Phosphorus availability in soils subjected to short periods of flooding and drying

Abstract

The effects of flooding and drying on the availability of original soil phosphorus, phosphorus added before flooding and phosphorus added after drying were studied. In four soils high in organic carbon and reducible iron, 2 or more days of flooding (at 25°C) caused the immobilization of phosphorus added after drying. Four or more days of flooding caused immobilization of original soil phosphorus. Phosphorus applied before the flooding period was immobilized to a greater degree than phosphorus applied after drying in a soil rich in organic carbon and reducible iron. In a soil low in these, phosphorus applied before flooding was immobilized, but phosphorus applied after drying was not. Changes in soil extractable iron and phosphorus, and in phosphorus sorption index, caused by flooding and drying, were consistent with immobilization of phosphorus added after flooding by a surface reaction, and the immobilization of phosphorus present during flooding by occlusion of phosphorus with iron(III) hydrous oxide, or by formation of iron(III) phosphate.