Residue and soil dissipation kinetics of chloroacetanilide herbicides on rice (Oryzae sativa L.) and assessing the impact on soil microbial parameters and enzyme activity

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English. The present investigation determines the persistence of herbicides like butachlor and pretilachlor in Indian soil, and their impact on soil biological properties including microbial biomass carbon (MBC), total microbial population numbers, and enzyme activities. Butachlor was degraded faster in autumn rice soil (t(1/2) of 10-13 days) than in winter rice soil (half-life of 16-18 days). The t(1/2) of pretilachlor in winter rice was 12-16 days. Regardless of the seasons under cultivation, no pesticide residue was detected in rice at harvest. Herbicides induced an initial decline (0-14th days after application) in MBC (averages of 332.7-478.4 g g(-1) dry soil in autumn rice and 299.6-444.3 g g(-1) dry soil in winter rice), microbial populations (averages of 6.4 cfu g(-1) in autumn rice and 4.6 cfu g(-1) in winter rice), and phosphatase (averages of 242.6-269.3 & mu;g p-nitrophenol g(-1) dry soil h(-1) in autumn rice and 188.2-212.2 & mu;g p-nitrophenol g(-1) dry soil h(-1) in winter rice). The application of herbicides favored dehydrogenase (averages of 123.1-156.7 g TPF g(-1) dry soil in autumn and 126.7-151.1 g TPF g(-1) dry soil in winter) and urease activities (averages of 279.0-340.4 g NH4 g(-1) soil 2 h(-1) in autumn and 226.7-296.5 g NH4 g(-1) soil 2 h(-1) in winter) in rice soil at 0-14th DAA. The study suggests that applications of butachlor and pretilachlor at the rates of 1000 g ha(-1) and 750 g ha(-1), respectively, to control the weeds in the transplanted rice fields do not have any negative impact on the harvested rice and associated soil environment.