Effect of Pretilachlor on Soil Enzyme Activities in Tropical Rice Soil

Pretilachlor treatments, namely, recommended dose at 600 g a.i. ha^-1 (RD), double the recommended dose at 1200 g a.i. ha^-1 (2RD), ten times of the recommended dose at 6000 g a.i. ha^-1 (10RD) along with control, were used to study the effects of pretilachlor on soil enzymes in tropical rice soil. Pretilachlor, at recommended dose completely dissipated 30 days after herbicide application. Twenty days after herbicide application, the dehydrogenase activity was inhibited up to 27 %, 28 % and 40 % of initial values of RD, 2RD and 10RD treatments, respectively. Increase in fluorescein diacetate hydrolase activity was observed during the first 25 days post herbicide application up to 29 %, 36 % and 10 % of initial values of RD, 2RD and 10RD treatments, respectively. β-Glucosidase activity in the experiment did not provide a specific trend. In general, urease and acid phosphatase activities were not influenced by pretilachlor application. There were significant differences in alkaline phosphatase activities among the treatments until 25 days after herbicide application. Hence, pretilachlor may cause short term transitory changes in soil enzyme parameters. However, it has negative impact on soil enzymes at very high dose.