Abstract

                                Effect of temperature, organic matter and pH on adsorption of dimethoate by clays and soils were investigated. Adsorption of dimethoate decreased as temperature increa- sed on both Ca-montmorillonite and Ca-Kaolinite. Among clays Ca-Montmorillonita was superior over Ca-Kaolinite. The values of change in free energies (AG) indicated that Vander Waal's forces were prominent in adsorption. Adsorption of dimethoate was highest in activated soil and least in soils where organic matter was removed by H,O, pre-treatment. Differences in K values of various treatments suggest that organic matter played a dominant role in the adsorbent of this insecticide. Adsorption of dimethoate was a function of pH and it was highest in all soils when pH was 5,0 and it was lowest when pH of soil was 8.6. It is postulated that adsorption was by physical means when pH remained 7 and above and by protonation and ion-exchange under acidic soil environment.

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