Rheological evaluation of soil microstructure stability during vegetation restoration on the Loess Plateau of China

Vegetation restoration is an effective measure to improve soil structure stability and thus decrease soil erosion. However, fewer studies have examined the effect of vegetation restoration on the mechanical stability of soil structure at the micro-scale level. In this study, we collected soil samples across a restoration chrono sequence spanning 160 years (from unrestored farmland to mature arbor forests). The soil microstructure stability derived from rheological parameters (shear strength and viscoelasticity) were investigated using a compact modular rheometer. Our results showed that restoration time had a positive effect on shear strength and then increased soil microstructure stability. With increasing restoration time, soil shear strength and elasticity generally improved across vegetation types. Forests exhibited a non-linear trend, with strength peaking at 110 years before declining in older stands (130–160 years). Correspondingly, the viscoelastic parameters (e.g., γ YP , I z ) also peaked at 110 years, indicating that soil structure is most stable and deformation resistance is greatest during this phase. The partial least squares path modeling revealed that increases of organic carbon and divalent cation contents were the main reason contributing to the enhancement of soil microstructural stability. In summary, the vegetation restoration process increased organic carbon and divalent cation content, thereby enhancing soil shear strength and elasticity, which subsequently stabilized the soil microstructure. This work provides important indicators for understanding the evolution of soil microstructure during vegetation restoration and supports a theoretical basis for the development of soil structure improvement and ecological restoration techniques suitable for loess derived soils.