Soil erodibility affected by vegetation restoration on steep gully slopes on the Loess Plateau of China

Vegetation restoration influences near soil-surface characteristics and thus likely affects soil erodibility. This study was performed to quantify the effects of vegetation restoration on soil erodibility on steep gully slopes, and to identify the potential influencing factors on the Loess Plateau. Three shrub and four grass types distributed on different gully slopes were selected, and six erodibility indicators and an integrated erodibility index (IEI) were applied to indirectly evaluate the effects of vegetation restoration on soil erodibility. The former included the soil erodibility K factor, aggregate stability (the mean weight diameter, MWD, and the mean number of drop impacts, MND), saturated hydraulic conductivity (Ks), cohesion (Coh), and penetration resistance (PR), and the latter was calculated using these indicators and a weighted integration method. The results showed that vegetation restoration on steep gully slopes was effective in reducing soil erodibility on the Loess Plateau, and grasses seemed more effective than shrubs. Compared with the control, the K of vegetation-restored gully slopes decreased by 4.1–24.0%, and MWD, MND, Ks, Coh, and PR increased by 64.0–284.3, 51.4–269.5, 100.5–417.4, 10.1–172.2, and 63.3–278.9% respectively. Consequently, the IEI of the vegetation-restored gully slopes declined by 33.1–81.9%, and the mean reduction percentage of the four grasses was 1.5 times that of the three shrubs. The variation in soil erodibility was closely related to the changes in the soil organic matter content and root mass density with vegetation restoration. The results will help in understanding the soil conservation mechanisms of vegetation restoration on steep gully slopes.