Field experiments were conducted to study the effect of pesticide applications on soil nitrification dynamics in cotton agroecosystem. The pesticides either alone or in combination (mixture) were applied according to the normal agricultural application rates in test, farmer (with pesticide applications) and control (without pesticide applications) fields. Soil samples were collected before and after two days, following pesticide applications and at sowing, before pesticide application, after all pesticide applications, at harvest and at post harvest time during the crop seasons 1997-1999. Soils were incubated under laboratory conditions using ammonium sulfate as substrate. In 1997 crop season soil samples were incubated for 28 days with a substrate of 144 mgkg -1 soil while in 1998-1999 the incubation period was 14 days with substrate of 212 mgkg -1 soil. The soil samples were analyzed for total (NO2 + NO3) N content using steam-distillation method. Othofonprox, profenophos + cypermethrin and bifenthrin + endosulfan inhibited while, endosulfan, imidachloprid, methamidophos, endosulfan alongwith dimethoate, profenophos + alphmethrin, chlorpyrifos + tralomethrin + acetamiprid and cyhalothrin + profenophos + diafenthiuron stimulated the nitrification. All other pesticidal applications have no effect on this parameter. Samples collected at different intervals of time from all the fields in three years study showed no differences in nitrification from sowing to harvest. The variations observed, in general, being very week and transient and resulting in a recovery of nitrification.
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Zafar Iqbal, Altaf Hussain, Muhammad R. Asi and Jamil A. Chaudhry, 2001. Impact of Pesticide Applications in Cotton Agroecosystem and Soil Bioactivity Studies II: Nitrification Dynamics. Pakistan Journal of Biological Sciences, 4: 588-592.
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