Effect of Chemical Weed Management Practices on Weed Dynamics, Soil Microorganism and Nutrient Uptake in Blackgram [Vigna mungo (L.)]

An investigation was carried out at Zonal Agricultural Research Station, Kalaburagi, India, University of Agricultural Sciences, Raichur, Karnataka, India during kharif 2021-22 to study the effect of pre and post emergent application of weedicides on seed yield, weed dynamics, microbial population and nutrient uptake by weeds in blackgram. The results revealed that, significantly lower weed density (grassy weeds, sedges and broad leaf weeds (0.71) and weed dry weight (0.71) was observed with hand weeding at 25-30 DAS and intercultivation at 45 DAS (control) followed by sodium acifluorfen 16.5% + clodinafop propargyl 8% EC @ 1.0 kg a.i. ha-1 at 20-25 DAS [grassy weeds (1.08, 1.26 and 1.83) sedges (1.03, 1.57 and 1.47) and broad leaf weeds (1.72, 2.06 and 2.11 at 25, 50 DAS and at harvest respectively]. Weed control efficiency was significantly higher with sodium acifluorfen 16.5% + clodinafop propargyl 8% EC @ 1.0 kg a.i. ha-1 at 20-25 DAS (89.52, 90.31 and 91.17 at 25, 50 DAS and at harvest respectively) that was on par with hand weeding. Hand weeding at 25-30 DAS and intercultivation at 45 DAS recorded significantly higher population of bacteria, fungi and actinomycetes (13.82, 12.49 and 5.25 cfu x 106 g-1 soil respectively). All chemical weedicides applied either pre-emergent or post-emergent significantly reduced population of total bacteria, fungi, actinomycetes. Significantly higher nutrient uptake by weeds was recorded with weedy check (71.03, 32.00 and 56.67 kg ha-1 nitrogen, phosphorus and potassium respectively). Where as, higher nutrient uptake by blackgram was with hand weeding at 25-30 DAS and intercultivation at 45 DAS (126.25, 28.20 and 109.30 kg ha-1 nitrogen, phosphorus and potassium respectively). After the harvest, soil available nutrients status was higher with  hand weeding at 25-30 DAS and intercultivation at 45 DAS (141.38, 42.10 and 298.53 kg ha-1 nitrogen, phosphorus and potassium respectively) and significantly lower nutrients were observed with weedy check (122.93, 30.17 and 220.10 kg ha-1 nitrogen, phosphorus and potassium respectively).