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

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Abstract
The point of zero charge of the variable charge components (pH0) of oxidic soils formed on basaltic parent material in humid tropical Queensland [Australia] 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 phosphrus have high pH0 values. Regression analysis showed pH0 to be reduced by about one pH unit for each 1% increase in organic carbon or for each 100 .mu.g/g increase in extractable phosphorus. Implications with respect to cation and anion exchange capacities are briefly discussed.