Weed control in transplanted and wet-seeded rainy season rice (Oryza sativa)

Abstract

A field study was conducted at Cooch Behar during the rainy seasons of 2006 and 2007 to find out the economically viable weed control practices in transplanted and wet seeded rice (Oryza sativa L.). In transplanted rice, Monochoria hastate Prest., Ludwigia parviflora Roxb., Nymphoides indicum (L) and Barnyardgrass [Echinochloa crus-galli (L.)] were dominant weed. In wet seeded rice Monochoria hastate Prest., Ludwigia perennis Roxb., Flatsedge [Cyperus flavidus (L.)], Cyperus difformis (L.), Scirpus juncoides (L.) and Bermudagrass [Cynodon dactylon (L.)] were aggressive and important weeds. In transplanted rice, butachlor 1.0 kg/ha at 3 days after transplanting + almix 20 WP (Chlorimuronethyl + Metsulfuron-methyl) 4.0 g/ha at 20 days after transplanting registered higher weed control efficiency and grain yield (3.17 and 3.50 tonne/ha) comparable with season long weed-free condition. This treatment gave maximum monetary returns of ` 14 843 and 17 728/ha as well as benefit:cost ratio of 1.09 and 1.31 during 2006 and 2007, respectively. In wet-seeded rice, drum seeding, followed by brown manuring [seeding of dhaincha (Sesbania rostrata) with rice seeds, followed by 2,4-D 0.50 kg/ha application at 25 days after sowing and subsequent incorporation of dried dhaincha with rotary weeder at 35 DAS, was comparable with season long weed-free condition in terms of yield (3.03 and 3.32 tonnes/ ha) and thus resulting in maximum monetary benefit of ` 14 204 and 16 829/ha with benefit:cost ratio of 1.10 and 1.30 in 2006 and 2007, respectively. Weeds in complete weedy situation removed 30.1 to 34.3 kg N, 5.8 to 7.4 kg P and 37.8 to 42.9 kg K/ha in transplanted rice and 37.7 to 50.9 kg N, 10.3 to 15.7 kg P and 47.4 to 63.7 kg K/ha in wet-seeded rice, respectively, during 2006 and 2007. Butachlor 1.0 kg/ha at 3 days after transplanting + almix 20 WP (Chlorimuron-ethyl 10% + Metsulfuron-methyl 10%) 4.0 g/ha at 20 days after transplating in transplanted rice and practice of brown manuring in wet-seeded rice were found effective to control weeds and these weed control practices prevented removal of 24.1 to 28.1 kg N, 5.4 to 6.9 kg P and 30.1 to 35.0 kg K/ha in transplanted rice and 30.7 to 42.4 kg N, 9.1 to 13.8 kg P and 38.3 to 52.9 kg K/ha in wet-seeded rice by the weeds-respectively.