Determining the mechanism of the root effect on soil detachment under mixed modes of different plant species using flume simulation

Soil detachment is the separation and dislodgment of soil particles from a soil mass by the force of raindrops and flow, which is also the initial process of soil erosion. Plant roots have significant effects on the soil detachment rate (SDR). Current studies have mainly focused on root effects on the SDR under single species. Because it is difficult to identify the roots of different species in mixed-plant areas, few studies have evaluated the root effects on the SDR under mixed-plants. Natural, undisturbed soil samples containing roots were collected from four natural sampling plots with single plant types, and six natural sampling plots with mixed plant types. Bare soil was used as the control. The samples were subjected to flow scouring through indoor hydraulic flume experiments under six shear stresses (3.65, 7.28, 7.67, 8.59, 10.15, and 12.19 Pa). The results showed that the root reduction effect on the SDR under the mode of tap roots mixed with fibrous roots was 55.54 % weaker than that the mode of fibrous roots mixed with other fibrous roots. When fibrous roots were mixed with tap roots, the fibrous roots indirectly affected the SDR through soil mechanical properties, while the indirect path of the tap roots on the SDR was not unique. However, the indirect effect of roots on the SDR was weaker than the direct effect. The mixed roots affected the SDR mainly by rill erodibility, not critical shear stress. The variation in rill erodibility at the mixed root sites was similar to the SDR variation at those sites. The mode of grasses with fibrous roots mixed with other grasses with fibrous roots was considered as better for soil and water vegetation conservation.