Optimizing post-emergence herbicide rates for enhanced growth, symbiotic efficiency and weed management in soybean (Glycine max)

The field experiment was carried out at Punjab Agricultural University, Ludhiana and Dr. J.C. Bakhshi Regional Research Station, Abohar, Punjab, India, during kharif (rainy season) 2021, in a randomized complete block design with 12 treatments [imazethapyr 75 g/ha, propaquizafop + imazethapyr at 75, 100, and 125 g/ha, clodinafop propargyl + sodium acifluorfen at 147, 196, and 245 g/ha, imazamox + imazethapyr at 42, 56 and 70 g/ha, two hand weedings (HW) at 20 and 40 DAS and weedy check] with three replications. Results revealed that 2-hand weedings (HW) significantly increased number & dry weight of nodules and leghaemoglobin content compared to the weedy check. Among post-emergence herbicides, imazamox + imazethapyr (70 g/ha) applied at 15–20 DAS produced the number and dry weight of nodules/plant, as well as the leghaemoglobin content statistically comparable to HW. The lowest weed density and dry weight were recorded under two HW at both locations, with imazamox + imazethapyr (70 g/ha) showing comparable effectiveness. Chlorophyll content remained unaffected by most herbicide treatments, though high doses reduced it marginally due to phytotoxicity. Maximum plant height and shoot dry matter accumulation were observed with two HW, followed by imazamox + imazethapyr (70 g/ha) at 15-20 DAS, which provided effective weed control and enhanced crop growth by reducing competition. The findings suggest that imazamox + imazethapyr at 70 g/ha is a viable alternative to manual weeding for soybean under labour scarcity.