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Improved Weed Management for Transplanted Aman Rice

C. R. Riches
Natural Resources Institute, University of Greenwich, Chatham Maritime, Kent ME4 4TB, UK

M. A. Mazid
Bangaldesh Rice Research Institute, Regional Station, Rangpur, Bangladesh

G. J. Uddin Ahmed
Bangaldesh Rice Research Institute, Gazipur, Bangladesh

A. M. Mortimer
School of Biological Sciences, University of Liverpool, Liverpool L69 7ZB, UK

M. A. Jabbar
Bangaldesh Rice Research Institute, Gazipur, Bangladesh

A. Orr
Natural Resources Institute, University of Greenwich, Chatham Maritime, Kent ME4 4TB, UK

Abstract/ Executive Summary:

Rainfed transplanted rice grown in the monsoon aman season accounts for more than 50% of the total area planted to rice in Bangladesh. Because of rising input costs, including labor, farmers are searching for ways to maintain income, by either increasing yields or reducing costs or both. On-farm trials in the High Barind Tract indicated that one-third of the farmers would be able to gain 0.5 t ha^–1 or more additional grain by undertaking more intensive or timelier weeding than is usual under current management practices. Higher yields were observed on-farm from a preemergence application of butachlor (1.25 kg a.i. ha^–1) compared with hand weeding twice. In Comilla District, trials of a range of weed management practices demonstrated that the yield advantage over the farmers’ practice, either one or two hand weedings, was on average 355 ± 18 kg ha^–1 for Rifit (pretilachlor), 281 ± 39 kg ha^–1 for Machete (butachlor), and 210 ± 34 kg ha^–1 for Ronstar (oxadiazon), each followed by one hand weeding in aman 2003. Partial budgets calculated for inputs and returns showed that hand weeding was less profitable than herbicides in rainfed rice, incurring US$72 ha^–1 lower return. Use of a push weeder plus one hand weeding was less profitable than herbicides, incurring $49 ha^–1 lower return. To date, herbicides have been largely promoted for irrigated rice in Bangladesh. The trial results demonstrate that under rainfed conditions early in the aman season, water levels are adequate for herbicides to work effectively. The use of herbicides allows timely weed control when there is a shortage of labor and avoids transaction costs, such as the provision of meals and time needed to source laborers. Herbicides are likely to be adopted by growers experiencing labor shortages, particularly on large farms and for farmers seeking to reduce input costs. Sharecroppers and tenant farmers who pay rent are primarily concerned about obtaining a high aman yield, so innovations that raise aman yields (such as herbicides that will have a similar effect as a timely first weeding) are also likely to be adopted on sharecropped plots, even when costs are not shared between the landlord and tenant.

Keywords: Weed management, Aman rice, Transplanted Aman rice

Location: In Bangladesh

Start Date: 00-00-2003

End Date: 00-00-2011

Program Area: Pest Management

Commodity: Weed management, T. Aman

Objectives:

To identify Improved weed management for transplanted aman rice.

Methodology:

The study was conducted in Nachole, Tanore, and Rajabari thanas (administrative areas) in Rajshahi District in 2000. Eighteen farmers in one village of each thana provided a field for a yield-gap study. Six were on each of three toposequence positions, identified by farmers as “upper,” “medium,” and “low,” covering little more than 5 m difference in elevation. Two plots of 25 m² were marked out in each field after farmers had transplanted. One plot was left unweeded and the other was maintained weed-free for the first 50 days after transplanting (DAT) by hand weeding at 21, 33, and 50 DAT in addition to any weeding done by the farmer. The farmer determined the timing and frequency of weeding on the rest of the field and other crop management practices for the whole field, including cultivar, time of transplanting, and nutrient management. Rice yield data were collected from subplots of 10 m² and from a third plot of this size from the part of the field where the farmer determined the timing and frequency of weeding. Data were analyzed using a mixed model design, farms being nested within villages, and toposequence being considered a fixed effect. The abundance of the five most prevalent weed species in unweeded plots was ranked at each site at 110 DAT on a 1–5 scale. A survey questionnaire was used in early 2001 to collect household-level information on socioeconomic variables and information on rice weed management from 119 households sampled from five Barind villages, including those where yield-gap plots were located. For comparison, data were also collected from 90 farms in three thanas in Comilla District. The questionnaire was designed to allow characterization of existing weed management practices, and to determine the causes of untimely weeding and how land tenure may effect adoption in alternative practices. In 2003, a trial was planted by 91 farmers at sites covering 15 extension blocks in 9 thanas distributed through Chapai Nawbgonj, Naogaon, and Rajshahi districts to evaluate timely weed control in aman rice with the granular herbicide Machete (active ingredient butachlor 5%). At each site, two plots were planted with cultivar Swarna and two with BRRI dhan 31. One plot of each variety was weeded twice by hand at 20 and 35 DAT. Machete (butachlor 1.25 kg a.i. ha^–1) was applied to the other plot within 3 days of transplanting and a follow-up hand weeding was undertaken at 35 DAT. On-farm trials of weed management practices were also carried out in T. aman of 2003 and 2004 at 20 sites per year across three thanas in Comilla District. Treatments were superimposed on fields managed by farmers’ choice of cultivar, planting date, and nutrient management. All herbicides were applied within 5 days of transplanting by knapsack sprayer, except for granular Machete that was broadcast, and a follow-up hand weeding was undertaken at 30 DAT. The following treatments were applied: 1. Rifit (pretilachlor 470 g a.i. ha^–1) + one hand weeding 2. Argold (cinmethalin 7.5 g a.i. ha^–1) + one hand weeding 3. Machete (granular butachlor 1.25 kg a.i. ha^–1) + one hand weeding 4. Hand weeding at 15 and 30 DAT 5. BRRI rotary push weeder at 15 DAT + one hand weeding at 30 DAT 6. Farmers’ practice of weed management—this was weeding either once or twice by hand with variable timing between sites 7. No weeding

Source of Information: International Rice Research Institute (IRRI), 2008, ISBN 978-971-22-0229-2

Article Link (Online Journal):

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Considerable risk is associated with rainfed rice production. In 2004, for example, flooding destroyed a large area of the crop in Comilla and lengthy periods of submergence reduced yield where rice survived. However, losses were less on plots where herbicides had been applied as these cost 50% to 65% less than hand weeding, depending on the product used. The timing and duration of standing water in rice fields early in the season influence weed infestations by the time a supplementary hand weeding is undertaken by 30 DAT. An important component of the knowledge that farmers need to use herbicides effectively, particularly in aman, is the need for timely follow-up hand weeding. This is particularly important on fields where perennial weeds, particularly the rhizomatous grasses Cynodon dactylon, Paspalum distichum, and Leersia hexandra are abundant, as observed at several locations in the Barind, as these are not controlled by herbicides.

Knowledge Management: Journal