The adsorption of atrazine and alachlor was studied on samples of three horizons from soils with different textures and organic carbon contents. Soils were equilibrated with five concentrations of atrazine and alachlor using batch techniques. Adsorption affinity for atrazine and alachlor was approximated by the Freundlich constant (Kf), distribution coefficient (Kd), and the normalized Kd based on organic carbon (Koc). Adsorption was not significantly correlated with soil depth, clay content, or organic carbon. Atrazine adsorption was a linear function of equilibrium concentration for nearly all soil horizons but was nonlinear in most horizons for alachlor. The extent of atrazine adsorption was greater in all horizons of the fine-textured soils (Kd = 1.5 to 5.5) compared to coarse-textured soils (Kd = 0.40 to 0.87). The same general trends with texture were not apparent for alachlor. Conversion of Kd to Koc failed to reduce the variability in the linear adsorption coefficient for atrazine and alachlor in the different soils of this study.
