Effects Of Herb Plantroots On Soil Detachment In The Alluvial Soil

Vegetation restoration is an important way to control the erosion of collapsing gully.Two typical herbs Pennisetum sp.(deep-root system)and Paspalum wettsteinii(shallow-root system),which were planted in the alluvial,were chosen as the research object to analyse the effects of plants’ root systems on the alluvial soil detachment.Soil detachment capacity was measured in a hydraulic flume with adjustable bed gradients,and analysed the characteristics of root system.we discussed the different influences of the two plant roots to soil detachment of alluvial soil.Main conclusions were as follows:The indexes of root systems characteristics of Pennisetum sp.and Paspalun wettsteinii decrease with increasing soil depth,all root indexes of Pennisetum sp.is greater than those of Paspalum wettsteinii;Vegetation cover decrease the soil bulk densities compare to bare land;Also the soil total porosity and capillary porosity of soil with vegetation covers are greater than those of bare land,decreasing with the increased soil depth;In addition,plant root systems increase the soil saturated water storage and capillary water storage,which are significantly different from those of bare land;In top soil,compared with Pennisetum sp.,Paspalum wettsteinii increase soil porosity and strengthen water holding capacity more greatly,the situation is on the contrary in deep soil;The capacity of root system to improve soil properties mainly depends on root length density and root total surface area,the roots whose diameters are smaller than 0.5 mm is the main effective factor of the soil moisture.The soil detachment capacity of different near soil surface characteristics in the alluvialare linearly increased with increasing shear stress.In the surface layer,the rate of different soil samples differs:loess soil>soil with dead root>soil with live root>soil with live root and biological soil crusts>soil with plant stem.Vegetation root system is the largest contributor to reducing the rate of soil detachments.The second largest contributor is the crust,the the stems.In the root system,the physical bonding effect of soil is obviously larger than the biochemistry function.In terms of the percentage of contribution degree of reducing the rate of soil detachment,the root system and aerial stem of Pennisetum sp.is larger than Paspalum wettsteinii,whose soil crust is larger than Pennisetum sp.The soil’s rill erodibility variation characteristic of near soil surface characteristics is similar to soil detachment rate.In terms of the soil rill erodibility,Paspalum wettsteinii with dead root and live root is larger than the Pennisetum sp.,but the Paspalum wettsteinii with live root and biological soil crusts is smaller than the Pennisetum sp..The critical shear stress of both the Pennisetum sp.and Paspalum wettsteinii of each treatment is greater than bare land.The relationship between the critical shear stress are as follows:soil with live root>soil with live root and biological soil crusts>soil with dead root.In terms of the critical shear stress,Pennisetum sp.with dead root and live root is larger than the Paspalum wettsteinii,but the Pennisetum sp.with live root and biological soil crusts is smaller than the Paspalum wettsteinii.In every soil layer,the soil detachment rate of Pennisetum sp.and Paspalum wettsteiniig linearly increased with increasing shear stress.The soil detachment and soil rill erodibility of Pennisetium sp.,Paspalum wettsteinii and loess soil increased as the increasing of soil depth.The soil critical shear stress decreases along with the change of soil depth.In every soil layer,the loess soil’s detachment and rill erodibility are the largest,followed by the Paspalum wettsteinii and Pennisetum sp.With the increase of soil depth,the effect of vegetation root system in reducing the soil detachment rate and rill erodibility is gradually reducing and the change of critical shear stress is not obvious.As the density of root length,root surface area,root volume and root weight increased,the soil detachment rate and the rill erodibility decline in the form of index,soil critical shear stress decreased with the increasing of root indexes.The model simulation equation of the root system characteristic index and soil rill erodibility is Kr = 0.016*e(0 505*RLD=0.045*RSA)(R2 =0.853,n=10,p<0.01).The model simulation equation of the root system characteristic index and soil critical shear stress is τc= 0.527*e(-0.291*RLD 0 032*RSA-2.427*Rw)(R2 =0.706,a=10,p<0.01).