Improvement in Red Soil Aggregate Stabilization Using Biopolymers

Red soils in southern China are highly vulnerable to water-induced structural breakdown and erosion because of their poor aggregate water stability. Although biopolymers have recently been proposed as environmentally friendly amendments for improving red soil stability, the links between their stabilization mechanisms and aggregate-level performance remain unclear. In this study, three representative biopolymers, namely calcium lignosulfonate (Ca-LS), xanthan gum (XG), and a bio-organic–mineral composite stabilizer (DK), were selected to improve the water stability of red soil aggregates. Controlled laboratory experiments were conducted to evaluate aggregate stability, microstructure, pore characteristics, and zeta potential of the amended soils. The results show that all three amendments improved aggregate water stability to different extents. XG showed the strongest overall stabilization within the tested conditions, whereas DK exhibited a gradual content-dependent improvement and Ca-LS displayed a non-monotonic response. Within the tested range, the optimal amendment contents for improving aggregate stability were 2.0% for DK, 1.5% for Ca-LS, and 1.0% for XG. In addition, biopolymer amendment increased the size of fragments generated after water-induced breakdown, suggesting a potentially lower susceptibility to detachment and transport. Microstructural analyses further showed that the amendments promoted particle cementation, network formation, and pore-structure adjustment, thereby enhancing aggregate stability through coupled interfacial bonding and structural reorganization. These findings provide a multiscale basis for understanding biopolymer-amended stabilization of red soil aggregates and for selecting suitable amendments for the remediation of degraded red soils.