Temporal variations in soil erodibility indicators of vegetation-restored steep gully slopes on the Loess Plateau of China

Near soil-surface characteristics change considerably with vegetation growth during one growing season, and thus likely induce the temporal variations in soil erodibility indicators. This study was performed to investigate the temporal variations in soil erodibility indicators under different vegetation-restored gully slope lands on the Loess Plateau of China. Soil erodibility indicators included the K factor, mean weight diameter (MWD), mean number of drop impacts (MND), saturated conductivity (K-s), cohesion (Coh), penetration resistance (PR), and one comprehensive soil erodibility index (CSEI). One slope cropland (as the control) and seven vegetation-restored gully slope lands were selected to measure soil erodibility indicators for seven times from April 23 to October 10, 2018. Near soil-surface characteristics were also measured to explain the temporal variations in soil erodibility indicators. The results showed that the temporal variations in soil erodibility indicators of different vegetation lands were similar. The K factor fluctuated considerably, while the MWD, MND, K-s, Coh, and PR gradually increased over time. However, all erodibility indicators of the control cropland fluctuated over time with no distinctive trend. The CSEI of all sites fluctuated significantly over time. Compared to the control cropland, the mean K factors of different vegetation lands decreased by 2%-24%, but the mean values of MWD, MND, K-s, Coh, and PR increased by 108%-217%, 152%-343%, 94%-306%, 73%-175%, and 30%-199%, respectively. Consequently, the mean CSEI of different vegetation lands was reduced by 41% to 86%. The temporal variations in soil erodibility indicators were closely related to the seasonal changes in root mass density. Bothriochloa ischaemum (Linn.) Keng was considered the most effective restoration community to reduce soil erodibility of steep gully slope lands. The results contribute to improving the eco-environment on the Chinese Loess Plateau.