From the color to the smell, manure does not have the best reputation. However, it proves to be a powerful resource, and one that is abundant on dairy farms.
There are multiple benefits to using manure as a soil amendment, which builds organic matter and replenishes nutrients. Manure is a variable source of nutrients because it is a biological source. While the nutrients do not become plant available as predictably as a commercial fertilizer, it is a great supplement to get nitrogen, phosphorus, and potassium, along with micronutrients, to the field. In turn, this reduces the amount of commercial fertilizer needed and saves the farmer money. In addition to the macro- and micronutrients, manure helps build organic matter. By adding a material full of beneficial bacteria into the soil to break down, organic matter increases, thus positively impacting soil structure and water-holding capacity.
All nutrients in manure are not available to crops. This is affected by the physical manure characteristics such as animal type and diet, moisture content, and manure stability. Nutrient availability from manure is also affected by storage type and application timing. Manure has to be broken down which takes time, however, if the manure is applied too early the nutrients can be lost. Bacteria transform the nutrients into different forms that make them accessible to plants.
Manure application methods vary depending on moisture content and available equipment. More often in the west than the east of the US, a dairy will have their lagoon hooked up to a pivot to apply effluent. Effluent, which is liquid manure, can be applied and used as a source of irrigation water for the field. Using a pivot, they can apply manure in-season. Using equipment, you can broadcast or incorporate manure. There are benefits of incorporating manure like less nitrogen volatilization and less phosphorus loss through erosion. Incorporation can be done using a specific type of machinery to apply or by running a tillage implement through the field following application. One of the biggest factors that dictates which fields receive manure is distance from the facility. Transporting and hauling manure is a challenge at many farms.
Each farm follows their state’s version of a manure management plan, which includes a detailed plan on storage and manure handling to reduce negative environmental impact. It determines the appropriate application amount for specific fields and crop types. Using soil tests and yield, the plan ensures the farm is not overapplying manure. It also mentions any resource concerns and avoiding application near waterways.
It is important to apply agronomically with guidance from a manure management plan and other resources. If excess nutrients are applied through manure, there is going to be a loss, similar to a commercial fertilizer. Using soil tests and applying in conjunction with commercial fertilizer allows manure to provide the most value and reduce risk of losing yield or nutrients. Overall manure is part of the sustainable feedback loop on a livestock farm. The livestock consume the crops that are grown, the livestock produces manure, and the manure provides nutrients to the growing crop. From trash to treasure, manure does not have to be a waste stream.
Sawyer, J.E. and Mallarino, A.P. 2016. Using manure nutrients for crop production. PMR 1003. Iowa State University.
University of Minnesota Extension. 2018. Manure Management.