Clomazone dissipation in four Tasmanian topsoils

Clomazone dissipation was examined in four soils in field experiments. Field half-lives were 6 to 59 d (average of four field sites was 35 d) for ferrosol (clay loam), kurosol (loamy sand), sodosol (silt loam), and vertosol (light clay). The Hoerl equation provided a better fit to the measured field concentration at all four sites than did a first-order equation. The order of clomazone dissipation rate was ferrosol > sodosol > kurosol > vertosol. Clomazone desorption varied with soil type, with apparent Kd values of 3.6, 1.7, 1.8, and 2.4 for ferrosol, sodosol, kurosol, and vertosol, respectively. Clomazone residues became more strongly sorbed with time, as indicated by desorption hysteresis, but detectable concentrations were present in all soils 1 yr after application. The data indicate that the potential for carryover injury to crops is greatest in the kurosol and least in the ferrosol.