

Recently a new index, called the General Thermal Index, was developed for corn hybrids in northern United States and Canada. The general thermal index was designed to be approximately equal to growing degree days. This index combines separate calculations for vegetative (before silking) and reproductive (after silking) stages of corn growth. Instead of the actual date of silking, a transition date of Aug. 1 can be used.

The equation for the vegetative phase represents a typical biological response curve that starts at 0°C (32°F), rises to a maximum near 30°C (86°F) and then declines. However, the reproductive index has substantial value at 0°C (32°F) and rises almost linearly as temperature increases. It fits the common observation that corn continues to mature even when temperatures fall to near zero. Poorly understood factors other than temperature are at work here. The General Thermal Index is more consistent than other indices, but is far from perfect.

Estimating Maturity and Silage Moisture at Harvest

Cutting at the right stage of maturity has a large effect on both the quality and quantity of corn silage. The heat unit system cannot yet predict moisture content of the crop because of the influence of hybrid, population density and weather, particularly rainfall. So the question still remains: when should corn silage be harvested? The best time is when whole-plant moisture content is between 62 and 70%. But when does this happen? Certainly before black layer formation.

Kernels reach their final size within two weeks after silking, then begin to fill. During the filling period, as dry matter accumulates and moisture drops, a white line appears near the top of the kernels (100% milk-line) (Fig. 1). As the crop matures, the line recedes to the base of the kernels (0% milk-line). When milk-line reaches zero, under normal conditions, a black line or layer appears at the base of the kernels signaling physiological maturity. However, the black layer can appear before 0% milk-line when grain filling is hampered by early fall frost. As this is happening, most hybrids have kernels that will dent at the top surfaces. While the most visible indicator of maturity is black layer formation, the most important maturity factor for both grain and silage is moisture content. Unfortunately, moisture content is not easily estimated by eye and for best accuracy must be measured directly.

In eastern Ontario, 50% milk-line in dualpurpose corn hybrids broadly indicates that 65% whole-plant moisture and over 85% of maximum yield has been reached— a good indicator for silage harvest. However, the relationship between kernel milk-line and plant moisture content varies with hybrid and weather conditions. For example, after the relatively cool summer of the year 2000, the 65% plant moisture level in four hybrids corresponded to kernel milk-lines ranging from 90 to 26%. In 2001, 75% milkline stage indicated 66 to 70% silage moisture and 50% milk-line indicated approximately 65% moisture. At 25% milk-line, silage moisture ranged from 57% for hybrids Maizex Leafy 4 and TMF94 to 62% for Pioneer 37M81 (Table 1). In all cases, large variations existed for % milk-line within plots and among replications. In an earlier study on grain corn, 50% milk-line ranged from 39% kernel moisture contents in 1995, a warm year, to 42% moisture in 1996, a relatively cool year. Furthermore, it is often difficult to determine the milk-line stages for Leafy hybrids (Fig. 1). As plant moisture was determined on a whole-plant basis (5-10 plants), variability in silage moisture was much smaller among replications and population densities (Table 1), highlighting the importance of determining harvesting time based on the actual silage moisture. There fore, a decision on silage harvest time should be based on the actual measurement of silage moisture (see Timing Harvest section).

Similarly, in Ohio, it was also found that kernel milk-line was a less reliable method for determining time for silage harvest (see next section).

Figure 1. Kernel milk-line stages from full dent (100% ML) to 0% ML (black layer) in a leafy hybrid. Note within an ear, kernel stages varied from full dent to 75% ML, sometimes black layer occurred at 25%ML, and the milk line stage is recorded on average kernels, which is evaluated when removed from the cob.

Table 1. Silage moisture at 75%, 50% and 25% milk-line stages of hybrids grown at two plant population densities in 2001

Window for Silage Harvest

Silage varieties should be harvested at maximum whole-plant dry matter yield with the ideal moisture at 62 to 70%. Unlike grain corn, silage hybrids should have the characteristics of slow maturing, soft starch kernels, slow dry down of stalks and low concentration of neutral detergent fibre (NDF) with high NDF digestibility. Recent studies indicate that hybrids with the “leafy” trait (having additional leaves above the ear) dry down more slowly than non-leafy types. For example, under cool conditions of the year 2000, leafy hybrid TMF94 had a harvest window of approximately 16 days, double that of Maizex Leafy 4 and Pioneer 37M81 (Table 2). In 2001, the whole-plant moisture of the dual-purpose hybrid Pioneer 37M81 dropped more quickly than the leafy hybrids. Based on the goal of 90% of maximum dry matter yield within the ideal moisture range for silage, harvest windows in 2001 were 8 days for Pioneer 37M81, 9 days for TMF94 and Maizex Leafy 4 and 15 days for NK Enerfeast I (Table 2). Harvest windows for both Maizex Leafy 4 and Pioneer 37M81 were similar under contrasting weather but the harvest window for TMF94 was weather-sensitive.

Table 2. Average silage yields through the ideal harvest window of each hybrid in 2000 and 2001.

Kernel Hardness

Kernel hardness has been found to be an indicator of silage digestibility. Kernel hardness is currently determined using two types of measurement: Stenvert and TARR. The Stenvert procedure involves passing a 20 g sample of air-dried kernels through a hammer mill and determining the time it takes to fill a certain volume. The TARR test measures the % weight loss of an air-dried kernel sample through a vibration machine. The less time required in the Stenvert procedure or the greater amount of weight loss in the TARR test, the softer is the kernel. Although affected by stage of maturity, kernels of leafy hybrids are consistently softer than those of dual-purpose hybrids (Fig. 2). Kernels make up 40-50% of total plant dry matter. The softer kernels in leafy hybrids indicate that under the same ensiling conditions, there will be more digestible energy produced by leafy hybrids than non-leafy dual-purpose hybrids.

Figure 2. Kernel hardness test results using a Stenvert or TARR in 2000 (0 milk-line) and 2001. Within a harvest time, bars with different letters are statistically different.

Summary

Corn development is governed by heat, which can be expressed as Growing Degree Days, Crop Heat Units or a Generalized Thermal Index. The indices are helpful in selecting silage varieties and anticipating the proper stage for silage harvest. Silage moisture content determines the window for harvest. Silage cannot be harvested close to physiological maturity when maximum dry matter is reached. Rather, silage should be harvested at around 65% whole-plant moisture content, which normally corresponds to 50% kernel milk stage. However, the relationship between kernel milk-line and silage moisture content is affected by growing conditions, especially rainfall; whole-plant moisture at 50% kernel milk-line, used for timing silage harvest, also varies with hybrid. Compared to dual-purpose hybrids, leafy silage hybrids have soft kernels and slow decline in whole-plant moisture content so they provide producers with a larger window for harvest.

Timing Harvest of Silage Corn

R.M. SULC
The Ohio State University, Columbus, Ohio

Determining the proper time to harvest corn for silage is critical because it influences the overall quality of the product that is preserved and stored in the silo. As described in the chapter “Making Good Corn Silage”, the moisture content critically affects silage fermentation and preservation. Harvesting corn too wet (low DM content) results in souring and seepage of the silage and reduction in animal intake. Harvesting too dry (high DM content) promotes mould development because the silage cannot be adequately packed to exclude oxygen. Harvesting too dry also results in lower digestibility, protein, and vitamins A and E. So harvesting corn at the proper dry matter content will result in better animal performance and lower feed costs.

Harvest Moisture Guidelines

Corn silage preserved between 30 and 40% DM (60 to 70% moisture) generally provides good silage fermentation and animal performance. The optimal DM content varies with type of storage structure (Table 1).

Table 1.  Optimal dry matter contents for different storage structures.

Determining Silage Moisture

Predicting when to harvest corn to achieve the proper % DM for ensiling is difficult because there is no easily identifiable plant trait that can be used to reliably and accurately estimate the whole-plant % DM. The only reliable method of determining the optimal time to harvest corn silage is to sample the crop and directly measure the % DM of whole plants. The following procedures were developed for sampling fields and measuring moisture content to plan harvest dates. The whole-plant % DM information combined with average whole-plant drydown rates can be used to roughly predict the proper time to harvest silage.

When to Begin Field Sampling
Sampling fields to measure whole-plant dry matter content should be done well before the anticipated harvest date in case corn is drying down faster than expected. Silking date can be used as a rough indicator of which fields are likely to be the earliest to harvest. The dent stage occurs about 35 to 42 days after silking, which is when fields should first be checked for kernel milk stage development.

While kernel milk stage cannot be relied upon to gauge optimal harvest timing, it can be a useful indicator of when to begin measuring whole-plant DM content. Table 2 describes the kernel milk stages when the first samples should be collected. These values are based on numerous studies conducted in Canada and the northern USA, and reflect the stages when 90% of the samples collected were consistently too wet for ensiling in a given storage structure.

Under drought conditions or south of the upper tier of states in the USA, samples should be collected slightly earlier than the stages shown in Table 2. Corn reaches harvestable % DM at earlier kernel stages as you move south.

Table 2.  Kernel milk stages when moisture sampling should begin for different storage structures.

How to Sample Fields
Collect 5 to 10 representative plants from the entire field. The plants should be uniformly chopped (using a cleaver, machete, chipper shredder, or silage chopper) and then mixed thoroughly to obtain a sample with representative grain to stover ratios for drying. Some farmers prefer sampling only 2 or 3 plants to reduce the chances of a non-representative grain to stover ratio. In this case, choosing representative plants is even more critical.

Moisture Measurement
Use one of the two methods described below to determine % DM of the sample. Each method requires a good scale that can measure in grams. These are available with the Koster Tester or postal digital scales can be ordered from NASCO or other mail order catalogs.

The accuracy of the % DM value obtained from either method will be largely determined by the amount of time and care taken in drying down and weighing the samples. This is especially true for corn silage where whole kernels and cob pieces can be difficult to dry completely without burning the leaf tissue.

a) Microwave Oven Method

1. Clip or chop the corn plants into 2-5 cm (1-2 in) long pieces. Place a representative 100 to150 g sample on a paper plate and spread in a thin layer leaving an open area in the center (doughnut-shaped). Record the weight of the forage + paper plate: this is the initial wet weight.

2. Place a 250 ml (8-ounce) glass of water (3/4 full) in the back corner of the microwave. Keep water amount somewhat constant during microwave use. You may need to replace the water in the cup with cold water to keep it from boiling over during the heating cycles. Heat the sample. Samples containing 50-75% moisture (25-50% DM) can be heated initially on high for 4 minutes. Samples with less than 30% moisture (over 70% DM) should be heated for only 2 to 3 minutes. Power of microwave ovens varies causing differences in drying times.

3. If sample feels almost dry, weigh and record weight of the plate + sample. Stir the forage and reheat for another 60 sec if sample was originally 50-75% moisture or 30 sec if originally less than 35% moisture. Repeat heating and weighing until either weight changes by less than 1 to 2 g or forage begins to char. If any charring has occurred, use the previous weight for calculating the moisture content.

4.The dry weight is the last weight recorded after which the sample does not decrease more than 1 to 2 grams and charring has not occurred.

5. Calculate the % dry matter (DM): % DM = (Dry weight/initial wet weight) x 100

Example: The initial wet weight of plate + forage was 130 g and the final dry weight of plate + forage was 46 g.  So, % DM = (46/130) x 100 = 0.354 x 100 = 35.4%

The % moisture content is calculated as follows: % moisture = 100 - % DM

Example: % moisture =100 – 35.4 = 64.6%

Notes: With a little experience, the microwave method can be run in less than 10 minutes. You may want to perform the procedure in the barn or work shed, because it does produce an odor.

Warning: Never leave microwave unattended while heating because samples can ignite!

b) Koster Tester Method
(available through Koster Crop Tester, Inc., 13477 Prospect Rd., Ste. 103C, Strongsville, OH 44136 or NASCO, www.nascofa.com)

1.To weigh exactly 100 grams of sample, take the weight of the container (Koster basket) and add 100 grams of forage to the basket.

Example: If the basket weighs 17 grams, the total weight is 117 grams

2. Place the basket in the Koster dryer. Samples with 50-75% moisture will take more than an hour to dry. After one hour, record weight of sample at 5-15 minute intervals.

3.Repeat steps 2 and 3 until weight becomes constant.

4. The final dry weight (forage + basket), minus the basket weight, is the dry matter percentage.

Example: dry weight (forage + basket) is 52 g and basket weighs 17 g
% DM = 52 –17 = 35%

5.To determine moisture content, subtract the % DM from 100.

Example: % moisture =100 – 35 = 65%

Predicting the Harvest Date

Once the target milk stage is reached and whole-plant % DM is determined, an average dry down rate of 0.5% unit per day can be used to estimate the number of days until harvest. For example, if a given field measures 30% DM at the early sampling date, and the target harvest DM content is 35%, then the field must gain an additional 5% units of DM requiring an estimated 10 days (5% units divided by 0.5 unit change per day).

This procedure provides only a rough estimate for the harvest date. Many factors affect the dry-down rate, including hybrid, planting date, general health of the crop, landscape position, soil type, and weather conditions. For example, in early planted fields or under hot and dry conditions, wholeplant % DM can increase at a rate of 0.8 to 1.0% unit per day. Fields should be monitored closely and whole-plant % DM determined again as the predicted harvest date approaches.

Spreading the Harvest Window

When planning harvesting operations, keep in mind the length of time required to harvest the field. Harvesting may need to start on the early side to ensure the field does not get overly dry by the time harvesting is complete. It is often better to err a little on the early (wet) side rather than to be too late unless kernal processors are used (see Processing Corn Silage section). Hybrid selection and planting date can be used to influence the timing and length of the harvest window.

Hybrid Selection

Select hybrids that vary in maturity to spread the risk of plant stress during pollination and to spread the harvest window. Greatest silage yields are usually achieved with full season hybrids. Hybrids can be 5 to 10 days later when used for silage than when used for grain.

Hybrids differ in rate of whole-plant drydown. Seed companies provide information on whole-plant dry-down rate for their hybrids. Recent studies in Canada demonstrated that hybrids with the leafy trait (with more leaves above the ear) dried down slower than standard types in some years (see Corn Growth and Development section).

Planting Dates

Staggering planting dates can help spread the harvest window. Full-season hybrids should usually be planted first to take advantage of their higher yield potential. Some producers like to plant an “ultra” short-season hybrid early to provide fermented feed during early fall. It is useful to keep records of planting dates and hybrid maturities for each field.

Summary

Harvest timing is a critical management decision to ensure corn will be ensiled at the proper dry matter content for effective fermentation and storage. The following steps will help producers harvest corn silage at the optimal time.

1. Record hybrid maturity and planting date for each silage field.

2. Record the silking date of each hybrid and field to be chopped for silage. Full dent of kernels will typically occur 35 to 42 days after silking.

3. Once the kernel milk-line appears and begins to move (soon after full dent stage), sample and measure the wholeplant % DM of fields to be harvested for silage. Use a dry down rate of 0.5% unit per day to roughly predict when the field will be ready for the storage structure used.

