Abstract: Biocrusts and herbs coexist in arid and semi-arid areas, playing an important role in soil and water conservation. However, the combined effects of biocrusts and herbs on process and mechanism of runoff and infiltration on slope are still unclear. In this study, simulated rainfall experiments with four treatments, including bare soil, biocrusts, Stipa bungeana and S. bungeana+biocrusts, were designed to investigate runoff, infiltration process and hydrodynamic characteristics of herbs and biocrusts on slope. The results showed that the runoff under the two treatments with biocrusts was stable. The total runoff of four treatments was in the following order: biocrusts > S. bungeana+biocrusts > bare soil > S. bungeana, indicating that biocrusts could inhibit soil infiltration and S. bungeana could promote soil infiltration. At soil depths of 16 cm and 24 cm, the cumulative infiltration of biocrusts treatment was significantly less than that of S. bungeana+biocrusts treatment, suggesting that with the increases of soil depth, S. bungeana reduced the negative effect of biocrusts on soil infiltration. The Froude number was greater than 1 under bare soil and less than 1 under other treatments, which was subcritical flow. Compared with the runoff kinetic energy of the bare soil treatment, the treatments of biocrusts, S. bungeana, and S. bungeana+biocrusts were reduced by 83.3%, 59.5%, and 88.1%, respectively. The variations of hydrodynamic parameters indicated that the role of biocrusts is greater than S. bungeana in regulating runoff.

Key words: biological soil crust, simulated rainfall, grassland, runoff, infiltration