THE EFFECT OF INSECTICIDES ON SOIL MICROORGANISMS

Abstract

An experiment was conducted in the laboratory of the Department of Agricultural Chemistry, Sher-e-Bangla Agricultural University (SAU). Dhaka. Bangladesh, during this period from July to December, 2009 to know the impact of 4 selected insecticide (Diazinon 60 EC, Marshal 20 EC, Dursban 20 EC and Admire 200 Si) on soil microorganisms and the impact was expressed as the amount of CO2-C evolution per gram soil and dehydrogenase activity (WV formation). The insecticides were injected in the soil samples and incubation. The data were taken after 2. 4.8.16 and 24 days of incubation for the determination of the microbial activity. The experiment revealed that all the insecticides tested had an effect on microbial activity or microbial population. The result shows that the amount of CO2 is higher in all insecticide treated soils than that of control soil after 2 days of incubation, which indicates the stimulatory effect of all the insecticides on soil microorganisms during this period. Moreover, the high amount of CO? evolution in Marshal 20 EC treated soils indicates a grate activity of soil microorganisms. On the other hand Diazinon 60 EC and Durseban 20 EC showed negative effect on microbial activity till 4 days of incubation: but the microbial activity increased there after. In case of dehydrogenase activity, the insecticide treated soils gave higher formazan yields than that given by controlled soil. Diazinon 60 EC consistently high positive dehydrogenase effect starting right from its application and continued to have, even up to the last days of incubation. Similar but slightly less positive effect was observed in case of Admire 200 SL. Marshal 20 EC and Dursban 20 NC.