Effect of Butachlor on Biochemical Process in Soil

Butachlor is a very commonly used pre-emergence herbicide. In the present study, the effect of butachlor at three different application rates (0.5, 1.0 and 2.0 kg a.i. / ha) on the activities of some soil enzymes, microbial population and transformation and availability of C, N and P in an alluvial soil has been analyzed. The result showed that in general, the application of butachlor has significantly increased activities of most of the enzymes as well as the microbial biomass with greater retention, mineralization and availability of oxidizable C, N and P in soil. The stimulation in activities of enzymes dehydrogenase and phenol oxidase was found to be more pronounced when the herbicide was applied at half recommended field dose (hRFD) . On the other hand, phosphatase, arylsulphatase and phenol oxidase were pronounced at double recommended field dose (dRFD) . As compared to untreated control soil, the application of butachlor induced higher proliferation of total bacteria at recommended field dose (RFD) , fungi at hRFD and actinomycetes at dRFD. Regarding the availability of plant nutrients, we also found that the greater retention of total N, exchangeable NH4+, and soluble NO3- was achieved by applying butachlor at RFD and that of organic C and available P by applying butachlor at dRFD. The correlation analysis showed significant positive correlation between hydrolase enzymes, phosphatase and arylsulphatase (r = 0.74), oxidoreductase enzymes, phenol oxidase and peroxidase (r = 0.706). The fungal population is related to total bacteria (r =0.73), actinomycetes (r = 0.50) and available P (r = 0.65) in soil. The results of the present investigation thus indicate that the application of butachlor significantly induces the growth and activities of microorganisms, resulting in greater retention, mineralization and availability of oxidizable C, N and P in soil but that the stimulation is depend on neither concentration of herbicide nor time of incubation.