AbstractSoil erosion were assessed at 30 sites in Ea Kao catchment of Vietnam by using fallout radio-nuclides. The soil samples was taken from top to foot of hill, in rectangular for Be-7 and cylindrical for analyzing Cs- 137. The radio-nuclides were determined by gamma spectrometry using high purity germanium detectors with a 30% relative efficiency. Soil erosion were estimated by models of He Q et al. (2002), Walling DE et al. (2002) and Tu TC and Hai PS (2014). The study results showed that soil erosion rates varied in a wide range and depended significantly on cover crops, slope, farming practices and soil conservation measures. Rate of soil loss in 2016 was higher than in average of 52 years (1964- 2016), because 20-30 years ago the land surface really covered by forest, which protected quite effectively soil from erosion. Land of annual crops had the highest rate of soil erosion, with 27.2-30.7 t ha-1 y-1 for upland rice and 29.8-33.6 t ha-1 y-1 for cassava, depend on model of Cs-137 or Be-7 applied. Coffee land had the least soil erosion rates. On high sloping land (more 25 degree), difference of average erosion in 52 years among land use types (coffee, tea, rubber, cashew, upland rice and cassava) were narrowed, due to the lands have just been used in recent time, 30-40 years before that they had been covered by forest. Making hedgerows of tephrosia between coffee rows, intercropping cassava and legumes, building terraces for upland rice were simple practices but high effectiveness to protect soil from erosion.
Keywords: Catchment; Farming Practices; Radio-Nuclides; Sloping Land; Soil Erosion.