4. Sample the field again to determine whole-plant % DM prior to chopping.

Kernel stage not a reliable guide for timing harvest
Dry matter content of whole-plant corn varies with maturity. Historically, recommendations were to harvest corn silage when kernels were at the black layer stage but today’s hybrids are too dry at the black layer stage. Through the 1990’s, timing silage harvest based on the kernel milkline position was widely recommended. But recent studies in Canada and the USA have demonstrated that the position of the kernel milk-line, used alone, is not a reliable indicator for determining harvest timing. Geo-graphic location, planting date, hybrid selection, and weather conditions affect the relationship between kernel milk-line position and whole-plant DM content. In a Wisconsin study, 82% of the hybrids tested exhibited a poor relationship between kernel milk-line stage and whole-plant % dry matter. Thus, it is impractical for seed companies to develop hybrid-specific calibrations for kernel milk-line stage as a guide for silage harvest. Similarly, timing corn silage harvest based on a heat unit system is also unreliable.

Chapter 8: Quality of Corn Silage

Understanding Corn Silage Quality

Plant Structure*

(*Based on C Holland and W Kezar, The Pioneer Forage Manual — Nutritional Guide. Pioneer Hi-Bred International Inc. 1999.)

Stover

The defining characteristic of plant tissue, such as that comprising the stems and leaves of corn stover, is that it contains a large portion of cell-wall material. The amount and type of plant cell wall material determines the nutritional quality of the stover.

A young plant cell has a single outer layer referred to as the primary cell wall (Fig. 1). As the plant matures, a second cell wall is laid down on the inside of the first cell wall. This secondary wall is thicker than the primary wall, giving plant cells tensile strength. The primary and secondary cell walls combined make up 40-80% of the dry matter content of corn stover. The main structural components of both primary and secondary cell walls are two complex carbohydrates called cellulose and hemicellulose. Cellulose is one of the most abundant organic materials on earth. Animals cannot produce enzymes to digest cellulose or hemicellulose. However, the micro- organisms residing in the digestive tract of ruminants (primarily in the rumen) produce enzymes which efficiently digest and utilize cellulose.

Figure 1. Diagram of a plant cell showing cell-wall structure
(from Advanced Forage Management, 1999).

With advancing maturity, forage cells insert a complex non-carbohydrate material known as lignin between the primary and secondary walls. Lignin gives the plants additional tensile strength and rigidity and can be thought of as the primary skeleton of the plant cell. Lignin is important from a nutritional perspective because it is totally indigestible and its presence reduces the availability of the cellulose and hemicellulose portions of the forage. The primary cell wall is like a layer of bricks, the secondary wall like a layer of cinder blocks laid inside the bricks and lignin is like mortar added later between the bricks and cinder blocks. As the corn plant advances in maturity, more lignin is added making the cell walls more difficult to digest.

Grain

A corn kernel is largely comprised of three parts: the pericarp (outer coating or hull), the endosperm, and the germ (or embyro) as shown in Fig. 2.

Figure 2. Parts of a corn kernel

The pericarp or hull of the corn kernel is a thin outer covering made up of two layers. Removal of this part of the corn kernel results in corn bran, commonly used for cooking. The endosperm, which comprises up to 82% of the kernel’s dry weight, is the source of energy for the germinating seed. In all field corn, the endosperm is comprised of two types of starch: vitreous and floury (Fig. 3). The proportion of these starches is controlled genetically. The floury endosperm is the softer starch, and as the kernel matures, this type of starch dries down to create the “dent” in the top of the kernel of dent varieties. Vitreous starch, more abundant in flint corns, tends to be harder for cows to digest because the starch granules are embedded in a dense protein matrix. Therefore, as the amount of vitreous starch present in corn kernels increases, total tract starch digestibility decreases, unless the silage is ‘processed’ (see Corn Silage Processing section).

Figure 3. Types and placement of starch within the corn kernel
(from Dairy Herd Management Vol. 35 No.11, Nov. 1998).

The germ of the kernel contains all the genetic information, some nutrients, and oil needed to enable germination and early growth. The germ is comprised of 25% fat (corn oil) which is high in linoleic acid (see Fats in Corn Silage section). The tip cap is not covered by the pericarp as it is the attachment point between the kernel and the cob.

Assessment of corn silage quality*

(*Based on C Holland and W Kezar, The Pioneer Forage Manual — Nutritional Guide. Pioneer Hi-Bred International Inc. 1999.)

What is ‘Detergent’ Fibre?

The ‘detergent-fibre’ method for assessing quality of forages was introduced about 1970. The earlier crude fibre system failed to generate accurate estimates of digestible nutrients over a wide range of forages; it tended to underestimate good quality forages and overestimate poor quality forages. The detergent system of forage analysis is now the most common way to assess forage quality. Fig. 4 shows a schematic of the detergent system of forage analysis. Detergent analyses are performed on dried and finely ground samples.

Figure 4. The detergent (Van Soest) procedure to
partition forage fractions.

Neutral Detergent Fibre (NDF)

For determining NDF, samples are boiled in a special detergent at a neutral pH of 7.0, then filtered. The soluble portion that passes through the filter contains highly digestible nutrients which were contained within the cells (see Table 1). The insoluble portion of the forage that does not pass through the filter is called the ‘neutral detergent fibre’. This fraction contains the cell wall material including cellulose, hemicellulose, lignin and silica (Table 1). The proportion of NDF in corn stover increases with the advancing maturity of corn. In recent years, seed companies have been developing hybrids for silage production where increasing maturity does not necessarily result in decreasing fibre digestibility.

On a simple level, neutral detergent fibre is sometimes used as a (negative) indicator of feed intake. As the NDF increases, animals tend to consume less forage. The relationship between NDF and intake is:

Feed intake (dry matter) as percent of body weight = 120/NDF(%)

Example: corn silage with an NDF value of 40% will be consumed at 120/40=3% of body weight.

The paradox of NDF is that while it can be a negative indicator of quality it is also required by ruminant animals.

Acid Detergent Fibre (ADF)

Acid detergent fibre is the portion of the forage that remains on the filter after a finely ground forage sample is treated with a detergent and strong acid. It includes the largely digestible cellulose, indigestible lignin and inorganic silica. Acid detergent fibre is important because it is negatively correlated with digestibility of forages. As the ADF increases, the forage becomes less digestible, primarily because the amount of indigestible lignin is increasing. Total digestible nutrients (TDN) values are calculated directly from ADF values as follows:

  • Corn silage: TDN = 87.8 - (0.70 x ADF%)
  • Legumes and grasses: TDN = 88.9 - (0.79 x ADF%)

Note that TDN declines less rapidly with increasing ADF in corn silage than in grass and legumes.

Lignin and silica

Lignin is the wood-like, non-carbohydrate component that cannot be digested by ruminants. Further, lignin decreases availability of cellulose and hemicellulose. The lignin fraction can be determined by further treatment of the ADF fraction with a very strong acid. All plants have the capacity to accumulate significant quantities of silica (or sand) although corn does not accumulate as much silica as many grasses. The silica fraction is left as ash after a forage sample is ignited in a special furnace. Mud or dust picked up on the corn will add to the silica content. Silica content can be reduced by raising the cutting bar (see Effect of Cutting Height).

 

Effect of Cutting Height on Nutritive Value of Corn Silage

J. Harrison and L. Van Wieringen
Washington State University, Puyallup, WA

At a given maturity, the nutritive value of corn silage can be changed by altering the cutting height. This has been called hi-chop or super silage and is the result of leaving as much as 50cm (20inches) of the lower portion of the stover unharvested (Quaife, 2000). Raising the cutting bar lowers the fibre content and increases the starch content compared to conventional cutting height. While a more digestible forage is harvested, there is also a loss in yield of harvested forage (Table 1). The economics of this practice varies from farm to farm.

Table 1. Effect of cutting height on quality and yield of corn silage.

Yield Components and Quality of Silage Corn in the Pacific Northwest

S.C. Fransen
Washington State University, Prosser, Washington

The yield of corn silage in our trials ranged from 15.8 t/ha (7.0 T/ac) with 20.7% dry matter content at the early dent stage to 25.2 t/ha (11.2 t/ac) with 34.8% dry matter at ½ milk-line stage (Table 1). If the crop were to remain in the field longer, harvestable yields would probably decline because of leaf senescence and drop, stalk breakage, lodging and pest damage. Silage corn yield is a sum of its 3 yield components: ears, stalks and leaves. Whole-plant dry matter content is highly related to corn ear maturity, since stalks and leaves retain high concentrations of plant moisture. With increasing crop maturity, the percentage of ears increase and stalks decrease, but the rate of this change declines from dent to 1/2 milk-line. Although stalk and leaf percentages decrease with advancing crop maturity, the ratio of leaves to stalks increases with maturity. Nevertheless, percentage of stalks remains proportionally higher than percentage of leaves. Leaf percentage remains similar after the crop reached the dent stage of growth. The average silage corn plant produces about 20 leaves, but they range from 12 to 25 leaves.

In our trials, digestibility of whole plant silage corn increased slightly after the crop reached the early dent stage (Table 1). Whole plant digestibility was generally related to the percentage of ears. Starch percentage followed the same pattern as total grain per acre. Crude protein percentage decreased as the crop matured, due to increasing ear percentage. Percent ash also decreased with advancing crop maturity. Three important minerals within the ash component are sulphur, phosphorus and potassium. Concentration of potassium declined more rapidly with maturity than sulphur or phosphorus.

Table 1. Change of yield, yield components and nutritional parameters with advancing maturity of irrigated corn in the Pacific Northwest (based on 64 hybrids, 4 years and 2 locations).

Fibre and Energy in Corn Silage

M.L. SWIFT
Abbotsford Veterinary Clinic, Abbotsford, British Columbia

Corn silage provides a palatable source of energy, protein and minerals for ruminant animals. However, like all forages, corn silage is inherently variable in nutrient value due to hybrid, climatic conditions, maturity upon harvest and conservation methods as shown in Table 1.

Table 1.  Nutrient values for 83 samples of corn harvested at different maturities in the lower Fraser Valley region of British Columbia. (Range of values in brackets)

Maturity of Corn

Immature Intermediate Mature

DRY MATTER (DM) (%)

22.2 (18.0-24.2) 27.5 (25.0-29.5) 32.0 (30.0-38.7)

FIBRE

Acid Detergent Fibre (%DM) 30.5 (26.1-38.2) 28.4(24.0-33.7) 25.7 (22.4-29.6)
Neutral Detergent Fibre(%DM) 49.3 (44.7-58.3) 45.6 (39.6-54.1) 42.3 (37.7-48.2)
NDF Disappearance(%at 30h) 54.8 (51.0-59.0) 52.8 (44.0-59.0) 51.7 (46.0-57.0)
Lignin (% of NDF) 6.8 (4.1-8.2) 7.1 (4.6-9.2) 7.2 (6.1-8.6)

SOLUBLE CARBOHYDRATES

Starch (%DM) 17.2 (0.5-26.4) 26.0 (14.5-33.4) 29.8 (20.9-37.6)
Sugar (%DM) 3.5 (0.5-12.2) 2.5 (0.4-10.7) 1.8 (1.0-3.3)
nonstructural carbohydrates* 34.3 (18.4-42.1) 38.9 (26.0-45.4) 42.8 (36.8-48.5)

PROTEIN

Crude Protein (CP) (%DM) 9.5 (8.1-12.1 8.7 (6.6-11.7) 8.4 (7.4-9.8)
Soluble Protein (% of CP) 52.8 (34.3-69.1) 56.2 (29.1-76.5) 52.6 (30.7-73.5)
ADF-CP (% of CP) 10.4 (7.7-13.8) 10.1 (6.1-18.8) 9.9 (6.7-14.6)
NDF-CP (% of CP) 18.7 (9.1-36.2) 15.3 (8.9-38.8) 14.6 (8.0-28.7)

FAT

3.2 (2.1-5.3) 3.4 (2.4-5.5) 3.2 (2.6-4.0)

MINERALS

Calcium (%DM) 0.23 (0.13-0.56) 0.18 (0.09-0.35) 0.18 (0.12-0.28)
Magnesium (%DM) 0.16 (0.12-0.25) 0.14 (0.07-0.23) 0.15 (0.10-0.22)
Phosphorus (%DM) 0.19 (0.13-0.27) 0.2 (0.13-0.25) 0.19 (0.14-0.26)
Potassium (%DM) 1.10 (0.63-1.61) 1.0 (0.68-1.34) 0.88 (0.62-1.18)
Ash (%DM) 5.5 (3.9-10.8) 4.8 (3.1-8.9) 4.5 (3.4-5.8)

Energy

Corn silage is included in ruminant rations primarily as a source of energy. The starch in corn grain accounts for approximately 45% of the energy value of corn silage. Table 1 shows that immature corn silage (defined as DM less than 25%) contains approximately 10% units less starch than more mature corn silage (DM more than 25%). Microbial digestion of cellulose and hemicellulose (NDF fraction) in the rumen contributes a further 25% to the energy value of corn silage. The remaining 30% of energy in corn silage comes from sugars, pectin, organic acids, crude protein and crude fat. Traditionally the energy content of feedstuffs has been expressed in terms of TDN (total digestible nutrients) or NE (net energy of lactation or gain). Values for TDN and NE of corn silage and other forages are computed using regression equations based on acid detergent fibre (ADF) content (Table 2 ) which broadly represents the content of cellulose and lignin contained within the plant.

Table 2. Prediction equations for energy content of corn silage based on fibre analysis.

 Location  Equation
 Midwest      %TDN = 87.84 - (0.70 x ADF)
 New Hampshire      NE lactation = 0.996 - (0.0126 x ADF)
 New York      NE lactation = 0.94 - (0.008 x ADF)
.      % TDN = 31.4 + (53.1 x NE lactation)

Although this approach accounts for the increasing grain content (ADF decreases, energy increases) and increasing fibre content (ADF increases, energy decreases) as the corn plant matures, it does not account for variation in starch or fibre digestibility.

Over the past decade, there has been increasing interest in improving nutrient value of silage corn hybrids by increasing digestibility of its fibre, in particular, the NDF fraction. Recent studies confirm that digestibility of the NDF fraction affects dry matter intake and milk production (1). In these studies, a 1-unit improvement in NDF digestibility increased dry matter intake by 0.17 kg (0.37 lb) per day and production of milk (4% fat corrected) by 0.25 kg (0.55 lb) per day.

Table 3 provides an interesting comparison between two corn hybrids, one selected for grain the other for silage production. Digestibility of NDF in the stalks and leaves was approximately 10% greater in the silage hybrid than in the grain hybrid. Since these plant fractions represent over 40% of the plant structure, NDF digestibility was 3.4% greater for the silage than for the grain hybrid.

Table 3.  Comparison of corn hybrids developed for grain and silage: plant components and their concentrations of crude protein, neutral detergent fibre (NDF) and digestibility of NDF (IVNDF).

