Study on the mechanism of plant root influence on soil properties in expansive soil areas

Abstract Expansive soil is a type of unsaturated soil that develops fissures within its body due to dry and wet cycles. These fissures are the primary factor contributing to slope instability in expansive soil regions. In this study, we conducted research on the impact of herbaceous plant root systems on soil properties in the Shangluo area of Shaanxi. This area is known for its distribution of expansive soils. We achieved this by planting three types of commonly used slope protection plants. The results revealed significant differences in root system characteristics among the three herbaceous plants: Lolium perenne, Cynodon dactylon, and Medicago. Particularly, Lolium perenne exhibited a well-developed and heterogeneous root system with a substantial number of roots. These roots were primarily concentrated within the interval of 0 < L ≤ 0.5 mm. The specific gravity of soil tended to decrease after herbaceous plant roots were planted. The growth of herbaceous plants greatly increased the soil’s ability to hold water. The presence of herbaceous root systems significantly improved the soil consolidation effect. The entanglement and interpenetration effects of the plant root system had a significant influence on the dispersion of soil macroaggregates and the formation of soil fabrics. The colloid content of the soil increased with the growth of the plant root system. Additionally, the root system of herbaceous plants greatly enhanced the angle of internal friction and cohesion of soil. The growth of herbal plants significantly enhanced the properties of expansive soils by improving the soil structure, increasing the nutrient richness, enhancing soil water retention, and augmenting both soil agglomeration and internal friction angles, thereby improving the soil’s solid capacity. This study elucidates the mechanisms by which herbaceous plants exert long-term beneficial effects on expansive soil areas, contributing to the prevention and control of regional ecological security.