Agricultural Phosphorus and Eutrophication

Inputs of phosphorus (P) are essential for profitable crop and animal agriculture. However, P export in watershed runoff can accelerate the eutrophication of receiving fresh waters. The rapid growth and intensification of crop and animal farming in many areas has created regional imbalances in P inputs in feed and fertilizer and P output in farm produce. In many of these areas, soil P has built up to levels in excess of crop needs and now has the potential to enrich surface runoff with P. The overall goal of efforts to reduce P losses from agriculture to water should be to increase P use efficiency, balance P inputs in feed and fertilizer into a watershed with P output in crop and animal produce, and manage the level of P in the soil. Reducing P loss in agricultural runoff may be brought about by source and transport control strategies. This includes refining feed rations, using feed additives to increase P absorption by animals, moving manure from surplus to deficit areas, finding alternative uses for manure, and targeting conservation practices, such as reduced tillage, buffer strips, and cover crops, to critical areas of P export from a watershed. In these critical areas high P soils coincide with parts of the landscape where surface runoff and erosion potential are high.