The herbicide sulfentrazone is classified as highly mobile and persistent and this study aimed to examine degradation of this compound on a Typic Hapludox soil that is representative of regions where sulfentrazone is used in Brazil. Soil samples were supplemented with sulfentrazone (0.7 mg active ingredient (a.i.) g À1 soil), and maintained at 27 1C. Soil moisture was corrected to 30%, 70%, or 100% waterholding capacity (WHC) and maintained constant until the end of the experimental period. Soils without added herbicide were used as controls. Aliquots were taken after 14, 30, 60, 120, 180, and 255 days of incubation for quantitative analysis of sulfentrazone residues by gas chromatography. Another experiment was conducted in soil samples, with and without the herbicide, at different temperatures (15, 30, and 40 1C), with moisture kept constant at 70% of WHC. The sulfentrazone residues were quantified by gas chromatography after 14, 30, 60, and 120 days of incubation. Sulfentrazone degradation was not affected by soil moisture. A significant effect was observed for the temperature factor after 120 days on herbicide degradation, which was higher at 30 1C. A half-life of 146.5 days was recorded. It was observed that the herbicide stimulated growth of actinomycetes, whereas bacterial and fungal growth was not affected. The microorganisms selected as potential sulfentrazone degraders were Rhizobium radiobacter, Ralstonia pickettii, Methylobacterium radiotolerans, Cladosporium sp., Eupenicillium sp., and Paecilomyces sp.

The aim of this work was to evaluate the effects of the herbicide sulfentrazone on soil microbial biomass C and on symbiotic processes associated with soybean (Glycine max (L). Merril). The experiment was conducted in greenhouse using a Red-Yellow Oxisol soil collected from Embrapa Meio Ambiente's experimental field, in Jaguariúna, São Paulo, Brazil and included the following treatments: control, without herbicide and sulfentrazone herbicide application (0.7 mg kg −1 soil) and three harvest periods. The nodule number and nodule dry weight on the onset of soybean development were negatively affected by the presence of the herbicide, as also observed for shoot biomass and shoot total N content. Pod dry weight and pod total N content decreased by 45% in the presence of the herbicide. The percentage of mycorrhizal infection was 50% lower in pots that received sulfentrazone throughout the soybean growing season. Microbial biomass C was lower in the presence of the herbicide only in the initial period of soybean development. Mycorrhizal and rhizobial performance in soybean were reduced by sulfentrazone use, and both possibly contributed to reduced plant growth.

Sulfentrazone is amongst the most widely used herbicides for treating the main crops in the State of São Paulo, Brazil, but few studies are available on the biotransformation of this compound in Brazilian soils.Soil samples of Rhodic Hapludox soil were supplemented with sulfentrazone (0.7 µg active ingredient (a.i.) g -1 soil) and maintained at 27ºC. The soil moisture content was corrected to 30, 70 or 100 % water holding capacity (WHC) and maintained constant until the end of the experimental period. Herbicide-free soil samples were used as controls. Another experiment was carried out using soil samples maintained at a constant moisture content of 70% WHC, supplemented or otherwise with the herbicide, and submitted to different temperatures of 15, 30 and 40º C. In both experiments, aliquots were removed after various incubation periods for the quantitative analysis of sulfentrazone residues by gas chromatography.Herbicide-degrading microorganisms were isolated and identified. After 120 days a significant effect on herbicide degradation was observed for the factor of temperature, degradation being higher at 30 and 40º C. A half-life of 91.6 days was estimated at 27º C and 70 % WHC. The soil moisture content did not significantly affect sulfentrazone degradation and the microorganisms identified as potential sulfentrazone degraders were Nocardia brasiliensis and Penicillium sp. The present study enhanced the prospects for future studies on the bio-prospecting for microbial populations related to the degradation of sulfentrazone, and may also contribute to the development of strategies for the bioremediation of sulfentrazone-polluted soils.