Land-Use Sustainability of Composite Swiddening in the Uplands of Northern Vietnam: Nutrient Balances of Swidden Fields during the Cropping Period and Changes of Soil Nutrients over the Swidden Cycle

This study examined the sustainability of the swidden component of the composite swiddening system practiced by the Tay ethnic minority in Tat hamlet, Hoa Binh province in Northern Vietnam. This farming system is thought to be suitable for the uplands where land degradation is a serious problem. The common swidden rotation of two years of rice, two years of cassava and five years of bush-tall grass fallow was evaluated for the extent of land degradation during the cropping period by nutrient balance analysis, and for soil nutrient status throughout the swidden cycle through soil analysis. Four fields representing the individual years of cropping and three fields representing the first, the third and the fifth years of bush-tall grass fallow were selected for field measurements. Nutrient balance analysis indicated substantial losses of all major nutrients, particularly K, in all cropping years. Soil analysis also showed a decline in soil fertility during the cropping period and a partial restoration of soil fertility during the fallow period. However, only five years of bush-tall grass fallow was not sufficient to restore the original level of soil fertility. Thus, swidden fields in Tat hamlet are degrading, posing a serious threat to their land-use sustainability.