Abstract
Plot experiments were conducted in a hilly farmland of northern Vietnam to evaluate the effects of slope, soil, land cover and rainfall on soil erosion. Each plot (100m2 in area) had a low or medium slope (8% or 14.5 % gradient) and either had a land cover of cassava or was bare. Rainfall in 10-minute intervals, daily soil loss from each plot, and monthly canopy cover for cassava plots were observed during the rainy season (May-September) of 2000. The effect of slope was evident, as bare and cassava plots on the medium slope yielded 3.3 and 5.0 times, respectively, greater soil losses than plots with low slope. Surface soil components of gravel, sand, silt and clay (>2.0, 2.0-0.02, 0.02-0.002 and <0.002mm in diameter, respectively) was not identified as affecting soil loss. There was a site-specific effect on the soil loss. The effect of crop cover on the soil loss did not exceed the maximum of the site-specific effect. The maximum 10-minute rainfall was 18.5mm. The percentage of 10-minute rainfall intensity greater than 25mm h-1, a threshold value proposed for soil detachment under tropical conditions, was characterized as low (7%) . A positive correlation between the daily maximum 10-minute rainfall and daily soil losses was found. The threshold 10-minute rainfall for the loss of soil was 2.3mm or 13.8mm h-1.
