Manure Phosphorus: Mobility in Soils and Management Strategies to Minimize Losses

Manure is a valuable source of plant nutrients; however, continuous application to soils may lead to accumulation of phosphorus (P), increasing the risk of P loss into waterways triggering freshwater eutrophication. This review paper summarizes and critically evaluates relevant research findings published within the last 5 years on manure P mobility in soils and management strategies to mitigate losses identifying future research needs. Past and recent research evidence on manure P mobilization and losses from soils have yielded inconsistent and often confounding results, because of the interactive effects of source factors and the existence of concurrent transport pathways. Although far from being conclusive, a few general trends are worth noting; P losses were greater with (a) increasing soluble P applied with manure, (b) vulnerable soils with limited P sorption capacity and/or susceptible to preferential flow/erosion, (c) conditions conducive to P release and transport, and (d) reduced soil-manure P interaction following application. Effective mitigating strategies included (a) generating low-P manure, (b) processing manure to reduce total and/or soluble P, and (c) adopting best management practices (BMPs) during and post-manure application. Future research should focus on a better understanding of the interactive effects of source factors on short- and long-term manure P loss via different transport pathways. Existing mitigation efforts and new directions should focus on reducing P buildup in soil by employing a combination of strategies during generation, processing, and application of manure, coupled with site- and time-specific BMPs selected based on the dominant pathway of P loss.