Phosphate sorption characteristics of soils of the north Queensland coastal region

Abstract

Phosphate-sorption curves covering the range of supernatant P concentration, 0-1 µg nil-1, have been determined for a number of agriculturally important soils in the high rainfall (2000-4000 mm) region of tropical Queensland. Where possible, soil samples were taken from both virgin and cultivated sites within a soil series. The soils occur on four major parent materials, namely basaltic, granitic and metamorphic rocks, and on alluvium derived from one or more of these rocks. The shapes of the P-sorption curves and the differences in magnitude of P sorption were related to the mineralogical composition of the clay fraction which, in turn, was determined by parent material. Past applications of phosphatic fertilizer have lessened soil P-sorption capacity, despite a reduction in soil organic matter resulting from clearing and cultivation.