Half of the Mekong Delta, about two million hectares, consists of acid sulphate soils (ASS). This is one of the largest concentrations of these soils in the world. The soil turns acid when drained, and aluminium is released from the clay, which is toxic to crops. When the aluminium leaks into surface water it kills plants and fish. Because of these properties ASS are not very suitable for agriculture. Small wonder that they remained virtually unused until the 1960s. After the Vietnam war the country faced serious food shortages. The part of the Delta where the acid sulphate soils are is close to densely populated parts of Vietnam and, at the time, seemed ideal for agricultural production, because of its flatness and favourable climate. Large scale state farms were established in the area, but these failed due to lack of knowledge on appropriate soil management. At that point WAU was asked to assist Vietnam in studying the acid soils.
In 1980 a cooperation programme between the university of Can Tho and Wageningen Agricultural University was established. It was under this programme that the three PhD theses were defended last week, June 18 and 19. The graduates were Le Quang Tri and Le Quang Minh from Can Tho University, Vietnam and Tini van Mensvoort from WAU.
Van Mensvoort, director of WAU's MSc Soil and Water Programme, has been involved in the cooperation since the start. In the beginning research focused on the technical features of the soil but subsequently more attention was paid to the strategies of farmers themselves in finding ways to overcome the constraints in cultivating the soils. All three theses focus on the interaction between farmers and researchers. Van Mensvoort continues: The local knowledge and experiences of farmers form an essential contribution in research on land use on acid sulphate soils in the Mekong Delta. Both local specialists, like extension workers and planners, and scientists still make too little use of farmers' knowledge. For combining local knowledge with scientists' research results, land evaluation proves to be a good method for improving land use practice."
Le Quang Tri, researcher and lecturer at the Soil Science Department at the University of Can Tho, studied four different land use systems on ASS and characterised the soil and hydrological conditions over time during the growing season. One way in which farmers deal with these soils is by combining rice cropping with shrimp cultivation. This practice is carried out in areas subject to salt water intrusion from the sea. Rice fields are surrounded by ditches. During the dry season salt water enters these ditches and at high tide shrimp fry are taken in, which are then raised and harvested. As the rainy season starts the fresh rain water washes out the salt and rice can be grown.
Another method developed by farmers is growing upland crops, like pineapple, cassava and yams, on raised beds. During the dry season the soil turns acid and aluminium accumulates in the soil. The first rains wash out the soluble aluminium and lower the level of acidity. The elevated beds prevent the crops from being flooded later on in the rainy season, when the Mekong river often bursts its banks. On the basis of farmers' knowledge and expert research, Tri recommends individualised integrated management packages to optimise each of the land use systems. He noticed, for instance, that mulching raised beds leads to a 46% increase in yam production.
Tri's colleague Le Quang Minh found the reason for these higher yields: mulching slows down the accumulation of aluminium in the soil. Minh's thesis focused on the environmental side effects of cultivating acid soils in general and specifically of aluminium release. From the two examples it becomes clear that water flows are an essential feature of all land use systems in the Delta. At the same time, water is the means by which aluminium, acid and salt are transported. Minh is the first to quantify the toxic effects of cultivating acid soils. He has worked at the Faculty of Water Management of Can Tho University since 1978. In 1985, he graduated from the MSc Soil and Water Programme at WAU and at present he is the dean of the Faculty of Technology of Can Tho University.
Van Mensvoort explains that all three theses have produced very interesting scientific results in the field of soil science. Nevertheless, the three colleagues decided to emphasize the interaction between farmers and researchers. Van Mensvoort concludes from his research that exchange of knowledge takes place among scientists and among farmers but hardly at all between the two groups. Exchange of knowledge is a necessary precondition if farmers are to improve their land use and scientists are to understand what is happening. As Tri puts it: An astronomer can forecast exactly where a star is at midnight, but he cannot forecast where his teenage daughter will be at the same time. Correspondingly, a simulation model may be able to predict the aluminium concentration in soil water but may fall far short in characterizing complex agro-ecosystems."
According to Professor Vo-Tong Xuan, vice-rector of the University of Can Tho and member of the National Vietnamese Assembly, an important problem in the delta is the absence of marketing opportunities for agricultural products other than rice. This wider context of the Mekong Delta was addressed in the workshop organised by the C.T.de Wit school for Production Ecology, on June 18.
In his contribution Xuan outlines some of the dilemmas faced in the Delta's development process. Infrastructure is weak, local markets are limited and knowledge of processing techniques for other crops is scanty. As a result, most farmers stick to rice cultivation, since post harvest storage is relatively straightforward. Vietnam is a rice exporting country and that production is still increasing. However, the price of rice is quite low and rice farmers belong to the poorest section of society in Vietnam. According to Xuan, priority should be given to improving soil and water management, as well as to product diversification. Farmers in the Delta have tried to cultivate a whole range of different crops on the acid soils, with some success. Xuan feels that improving food processing knowledge could contribute to solving the problem of diversification.
Plans for future cooperation between the two universities include upgrading the study of biotechnology at Can Tho University. For WAU's soil and water management departments the cooperation programme will focus on sustainable land use development in the coastal zone. The mangrove forest in the zone is over-exploited. The forest is being cut down for fuel wood and shrimp cultivation.