An evaluation of the sustainability of farming systems in the brackish water region of the Mekong Delta

• CSIRO Marine Research, Australia
• Sub Institute of Water Resources, Vietnam
• University of Western Sydney, Australia
• University of Can Tho, Vietnam
• Geological Survey of Vietnam, Vietnam
• University of Agriculture and Forestry, Vietnam
• Australian National University, Australia

The Mekong Delta is the 'rice bowl' of Vietnam, being responsible for nearly half the country's rice production. However, it is not suitable for year-round rice production, because when rainfall is insufficient during the dry season salty water moves up the Delta from the sea. The rice-shrimp farming system makes use of the land during this period, by growing and harvesting shrimp in the salty water. When the rains come, fresh water moves down the river, flushing out the brackish water and allowing rice cultivation again.
Rice-shrimp farming, started in the area in the 1960s, has become much more popular in recent years. Surveys have shown that this combined farming approach generates about twice as much income as rice-only farming. But it needs careful management to avoid problems such as increased salinisation of the land, build-up of marine sediment in the rice fields, and a proliferation of rice pests (traditional pesticides kill the shrimp and so cannot be used). Surveys show that yields of both rice and shrimp can decline over time.

The main aim of this project was to identify appropriate management strategies and government policies applicable to the farming systems that operate in this brackish water coastal region. The ultimate goal was to create sustainable management practices that would increase productivity and raise incomes without causing environmental problems.

The project was implemented through a detailed assessment of the economics, social characteristics and resource potential of farms in the region. Extensive data were gathered on farming in the region. These included experimental and observational data on soil type and condition, water availability and quality, and shrimp and rice production. Soil and groundwater mapping was also carried out.
Economic and social information collected through surveys and questionnaires was subjected to statistical analysis in Australia. Existing models of rice growth were assessed to find out which one best fitted the conditions in the shrimp-rice farms of the Delta.
The shrimp production system was examined by constructing nutrient budgets, measuring the water and sediment quality in shrimp ponds, and tracing major nutrients pathways in the ponds.
Rice-shrimp farming systems in the Mekong Delta increased dramatically after the project's inception. As a result, the project initiated additional activities. Firstly, the scope of the project was extended to include a new component on the response of rice varieties to saline conditions. The International Rice Research Institute (IRRI) undertook the additional component in collaboration with Cantho University. Secondly, an Australian shrimp health expert was brought in to examine newly emerging shrimp disease problems, to confirm that shrimp viral pathogens (causing white-spot disease) were the probable cause of the dramatic mortalities of farmed shrimp in the Mekong Delta, and to help define sustainable management strategies.

The project has greatly assisted the dramatic expansion of rice/shrimp farming taking place in the Mekong Delta. For example, a group of farmers formed a consortium to carry out shrimp farming using the best practice procedures identified by the project.
Reviewers found that significant progress had been achieved towards understanding the ecological processes, and other factors, underlying the environmental and economic sustainability of rice-shrimp farming systems in the Mekong Delta. Two subjects stood out - one was on the effect of salinity on growth and production of a variety of rice, the other on salinity dynamics in rice fields and their relation to rice production.
Sedimentation was another environmental issue examined. Shrimp culture has greatly accelerated the rate of accumulation of sediment because much greater volumes of water (carrying suspended sediments) are now introduced into the rice fields for flushing. The scientists showed that the practice of high water exchange, during the shrimp production cycle, had negative impacts on the rice-shrimp system, and demonstrated that reducing water exchange reduced sedimentation and improved shrimp production.
Bio-economic modelling was effective in establishing the complex relationship between the many environmental parameters faced by the shrimp-rice farmers and the considerable income risk they entailed. The model explained income risk in relation to operational factors in a way that could be presented easily to farmers and policy makers.
The project was partially responsible for a new Vietnamese Government decree, which recognised that farmers should be allowed more freedom to implement farming systems rather than being restricted to systems compatible with national level production targets. The Deputy Prime Minister of Vietnam decided on the basis of the project findings to allow farmers to diversify into shrimp culture in coastal areas and to extend the technology to other provinces.
As well, local policy makers are now trying to regulate land practices and thus reduce economic and environmental risks - in some areas in the Mekong Delta land has now been zoned as suitable only for integrated rice-shrimp farms.
To continue the study of shrimp health a fully equipped shrimp viral screening laboratory has been installed at Cantho University and is in constant operation for screening farm stocks and in ongoing shrimp virus research.