Yield and economics of drum-seeded rice (Oryza sativa) as influenced by broad- spectrum herbicides and herbicide mixtures

A study was conducted during the summer season of 2015 and 2016 at, Gerua, with 10 weed-control practices, to evaluate the efficacy of different broad-spectrum herbicides and their combinations on performance of drum- seeded rice (Oryza sativa L.) in lowland ecosystem of Lower Brahmaputra Valley Zone of Asom. Results of the ex- periment revealed that Cyperus difformis L., Schoenoplectiella juncoides (Roxb.) Lye; syn, Scirpus juncoides Roxb. among sedges; Echinochloa crus-galli (L.) P. Beaur.; E. glabrescens, Leptochloa chinensis Kossenko (L.) Nees, among grasses; and Anagallis arvensis L. among broad-leaf weeds were dominant in drum-seeded rice. The composition of grasses, sedges and broad-leaf weeds in weedy check at 60 days after sowing (DAS) was 15.1, 71.5 and 13.4% respectively. Crop-weed competition throughout the crop-growth period caused 37.4% grain yield loss. Mechanical weeding by paddy weeder at 20 DAS followed by manual weeding at 40 DAS registered 9.2% lower grain yield than manual weeding twice. Weed-free condition by repeated manual weeding recorded the highest cost of cultivation of 45,000/ha, whereas bensulfuron-methyl + pretilachlor (60 + 600 g/ha) at 10 DAS re- sulted in the lowest cost of cultivation ( 36,000/ha). Though higher grain yield of 5.82 t/ha was recorded in weed- free plots, it did not record higher benefit: cost (B: C) ratio. Bensulfuron-methyl + pretilachlor (60 + 600 g/ha) at 10 DAS recorded the highest B : C ratio (2.28) followed by flucetosulfuron (25 g/ha) at 20 DAS (2.24).