Recent work showed a large range in the NDF digestibility of corn stover in hybrids tested at two sites in British Columbia (Table 4). Digestibility of NDF was tested as the proportion of the NDF that disappeared after 30 h of incubation in rumen fluid. The differences among hybrids shown in Table 4 are reflected in the data presented in Table 1 for immature (DM 25%) corn silage samples. Silage harvested early showed an eight percentage point spread between lowest and highest NDF digestibility (51 to 59%). As the corn silage was allowed to mature, the differences between hybrids became increasingly evident as the variation in NDF digestibility increased to fifteen percentage points, ranging from 44 to 59%. Interestingly, there was no relationship between NDF digestibility and the content of DM or NDF in the sample.

Table 4.  Values for NDF and NDF digestibility in stover from hybrids grown in coastal BC in 2001

 Location  Hybrids  NDF %  NDF digestibility (%)
 SAANICH, BC  DK3947  59.4           48.0
 Funk 4066  59.7  51.0
 Hyland 2240  62.6  43.7
 Hyland S009  61.7  47.0
 Hyland S012  61.7  52.7
 NK 2555  62.5  48.0
 Pioneer 39K40  61.7  46.7
 Pioneer 39R42  61.8  47.7
 Pioneer 39T68  65.3  47.7
 TMF 2126  60.5  49.7
 UAPDG 7485  59.6  48.3
 Pioneer 38F70  63.8  47.7
 AGASSIZ, BC  Pioneer 38F70  68.2  42.3
 Excel  64.5  46.3
   Garst 8707  65.2  43.7
 Pride K378  68.6  44.0
 N35R7  65.4  41.3
 Pioneer 37Y15  64.0  43.0
 Pioneer 3845  68.6  46.0

In light of the work showing the effect of NDF digestibility on dry matter intake and subsequent production, producers are urged to incorporate nutritional quality assessments into their decision-making processes in choosing hybrids for corn silage production. Recently, computer software has been introduced which balances rations for ruminants based on digestibility and dry matter intake. One example is the program associated with the Nutrient Requirements of Dairy Cattle (2) in which the TDN or energy value of corn silage is computed as the sum of digestible nonfibre carbohydrates (e.g. starch), digestible crude protein, digestible fatty acids and digestible NDF.

 

Minerals:  The calcium to phosphorus ratio in corn silage is approximately 1:1 as shown in Table 1. However there is a large range in mineral content of corn silage. The low potassium content (

Protein in Corn Silage

J. BAAH¹ , J.A. SHELFORD¹  and M.L. SWIFT²
¹ Faculty of Agricultural Sciences, University of British Columbia, Vancouver, British Columbia and ² Abbotsford Veterinary Clinic, Abbotsford, British Columbia

Sources of protein: microbial and rumen-bypass

All animals need to consume protein to supply the building blocks, called amino acids, that are used to build the proteins in muscle, membranes, enzymes and milk. Ruminant animals are different from non-ruminants in how they obtain amino acids. Non-ruminant animals derive all their amino acids directly from the protein in their feed. Ruminants derive amino acids from two sources: from the microbes that grow in the rumen and are then digested in the intestines, and from the feed protein that passes through the rumen and is then digested in the intestines (Fig. 1). This protein is commonly referred to as bypass protein.

Figure 1. Schematic representation of protein digestion and utilization in the cow.

Microbes in the rumen require protein (nitrogen) and energy to grow and multiply. In order to acquire nitrogen for growth, these microbes break down feed protein into both amino acids and non-protein nitrogen compounds such as ammonia. Microbes derive energy from the carbohydrates (sugars, starches, cellulose and hemicellulose) found in grains and forages. Microbes pass out of the rumen and are digested in the small intestine providing 40 to 80% of the ruminant’s requirement for metabolizable protein, depending on stage of growth or lactation.

Rumen microbes grow best when the supply of energy and nitrogen is in synchrony. Slowly digesting carbohydrates such as cellulose are most compatible with protein sources having slow rates of degradation (breakdown) that provide a steady supply of nitrogen. Frequent meals also help to provide a steady supply of nitrogen for the microbes.

The proteins in corn silage and other forages contain both degradable and undegradable fractions (Fig. 2). The overall degradability of protein in the rumen is determined by two factors: the portion of protein that is digested by microbes in the rumen and the speed of digestion in the rumen relative to rate of passage out of the rumen. If the rate of passage out of the rumen is high (high feed intake), then the microbes will not have a chance to degrade the feed protein. Hence, rumen protein degradability will be decreased. The degradable protein fraction can be subdivided into those proteins that degrade rapidly and those that degrade over a longer period of time.

Figure 2. Disappearance of protein fractions in forages as a function of time.

Protein in silage corn

Although corn silage is low in crude protein (CP) content, a ration where corn silage is the main source of forage can contribute up to 25% of the crude protein requirement of a high producing dairy cow. Of interest is the proportion of corn silage crude protein that is soluble (assumed to be readily degradable) in the rumen and that which is slowly degradable (bypass protein) as shown in Table 1.

Microbes can use soluble protein if sufficient carbohydrate is supplied in the diet. Excess soluble protein will be absorbed through the rumen wall and excreted through milk (Milk Urea Nitrogen) or urine. As shown in Table 1, there is a large range in soluble crude protein values in corn silage. Soluble crude protein is increased by the ensiling process, hence samples of “green” or uncured silage will contain less crude protein in the soluble form. Similarly, there is a large variation in the amount of crude protein in corn silage.

Table 1. Crude protein degradation characteristics of corn silage collected from farms in coastal British Columbia

Mean      

Miniumum

Maximum

Soluble CP (% of CP)

47.4

12.7

80.1

Bypass CP (% of CP)

43.5

16.2

71.0

Rate of Ruminal CP Degradation (% per h)

4.4

0.1

11.1

From ML Swift, 2003.  PhD Thesis, U British Columbia, Vancouver, BC.

References

1. Swift, M.L. 2003. Ph.D. Thesis. University of British Columbia.

Fats in Corn Silage

P.S. MIR
Agriculture and Agri-Food Canada, Lethbridge, Alberta

The two grain crops grown extensively for whole-plant silage in North America are corn and barley. At the appropriate maturity the yield and energy content of these crops is very high and both crops are relatively easy to ensile and to use as feed for dairy and beef cattle. Other than the slightly higher protein content of barley silage relative to corn silage (11 versus 8%), there are generally only small differences in composition between the two silages. The content of fat and starch varies with maturity and grain content. Although most of the energy acquired by the ruminant is from the starch and fibre fractions of silage, the fat content also has significant impact. Corn silage with 50% grain has from 2 to 7% fat depending upon the variety and maturity at harvest, while barley silage has less than 2% fat. The fatty acid composition of the two silages is similar. Among nutrients, fat yields the most calories per unit weight. Although the fat concentrations are small, the total amount consumed by an animal can be substantial. Dairy animals that consume up to 50% of diet dry matter as silage or beef cows that consume only silage through the winter months would receive about 0.44 kg (1 lb) of fat per day from corn silage and 0.24 kg (0.5 lb) from barley silage.

Figure 1. Intercropping corn with oilseed sunflower produces
a high oil silage (Agassiz, British Columbia).

Unlike carbohydrates, fat does not undergo fermentation losses in the rumen. Instead, fat is hydrolysed in the rumen into its components, glycerol and fatty acids. The glycerol is fermented in the same manner as carbohydrates. Both barley and corn silages contain about 70% unsaturated fatty acids. The saturated fatty acids are incorporated unchanged into bacterial biomass while most unsaturated fatty acids are hydrogenated before absorption by the bacteria. Some fatty acids are also absorbed directly across the rumen wall, whereas the fatty acids associated with the bacteria pass to the small intestine. Here the fats are released from the microbes and absorbed via micells, formed through the action of bile from the gall bladder and lipases from the pancreas. Interestingly, the that will escape degradation (bypass protein) by rumen microflora. A recent study (1) showed that on average, 28% of corn silage crude protein escaping degradation in the rumen will be digested in the small intestine. However, values ranged from 0 to 58%. Hence, total tract disappearance of corn silage crude protein ranged from 50 to 100% with a mean value of 80%. Further study is needed to determine the reasons for the wide ranges in soluble and slowly degradable protein fractions in corn silage. released fatty acids decrease viscosity of intestinal contents (1), thereby improving efficiency of digestion and absorption. However, ruminants cannot withstand high levels of dietary fat as it interferes with rumen function; maximum added dietary fat of 6% on dry matter basis has been suggested (2).

Dietary fat in the rumen can influence the fermentation products formed. Long-chain unsaturated fatty acids are toxic to certain protozoa that colonize the rumen. Providing 6% oil in the diets of sheep, as either sunflower oil or whole sunflower seeds, substantially reduced protozoa in the rumen for over 84 d (3). Protozoa are closely associated with methaneproducing bacteria so decreases in protozoa numbers reduces these bacteria and reduce methane production. In a trial conducted in Alberta, feeding sunflower oil at 6% of diet reduced methane emission in cattle by 21.5% (4). Generally, protozoa are predatory on bacteria in the rumen so it can be expected that reductions of ruminal protozoa from feeding fat would lead to an increase in bacterial biomass. Thus dietary protein supplementation can be reduced, possibly minimizing excre- tion of N in manure. Although detailed studies have not been conducted, it can be expected that dietary oil from corn or barley silage may help to reduce the requirement for rumen bypass protein. This may help to explain the benefit of corn silage in managing nitrogen on dairy farms.

Both corn or barley fat contain high proportions of the three unsaturated fatty acids, oleic (C18:1), linoleic acid (C18:2) and linolenic acid (C18:3). These unsaturated fatty acids can serve as hydrogen sinks at the double bonds in their structure which directly decrease methane production. In fact, a large proportion of unsaturated fatty acids in the feed are bio-hydrogenated in the rumen. The process of bio- hydrogenation has several steps and various partially hydrogenated or isomerised compounds leave the rumen prior to completion of hydrogenation. Many of these compounds have been found to have biological activity. The cholesterol-lowering omega-3 fatty acids, derived from linolenic acid rich diets, will transfer into both milk and meat to provide the consumer with healthful foods.

There is now interest in an anticarcinogenic compound derived from omega-6, linoleic acid, called conjugated linoleic acid (CLA). It occurs naturally in ruminant products such as milk and meat, and additions of oil or oil-seed to ruminant diets can increase its concentration. It was originally believed to be produced exclusively in the rumen, but there is evidence that this fatty acid is produced at least at two locations in dairy cattle and secreted into milk. In the rumen during biohydrogenation the linoleic acid is converted to CLA or to an alternate oleic acid, which passes from the rumen into the intestines. The oleic acid is absorbed from the intestines, enters circulation in the animal, then is taken up by the mammary tissue where it is converted to the CLA by enzymes. Provision of unprotected dietary oil to dairy cows at 4% of diet will increase the CLA content of milk (4 mg/g fat) three- to fourfold. Feeding entire oil-seeds is more effective than just the extracted oil (5).

In view of the importance of dietary oil for ruminants, there may be advantage in re-examining the production and feeding of silages from inter-crops of corn and high-oil crops such as sunflowers (6, 7) on diet compositional and production parameters as well as the production of bio-active compounds and perhaps specialty milk or meat products.

 

References

Fisher, L.J., S. Bittman, Z. Mir, P.S. Mir and J.A. Shelford 1993. Nutritional evaluation of ensilges made from intercropped corn and sunflowers. Can. J. Anim. Sci. 73, 539-545.

He, M.L., P.S. Mir, K.A. Beuachemin, M. Ivan and Z. Mir 2003. Effects of dietary sunflower seeds on lactqation performance and conjugated linoleic acid (CLA) content of milk. IX World Congress of Animal Production, Porto Alegre, Brazil Oct 25 -3,12003. Page 13.

Ivan, M., P.S. Mir, K.M. Koenig, L.M. Rode, L. Neil, T. Entz and Z. Mir 2001. Effects of dietary sunflower seed oil on rumen protozoa population and tissue concentration of conjugated linoleic acid in sheep. Can. J. Anim. Sci. 41, 215- 227.

McGinn, S.M., K.A. Beauchemin and D. Columbatto 2003. Use of novel ingredients to reduce methane emissions from beef cattle. IX World Congress of Animal Production, Porto Alegre, Brazil Oct 25 -3,12003. Page 40.

Mir, P.S., M. Ivan, G.J. Mears, B.F. Benkel, C.M. Ross, S.D. Husar and Z. Mir 2002. Effect of sunflower oil on sheep intestinal digesta viscosity, composition and amylase activity. Small Ruminant Res. 45, 33-38.

Mir, Z. 1988. A comparison of canola acidulated fatty acids and tallow as supplements to ground alfalfa diet for sheep. Can J. Anim. Sci. 68, 762-767.

Mir, Z., P.S. Mir, S. Bittman and L.J. Fisher 1992. Ruminal degradation characteristics of corn and corn-sunflower intercropped silages prepared at two stages of maturity. Can. J. Anim. Sci. 72, 881-889.

Feeding High Corn Silage Diets

M.L. SWIFT
Abbotsford Veterinary Clinic, Abbotsford, British Columbia

As corn silage provides a palatable and digestible source of energy, it is not uncommon that corn silage will comprise a substantial amount of the forage component of the diet formulated for lactating dairy animals. In balancing these types of rations, the following points should be noted:

1. Reconsideration of bypass protein sources used to balance lysine requirements.

Corn, whether in the form of grain, by-products such as distillers grains or as silage, is limiting in the amino acid lysine. Lysine is recognized as one of the most frequently limiting essential amino acids in metabolizable protein used by cattle to produce meat or milk protein. Feeding corn based by-products such as corn gluten meal, or corn distillers grains accentuates low lysine levels in high corn silage diets. Therefore, bypass protein sources such as soybeans, soybean meal, fish meal or blood meal are recommended for inclusion in rations comprised of corn silage as the primary forage source.

2. Control of starch levels to maintain rumen pH and fibre digestion.

Corn silage consists of stover (leaves, stalks, husks) and the ear (cob and grain). The ear is comprised of the cob (16%) and corn grain (84%). Therefore, corn silage contains varying amounts of readily-available energy in the form of corn grain or starch.

Typically, it is recommended that diets for lactating dairy cattle contain 25 to 30% starch on a dry matter basis. However, there can be a great deal of variation noted in the starch content of different samples of corn silage. For example, results from the Pacific Field Corn Association’s evaluation trials for 2003 (www.farmwest.com) show a range in grain content of between 30.6 and 52.5% for early hybrids.

This is equivalent to a range in starch content of 19.7 to 32.2% (assuming the ear contains 64% starch). Analyses of corn silage samples harvested and processed late in 2003 indicate starch levels reaching as high as 40%. The failure to account for this additional starch provided by the corn silage can lead to ruminal acidosis and laminitis. Laboratory tests are available to determine the starch content. Another rough method is to calculate the Non-Fiber Carbohydrate (NFC) as: 100 - (CP + Ash + Fat + NDF).

