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Published in Soil Sci Soc Am J 42:570-574 (1978)
© 1978 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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Phosphate Desorption from Kaolinite Suspensions1

B. Bar-Yosef and U. Kafkafi2

ABSTRACT

Phosphate desorption from soil minerals is one of the factors which determine the rate of P uptake by plants. Under laboratory conditions desorption is usually obtained by drastic dilution or leaching of the clay, thus inducing its dissolution. The objective of this work was to study the effect of the desorption method used, equilibration time and the dissolved silica on the desorption of P from kaolinite. Two desorption methods were used: (i) diluting 1% suspensions by various volumes of the same electrolyte, and (ii) immersing a dialysis tube containing 0.25% suspension (+P) in an identical suspension initially free of P. The desorption process in both cases could be divided into a rapid and a slow first-order reaction. The rapid reaction rate constant was similar in both systems (about 4.65 x 10–3hours–1 at 25°C). The slow reaction constants were 0.3 x 10–3hours–1 and 1.15 x 10–3hours–1 for cases (i) and (ii), respectively. The activation energy of the desorption process in case (ii) was 16.2 Kcal/mole for the rapid and 4.8 Kcal/mole for the slow reaction. The amount of silica dissolved from kaolinite due to dilution with 0.01M KCl depended on the dilution ratio and reached 16 mg SiO2/g kaolinite when the suspension was diluted 100-fold. Readsorption of part of the dissolved silica is stipulated to contribute to the fast P desorption process.

NOTES

1 Contribution from the Agric. Res. Organ., The Volcani Center, Bet Dagan, Israel. 1976 series, no. 273-E.

2 Division of Soil Chemistry and Plant Nutrition, ARO, The Volcani Center, Bet Dagan, Israel.

Received for publication April 4, 1977. Accepted for publication March 22, 1978.






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Journal of Natural Resources
and Life Sciences Education		 Vadose Zone Journal
Journal of Plant Registrations Journal of
Environmental Quality		 The Plant Genome
Copyright © 1978 by the Soil Science Society of America.