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 drumseeded rice (Oryza sativa L.) in lowland ecosystem of Lower Brahmaputra Valley Zone of Asom. Results of the experiment 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 resulted in the lowest cost of cultivation (36,000/ha). Though higher grain yield of 5.82 t/ha was recorded in weedfree 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).