3. Recognition of the importance of effective fibre in high corn silage diets.

Originally, effective fibre was defined as the minimum amount of fibre needed to maintain milk fat percentage (through optimal fibre digestion and pH in the rumen). Several systems have been proposed to measure effective neutral detergent fibre (NDF). These systems have suggested that NDF in corn silage is approximately 90% as effective as NDF in grass silage or long grass hay. As fibre is needed to stimulate chewing activity and saliva production, and to maintain rumen pH, it is important to monitor the effective NDF content of high corn silage diets.

4. If feeding fat in the diet, reallocation of sources to rumen inert forms.

Corn silage contains approximately 3% crude fat, in the form of corn oil from the kernel. Feeding substantial amounts of high-grain corn silage can contribute approximately 225 grams of unsaturated fat to the ruminal environment. Therefore, if increasing the amount of fat in the ration is being considered, this fat should be added in the form of ruminally inert (bypass) fats (see Fat in Corn Silage section).

5. Rebalancing of mineral packages to reflect increased need for calcium and magnesium.

Corn silage contains low concentrations of calcium and magnesium as compared to other forage sources such as grass silages or hays. Therefore, it is important to further supplement these important macro-minerals when the diet contains a high level of corn silage. Corn silage contains substantially less potassium making it a popular choice for inclusion in transition cow diets. However, it is important to ensure adequate potassium levels during periods of heat stress.

Processing Corn Silage

J. HARRISON and L. VAN WIERINGEN
Department of Animal Sciences, Washington State University, Puyallup, Washington

Introduction

The major factor affecting the quality of corn silage is stage of maturity at harvest. Fig. 1 depicts the change in energy value of silage corn as it progresses in maturity. The initial increase in energy content is attributed to accumulation of highly digestible starch in the ear and the high fibre digestibility of the stover fraction of the corn plant. The point of inflection occurs at about 2/3 milk-line stage of the corn kernel (see Corn Growth and Development section). Beyond this point the increased nutritive value in the corn kernel is offset by a decrease in stover digestibility and passage of undigested corn kernels into feces (1). For mechanically processed corn silage, digestibility tends to plateau past 2/3 milk-line due to counteracting effects of increased starch digestibility and decreased stover digestibility.

Figure 1. Relationship between maturity and energy content in
silage corn with and without processing.

How Processing Affects Quality of Corn Silage

Digestion in the Rumen

Our studies have shown that processing corn silage consistently increased total disappearance in the rumen of both starch and fibre (NDF) fractions (Fig. 2). Therefore, processing also tended to improve the rate of whole crop dry matter disappearance in the rumen especially in warm, dry seasons when the silage was relatively dry for its stage of maturity at harvest.

Figure 2. Processing affects rate of dry matter (top) starch (middle)
and neutral detergent fibre disappearance in the rumen.

For both processed and unprocessed corn silages, the amount of disappearance of starch in the rumen was high (> 93%) after 96 hours of incubation (Fig. 2-middle). Despite variability, there was a trend for processed corn silage to have approximately a 3.0 percentage unit improvement in ruminal starch digestibility. Processing particularly improved rate of starch disappearance in drier silages (Fig. 2-middle). Similarly, processing improved rate of fibre (NDF) disappearance most in silage grown under relatively warm and dry conditions (Fig. 2-bottom).

Total-Tract Digestion

The increase in total tract starch digestibility due to mechanical processing was similar to the increase in ruminal starch digestibility. In 11 trials, we found that processing improved total tract digestibility of corn silage by almost 1% unit. This overall increase in digestibility can be attributed to improvements in total tract digestibility of starch (0.84% units), NDF (1.65% units), and fat (0.75% units) (Fig. 3).

Figure 3. Total tract digestibility of dry matter (DM), starch, NDF and fat.

The improvement in NDF digestibility was consistently greatest (4 to 10%) for mature corn silage. This trend was also observed for starch digestibility (1 to 1.3%). The effect of processing on starch digestibility of relatively immature corn (two-thirds milkline) was more variable (0.7 to 2.5%). In unprocessed corn, total tract starch digestibility decreased as the amount of whole intact kernels increased, whereas in processed corn, the amount of intact kernels was minimal so total-tract starch digestibility was always high (Fig. 4-left).

Figure 4. Effect of percent whole intact kernels (top) and post-ensiling
vitreousness (bottom) on whole tract starch digestibility.

The amount of vitreous and floury starch in the kernels in corn silage plays a significant role in total tract starch digestibility (Fig. 4-top). Vitreous starch tends to be harder for cows to digest because the starch granules are embedded in a dense protein matrix. In unprocessed corn silage, as the amount of vitreous starch increases, total tract starch digestibility decreases (Fig. 4). Processing disrupts the dense protein matrix of vitreous starch making it available for digestion. Therefore, total-tract starch digestibility is less influenced by amount of vitreous starch in processed than in unprocessed corn silage.

Energy Content of Total Mixed Rations Containing Processed Corn Silage

We tested the energy contents of the total mixed rations (TMR) containing 27% corn silage (harvested at . milk-line to black-line) which was either unprocessed or processed. These feeding studies involved measurements of all inputs and outputs (Fig. 5). Note that digestible energy (DE) provides the most accurate energy values because it is based on direct measurements of energy consumed (gross energy) minus energy excreted as feces. In contrast, metabolizable energy (ME) and net energy of lactation (NEL) are based on estimates of energy loss in urine, expelled methane and body heat. However the NEL values are particularly useful for ration balancing.

Figure 5. Energy partitioning system

The trials showed that processing of the corn silage improved energy content of the whole mixed ration. The difference in energy content was greater at black-line than at twothirds milk-line stage (Fig. 6). Digestible energy for diets with processed corn silage was about 0.7% greater at two-thirds milk-line and 3.5% greater at black-line than for diets with unprocessed corn silage. The concentration of net energy of lactation (NEL) of processed corn silage diets was about 0.6% greater at two-thirds milk-line and 3.9% greater at black-line than NEL of unprocessed corn silage diets.

Figure 6. Effect of processing corn silage at two stages of maturity on digestible energy (left) and net energy of lactation, NEL (right) of the total mixed ration containing 27% corn silage (for MJ/kg, multiply Mcal/lb X 0.53).

Processing Corn Silage Improves Milk Production

Johnson and Harrison (1) showed that, over 22 trials, cows fed diets based on processed corn silage produced an average of 0.5 kg (range of -0.5 to 1.7 kg) or 1.1 lb (range of -1.1 to 3.7) more milk per day than cows fed diets with unprocessed corn silage (Fig. 8). In addition, processing increased milk fat concentration by 0.08% (-0.18 to 0.29). Hence fat corrected (3.5%) milk production for cows fed processed corn silage based diets was 0.9 kg (0.8 to 2.2) or 2.0 lb (- 1.78 to 4.84) greater than for cows fed diets with unprocessed corn silage. Milk protein concentration was relatively unaffected by processing. Some of the improved milk production can be attributed to increased feed intake, generally 0.5 (-1.5 to 1.4) kg per cow per day or 1.1lb per cow per day (-3.3 to 3.1). Where milk production was not increased by processing, this was due to either decreased feed intake (for unknown reasons) or to inadequate fibre in the diet caused by reduction in particle size (see below).

Figure 8. Effect of feeding unprocessed and processed corn silage on feed intake (DMI) and milk production (left) and milk composition (right) (1 lb = 0.45 kg).

Silage Processing Affects Optimum Chop Length

Processed corn silage should be chopped at a longer theoretical length of cut (TLC) than unprocessed silage to maintain adequate effective fibre in the diet. It is now common to recommend that processed corn silage be cut at 19 to 25 mm (¾ to 1 in) TLC. Table 1 compares performance of cows fed conventional unprocessed corn silage at 10 mm (3/8 in) chop to processed corn silage chopped at 10 mm (3/8 in), 14 mm (9/16 in), and 19 mm (¾ in). For processed corn silage, the longer cuts resulted in less sorting of the diet and provided for the best overall performance (at least equal milk, increased protein and fat, and lower requirement for power).

We recently found that the optimum length of chop for processed corn silage depends on stage of lactation (6). Figure 9 shows that in the first four weeks of lactation, cows performed best on processed corn silage with a relatively short chop (16 mm or 5/8 in), whereas from 4 to 9 weeks, cows performed consistently better on much longer (40 mm or 1 9/16 in) chop lengths.

Figure 9. Effect of chop length of processed corn silage on fat-corrected
(4%) milk production through first 10 weeks of lactation.

 

Table 1.  Effect of chop length and processing on feed intake and production of milk and milk components in kg (lb).

Chop Length

Unprocessed

Processed

 

10 mm (3/8in)

10mm (3/8in)

14mm (9/16in)

20mm (3/4in)

Particle length mm (in)

9.4 (3/8)

6.7 (1/4)

8.9 (1/3)

9.2 (1/3)

Feed intake kg (lb)

25.2 (55.4)

25.9 (56.9)

25.9 (56.9)

25.8 (56.7)

Milk production kg (lb)

44.8 (98.6)

46.5 (102.2)

45.3 (99.7)

46.1 (101.4)

Fat yield kg (lb)

1.3 (3.0)

1.4 (3.2)

1.4 (3.1)

1.4 (3.1)

Protein yield kg (lb)

1.4 (3.1)

1.5 (3.2)

1.5 (3.2)

1.5 (3.2)

 

Does it Pay to Process Corn Silage?

Our economic analysis of processing takes into account many factors such as:

1) Increased costs

  • Increased machinery cost (Shinners, 1999)
  • Higher feed intake

2) Decreased cost

  • Lower storage loss

3) Increased returns

  • More milk
  • Better milk composition (milk fat)

4) Other factors

  • Milk production level
  • % Corn silage in diet
  • Effective fibre in diet
  • Starch digestibility of diet
  • Fibre digestibility of diet
  • Specific energy requirements of harvester
  • Throughput capacity of harvester

Our analysis was conducted using a computer model called DAFOSYM (8) which simulates the economic and environmental aspects of crop production, feed use, and nutrient cycling on a dairy farm (Fig. 10). For example, DAFOSYM can predict how increasing the amount of corn silage in the diet would affect milk production, ration costs, and overall economics at the whole farm level.

Figure 10. DAFOSYM simulates material and nutrient flows for various
dairy farm systems over many years of weather and determines the
economics of the farm.

We tested the economic impact of processing on dairy farms having 100 or 400 high-producing Holstein cows that were fed processed corn silage at 40 and 75% of forage requirement, respectively (Table 2). On the 100-cow farm feeding 40% corn silage, processing improved packing in the silo and increased the digestibility of silage, which reduced requirement for supplemental grain and improved milk production by 2.6%. However, the amount of purchased feed increased because the cows fed processed corn silage were producing more milk and therefore consuming more feed. As in the previous analysis, increases in milk sales exceeded increases in production costs by almost 50/cow/year (Table 2). On the 400 cow farm, feeding processed corn silage for 75% of the total forage requirement, processing increased milk production by about 4% and the economic benefit was $95/cow/year.

Table 2.  Economic Analysis of supplementing processed corn silage in the diet at 40 and 75% of the forage requirement (using DAFOSYM).

 

100 Cow Dairy

400 Cow Dairy

 

40% of forage requirement

75% of forage requirement

 

 UNPROCESSED

 PROCESSED

 UNPROCESSED

 PROCESSED

Corn silage produced, tonne (ton) DM

245 (269)

248 (273)

1810 (1988)

1820 (2002)

*Purchased feed, tonne (ton)

217 (239)

220 (242)

429 (472)

449 (494)

Milk production, kg/cow/year (lb/cow/year)

10,410(22,900)

10,680 (23,500)

10,320 (22,700)

10,770 (23,700)

*Purchased feed & bedding, $

50,042

50,677

178,054

184,044

Net return to management, $/year

44,820

49,605

287,265

325,163

Increase in income due to processing, $/cow/year

-

47.85

-

94.75

* The amount of purchased feed increased because the cows fed processed corn silage were producing more milk and therefore consumed more DM.

Summary

It is commonly agreed that the desirable range of maturity to harvest corn silage is 1/2  to 2/3 milk line or 25-40% DM. If corn silage is mechanically processed before ensiling, as much as 10% additional energy can be gained from the silage. Chop lengths from 5 to 25 mm (¼ to 1 in) can be stored and fed effectively, with longer chop lengths suggested for processed silage. The length of chop should be based on whether or not the silage is mechanically processed and on other forages in the diet.

 

Recommendations for Feeding Processed Corn Silage

Since mechanically processed corn silage has reduced particle size and increased starch digestibility, several practical feeding recommendations are warranted:

1) The greater the amount of processed corn silage in the diet the greater the expected improvement in energy content of the diet.

2) Ensure that there is adequate effective fibre in the diet to avoid milk fat depression.

3) Increase the amount of corn silage in the ration progressively over several days to avoid rumen upset and possible acidosis (see Feeding High Corn Silage Diets section).

Effect of Processing Brown Midrib (bm3) Corn Silage

Does processing increase the silage quality from the highly digestible brown midrib (bm3) corn?

One study, using low ADF diets (15.5-16.5%), found that processing bm3 corn silage with 19-mm (¾ in) chop length did not significantly improve milk production (2, 3). The explanation was that processing increased (whole-tract) starch digestibility but decreased fibre digestibility and processing also reduced eating time. The conclusion was that processing did not affect milk yield because there was very little difference in particle size of material entering the rumen after the initial mastication. A recent study reported that milk production (3.5% fat-corrected) was greater for cows eating processed than unprocessed bm3 corn silage (43.3 vs. 39.3 kg or 95.3 vs. 86.5 lb). The benefit was due to greater in-situ DM disappearance and total tract nutrient digestibility rather than increased intake (4, 5).

 

References

1. Johnson, L. and J.H. Harrison 2001a. Effects of mechanical processing on the nutritive value of corn silage and performance characteristics in lactating dairy cows: 1 Introduction. Washington State University Dairy News. V 10, No 2, March 2001.

2. Schwab, E.C. and R.D. Shaver 2001. Crop processing and chop length effects in brown midrib on dry matter intake and lactation performance by dairy cows. J. Dairy Sci. 84, 197 (Suppl 1).

3. Schwab, E.C. and R.D. Shaver 2001a. Crop processing and chop length effects in brown midrib on chewing activity and mean particle size of silage and masticates. J. Dairy Sci. 84, 197 (Suppl 1).

4. Ebling, L., J.M. Neylon, D.H. Kleinschmit, J.M. Ladd, C.C. Taylor, and L. Kung, Jr. 2002a. Comparison of physical and chemical characteristics of mechanically processed brown midrib, unprocessed brown midrib, or processed normal corn silage. J. Dairy Sci. 85, 383 (Suppl 1).

5. Ebling, L., J.M. Neylon, D.H. Kleinschmit, J.M. Ladd, C.C. Taylor, and L. Kung, Jr. 2002b. Effect of feeding mechanically processed brown midrib (PBMR), unprocessed brown midrib (UBMR), or processed normal corn silage (P7511) in diets for dairy cows on DM intake, milk production and digestion. J. Dairy Sci. 85, 383 (Suppl 1).

