Aims: Vetiver grass (Chrysopogon zizanioides) is considered highly effective for bioengineering, especially for stabilizing steep, erosion-prone slopes. This study evaluates the bioengineering potential of Vetiver in semi-arid regions by integrating analyses of root system dynamics, morphological traits, and responses under different slope gradients. Through assessing root biomass distribution, diameter, root area ratio (RAR), and their biomechanical contributions, the research provides an interdisciplinary understanding of how Vetiver responds to environmental stresses and enhances slope protection.
Materials & Methods: Vegetation-induced soil reinforcement is governed primarily by root mechanical properties, including root density, diameter distribution, and tensile resistance. Vetiver grass (Chrysopogon zizanioides) has been widely used for slope stabilization; however, quantitative field-based evidence linking slope geometry to root-mediated shear strength enhancement under semi-arid conditions remains limited. Seedlings were planted on slopes with similar soil properties but different gradients, allowing the gradient to act as the main factor. Field sampling was conducted on vegetated highway embankments with comparable soil texture and land-use history but differing slope inclinations (40–50°, 70–80°, and >80°). Intact soil cores containing Vetiver roots and corresponding root-free controls were collected at 0–20 cm depth. Direct shear tests were performed under controlled normal stresses to quantify apparent cohesion and shear resistance. Root biomass, diameter distribution, and root area ratio (RAR) were measured and statistically related to mechanical soil parameters.
Findings: Soils containing Vetiver roots exhibited significantly higher apparent cohesion than root-free soils (p < 0.05), attributable to increased root biomass and RAR, particularly at depths of 10–20 cm. Slope inclination itself did not directly alter soil cohesion; instead, variations in shear strength were explained by differences in root density and architecture. Direct shear tests were conducted on soil samples reinforced with Vetiver grass roots at three slope classes (40–50%, 70–80%, and >80%) and four soil depths (0–5, 5–10, 10–15, and 15–20 cm). The results demonstrate an apparent linear increase in shear stress with increasing normal stress, consistent with the Mohr–Coulomb failure criterion. For all slope classes, the presence of etiver roots significantly increased the peak shear stress, particularly at greater depths where root mass and root area density were higher.
Conclusion: The study confirms that Vetiver grass is a highly effective bio-engineering tool for soil stabilization. The reinforcement is most substantial at steep Slopes (≥70%), where denser root systems develop to adapt to higher mechanical stresses. Deeper soil layers (10–20 cm), higher root weight, and area density significantly improve post-peak residual strength and energy absorption. Its dual role as an effective bioengineering species and a valuable phytochemical resource is shaped by interactions between climate and soil.