Author(s): N. PANDA and P. RAHA

Abstract: Agricultural use of herbicides has often resulted in contamination of the soil ecosystem, by direct or indirect action, after short, average or long period of time. Under soil submergence a number of transformations in the soil environment are generated due to the effects of hypoxia and anoxia that seriously affect the rhizosphere of the crop particularly the nutrient dynamics. Various assessment techniques are utilized for quantifying the response of reducing soil conditions on nutrient transport and soil enzymatic responses. However, the impact of herbicides under soil submergence poses a challenge to compare its effect on Fe and Mn transformation and dehydrogenase activity. To test this hypothesis, a laboratory study was conducted to assess the effect of herbicide glyphosate, paraquat and pendimethalin on Fe and Mn reduction and soil dehydrogenase activity; used as a measure of the metabolic activity of microorganisms, under submerged soil conditions. Glyphosate at field application dose (0.90 µgg^-1) and double the field application dose (1.80 µgg^-1) inhibited the Fe and Mn reduction from 5.18 to 14.35% and stimulated the soil dehydrogenase activity from 11.64 to 43.12%. However, both inhibition and stimulation effect on Fe & Mn reduction and soil dehydrogenase activity was resulted from the application of herbicides paraquat and pendimethalin at their field (0.45 µgg^-1) and double the field application dose (). The present investigation concluded a stimulation as well as inhibition impact on Fe and Mn reduction and dehydrogenase activity.

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