Influence of organic matter and phosphate content on the point of zero charge of variable charge components in oxidic soils

Abstract

The point of zero charge of the variable charge components (pH,) of oxidic soils formed on basaltic parent material in humid tropical Queensland has been measured on samples from virgin rainforest and cultivated fertilized fields. The average amount of free iron in these soils is about 10%. Soils with low organic matter content and low extractable phosphorus have high pH, values. Regression analysis showed pH, to be reduced by about one pH unit for each 1% increase in organic carbon or for each 100 µg/g increase in extractable phosphorus. Implications with respect to cation and anion exchange capacities are briefly discussed.