1. Contribution from the All India Coordinated Research Project on Soybean, Bidhan Chandra Krishi Viswavidyalaya, Kalyani-741234, Nadia, West Bengal.
On a Gangetic alluvial sandy loam soil, the field experiments, conducted for two years on soybean [Glycine max (L.) Merrill], Tevealed that weeding thrice (at 15, 30 45, DAS), twice (at 30, 45 DAS) and once at 30 DAS) controlled weeds (at harvest) with 92, 84 and 68% efficiency and the soybean seed yields were as good as 95, 87 and 79% of the yield obtained in the weed free (weeding at 7 days interval) plot, respectively. Among the weeding once treatments, weeding at 30 DAS recorded highest seed yield and appeared to be very critical. Pre-em. application of nitrofen 1.0 kg[2, 4-dichlorophenyl 4 nitrophenyl ether], fluchloralin 1.5 kg [Npropyl-N (2 chloroethyl)-2, 6-dinitron-n-trifluoromethyl aniline1, and oxadiazon 0.5 kg [2-tert. butyl-4 (2, 4 dich'oro-5-isopro. pyloxyphenyl)-1, 3,4 oxadiazoline-5-one] 0.5 kg/ha showed weed control efficiency of 36, 21 and 32% and increased soybean yields by 57,43 and 42% over the yield in weedy check, respectively. Post-em, application ef bentazon [3-isopropyl-1 H-2, 1,3-benzoihiadiazin-4 (3 H) - one 2, 2-dioxide) at 2.0 kg ha showed 41% weed control effiiciency by controlling sedges and broad-leaved weeds and produced 62%more yield than in weedy check in 1980, but caused damage of soybean plants in 1E81.
