Horizontal Ridging with Mulching As the Optimal Tillage Practice to Reduce Surface Runoff and Erosion in a Mollisol Hillslope

Soil erosion features and ideal tillage practices are not very clear at the crop seedling stage in Chinese Mollisols. Simulated rainfall experiments were conducted at the rainfall intensities of 50 and 100 mm h-1 to investigate the differences in soil erosion of a 5° hillslope during the maize seedling stage between conservation and conventional tillage measures, including cornstalk mulching (Cm), horizontal ridging (Hr), horizontal ridging + mulching (Hr+Cm), vertical ridging + mulching (Vr+Cm), flat-tillage (CK), and vertical ridging (Vr). The results demonstrated that crops could remit soil erosion at the seedling stage by reducing the kinetic energy and changing the distribution of raindrops. The conservation tillage measures significantly alleviated total runoff (11.7%–100%) and sediment yield (71.1%–100%), postponed runoff-yielding time (85 s–26.1 min), decreased runoff velocity (71.5%–96.7%), and reduced runoff and soil loss rate, compared to the conventional tillage measures. Practices with mulching showed better performance than Hr. Mulching reduced sediment concentration by decreasing runoff velocity and soil particle filtration in a manner similar to buffer strips. The contour ridge ruptured earlier at 100 mm h-1 than at 50 mm h-1 and changed the characteristics of the soil erosion by providing a larger sediment source to the surface flow. Runoff strength, rather than soil erodibility, was the key factor affecting soil erosion. Decreasing runoff velocity was more important than controlling runoff amount. The Hr + Cm treatment exhibited the lowest soil erosion and is, thus, recommended at the corn seedling stage.