A thesis submitted in partial fulfillment of thesis requirements for the degree of Master of Science, School of Environment, Resources & Development

Thesis (M.Sc.) - Asian Institute of Technology, 1994

About 39% of the rice area in the Mekong Delta is cultivated under rainfed conditions. In recent years, increases in agricultural production considerably have come from the development of diversified rice-based farming systems in rainfed lowland rice areas (RLRs). For the purpose of understanding the existing farming systems and to help farmers to improve their farming practices, a survey was conducted to diagnose the major farming systems. The study area consists of two categories, shallow and semideep rainfed. 181 farmers in three locations in My Xuyen, Bae Lieu and Tran Van Thoi districts were interviewed. In this study, four major farming systems, rice monoculture, rice-shrimp, rice-upland crop and rice-fish system are described. The farm income and gross margin of major crops are determined. The results show that the four cropping patterns are adapted well to local ecosystem. The rice-shrimp and rice-upland crops systems take place in shallow rainfed area while rice-fish system is common in semideep rainfed area. Gross margin of rice production is lower than that of shrimp, fish and upland crops. Gross margin of water melon production is the highest at VN$ 14.5 million per ha (US$ 1 equal VN$ 10500 in early 1994). Fish, shrimp and upland crops production are the major sources of farm income. Rice-fish farmers obtain the highest net farm income at VN$ 18.7 million per year while rice monoculture farmers obtain only VN$ 2.8 million per year. Production function of rice, shrimp, fish, and upland crop is estimated. The level of economic optimum input use for rice, shrimp, fish, and upland crop is also examined. The results show that more input of seed, nitrogen, phosphorus, and herbicide should be used for rice production, but less nitrogen use should be practiced in rice-upland crops system. The inputs for shrimp and fish production such as seeds, feed, and other investments are in under-use level. For the production of water melon and mungbean, more nitrogen and phosphorus should be applied but less insecticides and labour should be used. The way to improve these farming systems, both economic and ecological aspects should be carefully considered. High yielding rice varieties should be applied in shallow RLRs so as to obtain high yield. The integrated farming systems e.g. rice-shrimp/fish, rice-water melon, and rice-mungbean systems should be promoted in suitable areas in RLRs