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

Artificially drained, agricultural soils that are high in P and have season ally fluctuating water tables may be significant nonpoint sources of P to D elaware's Inland Bays. Topsoil, unamended and amended with 4 g kg(-1) poult ry 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. so n pH and redox potential (Eh) were measured (mV) and P sorption isotherms w ere constructed for each horizon under oxidized, flooded, and drained condi tions. For each isotherm, P sorption maxima (b(max)), P sorbed at a solutio n P concentration of 1.0 mg L-1 (b(1.0)), and the equilibrium P concentrati on at zero sorption (EPC0) were calculated. Flooding decreased Eh and incre ased pH, and draining returned Eh and pH to near initial values. Flooding a nd 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 uname nded Pocomoke A horizon, but decreased EPC0 in the same PL-amended horizon. Draining reduced EPC0 values in both Pocomoke A horizons. Flooding and dra ining had little effect on EPC0 in other horizons. Our data suggest that la nd application of PL and fluctuating water tables may increase the potentia l for P loss from soils through both a decrease in soil P sorption rapacity and an increase in solution P concentrations in topsoils.