| Soil erosion and river jam, flooding, nutrient losses, soil degradation, water pollution aroused by erosion are the major environment concerns around the world. And they are the key points to sustainable agricultural development in China. Soil erosion in Jiangjiatang watershed in Lanxi county of Zhejiang province during exploitation from 1993-2000 was studied. 11 runoff plots and 6 catchments were built, and runoff and soil loss were monitored. Revised Universal Soil Loss Equation (RUSLE) and The Annualized Agricultural Non-Point Source Pollution Model (AnnAGNPS) were used to predict runoff, sediment yield and soil erosion. Results predicted by two models and monitored were compared. The major conclusions are as follows:1.Terrace, rotation by crop and grass, fir and bamboo notably reduce slope soil loss. Terrace, fir and bamboo markedly reduce runoff and large particle in sediment transported by runoff, rotation by crop and grass only evidently reduce large particle in sediment transported by runoff.2.Catchment 1, 2, 4 were mostly transformed from slope to terrace change since 1993, and chestnut , pomelo, orange, peach and bamboo were planted in 1993. Soil erosion were severe in first and second years, since then with plant cover increasing and soil consolidation, soil erosion has become steady3.Under condition of good light and heat in South China, if there were destruction by human vegetation could restored very well. So soil erosion could be ignored. Catchment 5, 3, 6 are reservation regions with plant coverage of 10-25%, 40-65% and 80% respectively, and their average erosion modulus is 21.77,7.37 and 2.75 Mg/ha/yr.4.Soil erosion in Jiangjiatang watershed mainly takes place between March and September, concentrated from April to July, especially in June. This is determined by the seasonal distribution of rainfall. Also serious erosion is brought by frequent farming activities.5.Rainfall, runoff and vegetation are mainly factors impacting soil loss in red soil watershed. Rainfall erosivity is more important than rainfall in slope soil erosion, but in watershed rainfall has more effect than rainfall erosivity in transporting sediment. Runoff is more important factor than rainfall in both slope and watershed. 6.Pluviograph data at Lanxi in the Western Zhejiang were used to compute the rainfall and runoff factor(R-factor), it is shown that the annual R value in Lanxi consists mainly of the period R value from 6 to 13 half month, the peak R valuecomes at 12 half month; Summer months (3-9) typically contribute 94.5% of the R-factor.The R value of 20-80mm rainfall makes up 55% of the annual R value, and the R value of 10-40mm/h rainfall erosivity holds 65% of the annual R value.7.A rainfall erosivity model using daily rainfall amounts to estimate rainfall erosivity was validated. The parameter of model is as follows:a=0.0043, b=48.13, c=1.09. The distribution of rainfall erosivity are highly seasonal with a single peak in June in western Zhejiang. The daily model could adequately describe the temporal variation and seasonal distribution of rainfall erosivity. The coefficient of determination of model is 0.89.8.RUSLE is a field model, when using the model in watershed, properly determining topographic factor is crucial. Based on GIS software Citystar length, gradient and area of slope profile can be extracted from topographic map.9.RUSLE can predict sediment yield, soil loss and soil detachment of slopes and watershed. The relative differences of sediment yields predicted by RUSLE over monitored in 1-5 catchment are 16.95%, -47.34%, -47.76%, 27.13% and -39.19% respectively. The predicted sediment yields are close to monitored.10.Based on RUSLE prediction, soil erosion in Jiangjiatang watershed can be divided in to 4 classes. 1) Serious erosion slopes, such as bare soil and sparse orchard, soil loss rate is more than lOOMg/ha/yr. 2) Moderate erosion slops, terrace, fruit garden in good vegetation and bamboo, the soil loss rate is 10-100Mg/ha/yr. 3) Slight erosion slopes, terrace and...
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