Variation in soil surface roughness under different land uses in a small watershed on the Loess Plateau, China

Soil surface roughness (SSR) significantly influences hydrological and erosion processes under different conditions. Land use and its adjustment may greatly influence SSR via altering near soil surface characteristics and tillage operations, but few studies have been performed to quantify their effects on soil surface roughness. This study was conducted to investigate the variation in soil surface roughness under different land use types, and identify the main influencing factors contributing to these changes in a small watershed on the Loess Plateau, China. Eighteen sites were selected from five typical land use types (cropland, grassland, shrub land, orchard, and woodland) to measure random roughness (RR) by a photogrammetric method. The results showed that random roughness was greatly affected by land use types, plant species, and tillage operations. The mean RR under different land use types ranged from 9.47 to 10.06 mm. Woodland had the maximum RR, followed by cropland, shrub land, orchard, and grassland. For a given land use type, RR differed significantly between different plant species. The variation in random roughness was greatly influenced by the changes in near soil surface characteristics and tillage operations induced by land use adjustment. For the testing sites without tillage operations, RR increased linearly with soil median grain size, sand content, organic matter content, plant litter coverage, litter thickness, and litter density, while it decreased linearly with soil cohesion, silt content, and clay content. For the testing sites with tillage operations, RR was dominated by tillage operations. These results are helpful to understand the potential effects of vegetation restoration on hydrological and erosion processes on hillslopes in arid and semi-arid regions.