Abstract: 【Objective】Soil surface microtopography is one of the important factors that affects processes such as surface depression storage, penetration rate and surface runoff. Conversely, some of these processes also alter microtopography due to erosion and deposition. The objective of this paper was to investigate the dynamic variation characteristics of microtopography under different rainfall patterns, which to further understand water erosion mechanism on sloping farmland, and to provide a scientific basis for optimizing the configuration of tillage measures and the prediction of soil erosion.【Method】This paper took sloping of ridge tillage in Hilly Area of Central Sichuan basin as the research object and the linear slope was used as control. From the perspective of soil roughness, methods involving artificial rainfall and GIS were adopted to analyze the variation characteristics of microtopography of purple soil.【Result】The range of relative elevation was from -180 mm to 80 mm on the sloping of ridge tillage under different rainfall patterns, which mainly focused on -20 mm-20 mm, the proportion of soil surface elevation reduction was relatively higher. However, the range of relative elevation was from -10 mm to 10 mm on the linear slope, which mainly focused on -5 mm-5 mm. The soil erosion area of increased rainfall series was higher than that of decreased rainfall series for different tillage measures. The value of soil roughness was from 57.47 mm to 65.32 mm on the sloping of ridge tillage under different rainfall patterns, and the value of soil roughness showed that upslope＞downslope＞midslope under different slope positions. The value of soil roughness was from 5.71 mm to 6.28 mm on the linear slope under different rainfall patterns, but soil roughness of different slope positions had obvious variability affected by the random roughness. Grid number of micro-slope of the sloping of ridge tillage showed a decreasing-increasing-decreasing with the increase of slope under different rainfall patterns, and the slopes were mainly concentrated at 0°-5°and 30°-35°. Grid number of micro-slope of the linear slope decreased gradually with the increase of slope, and the slope was mainly concentrated at 0°-10°. Grid number of micro-aspect of the sloping of ridge tillage mainly focused on the northern slope and the southern slope, and distributions of the other micro-aspect were relatively even, but there was an obvious difference in the linear slope under different rainfall patterns. 【Conclusion】The variation of elevation values and soil roughness reflected the vertical variability of microtopography, while the terrain factors could reflect the spatial distribution of microtopography in the process of water erosion. The combination of them reflected variation characteristics of microtopography of the sloping of ridge tillage well. The increased rainfall pattern was similar to the major erosion rainfall pattern in purple soil region in summer which resulted in relatively severe soil erosion on sloping farmland, and it was the main rainfall pattern of soil erosion prevention and control in the study area. This study could provide a new ideas for quantification of microtopography and reveal the essence of soil erosion on sloping farmland.

Key words: purple soil, microtopography, microslope, microaspect, ridge tillage