Based on on-farm surveys implemented in the Ganges Delta in Bangladesh and the Mekong Delta in Vietnam, the dynamics of shrimp aquaculture in salinity-influenced coastal areas were analysed. Qualitative data were collected through interviewing both individual and group farmers in 2005 and 2006, as well as key informants and value chain stakeholders, to obtain an overview of the dynamics of salinity-influenced aquaculture in these two deltas. The first phase of the coastal area's agroeconomic evolution is related to the policy and infrastructure in the course of agroeconomic transformation. A second phase is characterized by the spread of shrimp aquaculture (in successive levels of technology), causing these coastal zones to become areas of strategic export product generation. Different factors such as government policy, demography and international market demand drove this evolution in both deltas. In a third phase, the risk associated with shrimp farming because of shrimp virus outbreaks led farmers to diversify or intensify the aquaculture farming system. The evolution of shrimp farming systems in both deltas has been toward greater diversification of aquaculture technologies and is dependent on both natural environmental factors such as saltwater period duration and soil quality, technical factors such as access to drainage and socio-economic factors such as investment capacity and market demand. Comparing the coastal area of Bangladesh and the Mekong Delta in Vietnam, the key factors identified were land ownership, access to knowledge for the improvement of shrimp culture technology and diversification of aquaculture production. The alternating rice-shrimp system (i.e. rice in the rainy season, followed by shrimp in the dry season) and diversified brackishwater polyculture show more stable economic returns in comparison to extensive and intensive shrimp monoculture in both areas. In Bangladesh, water management infrastructure, access to information and the development of information networks were highlighted as key factors necessary for the improvement of brackishwater aquaculture. In Vietnam, the higher level of technology used in coastal aquaculture underlined the need for the development of better management practices to reduce the environmental burden and to evolve towards sustainable production systems.
This study was carried out to test the hypothesis that diversification and polyculture (growing more than one crop/commodity at the same time in the same field) could contribute greatly to increased profitability and reduced risk for both rice-based and shrimp-based production systems in the coastal zone. Local authorities, community associations and farmers collectively selected study sites in seven land-use zones (LUZ). In each study site, farmer communities selected one demonstration farm (demo) and five nearby farms (controls) where farming activities were managed under current practices. The demos tested new diversified cropping systems and new or improved technologies. At the end of each cropping season, farmer-managed on-farm workshops - in which the participants were local authorities, community associations, the press, farmers - were conducted to compare the ease of implementation, yields, profits and the benefit-cost of the demos and the controls. At the end of the 3-year study, final on-farm workshops were arranged to give final ratings and recommendations for the tested systems and technologies, which were endorsed by local authorities for wide dissemination, with support from extension workers, village authorities, community organizations and the mass media. The rice-rice&fish system was recommended for freshwater zones and the shrimp&crab-fish system for saltwater zones. For the intermediate water quality zone, the shrimp-rice&fish system was recommended only for areas near the freshwater zone. Component technologies recommended for outscaling included: new high-quality rice varieties; using a drum seeder for rice seeding; nitrogen fertilizer management using a leaf colour chart; appropriate stocking density of tilapia, anabas and silver carp for freshwater zones; and crab and elongated goby for saltwater zones. Extensive aquaculture techniques were recommended for shrimp in the shrimp-rice&fish system and semi-intensive for the shrimp&crab-fish system. After 3 years of study, approximately 8700 farmers adopted the recommended systems and technologies on 11,550 ha. The participatory approaches have been successful in outscaling diversified cropping systems and new technologies, generating more benefits to farmers.
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