Sustainable Sloping Lands and Watershed Management Conference Estimation of Erosion and Erodibility of Soil in a Slash-and-Burn Cultivation Area of Northern

Using 137Cs as a tracer, the authors estimated erosion rates in a slash-and-burn cultivation area of the Lao PDR. There was great variability in the estimated erosion rates at each site investigated, including, in one village area, 2.5 mm year–1 in a low-yielding field, 1.25-1.88 mm year–1 in moderate-yielding field (A), and 3.13 mm year–1 in moderate-yielding field (B). Net accelerated erosion rates caused by cultiva-tion were evaluated by deducting the erosion rates recorded on a forested slope. This paper attempts to explain the variations in erosion rates in terms of the topographic conditions and soil properties associ-ated with erodibility. Erosion that occurred on the low-yielding field is explained by the fact that the soil had relatively poor aggregation and was easily dispersed by the impact of raindrops. No evidence was found for a significant association between erodibility and the severe erosion that occurred in moderate-yielding field B. Soil erosion remains an often undetectable problem of soil degradation that does not lead directly to readily apparent decreases in production. For sustainable cultivation it is important that measures to prevent soil erosion start now