Preliminary survey on the rice cultivation in the Mekong delta was carried out in the dry season os 1985/86, supported by the Grant-in-Aid for Overseas Scientific Survey of the Ministry of Education, Science and Culture of Japan and helped by staff members of the Universuty of Can Tho, Socialist Republic of Vietnam. The preliminary survey aimed to elucidate the actual state of rice production in the Mekong delta. The survey team was organized from the specialists in crop science, plant pathology and soil science, to find out how increase the production of rice with high quarity without destroying the present ecosystem in the Mekong delta. From the viewpoint of soil science, acidity and ohosphorus deficiency are serious problems in the increase of rice production in the Mekong delta. Most of soils are derived from alluvial sediments. Among them, sediments of marine- and brackish-origin often contain large amounts of pyrite. Drainage and oxidation of sedimentscontaining pyrite are characterized by the development of storong acidity and lack of available phosphorus. Evwn if not so acid, most of soils in the Mekong delta are deficient in available phosphorus. This is problem common to the agricultural land of the tropical Southeast Asia and is due to the low level of total phosphorus. Application of phosphorus fertilizer is needed to increase rice production. Nitrogen fertilizer is also needed, but rice does not show any response to potassium fertilizer. Only soils of the narrow range along the big rivers of the Mekong system have good soil fertility. In this area, soils are derived from the sediments of river-origin and are rich in plant nutrients. The high soil fertility, along with good irrigation facility, supports the highest rice production of this area in the Mekong delta. Another problem from the land use is lack of irrigation water in the dry season. Construction of irrigation systems makes possible double-crooping of rice, but the irrigated land is kimited to about one-fourth of the total agricultural land in the Mekong delta and to the land near the big rivers. The area near the coast is suffered from salinity problem. Seawater intrudes into canals in the dry season. The rice cultivation in the dry season is difficult due to lack of fresh water for irrigation. However, the new cropping system, rice cultivation in the wet season and shrimp cultivation in the dry season, is prevailing in the area alng the coast.
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