Abstract:

【Objective】The aim of this study is to provide some references for decrease of soil loss and for improvement of ecological environment in Yanhe Basin of Loess Plateau by quantitatively assessing effect of returning farmland to forest (pasture) and changes of precipitation on soil erosion. 【Method】 The daily precipitation data from 35 gauges in the period of 1950-2000, soil type map, a digital elevation model (DEM), land use maps based on the interpretation of Landsat TM images acquired in 1997 and 2000 and NDVI maps from the images were used. The RUSLE was used as a model to calculate the unit soil loss and some suitable methods were also used to calculate the value of each erosion factor. Finally, the factor values and soil loss were calculated, the maps of the factor values and soil loss in each spatial unit were obtained. 【Result】 Firstly, the rainfall factor R value changed significantly from 775.32 MJ?mm?hm-2?h-1?a-1 in 1997 to 1 292.07 MJ?mm?hm-2?h-1?a-1 in 2000 primarily because of the change of precipitation. Secondly, the combined effect of the changes of slope cropland to forest land, pasture and the change in precipitation and the changes of the practice of engineering and tillage resulted in soil loss increased from 3 012 t?km-2?a-1 in 1997 to 4 671 t?km-2?a-1 in 2000. Thirdly, the C factor value which was defined by the land use and vegetation cover was 0.1714 before the change of slope cropland to forest land and pasture and 0.1592 after the change of slope cropland to forest land and pasture. The changes of C factor value resulted in the decrease of soil loss in this basin.【Conclusion】Returning from slope cropland to forest or pasture by itself decreased soil loss by 7.84%, whereas the precipitation itself increased soil loss by close to 71.28%, but both together increased soil loss by 59.26%. The effect of returning of the slope cropland to forest or pasture is obvious in decreasing soil loss.

Key words: soil erosion, change of slope cropland to forest land and pasture, precipitation change, Yanhe Basin