The Challenges of Managing Legacy Phosphorus Losses from Manure-Impacted Agricultural Soils

Historical application of manure to agricultural land in areas of intensive animal production, like the Delmarva Peninsula, has led to soil test phosphorus (STP) concentrations that far exceed agronomic optimum. While natural soils would typically serve as a sink for newly applied P sources, soils with P accumulation from long-term manure applications often serve as a source of P via a gradual release of dissolved P in runoff or leaching events. These losses of “legacy P” from manure-impacted soils are difficult to control and are linked to water-quality degradation in sensitive water bodies, like the Chesapeake Bay. In this review, we examine how long-term application of manure impacts soil P dynamics under P-buildup and -drawdown scenarios to better understand the behavior of legacy P in soils. We also examine the reasons that traditional best management practices (BMPs) fail to control legacy P losses from soils and discuss potential promising management strategies using the Delmarva Peninsula as a case study.