Topographic Differentiation Simulation of Crop Yield and Soil and Water Loss on the Loess Plateau
黄土高原作物产量及水土流失地形分异模拟

De-farming slope farmland has been an effective measure in recent years for the improvement of the eco-environment and the mitigation of soil and water loss on the Loess Plateau. This paper, taking the Yangou Basin as a case study and using day-by-day meteorological data of Yan'an station in 2005, simulated and analyzed the quantitative relation between crop yield, soil and water loss and topographic condition with the aid of WIN-YIELD software. Results show that: 1) Topographic gradient has important influence on crop yield. The bigger the gradient is, the lower the crop yield. Yields of sorghum and corn decrease by 15.44% and 14.32% respectively at 25o in comparison to the case of 0o. In addition, yields of soya, bean and potato decrease slightly by 5.26% , 4.67% and 3.84% , respectively. The influences of topographic height and slope aspect on crop yield are slight. 2) Under the same topographic condition, different crops' runoff and soil loss show obvious disparity. The benefit of soil and water conservation from high to low ranks soya, bean, potato, corn and sorghum. Topographic gradient has important influence on soil and water loss. In general, the changing trend is that the soil and water loss aggregates with the increase of gradient, and the maximal amount occurs around 20o. The influence of topographic height is slight. Topographic aspect has a certain effect, and the fundamental characteristic is that values are higher at the aspect of south than north. 3) Topographic gradients of 5o and 15o are two important thresholds. The characteristics about soil and water loss with the variation of topographic gradients show that: the slope farmland with gradients less than 5o could remain unchanged, and the slope farmland more than 15o should be de-farmed as early as possible.