Enhancing Soil Fertility in Northern Mountainous Areas of Vietnam by Developing Rhizobial Inoculants for Cowpea Vigna Unguiculata (var. Cylindrica) in Intercropping Systems

Cassava and maize are widely grown in the Northern mountainous regions of Vietnam. By applying huge amount of mineral fertilizers and promoting monocropping, the farmers have hugely contributed to soil degradation with as direct consequence to the decline of crop yield by unsustainable management practices. Legume-based intercropping system, one of the most widespread agroecology practices, have been widely promoted by scientists and the local authorities in Northern Vietnam because of their numerous advantages: better use of land, economic benefit, diminishing soil erosion, and also gradually increasing soil N content through biological nitrogen fixation as well as mulching legume residues. Nevertheless, the upland farmers have no idea about the use of commercial rhizobial inoculants and their potentials. This study aimed at assessing the needs to promote such rhizobial inoculants in the 2 districts in Yen Bai province of Vietnam, where cowpea is intercropped with cassava and maize. Our results showed that the natural nodulation of cowpea was really low at different soil characteristics and slope categories. There are indigenous rhizobial strains in the soils but it is not sufficient for them to form effective symbiosis with cowpea. Unfortunately, there is no valid commercial inoculant product on the markets in Vietnam until now, it is imperative to develop effective rhizobial inoculants for grain legumes for Vietnam, as well as in the whole South East Asia. There are markets for private companies willing to open new business on such activities. The presence of commercial inoculants on the markets would help in sense of agroecology to improving soil health and building sustaining agricultural systems in this zone.