The temporal evolution of soil erosion for corn and fallow hillslopes in the typical Mollisol region of Northeast China

The Mollisol region of Northeast China is affected by soil erosion and continuing land degradation. However, the temporal evolution of soil erosion for hillslopes during a year is still unclear. The objectives of this study were to investigate the impacts of hillslope patterns (corn and fallow hillslopes) and slope gradients (5° and 10°) on the total runoff, runoff rates, soil losses, and sediment concentrations over time. Four growth stages of vegetation were prepared in 2017: 1) representing an early growth stage during mid-July; 2) representing a vigorous growth stage during mid-August; 3) representing a mature stage during mid-September; 4) representing a harvest stage during mid-October. Natural runoff plots (20 m long and 5 m wide) were subjected to inflow scour experiments (l L min–¹ m–² lasting 40 min). The results showed that the effect of runoff regulation on fallow hillslopes worked earlier than that on corn hillslopes. The corn hillslopes produced soil losses that were 1.4–79.3 times greater than those on the fallow hillslopes, especially in stages 1 and 2. The soil losses during different growth stages at 10° were 1.7–15.4 and 4.5–38.3 times greater than those at 5° for the corn and fallow hillslopes, respectively. Moreover, the soil losses for both the corn and the fallow hillslopes significantly decreased over the temporal evolution. The slope gradient had a significant impact on the soil losses in stages 1 and 2, but the impact weakened with vegetation growth. Fluctuations in the runoff rates and sediment concentrations for the corn hillslopes were greater than those for the fallow hillslopes, and the fluctuations increased with an increase in the slope gradient. Therefore, the fallow measure was effective and suitable for the Mollisol hillslopes, as it prevented soil erosion before the vegetation reached critical maturity.