Singh, M.M.Talibudeen, O.2014-09-032014-09-031971Proceedings of the International Symposium on Soil Fertility Evaluation, New Delhi, Vol.1 1971http://hdl.handle.net/123456789/5310A thermodynamic treatment of cation exchange equilibria was used to interpret K.-AI exchange equilibria in 0.01N chloride solutions for 9 common acid soils of Malaya. In 7 of the 9 soils, K. was adsorbed more strongly than Al while for the remaining 2, the reverse was the case. The standard free energy for formation of K-soil from Al-soil varied from —2550 to 900 calories!mole. In all soils, the activity coefficient of the adsorbed K ions, fK , first increased and then decreased with decreasing K-satura-tion, while fAit the activity coefficient of the adsorbed Al ions, decreased continuously with decreasing Al-saturation. Between soils, changes in J'K with K saturation varied much more than changes in /A1. Excess free energy functions for.. AI-+K. exchange calculated from ( fK,fAl ) values for the soils showed distinct differences between all soils. For soils containing micaceous minerals, these differences in the surface chemistry of the soils were related to the release of initially non-exchangeable potassium in the soil to Pueraria phaseoloides in glass-house experiments.enArticle