6. Johnson, L. and J.H. Harrison 2001b. Kernel processing: Fermentation changes in the silo due to maturity and mechanical processing of corn silage. Washington State University Dairy News. V 10, No 4, May 2001.

7. Bal, M. A., R.D. Shaver, A.G. Jirivec, K.J. Shinners and J.G. Coors 2000. Crop processing and chop length of corn silage: Effects on intake, digestion, and milk production by dairy cows. J. Dairy Sci. 83, 1264-1273.

8. Rotz, C.A., L.M. Johnson, and J.H. Harrison 1999. Economics of corn silage processing on North America dairy farms. Applied Engineering in Agriculture. Vol 15(5), 411-421.

Additional References

Bolsen, K. 1995. Losses from the top spoilage in horizontal silos. Proc. 2nd National alternative feeds symposium. St Louis, MO. Sept. 245-26. Pp.159- 176.

Bolsen, K.K., J.T. Dickerson, B.E. Brent, R.N. Sonon, Jr., B.S. Dalke, C. Lin, and J.E. Boyer, Jr. 1993. Rate and extent of top spoilage losses in horizontal silos. J. Dairy Sci. 76, 2940-2962.

Fox, D.G., C.J. Sniffen, J.D. O’Connor, J.B. Russell, and P.J. Van Soest 1990. The Cornell Net Carbohydrate and Protein System for evaluating cattle diets. Part 1: A model for predicting cattle requirements and feedstuff utilization. Pages 7-83 in Search: Agriculture No. 34. Cornell Univ. Agric. Exp. Stn., Ithaca, NY.

Harrison, J., D. Davidson, and D. Linder 2001a. Evaluation of the nutritive value of low moisture corn silage stored in Ag Bag vs bunker silo. J. Dairy Sci. 84, 154 (Suppl 1).

Harrison, J.H., D. Davidson, and L. Johnson 2001b. Evaluation of processed corn silage harvested at three chop lengths. J. Dairy Sci. 84, 154(Suppl 1).

Harrison, J.H., and L. Johnson 2001. Management practices that enhance the nutritive value of ensiled forages. Proc. 10th International Symposium on Forage Conservation, Brno, Czech Republic.

Harrison, J.H., and L. Johnson 2001. Processed corn silage — what have we learned? Proc. Cornell Nutrition Conf.

Harrison, J. 2001. Corn silage management in bag and bunker silos. Proc. Pacific Northwest Animal Nutrition Conference.

Holmes, B.J. 1998. Choosing forage storage facilities. Proceedings of Dairy Feeding Systems, Management, Components and Nutrients Conference. NRAES-116. Ithaca, NY.

Jirovec, A.J., K.J. Shinners, R.D. Shavers, and M.A. Bal 1999. Processing wholeplant corn silage with crop processing rolls. Presented at the Feb 8-10, 1999 ASAE Ag Equip Tech Conf. Paper # 99AEC-105. Niles Road, St Joseph, MI 49085-9659 USA.

Johnson, L., J.H. Harrison, C. Hunt, K. Shinners, C.G. Doggett, and D. Sapienza 1999. Nutritive value of corn silage as affected by maturity and mechanical processing: A contemporary review. J. Dairy Sci. 82, 2813-2825.

Johnson, L. and J.H. Harrison 2001c. Effects of mechanical processing on particle size, pack density, and aerobic stability of corn silage. Washington State University Dairy News. V 10, No 3, April 2001.

Johnson, L. and J.H. Harrison 2001d. Kernel processing article # 4: Measuring rumen digestibility of processed corn silage using the macro in situ technique. Washington State University Dairy News. V 10, No 5, July/August 2001.

Johnson, L. and J.H. Harrison 2001e. Effects of Mechanical processing on ruminal and total tract digestibility in lactating dairy cows. Washington State University Dairy News. V 10, No 6, September 2001.

Johnson, L. and J.H. Harrison 2001f. Effects of Mechanical processing of corn silage on energy content of TMR fed to lactating dairy cows. Washington State University Dairy News. V 10, No 7, November 2001.

Johnson, L. and J.H. Harrison 2002. Economics of mechanical processing corn silage. Washington State University Dairy News. V 11, No1, February 2002.

Johnson, L., J.H. Harrison, D. Davidson, W.C. Mahanna, K. Shinners and D. Linder 2002. Corn silage management: Effects of maturity, inoculation, and mechanical processing on pack density and aerobic stability. J. Dairy Sci. 85, 434-444.

Johnson, L., J.H. Harrison, D. Davidson, J.L. Robutti, M. Swift, W.C. Mahanna and K. Shinners 2002. Corn silage management I: Effects of hybrid, maturity, and mechanical processing on chemical and physical characteristics. J. Dairy Sci. 85, 833-853.

Johnson, L., J.H. Harrison, D. Davidson, M. Swift, W.C. Mahanna and K. Shinners 2002. Corn silage management II: Effects of hybrid, maturity, and mechanical processing on digestion and energy content. J. Dairy Sci. 85, 2913-2927.

Johnson, L., J.H. Harrison, D. Davidson, M. Swift, W.C. Mahanna and K. Shinners 2002. Corn silage management III: Effects of hybrid, maturity, and mechanical processing on nitrogen metabolism and ruminal fermentation. J. Dairy Sci. 85, 2928-2947.

Johnson, L., J.H. Harrison, D. Davidson, W.C. Mahanna and K. Shinners 2002. Corn silage management III: Effects of hybrid, maturity, inoculation, and mechanical processing on fermentation characteristics. J. Dairy Sci. 85, in press.

Johnson, L., J.H. Harrison, D. Davidson, W.C. Mahanna and K. Shinners. 2002. Corn silage management III: Effects of hybrid, chop length, and mechanical processing on digestion and energy content. J. Dairy Sci. 85, in press.

Johnson, L., J.H. Harrison, D. Davidson, C. Hunt, W.C. Mahanna and K. Shinners 2002. Corn Silage Management: Effects of Hybrid, Maturity, Chop Length, and Mechanical Processing on Rate and Extent of Digestion. J. Dairy Sci. 85, in press.

Quaife, T. 2000. Try cutting corn silage at 20 inches. Dairy Herd Management. June 2000. Pp. 62-64.

Rotz, C.A. and R.E. Muck 1994. Changes in forage quality during harvest and storage. In Forage Quality and Evaluation. Amer. Soc. Agron., Crop Sci. Soc. of America, and Soil Sci. Soc. of Amer. Ed: Fahey.

Rotz, C.A., D.R. Buckmaster, D.R. Mertens, and J.R. Black 1989. DAFOSYM: A dairy forage system model for evaluating technologies and management strategies in forage conservation. J. Dairy Sci. 72, 3050-3063.

Ruppel, K.A., R.E. Pitt, L.E. Chase and D.M. Galton 1995. Bunker silo management and its relationship to forage preservation on dairy farms. J. Dairy Sci. 78, 141-153.

Shinners, K.J. 1999. Forage harvester crop processors and other new hay and forage equipment. In Proc. Tri-state Dairy Nutrition Conference, 137-166. 20-21 April, Fort Wayne, Ind. Columbus, Ohio; The Ohio State University.

Wallentine, M.V. 1993. Silage storage systems in the arid west. In Proceedings of Silage Production: From Seed to Animal. NRAES-67.

Making Good Corn Silage

E. CHARMLEY
Agriculture and Agri-Food Canada, Research Farm, Nappan, Nova Scotia

Introduction

Corn silage is a high energy feed source for ruminants. Being part forage and part grain, it has characteristics of both feed types and is a valuable component of dairy rations in regions where corn can be grown. Nutritionally, corn silage is lower in crude protein (CP) and higher in digestible energy (DE) than other forages. It also differs from other forages in that quality does not decline with advancing maturity. This is because the increasing amount of grain in the crop offsets the decline in digestibility normally associated with structural tissues (in the case of corn, stem). Compared to many crops corn is relatively easy to ensile. It is however a high-cost crop to grow, ensile and feed.

i) Moisture

One of the most critical factors affecting the process of fermentation is the amount of water present in the crop at ensiling (Fig. 1). Silage microbes need water in order to thrive and multiply. That is why drying hay, for example, is effective at preventing most microbial growth. However, the amount of water is important in determining which microbes grow best. In silage, we normally quantify water in terms of dry matter (DM) content of the crop. Thus a low DM silage contains more water than a high DM silage.

Figure 1. Moisture and silage fermentation. The drier the silage
the higher the pH can be for successful preservation.

The wetter a silage, the more biological activity, of all kinds, there will be. This is not necessarily a good thing. Managing the ensilage process means creating an environment that favours desirable microbes over undesirable microbes. However if a silage is too dry, there will not be enough moisture to support sufficient microbial growth to produce the acids which reduce the pH and preserve the crop. Optimum crop DM content is between 25 and 50%, depending on the type of crop and storage system. In most forage crops, optimum DM content is reached by wilting prior to ensiling, a sometimes tricky business.  However, in corn, the crop loses moisture as it matures and an optimum DM content of between 33 and 36% can be reached by waiting for the crop to mature (provided there are enough heat units). This feature, makes achieving the desirable DM content relatively simple in many silage growing areas. As a general guide, corn silage should be harvested when the milk line has descended 1/3 to 1/2 of the way from kernel crown to the base (see Corn Growth and Development section).

So why is wet silage undesirable? The wetter the crop the more active all bacteria become and the more food (substrate) is needed to sustain them. Since there is a limited amount of food reserves (substrate) in the harvested corn, beneficial bacteria have to compete with all the other types of bacteria. As crops dry, some types of bacteria are more affected than others. A major group of undesirable bacteria (the clostridia) are particularly susceptible to a scarcity of moisture. So by increasing the DM content we can weed out the bad bacteria from the good.

Wet silage is also problematic, because when it is piled in a bunker or, even worse, a tower, then pressure squeezes out water and many soluble sugars, proteins and minerals (Fig. 2). This silage effluent or run-off, not only represents a loss of nutrients, it is also a potent pollutant, having a very high biological oxygen demand (BOD). Upon entering waterways it causes eutrophication (rapid growth of biomass) and takes the dissolved oxygen out of the water. This will render a stream dead quite effectively.

Figure 2. Losses in a bunker silo.

So why is dry silage undesirable? Silage that is too dry will not ferment enough to reduce pH to a level that will kill spoilage-causing yeasts, moulds and aerobic bacteria (Fig. 3). In wet silage, the spaces between the plant material are filled with water, but in dry silages they are filled with air. Also, dry material tends to be more springy and resistant to compaction. Under these conditions aerobic microbes predominate, particularly yeasts and moulds. These consume valuable nutrients, produce heat and thus cause spoilage. Heating is a particular problem, because as the silage heats up, then the yeasts and moulds proliferate even faster. Heating, which starts in the silo, tends to continue in the feed bunk, reducing feed intake and leaving large amounts of rejected feed.

Figure 3. pH decline and silage stability.

ii) Substrate

Silage micro-organisms need a supply of soluble carbohydrate or sugars. Most crops, including corn, contain between 3 and 10% of their DM as sugar. Corn usually has close to 10% of DM as sugar, which makes it a reasonably easy crop to ferment. These sugars are used up by the microbes to produce acids. Since the role of acids is to reduce pH, strong acids are needed; the strongest acid produced by bacteria is lactic acid. In a good fermentation, the goal is to have as much of the sugars converted to lactic acid as possible. Since the sugars are a finite resource, efficient use is paramount. Manipulating DM content will help to ensure that the desirable or homolactic bacteria will predominate in the microflora, producing lots of lactic acid to effect preservation.

Unlike most other silages, corn silage can actually have too much sugar! The unfermented sugars can remain at quite high concentrations even months after the crop has been ensiled. These sugars can be used by aerobic bacteria once the silo has been opened for feed-out. In this case the so-called (but misnamed) secondary fermentation can take place. It is not fermentation at all but aerobic respiration and produces a lot of heat and ultimately leads to spoilage of the silage.

The fact that corn silages can have too much substrate for the traditional fermentation, has led researchers to look at the possibility of using some of that sugar to produce acetic (vinegar) or propionic acid. (Manufactured propionic acid is often used as an additive help preserve high moisture grass hay.) Although these are weak acids and not very effective at reducing pH, they are quite effective at inhibiting aerobic microbes, particularly yeasts. Recent research has looked at the possibility of adding specific strains of bacteria to corn silage to produce these acids (See below).

iii) Silage bacteria

When corn is harvested, plant surfaces are covered by a wide range of micro-organisms. These are known as epiphytic bacteria because they live on the host plant in a natural symbiosis. They are present in the thousands per gram of crop, but only a small fraction, namely the lactic acid bacteria (LAB), are of value in silage fermentation (Table 1). The numbers of lactic acid bacteria on corn at ensiling is low compared to the numbers needed for ensiling. After the crop is chopped and placed in the silo, the plant cells and aerobic bacteria continue to respire for a day or two and conditions in the silo become increasingly anaerobic. Eventually this aerobic respiration by the crop and microbes will use up all the oxygen in the silo. Then under these anaerobic conditions, the anaerobic bacteria, including the lactic acid bacteria, begin to proliferate. The anaerobic epiphytic bacteria now produce lactic acid, as well as a range of other acids, alcohols and related compounds from sugar present in the crop.

In the initial phase of ensiling, competition for substrate by the various types of bacteria is intense. Eventually, however, conditions will begin to favour one or another group. Under conditions of optimum moisture and substrate availability, the lactic acid bacteria will predominate (Fig. 4). The more rapidly they can proliferate, the more rapidly the pH drops and under these conditions lactic acid will be the dominant organic compound produced. Good silage fermentation will ensue.

Figure 4. Change in population over time of 4 bacterial groups in good fermentation (top), clostridial fermentation (middle), aerobic fermentation (bottom).

When conditions are sub-optimal for LAB, they may never dominate the fermentation. For example, in wetter silages the Clostridia may predominate (Fig. 4). These bacteria are always present on the standing crop but are particularly numerous in soil and manure. Although manure is a potential source of contamination in corn, the long interval between manure application and harvest and the fact that corn does not normally come into contact with the ground during harvest means that clostridial contamination from manure is unlikely. Another group of bacteria which sometimes come to dominate silage fermentation are the ‘coliform’ bacteria, or enterobacteria. These tend to dominate in silage when the rate of pH decline is slow or where the final pH is high. These bacteria produce a range of organic acids and alcohols and are not effective at preserving silage. They are also associated with the production of endo-toxins and ammonia. High levels of ammonia in drier silages are indicative of fermentation dominated by coliform bacteria.

Filling the Silo

i) Management

No matter what crop or system of ensiling is used, the single most important determinant for making successful silage is good management at the time of ensiling. The various aids to making good silage do not substitute for good management practices, and in fact are wasted if not used in association with good management.

