ADSORPTION AND DESORPTION OF GLYPHOSATE IN SOME EUROPEAN SOILS

The interaction of glyphosate [N-(phosphonomethyl)glycine] with four typical European soils is reported. Results of adsorption and desorption isotherms show that the interaction of glyphosate with these soils was mainly related to content of iron and aluminium amorphus hydroxides. Moreover, it was found that the presence of divalent cations in 2:1 clay minerals also contribute to glyphosate adsorption. The S-type form of the adsorption isotherms revealed the existence of two different binding sites. These were exchangeable cations at low herbicide concentration and Fe and Al at higher glyphosate concentrations. The K maximum values of adsorption provided by the linear form of the Langmuir equation were found to be more consistent with soil parameters than those calculated by the Freundlich equation. The order of desorption from the soils was the reverse of that found for adsorption. Moreover, desorptionvaried from around 15 to 80 % of the adsorbed herbicide according to the soil characteristics. This indicated that glyphosate adsorption on soils is far from being permanent and leaching to lower soil horizons with limited biological activity may occur.