Vetiver Root Trait And Its Effect On Soil Detachment On Purple Soil Slope

Purple soil is one of the most important soil resources in the upper and middle reaches of the Yangtze River.Under the common influence of geology,terrain,climate and other natural factors and human activities,soil erosion becomes a serious problem in purple soil area,which has significantly affected land production functions and ecological environment quality.Vegetation roots can effectively reduce soil erosion and enhance soil stability,which is the key to ecological restoration measures.In view of this,vetiver root system planted on purple soil slopes in Wanzhou,Chongqing was taken as the main research object in this paper.Through field investigation and sampling,root scanning and analysis,and soil detachment test of variable slope soil trough,the spatial distribution,tensile properties,and their effects on reducing soil detachment capacity of vetiver roots in purple soil area were clarified.The main conclusions of the study are as follows:(1)The root system of two-year-old vetiver among 91.72～96.33% were distributed in the soil layer of0-30 cm,the maximum root depth was 42-50 cm,and the horizontal growth range increased first and then decreased with the increase of soil depth.Vetiver root traits was significantly affected by the growth slope gradient.As the slope increased,the number of roots decreased,the horizontal distribution range decreased,and the root morphological parameters decreased.The root number,root length,root surface area and root volume of vetiver growing on the 20° slope were 51.3%,60.13%,91.59% and 102.61% higher than that of vetiver growing on the 40° slope.(2)The ultimate tensile force of single root was significantly affected by root diameter and root water content.The ultimate tensile force of single vetiver root increased significantly with the increase of root diameter and decreased significantly with the increase of root water content.The tensile strength of single root decreased significantly with the increase of root diameter,while water content only had a significant effect on the tensile strength of fine roots(root diameter <1.50 mm),but had no significant effect on the tensile strength of coarse roots(root diameter range 1.50-2.50 mm).The additional cohesion generated by vetiver root system was affected by the root traits.With the increase of the soil depth and growth slope,the additional cohesion produced by the root system gradually decreases,and the reinforcement effect of the root system is weakened,which leads to the decline of the soil safety factor.(3)Vetiver root system can effectively reduce the soil detachment capacity under the effect of slope runoff erosion,results showed that the soil detachment capacity of root-soil complex was reduced by 35.92%-49.40% compared with the bare soil.The rill erodibility of bare soil were 1.51-1.60 times that of root-soil complex and the critical shear force of root-soil complex was increased by 5.06%-138.46% compared with that of bare soil.Root length density of fine roots(0<D≤0.5 mm)and soil cohesion were indicated as the primary features which influencing the process of soil detachment.A model was developed to estimate soil detachment capacity based on hydraulic parameters,root traits,and soil properties on the purple soil areas,and its performance was satisfactory.In addition,root surface area density of fine roots(0<D≤0.5 mm)and soil organic matter content were indicated as the primary features which influencing rill erodibility.Based on these two indexes,a model of rill erodibility was established,which can accurately reflect the comprehensive influence of vetiver root system on soil resistance.In summary,this study revealed the vetiver root traits and its effect on soil detachment on Purple Soil Slope.The research results can provide important reference and guidance for the development of ecological remediation technology of soil erosion in purple soil area.