In order to boost grain yield of soybeans by cultural practices, an experiment was carried out with two most promising soybean varieties in Mekong Delta , VN. The experimental design is split plot design with three replicates . Plot size is 6. 5m x 2m , with and/or without nutrient foliar spraying in main plots , and seeding rate is in subplots with four different seeding treatments: 40 x 20 cm, 40 x 5 cm, 30 x 10 cm and 30 x 5 cm that is, from 25 plants per square meter to 66 plants per square meter .

Wild species of cultivated plants are well known to possess a high potential of adaptability manifested by high tolerance to unfavorable environmental conditions and to pathogens. They are often carriers of valuable biochemical properties. To have these properties transmitted to cultivated species would no doubt be advantageous from the point of view of agriculture .

The extension of soybean cultivation in the south part of Europe is limited by climatic conditions and, above all, by drought appearing each year during summer, in a time which is a critical period for water supply of soybeans: the grain and pod filling stages (Mingeau , 1975). By action of this drought, grain yields may decrease drastically. As irrigation is often impossible, one of the most important breeding objectives in France is drought tolerance . Although water relations of ten should be studied in soybeans , varietal differences were rarely investigated except by Mederski and Jeffers (1973) and Sammons et al. (1978 , 1979).

Soybean cyst nematode (SCN) has emerged as one of the most serious pests of soybeans. Over 80% of the cultivable area in southeast Missouri is infested with this organism . Several varieties resistant to SCN race 3 have been developed and released .