Direct seeding and weed control for rainfed and irrigated rice in northwest Bangladesh

The installation of shallow tube wells in many areas around Rangpur, in northwest Bangladesh, has allowed farmers to grow irrigated rice in the dry season in addition to rainfed rice in the monsoon season. While this raises land productivity, increasing costs are leading farmers to seek cheaper production methods and, in particular, reduce the requirements for labor.

Direct seeding of rice, in place of transplanting, is a potential means to achieve such savings as the need for a nursery and tasks such as pulling, transporting, and transplanting seedlings are avoided. Weeds constrain the adoption of direct-seeded rice, however, because we lose the advantage of weed suppression from transplanting rice seedlings into standing water. With direct seeding, the need for hand weeding may be reduced by the use of either a push weeder, in the case of row seeding with a drum seeder, or preemergence herbicides.

A team of scientists from the Bangladesh Rice Research Institute (BRRI), IRRI, University of Liverpool, and the Natural Resources Institute in the UK assessed the potential of direct seeding of rice in the dry and monsoon seasons of 2005, through field experiments and farmer participatory approaches.

Materials and methods. In on-station experiments, direct seeding was compared with the usual farmer practice of transplanting rice (TPR) in the dry and monsoon seasons. In direct-seeded (DS) rice, wet, germinated seed was sown on puddled land with a lightweight hand-pulled drum seeder or was hand-broadcast (BC only in 2005). Weed management options in the rice were compared: (1) hand weeding rice three times; (2) the BRRI push-weeder, followed by two hand weedings; (3) preemergence application of oxadiazon in DS rice or pretilachlor in TPR, each followed by one hand weeding. Establishment and weed control options were also assessed on-farm with five farmer groups in the 2005 dry season.

Results. The highest rice yields were associated with direct seeding and herbicide use (see table). Increased weed infestation resulted in a 40% increase in hand weeding for DS or BC rice compared with TPR.

Rice grain yield (tons per hectare) in on-station trials

Weeds

• The occurrence of important weed species among the different establishment treatments was similar.

• The fern Marsilea minuta accounted for the greatest biomass among the weeds, followed by the grass Echinochloa crus-galli. Cyperus difformis was the most important sedge.

• There was substantially more weed biomass in the broadcast and drum-seeded plots than in the transplanted plots.

• Ischaemum rugosum, Echinochloa colona, Fimbristylis miliacea, Paspalum distichum, and Cynodon dactylon were also present, though these are of minor importance.

Rice

• On-farm yields of irrigated rice established by the three methods were not significantly different. Across farms, these averaged 4.89 tons per hectare for TPR, 4.95 tons per hectare for broadcast, and 5.42 tons per hectare (± 0.185) for drum-seeded plots.

• Farmers reported lower labor requirements for DS rice (3 person-days per hectare) compared with uprooting seedlings and transplanting (77 person-days per hectare).

• Direct-seeded rice required less water with lower pumping costs than did transplanted rice.

Summary

• Yields of direct-seeded rice were as good as or better than those of transplanted rice in farmers’ fields and in station trials.

• With direct seeding, farmers had a labor savings of 74 person-days per hectare.

• Direct seeding by a drum seeder or broadcasting resulted in increased weed growth compared with transplanting.

• Attention needs to be focused on any changes in abundance of important grass and sedge weeds that may occur with the adoption of different establishment methods.

The trials continued in the 2006 boro season.

M.A. Mazid (BRRI), David Johnson (IRRI) (d.johnson@cgiar.org), and Joel Janiya (j.janiya@cgiar.org)

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