IMPACT OF TILLAGE ON MICROBIAL ACTIVITY AND THE FATE OF PESTICIDES INTHE UPPER SOIL

The impact of two tillage systems, plow tillage (PT) and no-tillage (N T), on microbial activity and the fate of pesticides in the 0-5 cm soi l layer were studied. The insecticides carbofuran and diazinon, and th e herbicides atrazine and metolachlor were used in the study, which in cluded the incubation and leaching of pesticides from untreated soils and soils in which microorganisms had been inhibited. The mineralizati on of ring C-14 labeled pesticides was studied. The study differentiat ed between biotic and abiotic processes that determine the fate of pes ticides in the soil. Higher leaching rates of pesticides from PT soils are explaned by the relative importance of each of these processes. I n NT soils, higher microbial populations and activity were associated with higher mineralization rates of atrazine, diazinon and carbofuran. Enhanced transformation rates played an important role in minimizing the leaching of metolachlor and carbofuran from NT soils. The role of abiotic adsorption/retention was important in minimizing the leaching of metolachlor, carbofuran and atrazine from NT soils. The role of fun gi and bacteria in the biodegradation process was studied by selective inhibition techniques. Synergistic effects between fungi and bacteria in the degradation of atrazine and diazinon were observed. Carbofuran was also degraded in the soils where fungi were selectively inhibited . Possible mechanisms for enhanced biodegradation and decreased mobili ty of these pesticides in the upper layer of NT soils are discussed.