SURFACE ACTIVITY OF INORGANIC SOIL PHOSPHORUS

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Abstract
Seven soil samples, including latosols and alluvial soils of a wide pH range, were used to investigate the surface aluminum, iron, and calcium phosphate, and their specific surface activities by the techniques of phosphorus fractionation and solid-solution phosphorus equilibration with P32. Surface aluminum and iron phosphates of these soils were found to be much greater than surface calcium phosphate. The specific surface activity of these phosphate species follows the decreasing order of aluminum phosphate, iron phosphate, and calcium phosphate discretely. In the calcareous soils, although the total amount of calcium phosphate is very large, its specific activity is extremely low. In the latosol, the specific surface activity of calcium phosphate is relatively high, although the total amount is small. The phenomena is explained by the distribution of the various inorganic phosphate species in the different particle separates of soils. Aluminum and iron phosphates are more concentrating in the clay, while calcium phosphate is more concentrating in the sand and silt, particularly in the less-weathered calcareous alluvial soils. The pedogenetical significance of particle size, functions of weathering sequence, and the agronomical significance of phosphorus availability to plants are mentioned.
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