Effect of herbicide and their combinations on crop growth, weed suppression and rice yield were evaluated at agronomic research farm of Rajendra Agricultural University, Bihar (Pusa) during Kharif season of 2009-10.Results revealed that weed control measures had a significant effects on weed population/m2. At 20 DAT minimum weed population/m2 was recorded with Butachlor @ 1.5 kg a.i/ha (PE) which was significantly superior to weedy check (no weeding) and hand weeding at 25 and 50 DAT and statistically at par with Butachlor @ 1.5 kg a.i/ha (PE) + Pyrazosulfuron@ 40g a.i/ha (PoE), Pretilachlor @ 0.5 kg a.i/ha (PE)and Pretilachlor @ 0.5 kg a.i/ha (PE) + Pyrazosulfuron (10WP) @ 40 gm a.i/ha (PoE).At 40 DAT lowest weed population/m2 was recorded with hand weeding at 25 and 50 DAT which was highly significant to weedy check and significantly superior to Butachlor @ 1.5 kg a.i/ha (PE) and Pretilachlor @ 0.5 kg a.i/ha (PE) but statistically at par with Butachlor @ 1.5 kg a.i/ha (PE) + Pyrazosulfuron@ 40g a.i/ha (PoE) and Pretilachlor @ 0.5 kg a.i/ha (PE) + Pyrazosulfuron (10 WP) @ 40 gm a.i/ha (PoE).At 60 DAT, minimum weed population/m2 was recorded with hand weeding at 25 and 50 DAT which was highly significant to weedy check but significantly superior to Butachlor @ 1.5 kg a.i/ha (PE), Butachlor @ 1.5 kg a.i/ha (PE) + Pyrazosulfuron@ 40g a.i/ha (PoE), Pretilachlor @ 0.5 kg a.i/ha (PE)and Pretilachlor @ 0.5 kg a.i/ha (PE) + Pyrazosulfuron (10 WP) @ 40 gm a.i/ha (PoE).A similar trend was observed at harvest. Response of weed control measures on weed control efficiency was found to be significant at all the stages of growth. AT 40 DAT maximum weed control efficiency was recorded with hand weeding at 25 and 50 DAT (91.61%) which was significantly superior to Butachlor @ 1.5 kg a.i/ha (PE) (82.00%), Butachlor @ 1.5 kg a.i/ha (PE) + Pyrazosulfuron@ 40g a.i/ha (PoE), Pretilachlor @ 0.5 kg a.i/ha (PE)(89.11), Pretilachlor @ 0.5 kg a.i/ha (PE) (82.77%) and Pretilachlor @ 0.5 kg a.i/ha (PE) + Pyrazosulfuron (10 WP) @ 40 gm a.i/ha (PoE) (88.22%). A similar trend was observed at 60 DAT and at harvest. The crop growth parameters, yield attributes and grain yield were recorded highest in spacing 15 x 15 cm over 20 x 15 cm and 20 x 20 cm in respect of number of tillers/m2, dry weight of plant (g/m2), LAI, CGR (g/day/m2), weed population/m2, weed dry weight (g/m2) and number of panicle/m2 but was found at par in case of weed control efficiency (%) and 1000-grain weight. The spacing 15 x 15 cm also showed superiority over 20 x 15 cm and 20 x 20 cm in respect of grain and straw yield (q/ha) and grain : straw ratio but influence of population density on HI was found to be non-significant. Simultaneously, closer plant spacing recorded significantly highest gross and net return as well as B: C ratio than wider spacing. The treatment weedy check (no weeding) recorded significantly higher plant height but achieved significantly poor growth parameters, yield attributing characters, yield and economics. Results revealed that among various weed control measures, hand weeding and chemical weedicides recorded significantly higher number of tillers/m2, dry weight (g/m2), LAI, CGR (g/day/m2), weed parameters, number of tillers/m2, length of panicle (cm), number of grains/panicle, 1000-grain weight (g), grain and straw yield (q/ha) and harvest index than weedy check treatment with at par response among themselves. However, chemical weed control practices fetched significantly higher yield and at par net return and B : C ratio as compared to hand weeding (twice) treatment in the experimentation

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