CLOMAZONE FATE IN SOIL AS AFFECTED BY MICROBIAL ACTIVITY, TEMPERATURE, AND SOIL-MOISTURE

Laboratory studies were conducted to investigate the fate of the herbicide clomazone [2-[(2-chlorophenyl)methyl]-4,4-dimethyl-3-isoxazolidinone] in soil. Effects of soil microbial activity, incubation temperature, and soil moisture on clomazone fate were determined up to 84 days following surface application of [C-14]clomazone uniformly labeled in aromatic rings ([AR-C-14]clomazone) to a Flanagan silty clay loam soil. On the basis of a comparison of clomazone fate in sterilized soil and reinoculated soil, clomazone degradation was biologically dependent. The greatest clomazone mineralization rate occurred at a lower temperature than did the greatest microbial respiration rate; respiration and clomazone mineralization increased with increasing soil moisture content. Clomazone volatilization increased with increasing temperature but was not significantly affected by soil moisture treatment. In all studies, 59% or more of applied clomazone was extracted from soil as parent clomazone 84 days after application. Unextractable radioactivity accounted for 12% or less of that applied. A single detectable metabolite, persistent only under conditions of low temperature or low soil moisture content, accounted for less than 5% of applied radioactivity at any sampling time. The metabolite did not contain the carbonyl carbon of clomazone. These data suggest the carbonyl carbon is converted to CO2 during formation of the clomazone metabolite.