Vertical Distribution of Vegetation Roots and Its Influence on Soil Erosion Resistance of Gully Heads on the Gullied Loess Plateau

The vertical distribution of gully vegetation root system and its effect on soil erosion resistance were explored, so as to provide a theoretical basis for optimizing the allocation of vegetation measures in gully erosion control.

In this paper, the gully heads covered with different vegetation (weeds (farmland), Agropyron cristatum, Artemisia gmelinii, and Medicago sativa) were taken as the research object. The scouring experiment of undisturbed soils was carried out to determine the soil anti-scouribility. Moreover, the root characteristics and mechanical and physiochemical properties of root-soil complex were measured using root scanner and ZJ series strain controlled direct shear test apparatus, and so on, respectively.

(1) The root distribution characteristics at the gully head varied among different vegetation types. Agropyron cristatum had the greatest root characteristic indexes (root weight density, root length density, root surface area density, and root volume density), followed by alfalfa, Artemisia, and weeds in farmland. In addition, the root indexes in the gully head soil of farmland decreased with the deepening of soil layer, while those of Agropyron cristatum, Artemisia gmelinii and Medicago sativa firstly decreased and then increased with the deepening of soil layer. Furthermore, the roots with the diameter of <0.5 mm dominated in the root system of each vegetation. (2) The variability of soil bulk density among different vegetation type was low, ranging from 1.17 g·cm^-3 to 1.37 g·cm^-3. The contents of >0.25 mm water-stable aggregates of farmland and Agropyron cristatum land were higher than that of Artemisia gmelinii land and Medicago sativa land. (3) The average soil cohesions of gully heads under different vegetation types were as follows: 12.75 kPa for Medicago sativa land, 9.05 kPa for Agropyron cristatum land, 8.60 kPa for Artemisia gmelinii land, and 7.25 kPa for farmland, respectively. Additionally, the soil cohesion of the farmland, Agropyron cristatum land, and Medicago sativa land decreased first and then increased with the deepening of soil layer, while that of Artemisia gmelinii land showed a decreasing trend in the depth of soil. (4) The average anti-scouribility coefficients of 0-100 cm soil at the gully head under different vegetation types were as follows: 39.31 L·g^-1 for Medicago sativa land, 25.49 L·g^-1 for Agropyron cristatum land, > 22.39 L·g^-1 for farmland and 14.75 L·g^-1 for Artemisia gmelinii land. Moreover, the soil anti-scouribility coefficient of the 0-20 cm soil layer, varying between 34.91 and 53.30 L·g^-1, was larger than that of the lower soil layers.

The combination of plants with tap roots and the plants with fibrous roots was suggested for the control of gully head erosion, and the results provided a theoretical basis for the research of gully headcut erosion and gully erosion control.