Fate of the herbicide clomazone in soil

Laboratory studies were conducted to gain information about the environmental properties of the soil-applied herbicide clomazone. The effects of soil microbial activity, temperature, and moisture on clomazone fate were determined following ($\sp{14}$C) clomazone application to the surface of a Flanagan silty clay loam. Degradation of clomazone was a biologically-dependent process. Following incubation for 84 days at 5 to 35$\sp\circ$C or 100 to 1500 kPa soil water tension, 59% or more of applied clomazone was extracted from soil as parent clomazone. The rate of clomazone dissipation was slower than predicted by a first-order kinetic model. Clomazone mineralization and volatilization were affected more by temperature than by soil moisture. A single detectable metabolite, which appeared rapidly after application but did not accumulate to more than 5% of applied clomazone, was most persistent under the coldest or driest soil conditions tested. Metabolite formation apparently involved cleavage of the isoxazolidinone ring of clomazone and conversion of the carbonyl carbon to CO$\sb2$.Under saturated batch conditions, clomazone sorption was described by a nonlinear, temperature-independent isotherm for the Flanagan soil. In unsaturated soil, clomazone did not reach sorption equilibrium within 84 days, as its apparent distribution coefficient (K$\sb{\rm d})$ increased up to four fold during this period. Higher incubation temperatures caused greater increases in apparent K$\sb{\rm d}$ over time, but soil moisture had minimal effect. Non-equilibrium sorption of clomazone may lead to decreased biodegradation and reduced off-site movement of clomazone over time.After 22 days of unsaturated flow in intact soil cores, clomazone movement in Cisne silt loam and Drummer silty clay loam was minimal; however, clomazone moved throughout Plainfield sand cores and was detected in the leachate. In Plainfield cores, clomazone was less mobile than atrazine. Starch-encapsulated herbicide formulations greatly reduced atrazine movement but had little effect on clomazone movement. Starch- and starch/clay-based granular formulations reduced clomazone volatilization. Clomazone volatilization was not affected by soil moisture between 33 and 1500 kPa water tension. Clomazone volatilization from both liquid and granular formulations increased following soil saturation. Volatilization was reduced more by large (14-20 mesh) granules than by small (20-30 mesh) granules. As granule size decreased, the rate of clomazone release upon granule wetting increased due to the greater surface area per unit mass.U of I OnlyETDs are only available to UIUC Users without author permissio