Understanding the principles of ensiling helps the farmer understand the critical control points for success. Since ensiling is an anaerobic process, rapid and effective filling and sealing of the silo is critical. It is essential to minimize the amount of air that gets into the silo. How this is done will depend on the type of silo used.

Silos come in many forms. The ‘Cadillac’ of silos is the gastight, glass-lined upright silo, which became very popular 20 to 30 years ago. These are expensive, but effective. The silo walls are totally airtight, and the silo is filled from the top. The weight of the crop provides the pressure for packing. Without any ingress of air to the system, the silage quickly becomes anaerobic and good fermentation usually results.

This system is generally best used in silages of 40% DM or higher. Corn silages, which are usually ensiled below this threshold, may have too much moisture. The pressures exerted in such a silo will produce silage effluent (also known as seepage or run-off ), which will either collect at the base or leak out of the silo. In either case, this is bad. The higher moisture will sour the silage at the base of the tower if it remains in the silo and the effluent poses an environmental threat. To maintain an anaerobic atmosphere during unloading, these silos typically empty from the bottom.

The concrete stave silo, is a less costly and less elaborate version of the upright tower. The principle behind achieving anaerobic conditions is the same, although the system is slightly less effective. These silos are unloaded from the top. It is critical to remove 10 –15 cm (4 to 6 in) of silage a day so that the silage is fed before it begins to deteriorate. These silos are relatively common, and those filled with corn silage are often seen weeping effluent from the sides in the lower portion of the silo — a clear sign the silage was too wet.

Bunker silos are effective. Although corn silage can be successfully stored in towers, the crop is eminently suited to bunker silos because there is less pressure to cause seepage in a bunker silo. To be effective, bunker silos have to be filled quickly and sealed effectively because of the large surface area.

Sealing is particularly crucial for corn silage because it contains a lot of sugar for microbes to grow on. If air is present, the sugars are used by aerobic organisms causing heating. Plant and aerobic microbial respiration using up the sugars produce heat warming the air and causing it to rise while bringing down cool air filled with fresh oxygen (called flue effect). This stimulates more aerobic activity and the cycle continues (Fig. 5).

Figure 5. Transverse section of a silo during filling, showing “flue effect”.

Compared to grass silages, corn silage is easy to pack, especially when well chopped or ‘processed’ (see Processing Corn Silage section). It tends to pack well, up to a point, beyond which further packing has little added benefit. Forage harvesters should be set for a theoretical chop length of 6–9 mm (¼ to 3/8 inch). About half the silage should be as particles 13 mm (½ in) long, with the rest somewhat longer. Excessive long particles indicate that the chopper needs sharpening and re-setting.

ii) Silage inoculants

Conventional microbial inoculants work by adding a fairly large amount of lactic acid producing bacteria—usually 100,000 organisms (or cfu) per g of crop in North America and 1,000,000 cfu per g of crop in Europe. The hope is, that these relatively large numbers of homolactic bacteria will be able to quickly dominate the natural, less efficient, lactic acid bacteria, and so produce a better silage. In many cases this does happen.

Research has shown that on average silage inoculants will result in small improvements in milk or beef production. Table 2 shows the results of a survey the author conducted in 1994. This survey considered all silages, not just corn silage. We found a small benefit in digestibility and intake. Combined, these resulted in a 2 to 10% improvement in animal performance. Since that time, it is reasonable to conclude that silage inoculants have improved, however more recent reviews of the literature still reach similar conclusions. Nevertheless, products are priced to ensure an economical return, on the average. However, in about . of cases, the additive will have no discernable effect on the silage fermentation, and about half the time they will have no effect on animal output (Table 3).

Table 2.  Animal response to silage inoculants.  Results of a survey by the author (1994).

Table. 3. Animal response to silage inoculants.  Results of a survey by Kung and Muck (1990 to 1995)

More recent commercial additives usually contain a cocktail of microbial strains and types. By providing a complex mixture, manufacturers claim better success. Some bacteria, such as Streptococcus or Pediococcus, will be active very early on in the fermentation, when the pH is still quite high and there is still some oxygen in the system. Others, like the Lactobacilli, will play a longer term role, continuing to reduce the pH once the “starter bacteria” have died off. However, single strain inoculants can still be very effective. In choosing an inoculant, the buyer should look for products that are from a recognizable company and have a proven track record. Generally, these have been vigorously researched and newer, more effective strains are continually being developed. Products with complicated formulations may not be any better and even if the bacterial name is the same in two different products, the strain will probably not be. Just as all Holstein cows are not created equal, neither are all strains of Lactobacillus.

Additives manufactured specifically for corn silages often contain enzymes as well as microbial inoculants. Corn silage contains a large proportion of starch, as a result of having a high grain component. By adding amylase enzyme that can convert starch to sugar, the expectation is that this will improve fermentation. While this approach may give some added benefit, the evidence for this is not strong. Given that corn silage already contains adequate sugars for fermentation, production of more may actually be detrimental. Additional sugar may serve as fuel for yeasts and moulds, particularly during feed-out.

 

Emptying the silo

i) Bunker management

As already mentioned, corn silage is susceptible to heating and spoilage during feed-out. So one of the main goals of bunk management is to work to reduce the opportunity for heating at every stage of the operation. The silo, whether tower or bunker, should be designed such that enough silage is removed each day to keep the face moving back at least 4 to 6 inches a day, on average. The more susceptible a silage is to deterioration, the faster it should be removed from the silo. The following steps are recommended when emptying the silo:

  • Minimizing disturbance to the silo face is essential. This prevents air getting further into the silage. Silage cutters (also known as shear grabs or block cutters) are an excellent tool for reducing waste at feed-out. They should however be well maintained to ensure it cuts and doesn’t tear.
  • Keeping the faces clean and free of spoiled silage is also essential. These can become reservoirs of heat and spoilage organisms if left close to the silo. 
  • Plastic should only be removed from the silage as the silage is used.

ii) Bunk management

Cleanliness is again crucial to minimize heating in the feed bunk. Old silage should be removed daily if possible. Heating silage left in the bunk, will cause the new feed to heat all the faster. These tips are particularly critical in hot weather.

Figure 8. Top: smaller bunker silo (12 ft face) designed to ensure face moves back 1 ft per week during summer feeding — minimal signs of spoilage. Bottom: surface spoilage on the same silo — close up view.

Concluding remarks

Corn silage is an excellent feed for high producing ruminants. Although making silage is always a potentially risky business, the risks with corn silage are often less than with grass and legume silages. The crop is naturally at the correct DM content for ensiling and almost always has ample sugars to ensure a satisfactory fermentation. Perhaps the biggest challenge with corn silage is controlling heating and aerobic deterioration. However, careful management both when filling and emptying the silo can reduce the risks. New silage inoculants just coming onto the market may one day prove to be very beneficial in controlling spoilage, thus reducing the risk still further.

 

Processing Silage Corn on Particle Size, Packed Density, and Silage Fermentation

J. Harrison and L. Van Wieringen
Department of Animal Sciences, Washington State University, Puyallup, WA

Processing silage corn results in forage with smaller particle size. Using the Nasco or Penn State forage particle separator we found that processing reduces the percentage of particles remaining on the top sieve (greater than 18 mm or ¾ in) and increases the percentage of particles remaining on the middle (between 5–18 mm or 3...–¾ in) and bottom sieves (Fig. 1). The decrease in particle size increases how densely corn silage is packed in silos, hence the porosity and rate of air infiltration, which ultimately determines the amount of spoilage that occurs at the time of feedout. Many studies have shown that processing corn silage increases wet pack density in the silo over a range of maturity (one-third milk-line to physiological maturity) and theoretical chop lengths (6–13 mm or ¼–½ in) (Fig. 2). The only exceptions were 2 experiments where the chop of the corn silage was long (10–38 mm or 2..–1½ in). Based on this, we expected that processed silage would undergo faster silage fermentation and result in more lactic acid (Fig. 3) and a lower pH (Fig. 4). However, in the majority of cases, we observed that mechanical processing did not enhance lactic acid production or pH decline at first. It appears that some of the mechanically processed corn silages had increased buffering due to the exposure of cell contents to the forage mix. This likely resulted in the higher pH of processed silage during fermentation in the silo. The processed silage did have lower pH and more lactic acid after several weeks in the silo.

Figure 1. Particle size distribution of processed and unprocessed corn silage (theoretical chop length 12 mm or 1/2 in).

Figure 2. Effect of processing on wet pack density (for kg/m3 multiply lb/ft3 X 16.1).

Figure 3. Effect of processing on increase of lactate during ensiling of corn silage harvested at blackline (greater than 40% dry matter).

Figure 4. Effect of processing on change of pH during ensiling of corn silage harvested at blackline (greater than 40% dry matter).

 

Aerobic Stability – Processed Corn Silage

J. Harrison and L. Van Wieringen
Department of Animal Sciences, Washington State University, Puyallup, WA

The greater wet pack density for processed corn silage tends to improve aerobic stability at feedout. Aerobic deterioration occurs as a result of microbial activity. The factors that influence deterioration include: oxygen (exposure time), composition of the microbial population, substrate type, and temperature. Yeasts are usually the initial cause of aerobic deterioration. As lactic acid (the major end product of silage fermentation) and other residual sugars are combusted and used by yeast, the temperature starts to rise. Aerobic stability can be measured as: 1) number of hours until temperature of corn silage increases 2°C (3°F) above ambient, 2) number of hours until corn silage reaches peak temperature, and 3) maximal temperature rise above ambient.

In our studies, processing of corn silage enhanced aerobic stability. While it took longer for processed corn silage to heat by 1.5°C (3°F) (Fig. 1), both silages reached maximum temperature in about the same amount of time. This indicates that the processed corn silage was more stable in an aerobic environment early on (i.e. took longer to start heating) due to greater pack density that limited exposure of processed corn silage to oxygen during the storage phase. However, once the silages were exposed to air there was nothing particular about the processed corn silage that inhibited growth of aerobic microorganisms.

Therefore, once they began to grow, the microorganisms in both silages multiplied causing both silages to heat at the same rate and the same amount (ranging from 6.4° to 13.1°C or 11.5° to 23.6° F).

Figure 1. Aerobic stability of processed and unprocessed corn silage.

 

Silo tips

J. Harrison and L. Van Wieringen
Department of Animal Sciences, Washington State University, Puyallup, WA

The amount of packing time and the thickness of the silage as it is layered in to the silo interact to affect silage density. It is desirable to layer the forage into a bunker silo at depths of 15 cm (6 in) or less and pack to a rate of 2-3 minutes per tonne (or Ton) of forage or 300–600 hrkg per tonne (600–800 hr-lb per T) of wet forage. When forage delivery to the silo is in the range of 40 wet tones (or Tons) per hour these rates are achievable and realistic. Delivery rates greater than this will require large packing tractors and likely multiple packing tractors. Common recommended feed-out rates are 15 cm (6 in) per day, but more is recommended in hotter weather. It is best not to “buck” into the silage mass when removing silage as this allows channels for the entry of air back into the silage mass.

Tools for Estimating Bunker Characteristics  A number of publications and computer software based tools for silage storage are available at website: http://www.uwex.edu/ces/crops/uwforage/storage.htm.  In particular look for two spreadsheets entitled “Bunker Silo Density Calculator” and “Bunker Silo Sizing Spreadsheet”. The software tool, DAFOSYM, is a whole farm economic model with particular emphasis on forage management.  A free copy of DAFOSYM is available at: http:/ /pswmru.arsup.psu.

Tips for achieving a well-sealed bunker silo

  • To minimize puncturing of silo plastic, it is critical to eliminate sharp edges from silos. Sharp concrete corners or tops of I-beams are common culprits causing holes along the “difficult to pack silo” sides or shoulders of silos which are especially troublesome. Cover all sharp edges.
  • Edges of bunker silos are the most difficult areas to seal and the most vulnerable to aerobic deterioration. It is difficult to pack effectively along the sides of silos and a tractor wheel or frontend loader tine can easily damage a sheet of plastic draped over a silo wall. The proper way to get the silo shoulders sealed is to lay plastic along the walls of the silo before filling begins (Fig. 6). Once the silo is filled, the side sheets are pulled to the centre “tucking” the silage in rather as you would a bed. After the sides are pulled in a top sheet is brought over the top. In this way most of the silage has at least 2 layers of plastic and the edges are effectively sealed. Often it is possible to temporarily cover parts of the silo that are no longer being packed, such as the back. It is impossible to seal a silo by pushing the top sheet down the sides of a filled silo!
  • Plastic sheeting should be held in place with sufficient weight to ensure good contact between the plastic and the silage. Old car tires have served well, but are inconvenient. Sandbags are easier to use, especially when filled with gravel which does not absorb water and become excessively heavy. Straw or hay bales are of limited use because they can puncture the plastic. Note that if the plastic is pulled tight and well secured around the edges, much less weight is required.
  • Birds and raccoons quickly discover that corn silage contains grain and will inflict severe damage to plastic sheeting if allowed. Covering the corn silage with a layer of grass silage will eliminate this problem.

Figure 6. Cross sectional diagram of a bunker silo during filling.

A new type of additive for corn silage

Corn silage is susceptible to aerobic deterioration during feed-out. This is attributed to three factors:

1.High levels of residual sugars
2. Potentially high yeast populations
3. Friable, open consistency of the silage heap

A new microbial inoculant has just been developed which is proving to be very effective at reducing aerobic spoilage during feed-out — Lactobacillus buchneri. This bacterium has a heterofermentative fermentation and produces acetic acid from lactic acid. Normally, this would be undesirable in silage. Acetic acid is weaker than lactic acid and therefore not as good at reducing the pH of silage. However, in corn silage, there is usually ample lactic acid produced to ensure preservation. The trouble is, if all the acid is lactic acid, then corn silages frequently heat and are prone to aerobic spoilage. Why is this?

Lactic acid reduces pH effectively, but has no direct anti-fungal properties. Acetic acid on the other hand, is less effective at reducing pH, but has anti-fungal properties, not related to pH. This phenomenon has come to light in recent years following the widespread use of lactic acid-producing inoculants. Corn silages have increasingly become more homofermentative (i.e. a higher proportion of their acids are as lactic acid). At the same time corn silages have also become less stable when the silos are opened up for feed-out.

Research has now shown that L. buchneri is quite specific in producing acetic acid and 1,2 propanediol (another anti-fungal compound). However, it produces these products not from the sugars initially present on the crop, but from lactic acid produced in the course of the normal lactic acid fermentation. Thus it is not in direct competition with the lactic acid bacteria, but comes into its own later on during the fermentation, producing the acetic acid when it is needed.

A recent example of its effectiveness is demonstrated by the work of Ranjit et al (2002) from the University of Delaware (Table 4). In that study they added a fairly high number of L. buchneri (400,000 cfu/g) and succeeded in markedly improving the aerobic stability of the silage by increasing the concentration of acetic and propionic acids. When fed to sheep, this resulted in a 70% increase in rate of gain. In the same work, the authors looked at different levels of application of L. buchneri. It is clear that high application rates are essential if this approach is to be effective. When lower rates of the L. buchneri were added, there was no effect on stability in laboratory-scale silos.

