Analysis of the processes that generate surface runoff and soil erosion using a short-term water budget on a mountainous sloping cropland in central Vietnam.

• Water erosion mechanisms on sloping cropland in central Vietnam were investigated. • Using the short-term water budget could successfully analyze water erosion processes. • Tropical storms strongly affect the rainfall regime of the research site. • Crop cover showed a substantial influence on soil loss and runoff generation. • The seasonal changes in water erosion mechanisms were significant. Water erosion has created severe degradation problems in Vietnam and its Thua Thien Hue Province because it lies on the tropical typhoon belt and frequently experiences typhoons and floods. To clarify which environmental factors affect runoff generation and soil loss under specific climatic and soil conditions in the study area, we analyzed the short-term water budget for almost two consecutive years, using small-scale runoff plots developed on a slope of the highland region. Four treatments were established: February cassava (Manihot esculenta) plot, bare land plot, April cassava (Manihot esculenta) plot, and April cassava (Manihot esculenta) + September acacia (Acacia hybrid) intercropping plot. Our results showed that the early planting of cassava (February cassava) was advantageous for decreasing soil loss by the early development of soil surface coverage and decreasing surface runoff. On the other hand, acacia intercropping did not seem as effective in suppressing surface runoff and soil loss, relative to cassava monocropping. Runoff generation was determined by rainfall volume and maximum rainfall intensity (at 10 min intervals). In addition, initial volumetric water content was an important driving factor of outcome variables in the plots cultivated during the minor rainy seasons. The mechanisms of water erosion were different in the minor and major rainy seasons: in the minor rainy seasons, the runoff volume generated during rainfall events was the decisive factor that triggered soil loss; whereas in the major rainy seasons, a threshold of 10 min of continuous rainfall was the driving force of soil loss. [ABSTRACT FROM AUTHOR]