The overall objective of this study is to enhance and stabilize farm production of feed and feed nutrients through strategic and judicious use of irrigation water.
The specific objectives of this study were to:
- Optimize water applications to maximize forage yield during typically dry summers in the Lower Fraser Valley while at the same time minimize nutrient losses.
- The approach is to find the ideal combination of timing and quantity of water application using various water deficit indictors.
Some of the overall impacts of climate change for BC agriculture have been identified as follows: http://www.bcagclimateaction.ca/overview/why-adaptation/
- More frequent occurrence and severity of summer drought; water shortages in more regions. Hotter and drier summers.
- Decreased snowfall in alpine areas leading to reduced snowpack and to water shortages
- Increased precipitation (frequently through more extreme events) and subsequent vulnerability to flooding, erosion, nutrient loss. Wetter and milder winters.
- More frequent and intense “extreme” weather events (wind-storms, forest fires, hail, droughts and floods)
- Increase in growing degree days (heat units) and a longer frost free season. Hotter summers with milder winters.
- Potential for broader range of viable crops in some regions. Milder winters.
- Increase in pest and disease pressure due to winter survival of pests.
Previous work at Agassiz showed annual yield increases of 13 to 35% from summertime irrigation for different grass species and varieties. The work showed substantial potential to increase grass production with irrigation during the dry summer months. See Table 1.
Table 1. Grass yield with and without irrigation for two years at Agassiz (t DM ha-1)
|Species||Variety||No Irrigation||With Irrigation||Increase in Yield (%)|
Annual yield (t DM ha-1)
Study Materials and Methods
The study examined four combinations of water application on an orchardgrass crop planted in 2015. Different soil moisture sensors were used in 2016 to monitor soil water deficit measured in units of water potential (negative pressure or suction) called centibars (cbar). At 80 cbar most of the easily available water is gone so growth slows down. If the deficits are short-lived plants can compensate. Most of plant roots are in the top 15 cm of soil, so water lower down is less rapidly available.
Different degrees of soil moisture deficit were then used as triggers for irrigation. Four water application strategies were compared to no watering for both 2015 and 2016.
In 2015 the newly seeded orchardgrass crop was watered using the following strategies: Frequent & Light, Frequent & Heavy, Infrequent & Light, Infrequent & Heavy. In 2016 soil sensors were installed at three depths and used as a guide for water applications as follows:
- 15 cm depth -30 cbar trigger, Frequent & Light
- 30 cm depth -30 cbar trigger, Less Frequent & Heavier
- 45 cm depth -30 cbar trigger, Infrequent & Heavy
- 15 cm depths -10 cbar trigger, Very frequent & Light
Nitrogen fertilizer was applied at 50 kg N/ha (45 lb/acre) to all harvests proceeding the dry summer months (one application for Cut 1 in the 2015 establishment year and two applications for Cuts 1 and 2 in 2016). For the anticipated dry summer months nitrogen fertilizer was applied at three rates (0, 50 and 100 kg N/ha) to each of the five watering treatments (one application for Cut 2 in 2015 and two applications for Cuts 3 and 4 in 2016). Other nutrients (phosphorus, potassium, sulphur, magnesium, micro-nutrients) and Calpril lime were applied according to soil test recommendations. Statistically, the design of the study is a randomized block design with 5 watering treatments and 3 nitrogen application rates. Each individual study treatment was repeated four times.
For each grass harvest dry matter yield, moisture content and nitrogen content were measured. Nitrogen capture is important because it means less lost to the groundwater and more in the plant contributing to protein formation. There is a direct relationship between plant protein and plant nitrogen.
Soil was sampled immediately after each grass harvest and analyzed for moisture, nitrate and ammonia content. Soil moisture sensor data, weather data and Evapo-Transpiration (ET) were recorded throughout the study. Evapotranspiration is available on www.farmwest.com
2015 Grass yield - Irrigation increased yield on a single cut of newly established orchardgrass stand by about 1.7 t DM/ha for N application rates of 0, 50 and 100 kg N/ha. This is over 10% increase for total annual yield. This equates to a yield increase for this single cut of 217, 112 and 94% for N application rates of 0, 50 and 100 kg N/ha respectively. See Figure 1.
2015 Soil nitrogen - Irrigation resulted in less soil N through the soil profile at the 0 and 50 kg N/ha rates. While irrigation method did not affect yield, it did affect soil nitrogen levels. The ‘Heavy’ irrigation also resulted in less soil N at the 100 kg N/ha rate (see Figure 2). Net of both removal of nitrogen by the crop (as protein) and soil nitrogen provided by the soil, there is more nitrogen lost below the root zone for the ‘Heavy’ irrigation as shown in Figure 3 for nitrogen ‘missing’ from the soil profile. The results suggest that there is an interaction between water and nitrogen fertilizer which has economic and environmental implications.
Figure 1. Grass yield on a newly established orchardgrass stand as affected by nitrogen and water applications, 2015.
Figure 2. Amount of nitrogen left in the soil at the end of the season first season, 2015. Note that the tow heavy irrigations leached N from the 100 nitrogen rate but apparently not form the lower nitrogen rates. The light irrigations did not leach nitrogen. (See also Fig 3 below)
Figure 3. ‘Missing’ nitrogen calculated from what was supplied by fertilizer and the soil and what was removed by the grass crop.
2016 Grass yield
Irrigation increased summertime yield by 0.5, 1.0 and 1.2 t DM/ha for N applications of 100, 50 and 0 kg/ha respectively in 2016. There was a significant interaction between Irrigation and N rate with irrigation increasing yield by 10, 25 and 75% for N applications of 100, 50 and 0 kg/ha respectively. See Figure 4.At the middle N rate there was about an 8% increase in annual yield. Note that soil nitrogen data for 2016 are not yet complete.
2016 Water use efficiency
Water Use Efficiency (WUE) was greatest for “Infrequent & Heavy” strategy (45 cm -30 cbar) which applied overall the least water. Improvement was 19, 26 and 27% for nitrogen applications of 0, 50 and 100 kg/ha respectively over the other three watering strategies. See Figure 5.
Figure 4. Dry matter yield of Cuts 3 and 4 2016 as influenced by water and nitrogen treatments.
Figure 5. Water use efficiency for harvests 3 and 4 in 2016.
Results from the first two years indicate:
- significant potential to increase yields in drier summer months
- there is a water x nutrient interaction which has significant economic and environmental implications
- need to modify watering criteria in terms of quantity and timing
- criteria will vary with decision tools (ie differences between sensors)
- criteria will vary with soil types