EFFECT OF 5 INSECTICIDES ON MICROBIAL AND ENZYMATIC-ACTIVITIES IN SANDY SOIL

A laboratory study was conducted to examine the effects of five insect icides on microbial and enzymatic activities important to fertility in sandy soil. Cyfluthrin significantly increased bacterial populations after 2 wks. Imidacloprid showed an inhibitory effect on fungal number s after 2 wks incubation while the others did not affect fungal popula tion. No inhibitory effect was observed on nitrification of soil indig enous nitrogen. All treatments stimulated S-oxidation after 4 wks. Wit h the exception of cyfluthrin and imidacloprid after 2 wks, denitrific ation in sandy soil indicated that all treatment inhibited denitrifica tion throughout the experiment. No inhibitory effects on biomass-e wer e observed during 2-wk periods. An inhibitory effect was observed on a mylase after 1 wk while significant recovery was observed after 3 wks. With the exception of HgCl2, no effect was observed on reducing sugar formation for 2 wks with all treatments. Formazan formation resulting from dehydrogenase activity was significantly greater with tebupirimp hos and Aztec for 1 wk. All treatments supressed phosphatase activity for 1 wk, while none of the treatments suppressed phosphatase activity after 2 wks. Amitraz, tebupirimphos and Aztec inhibited urease activi ty for 1 wk. With the exception of tebupirimphos, no treatments affect ed N-2-fixation in soil. Although short-lived inhibitory effects on ac tivities of microbes and enzymes were caused by the insecticides, the soil indigenous microbes can tolerate the chemicals used for control o f soil pests.