Mechanisms controlling the inhibiting effects of roots on soil detachment through the growth of herbaceous plants in Southwest China

Herbaceous roots have been recognized worldwide as effective in reducing topsoil water erosion. The root characteristics and (rooted) soil properties can greatly change through plant growth, inevitably affecting the capacity of roots in preventing soil detachment by concentrated flow. Although these changes suggest different mechanisms controlling roots inhibiting soil detachment, limited related research has been carried out. The present study aimed to explore the effects of the roots of alfalfa ( Medicago sativa L.) and green bristlegrass ( Setaria viridis (L.) Beauv.) on soil properties and soil detachment at 60-, 90-, 120-, and 150-days after sowing and reveal their controlling mechanisms. The results showed significant reductions in soil detachment capacity ( D c ) and rill erodibility ( K r ) during one plant growth period. Compared with the D c and K r values at 60-days, the maximum D c reduction rates under sowing alfalfa and green bristlegrass were up to 81.72% and 83.25%, while their respective maximum reduction rates of K r were about 74.53% and 82.43%. Root fork number was the primary root parameter reducing D c , showing a good power function fit with D c ( R 2 > 0.88) at each growth stage. With plant growth, the indirect root-reducing effect on D c increased as its contribution ratio rose from 16.26% at 60-days to 39.05% at 150-days. The indirect root-reducing effect was mainly attributed to the increase of soil water-stable aggregate content with the maximum increase reaching 25%. The staged-power functions of root fork number, soil water-stable aggregate content, and stream power efficiently predicted the D c values ( R 2 ≥ 0.97) of their respective growth stages. Our study provided further insights into the mechanisms of plant roots controlling soil erosion, as well as a useful reference for soil detachment capacity prediction.