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 wellstructured 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.