REDOX STATUS, POULTRY LITTER, AND PHOSPHORUS SOLUBILITY IN ATLANTIC COASTAL-PLAIN SOILS

Artificially drained, agricultural soils in Delaware's Inland Bays wat ershed are high in P from poultry litter and fertilizer applications. The potential loss of P from these soils to drainage waters during soi l reduction and reoxidation was investigated. Soil from three artifici ally drained, cultivated fields and two wooded areas was collected and characterized as Fallsington sandy loam (fine-loamy, mixed, mesic Typ ic Ochraquult), Pocomoke loamy sand (coarse-loamy, siliceous, thermic Typic Umbraquult), and Osier loamy sand (siliceous, thermic Typic Psam maquent). Topsoils, unamended and amended with poultry litter (PL), an d subsoils were reduced for 28 d and reoxidized for 14 d at 25 and 35 degrees C. The soils were analyzed for pH, redox potential (Eh), solub le P and Fe2+, and P fractions (unoccluded Fe-P and AI-P, occluded Fe- P and AI-P, and Ca-P) under oxidized, reduced, and reoxidized conditio ns. Reduction decreased Eh to moderately reduced (200-350 mV) and redu ced (-100 to 100 mV) values, and increased pH (0.8 +/- 0.1) and solubl e Fe2+ (44 +/- 24 mg/kg). Reoxidation returned Eh, pH, and Fe2+ to nea r initial values, Reduction increased soluble P in unamended cultivate d topsoils (0.69 +/- 0.42 mg/kg), decreased soluble P in amended culti vated topsoils (1.42 +/- 1.31 mg/kg), but had little effect in subsoil s or wooded soils. Reoxidation decreased soluble P in cultivated topso ils, but increased soluble P in subsoils and wooded soils. Reduction i ncreased the extractability of all P fractions in cultivated topsoils (20 +/- 12 mg/kg), but increased only Ca-P extractability in subsoils and wooded soils (9 +/- 3 mg/kg), Reoxidation decreased the extractabi lity of these fractions to near initial values.