Effect of pesticides on microbial diversity and urease in groundnut (Arachis hypogaea L.) soil.

The influence of four pesticides viz., profenofos, deltamethrin, thiram and difenoconazole and two insecticide combinations viz., profenofos + cypermethrin and deltamethrin + endosulfan at 0.0, 1.0, 2.5, 5.0, 7.5 and 10.0 kg ha were assessed for their effects on the activity of urease (measured in terms of hydrolysis of urea by sodium hypochlorite method) and microbial populations like bacteria, fungi and actinomycetes in two agricultural soils, collected from a fallow groundnut (Arachis hypogaea L.) fields of Anantapur district. The effects of selected pesticides profenofos, deltamethrin, thiram and difenoconazole and profenofos + cypermethrin and deltamethrin + endosulfan on microbial population and urease activity were dose dependent. Urease activity and microbial populations increased with increasing concentrations of the pesticides up to 5.0 kg ha. Higher rates (7.5, 10.0 kg ha) of these pesticides were either toxic or innocuous to the urease activity and microbial population. The significant stimulation in the activity of urease was associated with 2.5 kg ha of pesticides in black soil, where as in red soil it was 5.0 kg ha of profenofos, 2.5 kg ha of deltamethrin, thiram, difeneconozole. In the insecticide combinations urease activity was 5.0 kg ha profenofos + cypermethrin, 5.0 kg ha of deltamethrin + endosulfan in black clay soils whereas in red sandy clay soils, population of microorganisms increased with 2.5 to 5.0 kg ha of pesticides. With further incubation the activity of urease was significantly more at day 20 and enzyme activity decreased progressively with increasing incubation period. _____________________________________________________________________________________________________________