Closing the gap

Improving farmers' livelihoods in Bangladesh - resolving the problem of yield gaps due to weeds and identifying opportunities for innovation

Farmers in Bangladesh grow rice over a wide range of rainfed and irrigated lands. Researchers examined two contrasting farming systems in Comilla and Rajshahi districts to learn how different rice-cropping systems affect weed abundance and methods for their management.

Study Regions

Comilla District. The expansion of irrigation in Bangladesh over the past 30 years has resulted in intensification of rice production. In Comilla District in southeastern Bangladesh, cropping intensity has reached 188%. Some 17% of the area is single-cropped, 57% double-cropped and 26% triple-cropped. The three cropping seasons are boro, an irrigated, dry-season crop that is transplanted in February; aus, a rainfed crop that is direct-seeded or transplanted in the pre-monsoon period; and aman, the most widely planted season, in which rice is transplanted (T. aman) at the onset of the monsoon in July. The double-cropping pattern boro-fallow-T. aman covers the largest area of land in the district (nationally, it occurs on 2 million ha, producing 50% of the rice harvest in Bangladesh). The triple-cropping system boro-transplanted aus-T. aman is another major cropping pattern in Comilla. The district has long been recognized as progressive, planting modern rice cultivars for the entire boro crop, 80% of the T. aman crop and 55% of the aus crop.

Rajshahi District (BarindTract). Farmers here use predominantly a rainfed cropping pattern in which transplanted aman rice (T. aman) is grown during the wet monsoon period of June to October. Due to the limited irrigation potential of the area, there is relatively little production of boro (irrigated) rice in the rabi (dry) season. Small areas of wheat that require irrigation only once are planted adjacent to farm ponds. Chickpea, linseed or mustard may be planted in the dry season, but farmer preference for the high-quality but late-maturing rice cultivar Swarna (135-145 days duration) limits the opportunity to establish these crops on residual moisture. Thus, much of the land lies fallow during the rabi season. Cultivation intensity is only about 120%. Much of the area is owned by absentee landlords and sharecropped. Members of the adivashi (tribal) community commonly work as field laborers.

Measuring yield gaps

More than 100 farmers in both districts participated in measuring the yield gaps due to weeds. In each farmer's field one portion was left unweeded, and another portion was maintained weed-free (by researchers weeding at 21, 35 and 48 days after transplanting in addition to weeding completed by the farmer). The remainder of the field was weeded as usual. Cultivar choice and all other crop management activities were normal farmer practice.

Farmer-participatory studies in transplanted 
rice in Bangladesh (T. aman season). The pegs 
mark yield-assessment plots in a farmer's field.

The results in Comilla District were as follows:

• The highest yields from weed-free plots varied from 3.75 to 5.5 t ha-1. Yield gaps due to inadequate weeding varied from 0.2 to 1 t ha-1 on 67% of farms. Gaps of more than 1 t ha-1 were observed on 23% of farms.
• The yield gained from farmers' own weed-management practice ranged from near zero to 1 t ha-1, averaging 0.3 t ha-1.
• Some 30% of farmers could boost harvests a further 0.5 t ha-1 or more by investing in additional weeding.
• In the T. aman season, no significant gains resulted from additional nutrients or weeding. In the boro season, when irrigation gives farmers control over water, the mean yield gain from additional weeding was 0.2 to 0.7 t ha-1, depending on how much water the soil retained.

In Rajshahi District, studies across toposequences showed the following:

• Average attainable yields without weeds were higher than 3 t ha-1 on 85% of the farms. At 3.42 t ha-1, the mean yield on low-lying fields was significantly below that of fields on upper (3.9 t ha-1) and intermediary (4.0 t ha-1) positions in the toposequence.
• In 54% of the fields, yield gaps due to insufficient weeding were between 0.5 and 1 t ha-1, and in 26% of the fields the gap was over 1 t ha-1. The yield that farmers gained through customary weed management varied from 0.33 to 0.47 t ha-1. On average, farmers gained more by weeding fields low in the toposequence (0.51 t ha-1) than from weeding those in the upper (0.35 t ha-1) or intermediary (0.37 t ha-1) positions.
• At 34% of the sites studied, farmers stand to gain more than 0.5 t ha-1 in yield by additional weeding.
• Overall, applying more fertilizer did not significantly increase yield, but additional fertilizer combined with additional weeding raised yield by 0.76 t ha-1. The greatest yield increase occurred low in the toposequence, where fields showed a yield increase of 0.9 t ha-1 as a result of improved weeding and fertilizer.
• Funded by the Natural Resources Institute[PF1] (NRI) and the Department for International Development (DFID, http://www.dfid.gov.uk/), this work was a partnership of the Weed Ecology Workgroup, M.A. Mazid and J. Uddin Ahmed of the Bangladesh Rice Research Institute, C.R. Riches and A.W. Orr of the NRI in the U.K., and M. Mortimer and L. Wade of IRRI.

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