Modern agriculture depends upon the wide variety of natural and synthetically produced chemicals such insecticides, fungicides, herbicides and other pesticides This work studied the effect of synthetic and biological insecticides on microbial population and microbial activities in soil samples. The insecticides used in this study are cypermethrin, chloropyrifos, neem extracts and ginger extracts. Bacteria and fungi were isolated and identified from the soil samples. TBC, TCC and TFC were determined. Dehydrogenase activity, microbial respiration and microbial biomass carbon in the soil samples were also examined. The control soil samples recorded the highest TBC, TFC, TCC, dehydrogenase activity, microbial respiration and microbial biomass carbon. Soils treated with chloropyrifos recorded the lowest total coliform count of 0.10×105 ± 0.00 cfu/g, while cyperforce treated soils recorded the lowest total bacterial count of 0.58×105 ± 0.025cfu/g. Cyperforce treated soils had the lowest effect on CO2 respired in the soil with a value of 1687.50 ± 1.500 mg/kg. 500 g/ml Neem leaf extract had the highest microbial biomass carbon value of 9.40 ± 0.100 KgC/m2. This work has shown that treatment with both synthetic and bio-insecticides resulted in significant drop in microbial population and microbial activity of soil samples.
microbial respiration, dehydrogenase activity, microbial biomass carbon, microbial population, cyperforce, chloropyrifos