Alfalfa Hay Production to Lower Soil Phosphorus Levels Caused by Animal Waste Application
Efforts to manage the nutrients contained in poultry waste have traditionally emphasized nitrogen (N) management in order to reduce or prevent nitrate contamination of groundwater. By basing waste applications on N alone, phosphorus (P) in the waste is applied at two to three times its recommended rate. As a result, excessively high concentrations of P are accumulating in many Georgia soils. Because of the abundance of concentrated poultry operations in Georgia, erosion and runoff from soils that have received high rates of P have the potential to threaten water resources.
Some researchers and extension agents have suggested that producers purchase and apply commercial N and harvest hay from fields with high P levels. The grass takes up the P which is removed from the site when the hay is harvested, thus lowering soil P content. While this is an environmentally sound practice, producers who have access to abundant supplies of poultry waste are reluctant to purchase N fertilizer. Alfalfa has been suggested as a solution to the problem.
Many fields with a history of animal waste application already have the high P and K levels that alfalfa requires. Fertility levels in many of these soils are so high that it should be possible to maintain high alfalfa yields for several years without inputs of K, and for many years without inputs of P.
In this project, the producer plans to grow alfalfa to help him remove excess P from soils. While other hay crops may remove slightly more P from the soil than alfalfa, few other crops offer the same degree of animal digestibility, drought tolerance and N-fixation in addition to high levels of P removal.