Manure Management Considerations to Reduce Environmental Risks
Jordan Johnson, MSc, AAg, Agri-Environmental Specialist, Swift Current
When applied in an environmentally conscious manner, manure offers a valuable source of nutrients and contributes to improved soil structure for cropland and pastures. However, when managed improperly, manure can function as a pollutant to surface and ground water sources. With increasing costs and tight supply, the economic benefit of using manure as a fertilizer source for cropland and pastures may be a solution for some, but there are several important considerations to minimize the risk for runoff and water contamination.
Ensuring Appropriate Application
Soil and manure testing can help producers ensure that quantity of nutrients applied meets the crops requirements. Due to the high phosphorus to nitrogen ratio of manure, applying manure to meet nitrogen needs of a crop often results in over application of phosphorus. Using a calibrated spreader or injector helps apply manure as consistently as possible and reduces the risk of over application. If soils are over saturated with nutrients, risk of runoff or leaching into waterbodies is increased. Entry of excess nutrients into waterbodies contributes to the rapid growth of algal blooms through a process called eutrophication. When this occurs, the oxygen levels of water are reduced, lowering water quality and compromising the health of aquatic species.
Application timing can have a critical impact on nutrient retention. While spring application may be ideal to maximize nutrient uptake, it is not always achievable. Avoid applying manure to frozen or snow-covered ground to reduce risk of runoff and water contamination in the spring. Manure should be applied in late-summer or early-fall to allow adequate time for nutrients to infiltrate the soil and stabilize. Direct injection of manure or incorporation into the soil can reduce the amount of nitrogen lost to volatilization, reduce odours and minimize risk of nutrients being lost in runoff.
Manure Treatment Matters
Manure treatment refers to methods of storing or handling manure that reduce moisture content and volume, creating a more concentrated product. Manure treatment methods such as composting, stockpiling or drying manure result in a product that is more economical to transport than fresh or liquid manure. Composting before application can stabilize the nutrient profile, resulting in slower release of carbon and nitrogen and less gaseous losses after application. While manure compost piles can often achieve temperatures of up to 70 C, composting to 55 C sanitizes the manure by killing biological pathogens and weed seeds.
The Importance of Site Selection
To reduce the risk of water contamination, producers should take special care when selecting sites for application or storage of manure. Storage sites should have minimal slope to avoid risk of runoff; using dikes, diversion ditches or containment ponds may be necessary. When applying manure, use appropriate setback distances from waterbodies to minimize runoff to nearby water sources, this may be 30 meters or more depending on the slope of the land. Maintaining healthy riparian areas around waterbodies increases the filtration of nutrients and sediment in runoff before reaching waterbodies. Considering the soil structure of sites will allow producers to assess the risk of groundwater contamination. Coarsely textured soils such as sandier soils will have increased risk of nutrients leaching into subsurface water sources over finely-textured soils such as clay soils.
For more information on how to reduce the environmental risks associated with the use of manure on your operation, get in touch with your local agri-environmental specialist by calling your regional office or the Agriculture Knowledge Centre at 1-866-457-2377.