Ammonium, nitrate and nitrite nitrogen and nitrate reductase enzyme activity in groundnut (Arachis hypogaea L.) fields after diazinon, imidacloprid and lindane treatments

Impacts of diazinon (O,O-diethyl O-2-isopropyl-6-methylpyrimidin-4-yl phosphorothioate), imidacloprid [1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine] and lindane (1,2,3,4,5.6-hexachlorocyclohexane) treatments on ammonium, nitrate, and nitrite nitrogen and nitrate reductase enzyme activities were determined in groundnut (Arachis hypogaea L.) field for three consecutive years (1997 to 1999). Diazinon was applied for both seed- and soil-treatments but imidacloprid and lindane were used for seed treatments only at recommended rates. Diazinon residues persisted for 60 days in both the cases. Average half-lives (t1/2) of diazinon were found 29.3 and 34.8 days respectively in seed and soil treatments. In diazinon seed treatment, NH4(+), NO3(-), and NO2(-) nitrogen and nitrate reductase activity were not affected. Whereas, diazinon soil treatment indicated significant increase in NH4(+)-N in a 1-day sample, which continued until 90 days. Some declines in NO3(-)N were found from 15 to 60 days. Along with this decline, significant increases in NO2(-)N and nitrate reductase activity were found between 1 and 30 days. Imidacloprid and lindane persisted for 90 and 120 days with average half-lives (t1/2) of 40.9 and 53.3 days, respectively. Within 90 days, imidacloprid residues lost by 73.17% to 82.49% while such losses for lindane residues were found 78.19% to 79.86 % within 120 days. In imidacloprid seed-treated field, stimulation of NO3(-)N and the decline in NH4+NO2(-)-N and nitrate reductase enzyme activity were observed between 15 to 90 days. However, lindane seed treatment indicated significant increases in NH4(+)-N, NO2(-)-N and nitrate reductase activity and some adverse effects on NO3(-)N between 15 and 90 days.     

Endosulfan and quinalphos residues and toxicity to soil microarthropods after repeated applications in a field investigation

Endosulfan (1,4,5,6,7,7-hexachloro-8,9,10-trinorborn-5-en-2,3-ylenedimethylsulphite) and quinalphos (O,O-diethyl O-quinoxalin-2-yl phosphorothioate) persistence and their effect on soil microarthropods were studied after repeated applications in cotton fields. Dissipation behavior of insecticides after repeated applications was observed from 78 to 292 days after the first insecticide treatment. At any given time the concentrations of endosulfan beta residues were always higher as compared to endosulfan alpha. From 78 to 85 days, 5.0% and 20.4% decrease in alpha and beta endosulfan residues was observed, respectively. Endosulfan beta isomer decreased up to 93.0% in 292 days. Endosulfan sulfate was detected as a major metabolite in the soil samples. Total endosulfan residues decreased by 86.6% from 78 to 292 days. The amounts of quinalphos residues were less as compared to endosulfan at any given time. The residues observed after 78 days of application were 0.88 ng g-1 d wt. soil. At the end of 145 days, a 35.0% decrease in quinalphos residue was observed, which decreased further by 50.9% in 292 days. Among the soil microarthropods studied, Acarina was more sensitive to the applied insecticides as compared to Collembola. Three days after the last treatment, up to 94.5% (p < 0.01) and 71.2% (p < 0.05) decrease in Acarina population was observed in endosulfan and quinalphos treated fields, respectively, compared to control field. In general, no noticeable change in Collembola population was observed after the insecticide treatments.     

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