Vertical distribution of vegetation roots and its influence on soil erosion resistance along gully headwalls in the gullied Loess Plateau

Purpose On-wall flow on gully headwalls plays a critical role in gully headcut erosion, and the erosion morphology of gully headwalls caused by on-wall flow scouring varies under different land uses/covers due to variations in soil resistance. However, it is unclear how vegetation roots affect the soil resistance of gully headwalls to on-wall flow scouring. Materials and methods Taking bare land as the control, this study analysed the vertical distribution of vegetation roots and its influence on the soil properties and antiscourability (ANS) of gully headwalls under three land uses (forestland, grassland, and farmland). Results and discussion The results showed that root mass density (RMD), root length density (RLD), root surface area density (RAD), and root volume density (RVD) decreased overall with increasing soil vertical depth at the gully headwall under the three land use types. The soil ANS ranked highest to lowest in forestland, grassland, farmland, and bare land. Compared with that of bare land, the ANS of each soil layer (0-20, 20-40, 40-60, 60-80, and 80-100 cm) under the three land use types increased by 3.0-9.1, 6.7-8.6, 2.6-10.5, 3.9-5.6, and 0.2-1.9 times, respectively. The ANS of the gully headwalls had a logarithmic relationship with RLD, RAD, and RVD (R-2 = 0.45-0.56, P < 0.01). In particular, the most significant correlation was found between the ANS and RVD of fine roots (diameters of 0-0.5 mm). The ANS decreased with the decrease in root density with vertical depth. Conclusions Our results reveal that vertically distributed roots determine the vertical variations in soil ANS on gully headwalls in the gullied Loess Plateau.