Horse Manure - Managing a Valuable Resource (2008)

Return to Manure

Horse Manure: Myths and Misconceptions

Horse manure has gotten a bad rep lately! There is a misconception that all horse manure is too high in carbon and has no fertilizer value for crops or gardens. This is just not the case.

The average 455kg (1000 lb) horse produces 8165kg (9 tons) of manure per year or 23 kg (50 lb) per day. We can start by changing our perception from manure as a waste that needs to be dealt with to a resource that should be celebrated. This 8165 kg of raw manure translates to 45kg (100 lb) of Nitrogen (N), 8kg (17 lb) of Phosphorus (P), 28kg (62 lb) of Potassium (K), and 8084kg of organic matter.

Average Fertilizer Content in Horse Manure (as-is basis)
N / ton 8.6 kg (19 lb)
P2O5 / ton 6.4 kg (14 lb)
K2O / ton 16.3 kg (36 lb)

Source: Horse Manure Management (2004), Colorado State,
University Cooperative Extension, J.G. Davis and A.M. Swinker

These valuable nutrients can be easily utilized by pasture grasses, gardens (as fertilizer or mulch), as landscaping material or as a liquid fertilizer (compost tea). However, this manure needs to be transformed into a more useable form and one way to accomplish this is through composting. Composting is the best management tool to deal with these mountains of manure and transform them into a valuable fertilizer. A breakdown of the characteristics of many composting materials is listed in the table below.

Table 1. Characteristics of Composting Materials

Material

Nitrogen
(dry wt) (%)

Carbon:
Nitrogen ratio
(dry wt)

Typical
Moisture Content
(%)

Bulk Density
at moisture content
(kg/m3)

Horse Manure with Bedding

  • with straw bedding
  • with shavings

1.4-2.3
1.5
0.9

22-55
27
65

59-79
67
72

725-960

Beef Cattle

  • feedlot with bedding

1.3

-

68

-

Dairy Cattle

  • solid manure handing
  • liquid slurry
  • solids separated from slurry

1.7
2.4-3.6
1.45

18.0
-
-

-
88-95
23

-
-
-

Poultry

  • broiler breeder layer
  • broiler litter
  • turkey litter

3.6
4.7
4.2

10
15
14

46
25
33

470
330
380

Sheep Manure

1.3-3.9

13-20

60-75

-

Fish Scraps & Mortality

6.5-14.2

2.6-5.0

50-81

-

Oat Straw

0.6-1.1

48-98

-

-

Wheat Straw

0.3-0.5

100-150

-

-

Legume Grass hay

1.8-3.6

15-19

10-30

-

Straw

0.3-1.1

48-150

4-27

58-357

Grass Clippings

2.0-6.0

9-25

82

180-260

Grass Clippings & other garden waste

2.0

19.3

15

250

Leaves (freshly fallen)

0.5-1.3

40-80

38

60-80

Paper

0.2-0.25

127-178

18-20

-

Sawdust

0.06-0.8

200-750

19-65

350-450

Woodwaste (chips)

0.04-0.23

212-1313

-

445-620

Source: Composting Factsheet: Characteristics of On-Farm Composting Materials (1996) BC Ministry of Agriculture and Food

When manure is composted it is important to maintain the correct Carbon:Nitrogen (C:N) ratio to support the microorganisms. These microbes require carbon for energy and nitrogen for growth and the ideal C:N ratio is between 25 to 50:1. Horse manure lies in the range of 20-40:1 so when shavings are added this ratio can be thrown out of balance. We need to correct this by combining the appropriate amount of both carbon- and nitrogen-rich materials. The following table gives the Carbon:Nitrogen ratio for a variety of compostable materials.

