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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. •Tillage, residues, cover crops & herbicides effects on weeds of direct seeded rice (DSR). •DSR had more weeds than puddled transplanted rice in 1st year but, similar and less weeds in 2nd & 3rd years. •Pendimethalin fb bispyribac–Na effectively controlled diverse weed flora in DSR. [ABSTRACT FROM AUTHOR]

Water, energy and labour scarcity, increasing cost of production, diminishing farm profits and uncertain weather events are major challenges faced by the farmers under intensive tillage based conventional rice-wheat (RW) production system of Indo-Gangetic Plains (IGP) in South Asia. To address these challenges, conservation agriculture (CA) based crop management practices are being developed, adapted and promoted in the region. We evaluated agronomical productivity and economical profitability of various combinations of tillage, crop establishment and residue management practices in rice-wheat rotation of Eastern IGP of India: a smallholder, poorly resourced and most vulnerable regions for the climatic variability. The long-term trial was initiated in 2006 having 7 combinations of tillage, crop establishment and residue management in rice-wheat rotation. These consisted of conventional till puddled transplanted rice followed by conventional tilled wheat (CTR-CTW); CTR followed by zero tilled wheat (CTR-ZTW); direct seeded rice followed by wheat both on permanent raised beds (PBDSR-PBW); zero-till direct seeded rice followed by CTW (ZTDSR-CTW); ZTDSR followed by ZTW without residues (ZTDSR-ZTW); ZTDSR followed by ZTW with residues (ZTDSR-ZTW+R) and unpuddled transplanted rice followed by ZTW (UpTPR-ZTW). All these treatments were completely randomized and replicated thrice within a block. During the initial three years of experimentation, we recorded higher rice grain yield in conventional tillage based rice systems (i.e. CTR-CTW and CTR-ZTW) than in CA based systems (i.e. ZTDSR-ZTW, UpTPR-ZTW). During the fourth and fifth years, the rice yields under CT and CA were comparable whereas sixth year onwards, higher yields were recorded under CA based system than in CT based systems. However, the wheat yield was higher in CA based system right from second year onwards. We observed the lowest wheat yield in the system where preceding rice crop was grown with intensive tillage operations (CTR). RW system productivity was higher in almost all the CA based systems than in the CT based and mixture of CT and CA based systems from the second year onwards. The net returns were always higher in CA based systems than in CT based system although the significant differences were obvious only from fourth year onwards in rice and second year onwards in wheat as well as at the system level. The higher grain yields and economical advantage of CA was realized after 2-3 years as the adaptation of CA based component technologies evolved over the time. In medium term, we found CA based systems to be agronomically and economically superior to CT based systems for rice-wheat rotation in a smallholder production system of Eastern IGP of South Asia. Hence, CA based RW production system is one of the pathways for improving productivity, income and food security while sustaining the natural resources in smallholder production systems of Eastern IGP. [ABSTRACT FROM AUTHOR]