CLOMAZONE SORPTION IN SOIL - INCUBATION-TIME, TEMPERATURE, AND SOIL-MOISTURE EFFECTS

Sorption-desorption of the herbicide clomazone in a silty clay loam soil was evaluated for time, temperature, and moisture dependence. In unsaturated soil, clomazone sorption peaked at different times depending on incubation temperature. Soil moisture had little effect on clomazone sorption. The apparent K-d increased (2.4-fold at 5 degrees C and 4.1-fold at 35 degrees C) throughout the 84-day incubation period. Clomazone extractable with water in 15 min decreased with incubation time, while that recovered between 15 min and 24 h was essentially constant. Desorption kinetics were well characterized with a simple radial diffusion model by adjusting a single parameter (concentration of the labile pool). Batch equilibrium sorption isotherms (saturated soil) were temperature independent (5-35 degrees C). The data indicate that the time-dependent sorption of clomazone in unsaturated soil is controlled by a temperature-dependent process. Clomazone losses from solution explained much of the increase in apparent K-d over time.