Quantifying the effects of plant litter in the topsoil on the soil detachment process by overland flow in typical grasslands of the Loess Plateau,China

Plant litter can be incorporated into topsoil by a natural process, affecting the soil erosion process. This is a widespread phenomenon in erosion-prone areas. This study was conducted to investigate the effect of litter incorporation on the process of soil detachment on the Loess Plateau, China. Four common plant litters (Bothriochloa ischaemum L. Keng., Artemisia sacrorum Ledeb., Setaria viridis L. Beauv., and Artemisia capillaris Thunb.) were collected, then incorporated into the silt loam soil at five rates (0.1, 0.4, 0.7, 1.0, and 1.3 kg m^?2) on the basis of our field investigation. Twenty litter–soil treatments and one bare soil control were prepared. After 50 days of natural stabilization, 30 soil samples of each treatment were collected. We used a flume test to scour the soil samples under six flow shear stress conditions (5.66, 8.31, 12.21, 15.55, 19.15, and 22.11 Pa). The results showed that the different incorporated litter masses and morphological characteristics, such as litter tissue density (ranging from 0.52 to 0.68 g cm^?3), length density (2.34 to 91.00 km m^?3), surface area density (LSAD; 27.9 to 674.2 m² m^?3), and volume ratio (0.003 to 0.050 m³ m^?3), caused varied soil detachment capacities (0.043 to 4.580 kg·m^?2·s^?1), rill erodibilities (0.051 to 0.237 s m^?1), and critical shear stresses (2.02 to 6.83 Pa). The plant litter incorporated within the soil reduced the soil detachment capacities by 38%–59%, lowered the rill erodibilities by 32%–46%, and increased the critical shear stresses by 98%–193% compared with the bare soil control. The soil containing B. ischaemum (L.) Keng. litter was more resistant to erosion. By comparing different parameters, we found that the contact area between the litter and soil was the main factor affecting the soil detachment process. The soil erosion resistance increased with the increasing contact area between the soil and litter. Furthermore, the litter incorporation effect on rill erodibility can be comprehensively reflected by LSAD (R² = .93; Nash–Sutcliffe efficiency = 0.79), which could be used to adjust the rill erodibility parameter in physical process-based soil erosion models.