58 September 2009 Deepwater rice-fish integrated culture system: A viable option for increasing fish production as well as natural water harvest D. N. Das1, R. N. Mandal2, and P. K. Mukhopadhyay2 Deepwater rice (DWR), which constitutes traditional cultivars and plant height more than 140 cm, is usually grown under low-lying waterlogged areas that remain inundated by monsoon rains for 5-6 months a year, with water depth ranging 0.5-2 m. An international deepwater rice workshop in 1987 recommended the above concept of DWR based on Khush’s (1984), suggestion that the rice varieties, which were grown at the water depths of 0.5-1 m for more than one month, might be considered as deepwater rice (Mukhopadhyay et al. 1992). India has the largest area under DWR cultivation (Table 1), major areas of which are located in the states of Assam, Bihar, Orissa, eastern Uttar Pradesh, and West Bengal (Dutta 1981). Those states comprise 78.7 percent (21.1 million ha) of rice farming areas that are rain fed, out of which 16 percent (4.3 million ha) of the area is upland, 48 percent (12.9 million ha) lowland (0-50 cm water depth) and the remaining 14.7 percent (3.7 million ha) is deepwater areas. Most importantly, West Bengal is top among the five states (Table 2), having 24.32 percent (0.9 million ha) of DWR farming area in addition to having 0.82 million ha coastal saline low lands (Bhakta 1989, Kar et al. 2005). Such DWR areas, by and large, have low rice productivity, probably because of the immense variability in the area’s hydrologic conditions governed under several factors, such as variation in flood timing, depth and duration of submergence depending on rainfall, topography and flood overflows from the different sources. However, these areas are potentially capable of supporting the production of other yields like fish and freshwater shrimp. In waterlogged DWR areas, fish migrate from the nearby perennial water bodies and pass the major part of their life cycle. Usually, mature fish prefer those areas as their suitable niche for breeding, spawning and rearing of progenies, a scenario of common occurrence in DWR areas. Farmers of DWR areas traditionally collect those indigenous fish for their livelihood. Observations have reported that the production of those traditionally grown fish might range up to 100 kg/ha/season recorded in different DWR areas in West Bengal. That DWR areas are to be flooded during monsoon is a natural phenomenon, which cannot, perhaps, be averted. Hence, such a vast area should be accepted as nature’s gift A closed type of deep-water rice-fish farming plot having lateral trench rather than an adversity and be utilized for cultivation of at least one crop of fish along with rice. In this connection, the suitable technology (Mukhopadhyay et al. 1989), which can be widely accepted by the farming communities, should be implemented in those areas to culture fish so as to make them viable for production of rice and fish at the same time from the same area. Agro-Ecosystem of DWR Areas, a Suitable Fish Farming Zone The practice of rice-fish farming varies from zone to zone depending on the existing agro-ecosystem, which is then suitably modified with cultivation techniques such as field design, species used, stocking rates, sizes, crop rotation and crop availability (Ayyappan et al. 2004). Three types of field designs are primarily used: the shallow trench system within the rice field as seen in the Philippines, Indonesia and China; pond refuge adjacent to the rice field at one side as in India, Indonesia, Thailand and China; and the deepwater rice field system as in India and Bangladesh (Lightfoot et al. 1992a, Ayyappan et al. 2004).
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