Forms of Newly Fixed Phosphorus in Three Acid Sandy Soils

Abstract Soils were extracted successively with 1 N NH 4 Cl, 0.5 N NH 4 F, 0.1 N NaOH and 0.5 N H 2 SO 4 solutions to represent water‐soluble, aluminum, iron and calcium phosphates, respectively. Over 80% of the added phosphorus was retained by the soils as aluminum and iron phosphates. Less than 10% was in the water‐soluble and calcium phosphate forms. The balance not accounted for may have been in forms other than those mentioned. The ratio of aluminum phosphates to iron phosphates increased with the rates of applied phosphorus for the three soils. This was more evident for Red Bay fine sandy loam and Norfolk loamy fine sand than Leon fine sand. Increasing soil drying temperature decreased the percentage of phosphorus in the aluminum phosphate form, but increased that in the iron phosphate form. The prolonged alternate wetting and drying reduced the percentage of phosphorus in aluminum form in Red Bay fine sandy loam and Norfolk loamy fine sand, and increased the percentage distribution in iron form in Red Bay fine sandy loam and Leon fine sand.