Phosphorus Leaching from Agricultural Soils of the Delmarva Peninsula, USA

Leaching of phosphorus (P) mobilizes edaphic and applied sources of P and is a primary pathway of concern in agricultural soils of the Delmarva Peninsula, which defines the eastern boundary of the eutrophic Chesapeake Bay. We evaluated P leaching before and after poultry litter application from intact soil columns (30 cm diameter × 50 cm depth) obtained from low‐ and high‐P members of four dominant Delmarva Peninsula soils. Surface soil textures ranged from fine sand to silt loam, and Mehlich‐3 soil P ranged from 64 to 628 mg kg−1. Irrigation of soil columns before litter application pointed to surface soil P controls on dissolved P in leachate (with soil P sorption saturation providing a stronger relationship than Mehlich‐3 P); however, strong relationships between P in the subsoil (45–50 cm) and leachate P concentrations were also observed (r2 = 0.61–0.73). After poultry litter application (4.5 Mg ha−1), leachate P concentrations and loads increased significantly for the finest‐textured soils, consistent with observations that well‐structured soils have the greatest propensity to transmit applied P. Phosphorus derived from poultry litter appeared to contribute 41 and 76% of total P loss in leachate from the two soils with the finest textures. Results point to soil P, including P sorption saturation, as a sound metric of P loss potential in leachate when manure is not an acute source of P but highlight the need to factor in macropore transport potential to predict leaching losses from applied P sources.