Background Purple soil is one of the main types of sloping farmland in the Three Gorges Reservoir area, which causes a lot of soil erosion under the action of rainfall and runoff all the year round, posing ecological threats to the safety of the reservoir area. In order to study the effect of slope on the characteristics of sand yielding in purple soil sloping farmland, and to further clarify the characteristics of sand yielding in purple soil sloping farmland under different slopes, the process of sediment yielding in purple soil sloping farmland under rainfall conditions was studied.

Methods Based on the typical sub-rainfall and sediment production data of 5 runoff plots with different slopes (5°, 10°, 15°, 20° and 25°) in Tangfang Slope Runoff Observation Field, Wanzhou district, Chongqing from 2014 to 2017, combined with changes in rainfall, cropping system, field management and crop coverage, the characteristics of runoff and sediment yield in purple soil sloping farmland under different slopes were analyzed.

Results 1) The runoff depth of sloping farmland has a positive correlation with the slope as a whole. The increase of the runoff depth gradually slows down with the increase of the slope. When the slope increases from 5° to 10°, the runoff depth increases between 66.56% and 1 327.27%, and increases from 10°. When it reaches 20°, the runoff depth increases between 2.55% and 300.00%, the maximum runoff gradient is mainly 20°, and the minimum runoff gradient is mainly 5°.2) The sediment yield generally increases with the increase of the slope. When the slope exceeds 20°, the sediment yield begins to decrease; the maximum sediment yield slope is 20°, and the minimum sediment yield slope is 5°, the increase of the slope also leads to the weakening of the erosive force of raindrop splashing, and the sand production decreases with the increase of the slope. 3) The adoption of a reasonable planting system improved the crop coverage of sloping farmland, enhanced the soil fixation capacity of crop roots, and effectively reduced the runoff and sediment yield of sloping farmland by strengthening rainfall interception, slowing runoff and increasing infiltration.

Conclusions Overall, the maximum 30-minute rainfall intensity and sub-rainfall in the slope and rainfall characteristics were the main factors affecting the sand yield of the purple soil sloping farmland. The research results can provide a reference for the evaluation of soil and water conservation effect of purple soil slope farmland and the layout of farming management measures, and provide a scientific basis for soil and water conservation in small watersheds.