Assessing soil erosion in a terraced paddy field using experimental measurements and universal soil loss equation

The study assesses the effects of event rainfall on the soil erosion in terraced paddy fields under rice cropping, fallow, and green manure planting. A 0.75-ha terraced rice field was used to investigate the soil erosion under the regular cultivation of rice in 2005, fallow in 2006, and planting with green manure in 2007. The results show that infiltration rates significantly increase when a terraced paddy field is under fallow or is planted with green manure; the paddy is more vulnerable to embankment collapse and increased the rates of soil erosion. In an experimental field, suspended solid in run-off samples reached the maximal concentrations of 1700 mg/l for fallow in 2006, and 3400 mg/l for manure planted field in 2007, during heavy rainfall events. These values were significantly greater than the erosion rate of 500 mg/l recorded for rice cropped field during 2005. The estimated annual erosion rate was 4.15 ton ha(-1) yr(-1) for green manure planted field, which was significantly higher than that of the rice-planted terraced paddy (0.77 ton ha(-1) yr(-1)). Moreover, terraced paddy runoff significantly increased when planted with green manure. Soil erosion rates calculated by the Universal Soil Loss Equation (USLE) from the optimal available data were considerably higher than the field-measured values. The comparison revealed that soil conservation using rice-planted terraced paddy was more effective than that resulting from other uses. The government should formulate effective measures and maintain sustainable rice planting in the terraced paddies. (C) 2012 Elsevier B.V. All rights reserved.