Abstract:
Background Plant is widely used in protecting soil and water from erosion and shallow landslide, is regarded as an important role in soil and water conservation measures. Plant roots can affect soil cohesion in two ways: Mechanical (root physically penetrate into the soil) and chemical (change the chemical composition of the soil) reinforcement. This study investigated and compared two benefits of plant roots working on soil cohesion with different species restoration in the initial period.
Methods We selected tree (Symplocos setchuensis) and herb (Cynodon dactylon) as the research object and replanted them in a forest gap for 3 years in Jinyun of Chongqing. Soil shear strength, root distribution density, and root strength traits were evaluated, the benefits of vegetation restoration on soil were measured in different planting period and different soil layer. The chemical reinforcement was measured by direct shear tests, and mechanical reinforcement was measured using RBMw.
Results 1) Both species strengthened soil through mechanical and chemical soil stabilization mechanisms, the mechanical reinforcement ranged from 5 to 15 kPa and chemical reinforcement ranged from 0 to 7 kPa. Both of these two effects decreased with soil depth. 2)The C. dactylonis only provided a higher increase in soil cohesion in the 0-20 cm soil layer than the tree by 12% in the second year of planting, due to its faster growth characteristic. After the third year, the increase in soil cohesion provided by the C. dactylonis was higher than the tree by 7%. 2) Both plant species demonstrated a higher effect of mechanical soil stabilization over chemical soil stabilization, with the mechanical effect of C. dactylonis being approximately 52% higher than the chemical effect, while S. setchuensis was 34%.
Conclusions Compared with chemical reinforcement of root, root mechanical reinforcement plays a more important role on soil cohesion, but they varied with different soil layer and different species. More details, different species reinforced the soil via vary mechanisms, some had strong and high-density roots, that provided a higher mechanical reinforcement; while others affected the soil cohesion and internal friction angle via remold and change soil structure, soil organic carbon, and etc., that provided a higher chemical reinforcement. Thus, this study expands our acknowledge on the mechanism of vegetation works on soil reinforcement and helps us on plant selection for soil conservation.
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