What are nutrients?
Nutrients are naturally occurring elements in soils that support plant growth. Prairie crops require 17 nutrients, but the most important are nitrogen and phosphorus. These two nutrients are often added to the soil through fertilizers and manure in modern crop production. While relatively large amounts of nitrogen and phosphorus are needed to sustain crop production, over-applying these nutrients can have negative consequences for local and regional water supplies.
What is runoff?
Runoff is any excess water which saturated soils can’t absorb. In the prairies, runoff is primarily tied to spring melt, when large amounts of surface water drain off flooded fields. Spring runoff isn’t just water, though; it includes all the materials and nutrients the snow retained through the winter. That means prairie farms can lose key crop-growing nutrients like nitrogen and phosphorus during spring snowmelt events.
Why should I be aware of nutrients and runoff?
Runoff from storms and snowmelt can wash nutrients into water supplies, where they end up fertilizing lakes and wetlands instead of fertilizing your crops. The algae blooms affecting Lake Winnipeg and other prairie lakes, for example, are largely caused by nutrient runoff from farms. This excess of nutrients — called eutrophication — encourages algae blooms, which are unsightly and hazardous. Eutrophication can suffocate fish and trigger toxic effects in the water.
Lakes are incredibly sensitive to fertilizer inputs. Though producers manage fertilizer by the kilogram, lakes can respond to microgram-level increases, akin to drops of water in an Olympic-sized swimming pool. To maintain or improve our water quality, we need to minimize nutrient losses from fields as much as possible. In regions with intensive livestock production, nutrients need to be managed with additional care because repeated manure application can pool nutrients in the soil, creating a long-term source of nutrient loss.
Why is effective nutrient management crucial in the prairies?
- First, our climate and landscape can make it challenging to keep nutrients on fields. Crop growing season is short in the prairies. When snow accumulates on fields, nutrients can dissolve into the snow and wash away in spring. Snowmelt is a key source of runoff and a critical period of nutrient transport on the prairies. Unfortunately, many beneficial management practices developed for warm conditions or soil erosion control do not work at full capacity with prairie climate and landscape.
- Second, our lakes are highly vulnerable to nutrients. Prairie lakes are often shallow, with large watersheds encompassing agricultural land. These factors can make prairie lakes even more vulnerable to nutrient pollution and algae blooms.
- Third, some management practices — such as reduced tillage and bale grazing — can build up nutrients on the soil surface and thus increase nutrient export with snowmelt runoff. As a result, we must act to minimize nutrient transport if we want to help address growing problems in our prairie lakes.
What can I do about nutrients?
Improve animal feed management: If you’re importing animal feed, you’re also importing phosphorus. Studies show feeding phosphorus to livestock above the minimum requirements doesn’t help your animals grow more, so try to practice precision feeding — feed livestock only the minimum phosphorus needed to support growth. Manitoba Agriculture reports reducing dietary phosphorus for dairy cows from 0.48% (a common rate) to 0.4% (the recommended rate) will reduce phosphorus in manure by 25 to 30%.
Also, look for feeds with phytase, which specifically helps chickens and hogs digest and absorb phosphorus. This will reduce your costs on phosphorus supplements and reduce the phosphorus content in manure. Poultry recommendations for phosphorus uptake are available here in table 1.
Minimize nutrient loss via infrastructure changes: You can make several structural additions to improve water quantity and quality on your land. Consider moving corrals away from creeks or adding fencing to keep cattle out of waterways where possible. Construct a holding pond downstream of your barnyard to capture runoff. Install manure handling, treatment or storage systems to help ensure you have sufficient manure storage to avoid winter application.
Keep livestock away from streams. Nutrients can only cause downstream problems when they enter the water supply. By locating cattle away from streams or providing offstream water sources, nutrients found in manure are less likely to contaminate regional water supplies, and erosion risks are lower.
Use sustainable stocking rates: Overgrazed pastures often have deteriorating soil structure. That leads to increased erosion and, with it, a loss of particulate nutrients in the soil. Overgrazing can increase the availability of dissolved nutrients for transport as well.
Consider rotational grazing: By moving livestock away from streams at times when runoff is likely — like during spring snowmelt and rainstorms — you can minimize threats to regional water quality.
Place winter bale sites away from streams: On that note, avoid winter bale grazing in high risk areas. Place winter bales in areas with low snow accumulation or where meltwater has a low likelihood of entering streams (like above holding ponds).
Farm/watershed system-level management:
Drainage management: Connecting wetlands to waterways has effects far beyond the farm. Drainage reduces the storage capacity of your land, leading to more nutrient loss across a wider area. If you plan to drain, consider reducing your nutrient inputs to reduce the downstream impact. If possible, maintain or create water storage at low elevations on your land.
Target manure application to low-risk fields: Nutrients are a problem under two conditions: when nutrient levels are high, and when potential for runoff is high. Focus manure application on parts of your land that don’t drain to regional waterways to minimize effects of water quality.
Cycle manure (and nutrients) among area farms: The economics of agriculture creates a nutrient imbalance: crop producers become nutrient-poor as phosphorus and nitrogen are taken up by plants, and livestock producers become nutrient-rich as those plants are consumed by their animals in feed. This creates areas of nutrient deficits and surpluses. If possible, export excess manure to nearby farms with nutrient needs.
Reducing nutrient loss is environmentally smart and economically sound. Implementing strategies to reduce nutrient loss will benefit water supplies and save on fertilizer expenses. Your local knowledge is vital. You know how water moves on your land, where nutrients might accumulate, and what strategies will work best in the context of your farm. By implementing one or more of these strategies, you can help reduce nutrient runoff and protect drinking water in your area. Maintaining the lowest input you can, to sustain crop yields, will help water quality.
Chen, G., Elliott, J., Lobb, D., Flaten, D., Braul, L., & Wilson, H. (2017). Changes in runoff chemistry and soil fertility after multiple years of cattle winter bale feeding on annual cropland on the Canadian prairies. Agriculture, Ecosystems & Environment, 240, 1.
Clark, K. & Beegle, D. (2014). Nutrient Management to Improve Nitrogen Use Efficiency and Reduce Environmental Losses. Penn State College of Agricultural Sciences research and extension programs.
Li, S., Elliott, J., Tiessen, K., Yarotski, J., Lobb, D., & Flaten, D. (2011). The Effects of Multiple Beneficial Management Practices on Hydrology and Nutrient Losses in a Small Watershed in the Canadian Prairies. Journal of Environmental Quality, 40(5), 1627-1642.
Liu, Jian, Kleinman, Peter, Aronsson, Helena, Flaten, Don, McDowell, Richard, Bechmann, Marianne, . . . Veith, Tamie. (2018). A review of regulations and guidelines related to winter manure application. Ambio, 47(6), 657-670.
Liu, J., Macrae, M., Elliott, J., Baulch, H., Wilson, H., & Kleinman, P. (2019). Impacts of Cover Crops and Crop Residues on Phosphorus Losses in Cold Climates: A Review. Journal of Environmental Quality, 48(4), 850-868.
Manitoba Agriculture Food, and Rural Initiatives (2020). Are we feeding too much phosphorus? https://www.manitoba.ca/agriculture/livestock/dairy/are-we-feeding-too-much-phosphorus.html
Shapley, A. & Beegle, D. (2001). Managing Phosphorus for Agriculture and the Environment. Penn State College of Agricultural Sciences research and extension programs.
Wilson, H., Elliott, J., Macrae, M., & Glenn, A. (2019). Near‐Surface Soils as a Source of Phosphorus in Snowmelt Runoff from Cropland. Journal of Environmental Quality, 48(4), 921-930.