Rates of chlorsulfuron degradation in three Brazilian oxisols

Abstract

The degradation of chiorsulfuron wa.s studied in laboratory experiments in three oxisois 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 chlorsutfuron decotnposition. 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 to40°C) increased chlorsulfuron degradation. Further, an increase in moisture content increased chlorsuifuron 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-iife on reapplication) was observed oniy in sosi from A horizons, where a higher microbial activity was likely.

Fate of chlorsulfuron in the environment. 2. Field evaluations

“…This type of degradation (lacking a second, slower stage) was also observed in a study with Brazilian oxisols maintained at a relatively high temperature, 40¡C. 36 The high temperatures, coupled with an abundance of soilwater (the site received a total of 283 mm precipitation, supple-mented with 728 mm from bi-weekly irrigations) probably resulted in enhanced aqueous hydrolysis of chlorsulfuron before signiÐcant di †usion to sites of lesser reactivity or lesser availability to microbes could occur. A factor which potentially limited our ability to establish the portion of decline curve after the 120-day sampling was that the detection limit was at 5% of applied radioactivity.…”

Degradation Rate of Chloridazon in Soil as Influenced by Adjuvants

“…Whereas the DT 50 value obtained after fitting the curve to first-order kinetics was lower (35 days); (Table 1). The same model of the kinetics equation has been noticed for other herbicides (Pettygrove and Naylor 1985;Allen and Walker 1988;Ravelli et al 1997;Cuevas et al 2007). The DT 50 values for soil in this experiment, are from the data of Tomlin (2006).…”

Degradation of chlorsulfuron and triasulfuron in alkaline soils under laboratory conditions

“…Observed DT 50 values varied from as low as 34 d at 0±10 cm depth to nearly 148 d at the lowest depth (30±40 cm). Reduced rates of degradation with increasing depth in the soils were also demonstrated for chlorsulfuron and metsulfuron-methyl in a number of European subsoils and most recently for chlorsulfuron in three Brazilian oxisols (Ravelli et al, 1997).…”

“…ha ±1 , assuming that the herbicide is incorporated in the top 5-cm layer in one hectare of land having an average bulk density of 1500 kg m ±3 . Most of the previous studies (Thirunarayanan et al, 1985;Ravelli et al, 1997) have used initial concentrations greater than normally would be expected in ®eld soils. Walker & Brown (1983) reported a chlorsulfuron degradation study based on a bioassay using 40 lg a.i kg ±1 .…”

“…The eect of soil pH on the degradation of sulfonylurea herbicides has been the subject of a number of investigations (Joshi et al, 1985;Thirunarayanan et al, 1985;Fredrickson & Shea, 1986;Ravelli et al, 1997), and most have used acidic to neutral soils. To our knowledge, there are no reports available about laboratory degradation studies on highly alkaline natural soils (pH > 8.0).…”