Another similar approach being developed is to add strains of propionic acid producing bacteria to silage. In the same way as the acetic acid-producing bacteria, these ‘Propionibacteria’ produce propionic acid. Initial research suggests that this approach also holds possibilities, but these bacteria appear to be less aggressive in the silo and unrealistically high numbers need to be added in order to improve aerobic stability. With further development, however, the propionic acid bacteria may well become another tool to increase aerobic stability of corn silage.

Table 4.  Effect of Lactobacillus buchneri on the composition and aerobic stability of corn silages and on animal performance in sheep¹

¹ Ranjit, N.K., Taylor, C.C. and Kung, L. (2002).  Grass and Forage Science, 57:73-81.

Effect of Moisture Content on Corn Silage Effluent

S.C. Fransen
Washington State University, Prosser, Washington

Effluent from corn silage harvested at excessive moisture content represents a loss of valuable nutrients and poses an environmental risk because the effluent is very rich in soluble nutrients. In our study there was a curvilinear relationship between corn silage moisture content and amount of silage effluent (Fig. 1). Silage containing 20% dry matter lost as much as 10% of total silage weight as effluent. As dry matter increased above 20%, there was a sharp decrease in effluent, and very little effluent was lost from corn silage with more than 30% dry matter. At equivalent dry matter contents, corn silage produces more effluent than grass silage. Dry feedstuffs can be added to wet silage to reduce effluent; we found that beet pulp was most effective, alfalfa cubes was intermediate and barley grain was least effective in reducing effluent from wet corn silage. Silage with alfalfa cubes contained somewhat more lactic acid and less acetic acid than the silages with the other additives. 

Figure 1.  Relationship between moisture content of corn silage
at harvest and loss of effluent.

The Fermentation Process*

* Based on C. Holland and W. Kezar, The Pioneer Forage Manual - Nutritional Guide.  Pioneer Hi-Bred Interational Inc. 1999.

PHASE 1
At the time of harvesting, aerobic microorganisms predominate on the forage surface. Aerobic respiration by freshly cut plant material and aerobic bacteria begins at harvesting and continues after the forage is piled and packed. Aerobic respiration by bacteria and plant material consumes soluble carbohydrates needed by the beneficial lactic acid bacteria (or the animal consuming the forage). Aerobic respiration consumes the oxygen contained within and between the forage particles creating the desired anaerobic conditions. The respiration process produces water and heat in the silage mass. Excessive heat build-up resulting from an extended Phase 1 period can greatly reduce the digestibility of nutrients such as proteins.

Another important chemical change that occurs during this early phase is the breakdown of plant proteins called proteolysis. Proteins are first reduced to amino acids and then to ammonia and amines. Up to 50 percent of the total plant protein may be broken down during this process.  The extent of protein breakdown is dependent on the rate of pH decline in the silage. The acid environment of the silage eventually reduces the activity of the enzymes that break proteins down.

Phase 1 ends once the oxygen has been eliminated from the silage mass. Under ideal crop and storage conditions, this phase will last only a few hours; with improper management, this phase may continue for several weeks. The primary objective for putting up silage is to minimize air infiltration to shorten the time required to achieve an anaerobic environment. Key management practices are crop choice, proper crop maturity, moisture, chop length, and rapid filling with adequate packing and proper sealing of the storage structure.

PHASE 2
Phase 2 begins after the oxygen in the ensiled forage has been utilized by the aerobic bacteria. Anaerobic bacteria take over. These bacteria ferment soluble carbohydrates into acetic acid. Acetic acid production is desirable because it reduces pH and because it can be used as an energy source for rumen microbes. As the pH of the ensiled mass falls below 5.0, the acetic bacteria decline in numbers. This signals the end of Phase 2 which usually lasts no longer then 24 to 72 hours.

PHASE 3
The lower pH enhances the growth of an anaerobic group of bacteria that produces lactic acid.

PHASE 4
This is a continuation of Phase 3 as the lactic acid bacteria increase, fermenting soluble carbohydrates and producing lactic acid. Lactic acid is the most desirable of the fermentation acids and after efficient preservation, should comprise greater than 60 percent of the total silage organic acids produced. Lactic acid can be utilized by cattle as an energy source. Phase 4 is the longest phase in the ensiling process as it continues until the pH of the forage is low enough to inhibit the growth of all bacteria. When this pH is reached, the forage is in a stable state so long as oxygen is excluded.

PHASE 5
The final pH of the ensiled forage depends largely on the type of forage being ensiled and the condition at the time of ensiling. Haylage should reach a final pH of around 4.5 and corn silage near 4.0. The pH of the forage alone is not a good indicator of the quality of the silage or the type of fermentation that occurred. Forages ensiled at moisture levels greater than 70 percent may undergo a different version of Phase 4 where clostridia bacteria proliferate rather than lactic acid bacteria. Clostridia bacteria produce butyric acid rather than lactic acid, which results in sour silage. With this type of fermentation the pH may be 5.0 or above.

PHASE 6
This phase refers to the silage as it is being fed out from the storage structure. This phase is important because up to 50 percent of the silage dry matter losses occur from secondary aerobic decomposition. Phase 6 occurs on any surface of the silage that is exposed to oxygen while in storage and in the feed-bunk. High populations of yeast and mould or the mishandling of stressed crops can lead to significant losses due to aerobic deterioration of the silage. Proper management is vital to reduce these losses and improve the bunk-life (aerobic stability) of the silage.

Moulds and Mycotoxins in Corn Silage

K.M. WITTENBERG
Dept. Animal Science, University of Manitoba, Winnipeg, Manitoba

Introduction

Efficient crop and animal production is dependent upon the many microbes that exist in the farm ecosystem. Moulds, which include filamentous fungi and yeasts, are an important part of this microbial community. There are more than 10,000 known species of fungi, and many are considered beneficial in the process of food production. Others, particularly those found on the growing plant or in stored feeds can be detrimental to our efforts for high quality food production. Fungi can grow under a wide variety of environmental conditions, and generally are associated with reduced nutrient density of the feedstuff. Under the right growing conditions, these fungi will produce spores, which pose health problems upon inhalation or ingestion, and mycotoxins, which are secondary metabolites that are toxic to animals consuming them.

Approximately 100 species of fungi are known to produce secondary metabolites that are toxic to animals and humans. Fungi produce these mycotoxins to give themselves an edge in competing for nutrients that would otherwise be used by the plant itself or by competing microbes growing on the living plant or harvested herbage. Once produced, many of these toxic compounds remain on the herbage because they are resistant to breakdown by heat, time or fermentation.

Toxin-producing fungi can grow on the growing plant, harvested plant material wilting in the field or ensiled herbage. The most common toxin-producing fungi found in corn silage include the Fusarium, Aspergillus and Penicillium species (Table 1). Unfortunately, detection of a toxin-producing fungus in corn silage is not positive proof of the presence of a given mycotoxin. The opposite has also been observed, namely a silage may not have any visible mould and yet it can contain a high level of mycotoxins. Coupled with limited frequency data on the incidence of mycotoxins in animals feeds, and limited capability of many commercial laboratories to identify organisms and toxins in problem silage, management and identification of mycotoxin feeding problems in silage is difficult.

Table 1. Mycotoxins found in field corn and/or corn silage.

Controlling mould and mycotoxin contamination on the growing plant

Moulds are everywhere in the field environment, overwintering in soil, on plant debris, or introduced on seed and by prevailing winds. The growing corn plant provides a complex set of environments for fungal colonization. Frequently, the leaves at the top of the plant are exposed to extreme fluctuations in temperature, relative humidity and radiation, whereas lower plant parts experience moderate, humid conditions and shade. Moisture on leaves from rain or dew may carry soluble nutrients from the plant’s cells or other microbes, to support colonization. During the course of the growing season, there is an increased incidence of plant wounds caused by insect, wind or hail damage. Fungi and their spores can enter these plants through the roots, by pollen transfer down the silks, through the seed pericarp and through plant wounds.

Controlling mycotoxin production in the corn field is an important step in the production of high quality corn silage. Recent research in the United States has clearly established that aflatoxin production by Aspergillus flavus and A. parasiticus generally occurs on the growing crop. Similarly the Fusarium spp. are most active in the field, not in the silo. Control measures to prevent mould and mycotoxin (see Corn Diseases section) development in corn silage include:

1. High crop residue associated with minimum tillage systems provides an overwintering habitat for moulds, in particular the Fusarium spp. Producers adopting minimum tillage practices for soil or water conservation have a greater need for good crop rotation planning. Crop rotations must include non-host crops to break plant disease cycles and reduce soil and litter mould spores levels. Agronomic practices resulting in increased plant stress or disease will increase the opportunity for Fusarium and Aspergillus colonization.

2. A balanced soil fertility program reduces plant stress and the likelihood for subsequent disease development. Specifically, research in the United States has identified inadequate and excessive levels of soil N, and low levels of soil K and chloride to contribute to stalk rot.

3. Corn hybrids differ in their susceptibility to various diseases and pests. Selection of seed with high resistance ratings against corn stalk, ear and leaf diseases will also reduce the opportunity for colonization by toxin-producing fungal species. Similarly, hybrids identified to be resistant to ear and stalk boring insects will provide more protection against toxin-producing fungi. Seed companies are continuously working toward improving hybrids.

Controlling mould and mycotoxin development in the silo

After harvest, the development of micro-flora is controlled by storage conditions, the most critical being temperature, water availability and atmosphere gas composition. During ensilage, water is freely available as plant cells die and cell walls become more permeable. Oxygen trapped in the forage material is quickly used up during microbial and plant cell respiration. The facultative anaerobic bacteria, which become predominant, decrease the silage pH through fermentation of available sugars. With proper harvest and ensiling, there is little opportunity for mould growth. However, subsequent aeration of the silage can cause fungi to proliferate, and if conditions are suitable, mycotoxin may be produced. Harvesting and ensiling practices conducive to good silo management can ensure that mycotoxins are not produced during this phase of corn silage production:

1. Harvest the corn plant at the recommended maturity and moisture level for your storage systems. Do not let corn stand in the field after completed maturity or killing frost. Long dry down periods can be conducive to stalk and ear mould development.

2. Rapid elimination of oxygen as the corn herbage enters the silo is critical to prevention of storage moulds. This can be accomplished by ensuring that chopper knives are sharp and cutting at the correct length to ensure good packing, equipment used for filling and packing the silo are matched, forage harvest is done quickly and the silo is properly sealed once filled.

3. Use of silage additives (acids, enzymes, inoculants) to ensure acidic conditions are attained will help to eliminate mycotoxin production during the initial phases of ensiling, but will not decrease the mycotoxin that may already be present from the harvested crop.

4. Once the silage is stable, focus should be directed toward management of the silo during storage and feedout. Exposure to oxygen can provide fungi with the opportunity for mycotoxin production at this stage. Silos should be checked on a regular basis to ensure that holes in the seal are patched. Also, silo size should match herd size to ensure silage exposed to oxygen is removed within 24 h of exposure (at least 10 cm or 4 in/day, depending on ambient temperature).

Controlling mould and mycotoxin contamination at the feedbunk

Good feed management practices at the feedbunk can reduce encounters with mycotoxins when feeding corn silage:

1. Obviously spoiled silage, usually associated with an oxygen leak during storage or slow oxygen removal due to poor packing or dry silage, should be discarded.

2. Clean leftover feed from feedbunks on a regular basis, both to ensure high intake and to reduce the opportunity for mycotoxin production.

3. Producer options to detoxify feeds are increasing. The use of sodium bentonite and other adsorbent materials have been used in Total Mixed Rations (TMR’s) with limited success. Unfortunately, no one product can protect the animal from all mycotoxins, and usually producers must wait for extended periods of time to find out which individual or combination of mycotoxins they are dealing with. An alternative to use of adsorbent materials, is dilution of the problem silage with other forages. Again, lack of information about the level and type of mycotoxin in the silage means that producers are required to proceed by trial and error.

Determining the Economic Value of Corn Silage

W.P. WEISS
Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster, Ohio

Corn silage is a very common ingredient in diets for beef and dairy cows, however, corn silage is not commonly bought and sold at the present time. In the future, as herds become larger and more specialized, more corn silage will be purchased from farmers specializing in corn production. Prices for many commodities fed to cattle (e.g., corn grain, barley, oilseed meals, etc.) are established by large competitive markets. It is unlikely that true markets for corn silage with many buyers and sellers will develop because corn silage cannot be shipped long distances (high water concentration and perishability). In the absence of a true market other methods must be used to establish a realistic price for corn silage.

Cows do not require corn silage; corn silage is simply a vehicle to deliver required nutrients to a cow.  Therefore, the true economic value of corn silage should mirror the economic value of the nutrients it provides. If we know market prices for numerous commodities and know the nutrient composition of those commodities we can calculate the market value of the nutrients. Once the market value of nutrients is known, then the economic value of corn silage can be determined as the sum of the market value of the nutrients contained in that feed.

Methods to Price Corn Silage

Several methods have been used to determine the price of corn silage. Perhaps the most common is to base the price of corn silage on the price of corn grain. For example:

7.7 times corn grain price ($/bu) = price of corn silage ($/ 1000 kg assuming 35% dry matter).

Equations such as this wrongly imply that corn silage and corn grain are fed for the same reason and are interchangeable in diets. The ‘Petersen method’ calculates the price of corn silage from the economic value of energy in corn grain and of protein in soybean meal. This method is flawed in that it assumes corn is the only source of energy available and soybean meal is the only source of protein available and that both are perfectly priced. Furthermore, it ignores the fact that corn silage provides more than energy and protein.

St. Pierre and Glamocic (1)  developed a method to estimate the market value of individual nutrients based on the current market price of many feeds (the more feeds entered, the more accurate the results) using a statistical technique called maximum likelihood. A computer program that makes all these calculations, called SESAME (version 2.0), is now available from Ohio State University Extension (Columbus OH 43210). Users enter either library values or their own values for nutrient composition. The program then calculates the $ value of each nutrient specified. If users do not have access to SESAME, Ohio State University Extension also calculates and posts the $ value of nutrients once every two months on the website http://dairy.osu.edu/bdnews/bdnews.html. Note that the $ values shown at that website are calculated from national markets (U.S.) and may differ from those in local markets.

Why is Corn Silage Fed?

Corn silage is an extremely common ingredient of dairy rations in most areas of North America. The widespread use of corn silage implies that it has certain competitive advantages over other feedstuffs. This means that over the long term, diets with corn silage must result in higher income over feed costs than do diets that include less commonly used feeds. More specifically, corn silage must provide certain nutrients at lower costs than do other feedstuffs. To accurately value corn silage, the important nutrients provided by corn silage must be determined. Cows require energy (expressed as net energy for lactation, NEL), rumen degradable protein (RDP), rumen undegradable protein (RUP), effective neutral detergent fibre (eNDF), and a host of minerals and vitamins. For determining economic value of corn silage, the value of the minerals and vitamins can be ignored with little loss of accuracy and for this article only NEL, RDP, RUP and eNDF will be used to determine economic value. Those four nutrients are the major nutrients influencing animal production and are responsible for more than 80% of total feed costs. Although these important nutrients cannot be measured by feed labs, they can be estimated (2) .

