Soil aggregate stability and erodibility under forest vegetation in the Loess Plateau using the Le Bissonnais method

The composition and stability of soil aggregates are the main indicators of soil structure and quality. For sustainable ecological restoration, soil aggregates stability under different vegetation types in the forest zones of the Loess Plateau was studied using the Le Bissonnais (LB) method. Three sieving methods of LB (SW: slow-wetting sieving method; FW: fast-wetting sieving method; WS: wet-stirring sieving method) were used to simulate light rain, heavy rain and disturbance. Soil samples were collected from 10 types of vegetation in Yanhe Catchment of Yan'an City. The mean weight diameter (D_MW), geometric mean diameter (D_GM), mass fractal dimension (D) of soil aggregates and soil erodibility (K) were calculated. The results showed that FW treatment was the most destructive to soil aggregate stability, under which soil water-stable aggregate particle size was mainly concentrated in the <0.2 mm size group. The SW treatment showed the least destructiveness to soil aggregate stability with soil water-stable aggregate particle size mainly concentrated in the >2 mm size group. It then explained that light rains had no strong damaging effects on soil aggregates. The orders of D_MW, D_GM, D and K were SW > WS > FW, SW > FW > WS, WS > FW > SW, and FW > WS > SW, respectively, in both 0-10 cm and 10-20 cm soil layers. Under SW, Artemisia gmelinii community and Rosa xanthina community had greater D_MW and D_GM, and smaller K, indicating the two vegetation types had advantages in soil protection under light rain. Under WS and FW, Platycladus orientalis community and Acer buergerianum communities had D_MW and D_GM, and smaller K. They were appreciate vegetation types for soil protection under heavy rain and strong disturbance. The results suggested that LB method was appropriately applicable in measuring soil aggregate structure in the Loess Plateau. The LB method not only simulated traditional wet sieving results, but also explained the mechanisms involved in the disintegration of soil aggregates under different conditions in terms of soil structure stability. The results also suggested that the vegetation types significantly influenced soil water-stable aggregates in the region. In summary, the stability of soil aggregates was improved by vegetation restoration in the forest zones of the Loess Plateau.