| The engineering problems left over from expressway construction seriously restrict the development and stability of the regional environment,in which the degradation of exposed slopes is particularly prominent and needs to be solved urgently.Prevention and control of soil erosion is an important part of soil restoration and protection of exposed slopes.Forest and grassland protection can increase slope vegetation cover,reduce external environmental erosion,improve soil erosion resistance and delay slope soil loss.Therefore,it is widely used in soil restoration engineering of bare slope,in which herbaceous plants become the important and primary object of bare slope restoration because of their rapid growth capacity and wide adaptability.The aboveground part of plants can effectively resist external erosion,and the root system,as the main body of plants,is more important in improving soil structure,physical and chemical properties and various properties.At present,the effect of plant roots on soil structure stability and water erosion resistance is a hot topic in water and soil conservation,and field positioning observation is mostly used in research.There are few studies on the effects of different root types and diameter classes on soil aggregate stability and erosion resistance.On the basis of in-depth analysis of domestic and foreign research results and field investigation of highway slopes in the field,this study selected two different root types of herbs,alfalfa（Medicagosativa,taproot）and tall fescue（Festucaarundinacea,fibrous root）,which are commonly used in soil restoration of highway slopes in North China,for indoor culture at different times（30D,60D,120D,and 180D）,and studied the root-soil complex formed under the conditions of single and mixed species of the two plants.The growth and development characteristics and vertical distribution characteristics of herbaceous plant roots and their effects on soil aggregate structure,physical and chemical properties,shear strength,decomposition resistance and erosion resistance were analyzed,and the mechanism of soil improvement and soil consolidation by herbaceous plant roots was revealed.To provide scientific theoretical basis and practical guidance for the restoration and subsequent monitoring of the bare slope of expressways.The main results are as follows:（1）Changes in tensile strength of two types of roots follow the power function with root diameter.The root tensile strength range of alfalfa is 6.81-72.61MPa,and that of tall fescue is 13.11-104.41MPa.When the root diameter is less than 0.5mm,the tensile strength of the alfalfa root system is higher,while when the root diameter is greater than 0.5mm,the tensile strength of the tall fescue root system is higher.（2）With the increase of growth time,the contents of RLD,RSAD,RVD and RMD in plant treated soil increased continuously,among which the root density of<0.5mm diameter class was higher.Compared to alfalfa,tall fescue had a higher density of fine roots（<0.5mm）,but lower density of middle roots（0.5-1mm）and coarse roots（>1mm）.The root system of alfalfa grew rapidly in the early stages and had a higher density at30 days,while the root density of tall fescue was higher in the later growth stages（120D and 180D）.With the increase of soil depth,the RLD of tall fescue increased,while the RLD of alfalfa and mixed treatments initially increased and then decreased,and the RLD was the highest in the 10-15 cm depth range.The root density of each<0.5mm diameter class increased with depth,while the root density of other diameter classes decreased with depth.（3）Root growth and development of both herbaceous plants increased soil moisture content,porosity,and organic matter content at each depth,and decreased soil bulk density.The soil organic matter content of each plant treatment initially increased and then decreased with root growth time.At the same time,the organic matter content of surface soil（0-5cm）was significantly higher than that of other depths.There was no significant difference in soil physical and chemical properties between different plant treatments.Root parameters of<0.5mm were positively correlated with soil density and water content,and negatively correlated with soil porosity,while those of>0.5mm were positively correlated with soil porosity and negatively correlated with soil density and water content.In addition,soil organic matter content was positively correlated with root density of each diameter class,but only with RLD<0.5.In addition,there was no significant difference in soil physical and chemical properties between different plant treatments.（4）The root growth and development of the two herbaceous plants improved the mechanical and water stability of soil aggregates,and the water stability of soil aggregates increased with the increase of culture time and soil depth.After 30 days of plant growth,the aggregate stability index of single tall fescue treatment was lower than that of single alfalfa and mixed treatment,and the aggregate stability of single tall fescue soil was maintained at a high level in other growth periods.RLD and RSAD are good indexes to reflect the stability of soil aggregates,among which the root system of<0.5mm diameter class makes the greatest contribution to improving the stability of soil aggregates.The root parameters of each diameter class were positively correlated with the water stability index of aggregates,and the correlation decreased with the increase of root diameter.The mechanical stability of aggregates has a greater demand for fine roots,and only root parameters of<0.25mm are positively correlated with the mechanical stability index of aggregates,while the increase of coarse roots（>1mm）density is not conducive to the stability of aggregates.（5）The root system of two kinds of herbs can improve the shear strength of soil at different depths.The range of cohesion increment of three treatments（ST,SA and M）is 0.620-8.138KPa,and the increment of internal friction angle is 2.124-4.162°.The improvement in soil shear strength of mixed treatment was between two single treatments,but the whole was closer to single alfalfa treatment.The increase in soil cohesion of tall fescue root（fibrous root）was higher than that of alfalfa root（taproot）,but the increase in internal friction angle was lower than that of alfalfa root.The results of correlation analysis showed that the increase of root density of<0.5mm diameter class could effectively improve soil cohesion,while the increase of root density of>0.5mm could effectively increase soil internal friction angle.（6）The root growth of the two herbaceous plants significantly improved the anti-disintegration and anti-erosion ability of the soil at different depths,especially the root system of tall fescue.The amount of soil decomposition of single tall fescue treatment was lower than that of single alfalfa and mixed treatment at different times,but the change curve of disintegration residual mass of single alfalfa and mixed treatment was consistent with time.At different depths,the reduction ratio of single tall fescue treatment to total soil decomposition was in the range of 55.8-63.2%,that of single alfalfa treatment was 39.8-48.8%,and that of mixed treatment was 39.6-55.7%.The soil resistance of single tall fescue treatment to concentrated water erosion was higher than that of single alfalfa and mixed treatment.Under concentrated water scouring,the soil separation ability of plants in deeper soil（10-20cm）was significantly lower than that in topsoil,and root length density RLD<0.5 was the main influencing factor,and the correlation between other diameter class root parameters and soil separation ability was weak. |
PDF Full Text Request