Effects of different vegetation restoration measures on soil aggregate stability and erodibility on the Loess Plateau, China

Vegetation restoration may affect soil aggregate stability and the ability of soil to resist erosion. To evaluate the influence of vegetation restoration measures on the stability of soil aggregate and soil erodibility, we chose 7 types of vegetation restoration measures, which included artificial forest (AF), artificial mixed forest (AMF), economic forest (EF), artificial shrub (AS), natural shrub (NS), artificial grass (AG) and natural grass (NG). Then, we analyzed the distribution of water-stable aggregate fractions, mean weight diameter (MWD), geometric mean diameter (GMD), soil erodibility (K value) and other soil properties in the 0-20 cm and 20-40 cm soil layers, as well as aboveground and underground biomass (AGB and UGB). The results showed that under 7 kinds of vegetation restoration measures, the aggregate fraction < 0.25 mm was the main component (40.40-77.86%) and the proportion of the > 5 mm aggregates fluctuated greatly and ranged from 1.87% to 32.50%. And for 7 different vegetation restoration measures, the percentage of aggregate < 0.25 mm was lower than that of CK (abandoned land), however, the proportion of aggregate > 5 mm was higher than the CK. Overall, compared with CK, the MWD (2.22 and 1.93 mm) and GMD (2.86 and 2.66 mm) were both highest in two soil layers under the NS but lowest under the EF (MWD 0.68 and 0.49 mm, GMD 1.08 and 0.93 mm). The trend of the K value was opposite to these values. These results indicated that the stability of soil aggregate and the ability of soil to resist erosion under NS were strongest. The soil organic carbon (SOC), total nitrogen (TN) and UGB had significantly positive correlations with the proportion of > 1 mm aggregates and MWD but had negative correlations with the percentage of < 0.25 mm aggregates (p < 0.05), which indicated that SOC, TN and UGB were involved in the formation of macroaggregates and increased the stability of soil aggregates. These results suggested that natural shrub restoration measures could improve the soil aggregate stability and ability to resist erosion better than forest and grass restoration measures, which can provide a reference for the assessment of vegetation restoration measures.