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

The present investigation determines the
persistence of herbicides like butachlor and pretila
chlor in Indian soil, and their impact on soil biologi
cal properties including microbial biomass carbon
(MBC), total microbial population numbers, and
enzyme activities. Butachlor was degraded faster in
autumn rice soil (t1/2 of 10–13 days) than in winter
rice soil (half-life of 16–18 days). The t1/2 of preti
lachlor 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 phos
phatase (averages of 242.6–269.3 μg p-nitrophenol

g−1 dry soil h−1 in autumn rice and 188.2–212.2 μg
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 pre
tilachlor 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.