Effect of three carbamate pesticides on population dynamics of soil microorganisms

The response of soil microflora to increasing concentration (300 and 500 mg kg(-1) of soil) of three carbamate pesticides, viz. Oxamyl (I); S-ethyl-N(methylcarbamoyl) oxythioacetamidate (II) and N-Phenyl-4-ethylcarbamoyl propyl carbamate (III) was determined under fields conditions over a period of 91 days. After 0,7,14,21,28,35,42,49,56,63,70,77,84,91 days of application the number of bacteria, fungi, actinomycetes and protozoa population was estimated in soil. All the studied pesticides at both the rates of application initially (35-49 days after treatment, DAT) significantly decrease the population of fungi and actinomycetes and thereafter an enhancement of population occurs. Whereas bacteria population at lower dose of application initially (35-49 DAT) increased and thereafter decreased while at higher dose of pesticides population of bacteria continuously decreased. The protozoa population at both the studied concentration for all the studied pesticides decreased with time. The increase in bacteria population and decrease in population of fungi and actinomycetes up to 35-49 days may be due to stimulation of the mineralization rate of organic carbon and ability of bacteria to breakdown the pesticide and utilization of carbon source for their activity. The results also denote that activity of all the studied pesticides is almost same.