PHOSPHATE ADSORPTION CHARACTERISTICS OF SOME MALAYSIAN SOILS II. RELATIONSHIPS WITH OTHER SOIL PROPERTIES

ABDUL RASHID AHMAD AND HUGH L. FOSTER

SUMMARY

An attempt was made to relate phosphate adsorption capacities, quantified by the adsorption parameters, estimated from Freundlich and Langmuir equations, to other soil properties. The adsorption parameters used are the Freundlich adsorption coefficient (F-a) and the Maximum Buffer Caoacitv (MBC) . From simple correlation analysis, the level of free iron oxides and organic matter and the size of the silt + clay fraction were found to be significantly related to P-adsorption. Partial correlation analysis indicated that pH and silt + clay % played the most important role in P - adsorption. The soils under study may be divided into two groups of P - adsorption capacity depending on the site + clay content being lower or greater than the critical value of 45%. On further examination of the effect of pH it was found that the interplay of redox potential and pH, determined the formation of free iron oxide in soils. Free iron oxide in turn dictated the process of phosphate adsorption. Equations relating the two adsorption parameters to pH, pe + pH and silt + clay % of a soil were formulated. A simple method of estimating P - adsorption capacity was suggested.

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