SORPTION OF TERBUTHYLAZINE AND ATRAZINE IN RELATION TO THE PHYSICOCHEMICAL PROPERTIES OF 3 SOILS

The adsorption and desorption of the herbicides atrazine and terbuthylazine in loamy clay, calcareous clay an high clay soils were studied using a batch equilibration method. The main differences between soils were the clay content, 31.7%, 51.3% and 62.5% for the loamy clay, the calcareous clay and the high clay soils, respectively, and the organic carbon content, 1.11%, 1.50% and 1.08%, respectively. Adsorption and desorption isotherms were well described by the Freundlich equation. Terbuthylazine was more adsorbed (Freundlich K(f) coefficient ranged from 1.88 to 2.33) than atrazine (K(f) ranged from 0.96 to 1.22) by the three soils. The desorption studies showed that the bondings between terbuthylazine and soil were less reversible than those of atrazine. The adsorption of these triazines was not related to clay or organic carbon contents, but to the degree of humification of the organic matter.