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attested by Fig. 2). Diversity in the weed flora results from differential patterns offlooding and drainage that selectively determine seed germination, seedling emergence,and survival. However, on poorly leveled fields with rain-dependent flooding to veryshallow depths, heterogeneous soil surfaces will offer different depths of and durationof flooding, which will enhance diversity and potentially lead to similarity in the floraof transplanted and direct-seeded rice.Interspecific selection of known strongly competitive weeds of rice such asIschaemum rugosum and Echinochloa species is likely to occur with the serial useof direct seeding. Increased use of fertilizer to improve rice yield may influence thisprocess, although further scientific evidence is needed.The use of early postemergence herbicides that have broad-spectrum activitymay, however, lead to the subsequent dominance of rhizomatous or stoloniferousweeds (e.g., Cynodon dactylon, Paspalum distichum), which require close attentionin later manual weedingAlthough it is clear that the introduction of DSR into the Barind has significantyield and economic advantages for farmers, sustainability of the production systemwill depend upon an awareness of the responsiveness of the rice weed flora to bothcrop establishment and management practices. Strategies of weed management mustanticipate a change in target weed species against the background of high diversityand seasonal variation in the weed flora.Experience elsewhere suggests that, when diversification of herbicide mode ofaction occurs in the market place, there are consequential responses in target weedspecies. This will continue to place reliance on manual weeding.ReferencesAzmi M, Mortimer AM. 1999. Effect of tillage practices, seeding rates and herbicides on barnyardgrassinfestation (Echinochloa crus-galli) in direct seeded rice. 17th Asian-PacificWeed Science Society Conference. 2:199-204.Brammer H. 1997. Agricultural development possibilities in Bangladesh. Dhaka: UniversityPress Limited.Fujisaka S, Moody K, Ingram K.1993. A descriptive study of farming practices for dry seededrainfed lowland rice in India, Indonesia and Myanmar. Agric. Ecosyst. Environ. 45:115-128.Hill JE, Mortimer AM, Namuco OS, Janiya JD. 2001. Water and weed management in directseededrice: are we headed in the right direction? In: Peng S, Hardy B, editors. Riceresearch for food security and poverty alleviation. Los Baños (Philippines): InternationalRice Research Institute. p 491-510.Mazid MA, Jabber MA, Mortimer M, Wade LJ, Riches CR, Orr AW. 2003. Improving rice-basedcropping systems in north-west Bangladesh: diversification and weed management. TheBCPC International Congress, Crop Production and Protection. p 1029-1034.Mazid MA, Jabber MA, Riches CR, Robinson EJZ, Mortimer M, Wade LJ. 2001. Weed managementimplications of introducing dry-seeded rice in the Barind Tract of Bangladesh.Proceedings of the BCPC Conference – Weeds 2001. 1:211-216.Long-term sustainability in weed management for direct seeding of rainfed rice 77