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This article in SSSAJ

  1. Vol. 57 No. 4, p. 937-945
     
    Received: May 9, 1991
    Published: July, 1993


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doi:10.2136/sssaj1993.03615995005700040011x

Phosphate Sorption-Desorption Behavior of Some Acidic Soils of South and Southeast Asia

  1. S. K. Sanyal,
  2. P. Y. Chan and
  3. S. K. De Datta 
  1. Agronomy, Physiology, and Agroecology Division, IRRI, P.O. Box 933, Manila, Philippines
    Crop and Soil Environmental Sciences, Office of International Research and Development, 1060 Litton Reaves Hall, Virginia Polytechnic Institute and State Univ., Blacksburg, VA 24060-0334

Abstract

Abstract

The equilibrium phosphate sorption and release behavior and the kinetics of adsorption were studied in some acidic soils of South and Southeast Asia. Phosphate sorption data at 25 °C were fitted to the Tempkin, Freundlich, and Langmuir adsorption isotherms. The soils varied widely in their capacity to sorh and retain P. During desorption, the amount of sorbed P at a given equilibrium P concentration was always higher than that during sorption, indicating low desorbability of the sorbed P. The kinetic P sorption data at 21 and 35 °C were fitted to a modified Freundlich type of kinetic equation to obtain a parameter related to the sorption rate coefficient. The effect of temperature on the kinetics of sorption was small, suggesting the process is diffusion controlled. Equilihrium and kinetic P sorption parameters were found to he closely correlated with clay and organic matter contents and surface area of soils. A negative correlation between specific P sorption by clay or organic matter and clay or organic matter content of the soils suggests an association between the two colloidal components of the soils, causing loss of effective P-sorhing surface area. An attempt was further made to evaluate the differential change in free energy of P sorption at infinite dilution from the corresponding thermodynamic equilibrium constant for P sorption by the given soils. The results suggest that the stability of the P sorption reaction products in the given soils contribute to the P-fixing characteristics of these soils.

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