Adsorption of Metoxuron on Soil Particle Size Separates of four Alfisols and Four Vertisols from Hyderabad

Adsorption of metoxuron [3-(3-chloro-4 methoxy phenyl)-l, 1-dimethyl urea) was studied on soil particle separates of four Alfisols and four Vertisols. The isotherms were parabolic with S-shaped curvature confined to initial stages of adsorption. Data fitted to Freundlich's equation; constants ‘K_F’ and ‘n’, distribution coefficients ‘K_d’ and ‘K_OC’ increased with decreasing particle size. Amount of herbicide adsorbed per unit weight of organic carbon (a_oc) was plotted against respective equilibrium concentrations for all fractions, a single coalesced isotherm was obtained for which K_oc and n were worked out. The K_oc and n values were closer to K_oe and n values of individual fractions suggesting that organic matter of soil particle size separates is primarily responsible for adsorption of metoxuron. Similar values of K_oc of individual soil size separates and K_oc of coalesced isotherm suggest that the adsorption capacity of different soil particle size separates can be estimated from the organic carbon content and K_oc determined for a single or limited number of separates.