Material C:N Ratio
horse manure 20-40:1
grass clippings 25:1
horse manure with bedding 30-60:1
grass hay 30-40:1
straw 40-100:1
paper 150-200:1
wood chips, sawdust 200-500:1

Source: Caring for Alberta’s Rural Landscape: Manure and Pasture Management for Horse Owners (2003), Alberta Agriculture, Food and Rural Development

A soil testing kit from a local garden retailer can help determine the amount of nitrogen in your compost. If the nitrogen content is too low then you will need to decrease the amount of carbon in your compost pile. Reducing the amount of bedding material or changing the type of bedding can greatly reduce the carbon content of your compost. This is important because spreading compost with too high a carbon level can cause the compost microbes to ‘rob’ your pasture grasses of nitrogen in order to complete the composting process. Obviously, this is the opposite effect of what you want to see happen in your pastures.

One way to determine if your compost is ready for use is if a temperature of at least 55 – 65 degrees Celsius has been maintained for at least 21 days or three weeks. At this point you can be quite confident that the composting process is finished and that weed seeds and parasites have been destroyed. The temperature can easily be monitored with a long composting thermometer purchased from a garden centre.

Sometimes the finished compost doesn’t appear to be broken down, but as long as temperatures have reached the critical point and were maintained for three weeks you can be confident that it is finished. If you prefer the compost to have a finer texture then you can turn the pile a few more times before use. You can also run the compost through a mesh screen to remove the larger materials, which can be added back to the actively composting pile. The final moisture content of the compost should be approximately 50% and feel like a damp wrung-out sponge.

One question often asked is “Why do I need to compost my animals’ manure? Can’t I just spread it raw on the land?” Composting may be slightly more time consuming than working with raw manure, but it will be worth it in the long run. When raw manure is spread onto pastures the nitrogen (N) content tends to volatilize and immobilize, rendering it unusable for microorganisms. In order to replace the N content, the microbes in the compost will ‘suck’ it up from the pasture grasses in order to complete the composting process. Through the act of composting, microbes recycle the nutrients they use and retain them in the compost, which creates a nutrient rich fertilizer source for your pastures.

Also, through spreading composted manure instead of raw manure you can protect local water resources. The run-off (leachate) from raw manure can cause algal blooms and growth of other aquatic plants in nearby streams. When these plants decompose they deplete the water of oxygen content and as many aquatic organisms require oxygen to breathe they are not able to survive in this habitat. In addition, the run-off from manure piles can contaminate your drinking water supply and that of your livestock if the piles are located near a well head or septic field.

Some of the other benefits of using composted manure instead of raw manure are:

• Increased water-holding capacity of your soil

• Destruction of parasite eggs/larvae and weed seeds

• Reduced odour

• Reduced total waste volume

• Reduced money spent on chemical fertilizers and soil amendments

• Easier manure handling

• Provides a great source of fertilizer for your pasture or garden.

Finished compost can be used on pasture grasses to achieve some of the benefits listed above. If the compost is still a bit clumpy when spread then you can run a chain harrow over the top of this to break it down further. You can also use finished compost on gardens and in landscaping as a mulch or soil amendment. It provides a great fertilizer source and will help to keep the weeds down. You can also pass it along to your neighbours and find them begging for more the next year!

References:

Davis, J.G. & Swinker, A.M., 2004, Horse Manure Management, Colorado State, University Cooperative Extension, http://www.ext.colostate.edu/pubs/livestk/01219.html

BC Ministry of Agriculture and Food, 1996, Composting Factsheet: Characteristics of On-Farm Composting Materials, http://www.agf.gov.bc.ca/resmgmt/publist/300series/382500-3.pdf

Alberta Agriculture, Food and Rural Development, 2003, Caring for Alberta’s Rural Landscape: Manure and Pasture Management for Horse Owners, http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex9377

Article by:
Andrea Lawseth B.Sc. (Agro), A.Ag.
Agricultural Stewardship Coordinator
Langley Environmental Partners Society
Phone: 604-532-3515
Email: info@manuremaiden.com
www.manuremaiden.com
www.leps.bc.ca

Return to Manure