Average corn silage (2)  has 1.45 Mcal/kg of NEL, 45% NDF, 5.7% RDP, and 3.1% RUP (all values on a dry matter basis). Because of positive effects on rumen health, NDF mustbe described in terms of effectiveness, i.e., its ability to stimulate chewing. The NDF in brewers grains is not as effective as the NDF in properly made corn silage and the economic value of corn silage must reflect this difference. SESAME calculates the market value of eNDF and noneffective NDF (eNDF is always worth much more than noneffective NDF). A major reason for feeding corn silage (or any forage) is to provide eNDF and the market value of corn silage must include its value as a source of eNDF. Because of the importance of eNDF, the value of corn silage cannot be tied solely to the price of corn grain. For this example, the NDF in corn silage is assumed to be 100% (i.e., eNDF=NDF). If corn silage is chopped too finely, eNDF will be lower than NDF.

Market Value of Nutrients

The dollar value of nutrients is dependent on the prices of all available feeds within a given market. They are not constant and will vary across locations and time. The numbers used in this paper probably will not reflect your local conditions and are presented only as an example.

The market prices (Wooster OH, November, 2002) of several feed grains, byproducts, and hays (a total of 30 feeds) were entered into SESAME and nutrient composition from NRC (2001) were used. The program calculated the market value of NEL ($/Mcal), RDP ($/kg), RUP ($/ kg), and eNDF ($/kg) as shown in Table 1.

Table 1. The Concentrations (dry matter basis) of various nutrients (NRC, 2001) and market value of those nutrients based on prices at Wooster OH in November 2002.  These values are not constant and will vary across locations and time.

To calculate the market value of average corn silage (assumed composition equal to that in NRC)(2), the quantity of each nutrient in a metric ton of corn silage is calculated. One metric ton of corn silage with 35% dry matter contains:

1,000 kg (2,200 lb) x 0.35 x 1.45 = 508 Mcal of NEL

1,000 kg (2,200 lb) x 0.35 x 0.057= 20 kg of RDP

1,000 kg (2,200 lb) x 0.35 x 0.031 = 11 kg of RUP

1,000 kg (2,200 lb) x 0.35 x 0.45 = 158 kg of eNDF

The value of the nutrients in 1000 kg of corn silage is determined by multiplying the quantity of nutrients by their market value and adding them together:

508 Mcal of NEL x 0.06 = $30.48

20 kg of RDP x 0.024 = 0.48

11 kg of RUP x 0.410 = 4.51

158 kg of eNDF x 0.079 = 12.48

Total $/1000 kg = $47.95

This means that in the market from which the value of nutrients were determined, 1 metric ton of corn silage (35% dry matter) is worth about $48 when fed to the cow. If the selling price is greater than about $48/metric ton, other feedstuffs can provide the nutrients needed at a lower cost than can corn silage. If the selling price is less than about $48/metric ton, the corn silage is a good buy.

From the above example, you can also see the impact eNDF has on the value of corn silage. About 64% of the value of corn silage is from energy, 26% from eNDF and about 10% from protein fractions.

Pricing Standing Corn for Silage

The above method works for corn silage that is ready to feed. It has been harvested, fermented, and a sample has been analyzed for nutrient composition. Standing corn is often purchased prior to chopping for silage. Because of inadequate data, price estimates for standing corn are inherently less accurate than pricing silage that has already been made. However, the method described above can still be used in the following manner:

1. Estimate nutrient composition. The NRC (2) gives average composition for immature, normal, and mature corn silage. Extension agencies and local nutritionists may have data on average composition of silages from a local area and under more specific situations. Attempt to find the best estimates of expected concentrations of NEL, RDP, RUP and NDF in the resulting silage.

2.Measure the dry matter of the chopped silage.

3. Estimate market value of silage using the method described above using measured dry matter.

4. Estimate the costs associated with chopping and storage. Several universities and extension agencies have developed budgets with average chopping and storage costs. In Ohio (these are not constant and will differ for specific situations) chopping corn costs $4 to $5.5 and storing costs $3 to $4/1000 kg of 35% dry matter silage. If you are purchasing chopped corn plants only storage costs have to be estimated.

5. Adjust for shrink. The amount of dry matter chopped will be greater than the amount of dry matter available for feeding. Dry matter is lost by fermentation and spoilage. On average about 10% of the dry matter is lost during fermentation and feed-out but this will be higher for poorly made silage.

6. Calculate the market value of the standing crop. Subtract chopping and storage costs from the market value of the silage, then multiply by 0.9.

Example: Using the data in Table 1 and a measured dry matter of 32%, 1,000 kg (2,200 lb) corn silage, not standing corn, has a market value of

1000 kg x 0.32 x 1.450 x 0.060 = $27.84 for NEL

1000 kg x 0.32 x 0.057 x 0.024 = $ 0.44 for RDP

1000 kg x 0.32 x 0.031 x 0.410 = $ 4.07 for RUP

1000 kg x 0.32 x 0.450 x 0.079 = $11.38 for eNDF

Total per 1000 kg (2,200 lb) at 32% dry matter = $43.73

From that value, chopping and storage costs are subtracted:
43.73 - 4.75 - 3.5 = $35.48

Multiply that value by shrink factor:
35.48 x 0.9 = $31.93.

In this example standing corn would be worth about $32/ 1000 kg (2,200 lb) at 32% dry matter.

Other Adjustments to Price

Dry matter: Wet silage (40% dry matter) ferments poorly and is prone to spoilage. The method outlined above does not account for these negative effects. Based on responses measured in research studies and a few assumptions regarding intake effects on milk production and feed: milk price ratios, adjustment factors (Table 2) can be derived to account for wet and dry silage (these adjustments are in addition to simply accounting for dilution with water).

For example, if the market value of corn silage with 26% dry matter was $40/1000 kg, its adjusted value would be 40 x 0.85 = $34/1000 kg.

Table 2.  Expected change in value for wet and dry corn silage.  The values in this table are multiplied by the market value determined as described above to obtain the final value for wet and dry silage.  A value of 1 = no adjustment.

Higher than average NDF digestibility (measured in vitro):  A major determinant of animal performance is the dry matter intake potential of a forage. Cows consume more DM when fed a diet containing a forage with higher in vitro NDF digestibility (IVNDFD). On average total dry matter intake increased about 0.14 kg (0.3 lb)and milk production (4% fat-corrected) increased about 0.25 kg (0.55 lb) per unit increase in IVNDFD (3). Assuming 1 kg of milk is worth twice as much as 1 kg of feed dry matter, the economic value of a 1 percentage increase in IVNDFD is worth about $5.4/1000 kg of corn silage dry matter (about $1.9/1000 kg of 35% dry matter silage). This factor is easy to apply when two silages are being compared (relative value). For example, if two silages were equal except that the IVNDFD differed by 5 units, the silage with higher digestibility would be worth 5 x 1.9 = $9.5/ 1000 kg (35% dry matter) more than the other silage. To determine absolute worth a standard or base IVNDFD is needed which at this time has not been established. However, hybrids with consistently higher than average IVNDFD are worth more than the value calculated above.

 

Refernces

1. St-Pierre, N.R., and D. Glamocic 2000. Estimating unit costs of nutrients from market prices of feedstuffs. J. Dairy Sci. 83, 1402-1411.

2. National Research Council 2001. Nutrient Requirements of Dairy Cattle. Natl. Acad. Press, Washington DC.

3. Oba, M., and M. S. Allen 1999. Evaluation of the importance of the digestibility of neutral detergent fibre from forage: Effects on dry matter intake and milk yield of dairy cows. J. Dairy Sci. 82, 589-596.

Winter Grazing Stockpiled Corn

D. THOMPSON1, D. VEIRA1 and E. MOORE2
1Agriculture and Agri-Food Canada, 2BC Ministry of Agriculture, Fisheries and Food, Kamloops, British Columbia

Winter feed is very costly for livestock operations, and beef producers with generally small profit margins are particularly interested in low-cost feed alternatives. Grazing stockpiled forage after the growing season reduces harvesting and feeding costs. Most perennial forages are harvested for multiple cuts; leaving a standing crop for a long period results in very poor feed quality. But with corn, the entire season’s growth can be left standing with less threat of deterioration, resulting in a potentially high carrying capacity. At Kamloops the 2 year average yield for stockpiled corn was 18 t/ha (8 T/ac) which provided feed for 1080 cow-days/ha (430 cow-days/ac). By comparison, only 5 t/ha (2.3 T/ac) of tall fescue could be stockpiled (270 cow-days/ha or 110 cow-days/ac). Significant quantities of standing corn were also reported in Brandon, MB (15 t/ha or 6.7 T/ac), Brookes, AB (13 t/ha or 5.8 T/ac) and Lacombe, AB (13 t/ha or 5.8 T/ac) (1, 2). Stockpiled corn has the potential to extend the grazing season as the plants stand above the snow. The nutritional value of standing corn should be adequate to support pregnant beef cows in the first and second trimester (3).

Corn varieties specially designed for grazing are generally lower yielding than conventional hybrids. ‘Amaizing graze’ corn yielded 5 to 7% less than conventional early hybrids at Lacombe and Brooks. At Kamloops ‘Amaizing Graze’ yielded 15% less than Pioneer 34G81. ‘Amaizing Graze’ has very high CHU requirements compared to the hybrid corn varieties grown in these regions, accounting for the lower yields. An unusual short stature variety ‘Canamaize’ yielded 20% less than the conventional hybrids at Lacombe and 25% less Brooks.

A key question to consider is how well stockpiled corn weathers. Averaged over three early-season hybrids, the proportion of the late Sept. corn still standing in late Jan. was 75% at Brooks and 80% at Lacombe. At Kamloops 80% of the material stockpiled by mid-Nov. was still standing on Jan. 15. The losses are due mostly to shedding of leaves which decompose quickly on the ground.

When the cattle are turned into a fresh strip of standing corn, they pick off the cobs and leaves (Fig. 1) and in the process trample down the stems (Fig. 2). It is necessary to restrict access with electric fences to minimize trampling (Fig. 3). On frozen ground, cattle will eat the downed stems, but when the ground is not frozen the stems may by trampled into the mud. At Kamloops we observed 80-90% utilization of standing corn from mid-Dec. to Jan. on frozen ground but only 70% utilization on unfrozen ground.

Figure 1. Cow preparing to swallow a whole corn cob; no choking was noticed.

Figure 2. Cows grazing corn on frozen ground at Gus Fischer’s farm near Cache Creek.

Figure 3. Cows strip grazing corn at Kamloops; notice preference for cobs and leaves.

What quality does stockpiled corn offer to cows and how does it vary over the winter? Average winter-time levels of ADF ranged from 25% in Brooks, 29% in Lacombe and 38% in Kamloops. The high values at Kamloops were likely due to the more advanced maturity of the crop. At all sites there was a slight increase in ADF through the winter. Whole-plant NDF values in late Sept. averaged 53% at Lacombe and 51% at Brooks. There was a slight increase in NDF throughout the winter. With increased NDF, there is generally a reduction in forage intake by cattle. Stockpiled corn averaged 7 to 9% crude protein (CP), which meets the minimum value of 7% for beef cows in early or mid pregnancy (NRC 1996). The crude protein content did not decline substantially throughout the winter at any of the sites.

‘Amaizing Graze’ corn tended to have slightly greater CP than the conventional hybrid at Lacombe (10 vs 9%) and at Kamloops (9 vs 8%) but not at Brooks. Higher CP can be tied to an earlier stage of maturity at harvest.

How do pregnant cows perform on grazing corn? It appears that grazing corn provides an adequate maintenance diet for pregnant cows in winter. At Kamloops cow gains averaged 0.1 kg/day (0.05 lb/day) confirming an earlier report from Lethbridge, Alberta (3). In fact, at mid-gestation beef cows can afford a minor loss in condition. So if the cows are in good condition before grazing corn, they are likely to maintain their condition.

Some economics for grazing corn:

The cost of grazing corn is estimated at $0.96/day compared to $1.65/day for hay and $1.68/day for corn silage (Keyes 2002, unpublished). Although it costs more to plant and grow corn than other forages, considerable savings are realized with no harvesting costs and low feeding costs.

Challenges of grazing corn

  • Specialized seeder or modified grain drill needed for planting.
  • Weed control
  • Moulds (eg. Fusarium) on leaves and cobs under wet conditions which can be a health hazard for cattle (see Moulds and Mycotoxins in Corn Silage section).
  • Soil compaction can be minimized by excluding cows after grazing. However, compaction may be a problem in lanes or around troughs. Moderate levels of compaction may be alleviated by frost heaves during the remainder of the winter and by spring tillage.
  • Replanting may be difficult due to stalk residue.
  • Only feasible in geographic areas where there is adequate moisture and heat for corn growth and but where the winters are cold and dry enough to minimize trampling and mould.
  • Stockpiled corn may be very susceptible to wildlife depredation; blackbirds can feed on developing cobs while deer or elk may consume and knock over standing corn in winter.

Weed control for the non-corn grower

Corn grazers ma y be able to accept a greater amount of weeds in their crop so long as the corn is not smothered. Weed control may be the major challenge for most corn grazers. Planting corn directly into the residue from a winter cover crop such as cereal rye or annual ryegrass, sprayed with glyphosate (Roundup), helps to control weeds. Another strategy is to delaying seeding the corn until after the first flush of weeds is sprayed with glyphosate. In both these cases corn is direct-seeded into the dead plant cover. Another option is using ‘Roundup Ready’ corn hybrids but know that they are genetically modified. Non-herbicide options are limited. Start with ‘clean’ land and use inter-row cultivation. If a fall cover crop such as annual ryegrass winter kills, seed directly into it. Be aware that even if your previous alfalfa stand was free of annual weeds, you are still likely to get a flush of annual weeds; weed seeds can lie dormant in the soil for many years until conditions are right for their germination. Because corn is planted later than most forages, intensive competition from ‘warm season’ annual grasses such as barnyard grass and foxtail is likely unless they are controlled (see Weed Control section).

 

References:

1. McCuaghey, P., J. Small, S. Scott and B. Irvine 2002. Foxtail Millet and Corn: New crops to extend grazing season and cut feeding costs. Brandon Res. Centre News Notes. Feb. 2002.

2. Baron, V.S., H.G. Najda, D.H. McCartney, M. Bjorge, and G.W. Lastiwka 2003. Winter weathering effects on corn grown for grazing in a short-season area. Can. J. Plant Sci. 83, 333- 341.

3. Willms, W.D., L.M. Rhode, and B.S. Freeze 1993. Winter performance of cows on fescue prairie and in drylot as influenced by fall grazing. Can. J. Anim. Sci. 3, 881-889.