Phosphorus sorption in manured Atlantic coastal plain soils under flooded and drained conditions

Artificially drained, agricultural soils that are high in P and have seasonally fluctuating water tables may be significant nonpoint sources of P to Delaware's Inland Bays. Topsoil, unamended and amended with 4 g kg(-1) poultry litter (PL), and subsoil horizons from two soil series in the Inland Bag's watershed were flooded for 28 d and drained for 14 d at 25 degrees C. son pH and redox potential (Eh) were measured (mV) and P sorption isotherms were constructed for each horizon under oxidized, flooded, and drained conditions. For each isotherm, P sorption maxima (b(max)), P sorbed at a solution P concentration of 1.0 mg L-1 (b(1.0)), and the equilibrium P concentration at zero sorption (EPC0) were calculated. Flooding decreased Eh and increased pH, and draining returned Eh and pH to near initial values. Flooding and draining decreased b(max) in ail horizons. The b(1.0) values were always significantly less than b(max) values; however, flooding and draining had inconsistent effects on b(1.0) values. Flooding increased EPC0 in the unamended Pocomoke A horizon, but decreased EPC0 in the same PL-amended horizon. Draining reduced EPC0 values in both Pocomoke A horizons. Flooding and draining had little effect on EPC0 in other horizons. Our data suggest that land application of PL and fluctuating water tables may increase the potential for P loss from soils through both a decrease in soil P sorption rapacity and an increase in solution P concentrations in topsoils.