Soil–Water–Plant–Biopolymer Dynamics and Their Effects on Vegetation Growth and Soil Physio-Mechanical Behavior

Sustainable alternatives to chemical stabilizers are increasingly needed as climate-driven moisture extremes accelerate erosion and slope instability. Nature-based solutions that integrate vegetation and biodegradable soil amendments offer a promising pathway for improving soil resilience while reducing environmental impacts. However, the combined hydro-mechanical behavior of soil-water-plant-biopolymer systems remain insufficiently understood. This study investigates how three natural biopolymers—xanthan gum (XG), beta-glucan (BG), and guar gum (GG)—applied at 0.25–0.5% concentrations, interact with Zoysia japonica to influence the hydraulic and mechanical behavior of sandy soil. Through plant cultivation experiments, soil-water retention testing, infiltration measurements, and unconfined compression tests, the study captures previously unexplored interactions between biopolymers and root systems. BG and GG increased air-entry values by up to three- to four-fold, while root presence elevated saturated water content by 60–150% and refined soil pore structure (n decreased by approximately 12%). Biopolymers increased dry compressive strength by up to 240%, and combined root reinforcement raised total strength gains to 500–625%. Moderate biopolymer dosages (0.25%) consistently produced the most balanced improvements in hydraulic and mechanical performance. These findings demonstrate that integrated biopolymer–vegetation systems can function as effective nature-based solutions for climate-resilient erosion control and sustainable slope stabilization.