Adsorption of Diuron and 2,4,5‐T on Soil Particle‐Size Separates

Abstract

Abstract Equilibrium isotherms for the adsorption of herbicides, diuron, and 2,4,5‐T on whole soil and various‐size separates of Webster soil (Typic Haplaquolls) were measured. The Freundlich adsorption coefficient, K , for diuron varied by a factor of about 7 among the different particle‐size fractions. However, the sorption coefficient, K , normalized with respect to soil organic carbon (OC) content, denoted as K oc = ( K /OC), varied only within a factor of 1.5. For 2,4,5‐T herbicide, the K oc values for the silt and clay‐size fractions, as well as the whole soil, were essentially identical and about 3 times larger than that for the sand‐size fraction. The results suggested that the soil particle‐size separates may be grouped into two size classes: “fine” (≤ 50 µ m) and “coarse” (2,000‐50 µ m). For a given pesticide, a specific K oc value may be assigned to each class.