The effects of tillage on sheet erosion on sloping fields in the wind-water erosion crisscross region of the Chinese Loess Plateau

Tillage complicates erosion on sloping fields, especially in regions of combined wind and water erosion. The wind-water erosion crisscross region of the Chinese Loess Plateau is an example of such a region wherein erosion is caused by the stimulating effects of tillage, rainfall, and wind. Sheet erosion is an important form of cropland soil erosion and is closely correlated to the productive capacity of land. It is important to better understand the influence of tillage on soil sheet erosion in order to estimate the loss of fertile surface soil and to provide suitable tillage recommendations for the cultivation of sloping cropland in this region, which is susceptible to multiple erosion factors. This study aims to clarify spatial distribution and variation of sheet erosion rates as affected by different tillage patterns on sloping cropland under different slope conditions. We applied beryllium-7 measurements and sediment collection methods to estimate sheet erosion rates to reveal the distribution of sheet erosion on bare sloping fields, to determine correlations between sheet erosion rates and slopes (0, 5, 10, 15, 20, and 25), and to analyze variation in sheet erosion affected by tillage patterns on a plot scale. Results show that sheet erosion increased in a top-down direction and achieved maximum values at the mid- or lower-mid section of slopes, then erosion rates decreased or sediment deposition occurred at the base of slopes. Sheet erosion intensified with an increase in slope gradient fitting to linear or exponential functions regardless of the tillage pattern used (i.e., whether solely applying autumn plowing or a combination of autumn and spring plowing). However, tillage patterns had an obvious effect on sheet erosion. Differences in sheet erosion caused by tillage patterns increased from 5 to between 15 and 20 before decreasing at 25. This demonstrates that steep slope gradients will weaken tillage pattern effects on sheet erosion, thus becoming a significant impacting factor on sheet erosion. Based on sheet erosion rates, we recommend that cropland be converted to grassland or shrubland when slope gradients are greater than 20 in the study region. Notably, a decrease in tillage intensity (frequency) helped in the reduction of sheet erosion on sloping croplands, and further tillage practices associated with conservation tillage should be applied on sloping cropland to obtain better soil erosion control results.