Root system responses of three herbs to soil anti-erodibility

To explore the relationship between herb roots and anti-erodibility in the red soil region of southern China, we examined three herbs (Vetiveria zizanioides, Trifolium repens and Lolium perenne) that naturally grow in two types of soil (yellow-brown and red) in Hubei Province. The soil-root composite of the three herbs were collected from two types of soil, with a total of six soil-root composite treatments. Each treatment (including the control) was subjected to concentrated flow scouring (hydraulic flume: 4.00 m long, 0.20 m wide) under three different water-flow shear stresses ranging from 2.41 to 15.03 Pa. Soil rill erodibility and root parameters were measured to investigate the effects of different soil erodibility characteristics. Results show that roots strengthen soil erodibility significantly. However, the influence of roots varied for different herbs, with Vetiveria zizanioides and Lolium perenne showing the largest and smallest enhancement effects, respectively. Root length density (RLD) was the root parameter that had the largest effect on soil erodibility, as RLD provided the most accurate simulation (R² ≥ 0.930) of the soil detachment capacity change of two soil-root composites. Root mass density (RMD) and root area ratio (RAR) also had large effects on soil erodibility. Root diameters of less than 1.0 mm increased soil-root composite anti-erodibility, with the most significant effects observed for root diameters of 0.5～1.0 mm (P < 0.01). Overall, we found that Vetiveria zizanioides is an important plant species that can improve soil and water conservation in the red soil region of southern China. Results from this study provide an herb selection reference for regional restoration projects and describe the relationship between root features and soil anti-erodibility.