STRATEGIES TO REDUCE NUTRIENT LOSSES FROM LAND APPLIED ANIMAL MANURE

Nitrogen (N) and phosphorus (P) losses in runoff from fields fertilized with animal manure contribute to eutrophication of U.S. surface waters. In lakes and reservoirs, P loss from manure applications is often more detrimental to water quality than N loss, since algal growth in most of these water bodies are P limited. There are several ways animal producers can reduce nutrient losses from manure applications, including: (1) dietary modification; (2) manure amendments; (3) physical treatment of fields to which manure is applied; (4) using buffer strips or setbacks; and (5) applying manure according to a P index. Producers can reduce the levels of P fed to animals by increasing the bioavailability of P in the feed. This can be accomplished by using high available P varieties of grains or enzymes, such as phytase. Researchers have found mixed results for P reductions in runoff with this practice, as published reports have shown reductions in P losses as much as 50% or increases as great as 100% when comparing phytase to commercial diets. Amendments containing aluminum, iron, calcium or magnesium can be used to precipitate P in manures. Manure amendments have been shown to reduce P losses in runoff by as much as 90%. Other research has identified methods such as incorporation of manures in the soil or using a pasture renovator to maximize manure/soil contact or improve infiltration or rainwater. Buffer strips and setbacks are areas between fields and waterbodies, where manure is not applied in order to reduce the direct impact of manure application. Recently, nearly all states have adopted a P index, which accounts for the inherent P levels in soils, the P in manures, and the cropping systems used. The P index then calculates whether manure should be applied at a rate for N uptake by the crop, P uptake for the crop, or no manure application should be made. Although improvements still need to be made, these practices are being used by responsible animal producers to minimize the risk of nutrient losses to surface waters.