Persistence of Insecticide Residues in Paddy Soil

Chemical determination of pesticide residues in soil samples drawn 4 hr, 1,3,5,10.20,30,45 and 60 days after treatment indicated that while phorate. disulfoton and dimethoate had a half life of 5 days in the paddy soil. chlorpyrlfos on the other hand dissipated to 50 per cent of the initial deposit after 10 days. The studies also revealed that 0 23 to 0 32 ppm of phorate 0.15 to 0.20 ppm of disulfoton; 0.28 ppm of dimethoate and 0.84 ppm of chlorpyrifos was still available at the time of final assessment i.e., 60 days after the treatment. Results further indi-cated more deposition or phorate and disultofon residues during kharif 1977, probably due to comparatively higher clay and sand content in the soil, as compared to kharif 1979 trials.