Soil organic phosphorus

Abstract

The extraction and resin fractionation procedures for determination of amounts and kinds of soil organic phosphorus (Pt IV of this series) were applied to a sequence of four soils having common parent material and vegetation but varying in altitude, rainfall, and temperature. Three different zonal soil groups were represented in the sequence: the brown-grey earths, yellow-grey earths, and high country yellow-brown earths. For each soil type, samples of the topsoil and of three individual horizons (A, AB, and B) were examined. The amount of organic phosphorus extracted and its occurrence in different fractions were similar for comparable samples from each soil type, suggesting that the amount and nature of soil organic phosphorus are determined primarily by parent material and biological factors. The kinds of organic phosphorus compound present in different horizons of each soil were clearly differentiated. Humic acid-associated organic phosphorus and inositol phosphates were present in comparable amounts in topsoil samples, but only inositol phosphates were detected in quantity in the B horizon samples. There was also a marked narrowing of organic C/organic P ratios down the soil profile.