Rates of chlorsulfuron degradation in three Brazilian oxisols

The degradation of chlorsulfuron was studied in laboratory experiments in three oxisols from south and south-east Brazil. Three soil profiles were sampled by horizon, and classified according to USDA soil taxonomy and the Brazilian system. Degradation assays were made to evaluate the influence of temperature, humidity and liming on chlorsulfuron decomposition. Further experiments were set up to study enhanced biodegradation. Abiotic degradation was also studied in sterile soils, to evaluate, by comparison with non-sterile soils, the role of microorganisms in degradation. The degradation always followed first-order kinetics and was generally faster in samples from A than B horizons. An increase in temperature (from 25 to 40 degrees C) increased chlorsulfuron degradation. Further, an increase in moisture content increased chlorsulfuron degradation in samples from the A horizons of all soils, whereas for two out of three soils, degradation in samples from the B horizon was greater at lower water content. The biotic contribution to degradation was significant only for the soil with higher fertility. Soil liming significantly increased chlorsulfuron half-life in all samples. Significant enhancement of degradation (decrease in half-life on reapplication) was observed only in soil from A horizons, where a higher microbial activity was likely.