Careful manure management is vital to optimize returns from field applications. As well, improper use can result in over-application of nutrients, a growing concern to the sustainability of farmland.
Manure nutrients are valuable to feed crops and build soil organic matter. Manure contains essential plant nutrients, such as nitrogen, phosphorus and potassium, along with a variety of secondary and micronutrients.
Unlike commercial fertilizer, which has a guaranteed analysis, manure nutrients are variable based on the source, feeding management, collection and storage practices. The variability means that manure analysis is essential for effective nutrient application practices.
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Manure nitrogen is sometimes hard to estimate relative to fertilizer nitrogen. Almost half of the nitrogen in fresh manure is in the ammonium form, readily available to plants if properly managed.
In the case of swine manure, the plant-available nitrogen can be higher. The remaining, or organic nitrogen, is released based on microbial processes, with the help of warm soil temperature and water.
This provides a release of nitrogen over several years, a benefit that can be significant with manure that contains lots of straw. Remember that ammonia can be lost from manure when ammonium is converted to ammonia. Incorporation or injection into the soil is critical to capturing this nitrogen.
Phosphorus and potassium availability varies from 50 to 100 percent in the application year. There are few environmental concerns associated with excessive potassium in soils, but not for phosphorus.
Be aware that manure runoff and loss from fields, as well as treated soil, can pollute surface waters when high in phosphorus.
While many farmers focus on improving the use of manure to avoid high fertilizer costs, manure also helps improve soil organic matter, soil physical structure and water holding capacity.
Manure application is going to be scrutinized. Producers must ensure they are ready for an environmental audit. While manure will not replace commercial fertilizer, there are many acres that would benefit from its application.
