RATES OF CHLORSULFURON DEGRADATION IN 3 BRAZILIAN OXISOLS

The degradation of chlorsulfuron was studied in laboratory experiments in three oxisols from south and south-east Brazil. Three soil profile s were sampled by horizon, and classified according to USDA soil taxon omy and the Brazilian system. Degradation assays were made to evaluate the influence of temperature, humidity and liming on chlorsulfuron de composition. Further experiments were set up to study enhanced biodegr adation. Abiotic degradation was also studied in sterile soils, to eva luate, by comparison with non-sterile soils, the role of microorganism s in degradation. The degradation always followed first-order kinetics and was generally faster in samples from A than B horizons. An increa se in temperature (from 25 to 40 degrees C) increased chlorsulfuron de gradation. Further, an increase in moisture content increased chlorsul furon 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 degrad ation was significant only for the soil with higher fertility. Soil li ming significantly increased chlorsulfuron half-life in all samples. S ignificant enhancement of degradation (decrease in half-life on reappl ication) was observed only in soil from A horizons, where a higher mic robial activity was likely.