Impact of Three Carbamate Pesticides on Soil Microbial Diversity and Soil Enzymatic Activities

Effect of different doses of three carbamate pesticides[oxamyl, l{methyl-2-(dimethylamine)-N-[(methylamino) carbonyl)oxy]-2-oxoethanimidothioate (I);{S-ethyl-N-ethyl (carbamoyl) oxy] thioacetimidate (II) and {N-phenyl (ethylcarbamoyl) propyl carbamate (III) on soil microbial biomass, microbial population and soil enzymatic [dehydogenase (DHA), acid and alkaline phosphatase, urease and catalase] activities in an alluvial soil in laboratory is reported. The enzymatic activities were additionally analyzed in soil amended with sewage sludge and a combination of sewage sludge and pesticides. The microbial biomass increased significantly over the control up to 35 days of incubation under lower doses of pesticides (up to 0.25 g for I, 0.2 g for II and 0.3 g for III kg⁻¹ soil). At lower doses of the pesticides, the microbial population also increased up to 5 weeks of incubation. The higher doses showed adverse effect on microbial biomass and population. All the enzymatic activities significantly decreased up to 2–3 weeks of incubation (14 d for DHA, acid phosphatase and urease, 21 d for alkaline phosphatase and catalase). The activities of all the studied enzymes decreased with increase in pesticide dose. Enzymatic activities were comparatively higher in sewage sludge amended soil in comparison to the unamended soil. A mixture of pesticides and sewage sludge showed no appreciable effect on enzymatic activities.