Study On Soil Anti-scouribility Of Gully Head With Different Vegetation Types In The Gully Region Of The Loess Plateau

With the implementation of a series of ecological construction projects,such as returning farmland to forest and grassland,regulating sloping farmland,consolidating ditches and protecting Tableland and comprehensive treatment of three lines of defense,the vegetation area in the gully area of the Loess Plateau has increased significantly,the soil erosion process has changed significantly,the problem of water and soil loss has been effectively controlled to a certain extent,and the regional ecological environment has been improved effectively.However,under the condition of extreme precipitation,the gully head of the Loess Plateau is still unstable under the continuous scouring of runoff,,resulting in severe gully head traceability erosion and soil erosion.Due to the differences of soil properties and root distribution characteristics in gully heads of different vegetation types,the occurrence probability and development degree of gully head traceability erosion are different.At present,the influence mechanism of soil properties and root system parameters on gully soil erosion resistance of different vegetation types is not clear.Therefore,this paper selected five vegetation types gully heads in the Loess Plateau gully region as the research object.The soil properties and anti-scour properties of different soil layers（0～20,20～40,40～60,60～80,80～100 cm）in gully head were studied by laboratory analysis and measurement,as well as indoor undamaged soil trench scouring tests.The variation rules and differences were analyzed among soil properties、roots distribution characteristics and soil anti-scour properties from gully-heads in the five kinds of vegetations.Impact factors of soil anti-scour properties were illuminated on gully-head of different vegetation types.It may provide important experimental data and analysis for gully erosion mechanism and control in the Chinese loess plateau.The main research results are as follows:（1）On the vertical section of 0～100 cm soil layer,the soil properties,root biomass,root surface area density,root length density,root volume and root mean diameter of gully head basically decreased with the increase of soil depth.In terms of the average of soil parameters in the gully head,the average of sand content、soil bulk density、water stable aggregate content、soil cohesion and internal friction angle was the largest in the gully head of Agropyron cristatum+Medicago sativa+Artemisia vestita;the average of silt content、soil organic matter content and water content was the largest in the gully head of Agropyron cristatum+Artemisia vestita;the average of soil total porosity was the largest in the gully head of Artemisia vestita;the average of clay content was the largest in the gully head of Agropyron cristatum.（2）Compared with the gully head of Platycladus orientalis,the average clay content,average water content and organic matter content in the gully head of other vegetation types increased by 2.4%～11.8%,7.6%～46.6%and 4.4%～53.2%respectively;Compared with the gully head of Agropyron cristatum+Medicago sativa+Artemisia vestita,the average silt content and porosityin the gully head of other vegetation types increased by 2.3%～4.4%and 0.39%～6.12%,and the average soil bulk density decreased by0.4%～6.5%;Compared with the gully head of Agropyron cristatum+Artemisia vestita,the average sand content in the gully head of other vegetation types increased by 3.3%～26.2%;Compared with the gully head of Artemisia vestita,the average content of soil water-stable aggregate（>0.25 mm）in the gully head of other vegetation types increased by50.2%～66.1%.The average of soil cohesion and internal friction angle of the Agropyron cristatum+Medicago sativa+Artemisia vestita gully head were 1.08～1.56 times and1.01～1.13 times higher than those of other vegetation types,respectively.（3）The average of root biomass and root surface area density were the largest in the gully head of Platycladus orientalis,which were 1.73～1.95 and 1.59～2.89 times that of other vegetation types,respectively;The average specific surface area was the largest in the gully head of Agropyron cristatum+Medicago sativa+Artemisia vestita,which was1.12～1.63 times that of the other vegetation types;The average root length density was the largest in the gully head of Agropyron cristatum,which was 1.19～2.54 times that of the other vegetation type.（4）The soil anti-scouring coefficient shows a fluctuating decreasing trend with the increase of soil depth in the gully head of each vegetation type.Under flow discharges of21、27、32 and 37 L·min^-1,the soil anti-scouring coefficient of 0-20 cm soil layer in the gully head of each vegetation types is reduced by 38.5%～88.4%,41.7%～88.7%,32.5%～87.6%and 30.2%～87.2%respectively.The average soil anti-scouring coefficient of gully head under the flow discharge of 21 L·min^-1 of all vegetation types is the smallest,which is 1.10～1.44,1.26～1.58,1.15～1.41,1.31～1.78 and 1.26～1.88 times that under other flow discharges.The average soil anti-scouring coefficient is the smallest in the gully head of Platycladus orientalis,Compared with other vegetation types,it decreased by19.4%～59.6%,15.5%～53.7%,21.4%～49.5%and 21.0%～47.0%respectively.（5）The soil anti-scourability had the most significant correlation with root biomass,showed a very significant linear function increasing relationship in the gully head of Platycladus orientalis、Agropyron cristatum and Artemisia vestita;The correlation between soil anti-scourability and root surface density is the largest in the gully head of Agropyron cristatum+Artemisia vestita,showed a very significant linear function increasing elationship;There is the most significant correlation between the soil anti-scourability and the content of water stable aggregates（>0.25 mm）in the gully head of Agropyron cristatum+Medicago sativa+Artemisia vestita,showed a very significant exponential function increasing relationship.