Thermodynamic Assessment of the Nutrient Status of Rubber-Growing Soils
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1969
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Abstract
Schofield s thermodynamic concepts of intensity and quantity were used for measuring the potassium and phosphorus status of Malayan rubber-growing soils. It was shown that for acid soils in Malaya, intensity and quantity measurements need be done using aluminium as the reference ion instead of calcium used elsewhere. For phosphorus, intensities were measured in dilute ammonium chloride solutions instead of calcium chloride solutions used elsewhere and quantities were measured by isotopic exchange. l These thermodynamic indices and the conventional indices of acid-extractable and exchange-. able values for potassium, and total and available indices for phosphate, which are in current routine use, were related to uptake by Pueraria phaseoloides in the glasshouse. This showed that for assessing the potassium status of Malayan soils, the buffer capacity value obtained from the slope of the quantity! intensity relationship curve was better than the conventional acid-extract-able and exchangeable values currently used for determining the fertiliser requirements of rubber. For phosphorus, both conventional and thermodynamic quantity indices related directly to glasshouse cropping. More work is however necessary for a systematic correlation.
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J. Rubb. Res. Ins. Malaya, 21(2), 240-249 (1969)