Traditionally, it has been thought that phosphorus applied to soil for crop production would remain in place with little movement by water solubility. Fertilizer was generally incorporated into the soil during land preparation for crop production. The use of animal waste from CAFOs as a nutrient source for crop and forage production presents new problems. Much of the forage production consists of perennial species requiring that waste application be largely limited to the soil surface without soil incorporation. Animal waste applications may reduce the sorption capacity of soils because of the humic acid residual of the organic matter.
Animal waste provides significantly more phosphorus than nitrogen relative to plant requirement.
Therefore, waste application based upon nitrogen requirement results in excess phosphorus application. For many years rates of animal waste application have been based upon nitrogen content of the waste or upon the need for disposal without regard to nutrient content. While animal waste is a plant nutrient source, its nutrient concentration is relatively low and transportation cost per unit of nitrogen or phosphorus is high relative to commercial fertilizer. High transportation cost, convenience of application, lack of regulation, and ignorance of the potential for problems has resulted in high soil phosphorus levels in many areas that have received large applications of animal waste. High levels of soil phosphorus have recently been related to elevated amounts of phosphorus in runoff water from these soils.