CHARGE DISTRIBUTION AND THE CATION EXCHANGE CAPACITY OF AN IRON‐RICH KAOLINITIC SOIL

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Summary: The positive charge on an iron‐rich kaolinitic soil was found to increase from 11.1 to 14.2 me per 100 g as a result of lowering the pH from 8.5 to 3.0 in M NH 4 Cl solution and the negative charge decreased from 22.2 to 14.1. In 0.002M NH 4 C1 the positive charge increased from 0 to 0.3 and the negative charge decreased from 5.6 to 3.2. The variations in charge can be explained by the presence of 3 me per 100 g of permanent negative charge, pH dependent positive and negative charge influenced by the indifferent electrolyte concentration, and the overlap of diffuse layers causing a neutralization of charge. The ability of this soil to hold cations under field conditions is overestimated by m ammonium acetate at pH 7. Instead, a solution approximating to the pH, composition, and concentration of the soil solution should be used.

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