Impacts of Corn Straw Coverage and Slope Gradient on Soil Erosion and Sediment Size Distributions in the Mollisol Region, NE China

The Chinese Mollisol region has the highest fertility and productivity in the country but also suffers from soil erosion. However, the characteristics of soil erosion and sediment size distributions in different seasons based on natural croplands with or without corn straw coverage at different slope gradients remain unclear. This study investigated the effects of corn straw coverage (0, 50, and 100%) and slope gradients (5° and 10°) on the soil water content, bulk density, runoff, soil loss, and eroded sediment size in autumn and the following spring in the Mollisol region of NE China. Natural runoff plots, which were 20 m long and 5 m wide, were used to conduct inflow scour (l L min–1 m–2) experiments. The results showed that the soil water contents generally increased and that the bulk densities decreased in spring compared with those in autumn. For treatments without corn straw coverage, the runoff values and soil losses in spring were 1.2–6.7 and 3.4–25.0 times greater than those in autumn, respectively. For treatments with corn straw coverage, the runoff was effectively decreased under 50% corn straw coverage for the 5° croplands but under 100% corn straw coverage for the 10° croplands; the soil losses were 0 for the 5° croplands and increased 2.3–2.6 times for the 10° croplands in spring compared with those in autumn. As the slope gradient varied from 5° to 10°, the runoff and soil losses significantly increased, but the loss of <0.25 mm soil materials in proportion to the soil erosion generally decreased. The seasonal changes affected the soil material size distributions of the eroded sediment, especially for finer sediments. In conclusion, soil conservation measures used to decrease the slope gradient and seasonality impacts on soil erosion and sediment size distributions in the Mollisol croplands are noteworthy.