Tillage, crop establishment, residue management and herbicide applications for effective weed control in direct seeded rice of eastern Indo-Gangetic Plains of South Asia

Weeds are the major production constraint in direct seeded rice (DSR) due to the concurrent emergence of competitive weeds and absence of water at initial growth stages to smother weed growth, leading to decreased crop yield. DSR has emerged as an alternative to the conventional water, labour and energy-intensive puddled transplanted rice (PTPR) in the eastern Indo-Gangetic Plains (IGP) of India. Hence, three field experiments were conducted (2008-2010) to evaluate integrated weed management options that included transplanted rice under puddled and unpuddled conditions, zero till DSR with or without residue retention and cover crops, zero till transplanted rice (ZTTPR) (experiment I); different combination of herbicides with or without cover crops (experiment II and III). Results revealed that during 1st year of study, zero-till direct seeded rice (ZTDSR) with (ZTDSR + R) or without (ZTDSR-R) residue retention and ZTDSR after the cover crops of sesbania [Sesbania aculeata (Willd.) Pers.] (ZTDSR + SB) or cowpea [Vigna unguiculata (L.) Walp.] (ZTDSR + CP) had greater weed density and dry matter accumulation than puddled transplanted rice (PTPR). However, in the 2nd and 3rd years, similar or lower weed density and dry matter accumulation was recorded in zero-tilled (ZT) plots. In 3rd year, plots under ZTDSR-R, ZTDSR + R, ZTDSR + SB, and ZTDSR + CP accumulated 14.3, 33.3, 23.1, and 60%, respectively, less weed dry matter over PTPR. Plots under ZTDSR produced almost similar or more grain yield to PTPR in all the three years of experimentation. On the basis of 3 years average data, the highest grain yield was recorded in plots under ZTDSR + R or R followed by ZTTPR and ZTDSR + CP. While in experiment II, mungbean [Vigna radiata (L.) R. Wilczek] as cover crop fb bispyribac-Na at 25 g ha(-1) resulted in the highest grain yield in 2008; but in 2009, weed free plots were superior-most. With regard to herbicides, pre-emergence application of pendimethalin EC at 1000 g ha(-1); effectively controlled aerobic grassy weeds such as Eragrostis tenella var. japonica (Thunb.) Roem. & Schult. but was ineffective against Echinochloa colona (L.) Link. Similarly, bispyribac-Na at 25 g ha(-1) was most effective for control of E. colona and Commelina benghalensis L., but incompetent against E. tenella. Overall, from the weed management viewpoint, this study recommends combination of pendimethalin at 1000 g ha(-1) fb bispyribac-Na at 25 g ha(-1) for effective control of diverse weed flora encountered in DSR.