Effects Of Root Characteristics Of Three Herbaceous Plants On Soil Erodibility

The Red Soil Area in South China is an important agricultural resource area,which plays an important role in the development of Chinese agricultural economy.The area boasts abundant rainfall as well as ideal water and heat conditions.However,excessive human activities cause serious damage to most of the vegetation on the surface,in addition to the complex terrain and rainfall of high intensity and quantity,which leads to serious soil erosion,thus resulting in great soil and water losses,soil layer thinning,rock baring,and the reduction of the quality of arable land and agricultural production.Because of its significant effects on reducing soil erosion,vegetation is considered as one of the most effective measures to control soil and water losses in agricultural catchments.Plant roots worked significantly in indirectly enhancing the soil erosion resistance,such as stabilizing soil structure,improving soil permeability and shearing resistance,as well as directly enhancing the soil erosion resistance like impacting on the erosion mechanism.However,the effect of roots on soil physical and chemical properties and the relative contribution to the inhibition of soil erosion are not well studied due to difficulty in root sampling.Based on the analysis of the available data and the field investigation,three kinds of common grasses-vetiver(Vetiveria zizanioides(L.)Nash),white clover(Trifolium repens L.)and ryegrass(Lolium perenne L)in this area were selected for testing their effects on erodibility of the typical soils(yellow brown soil and red brown soil),and seasonal variation law of the effects that simulated white clover,ryegrass and its mixed grass have on the erodibility of yellow brown soil.Using the method of intensively flushing undisturbed soil samples to further study the impacts that plant roots have on enhancing soil erodibility and to provide theoretical support and technical reference for grassland selection in water and soil conservation and prevention and control in soil erosion in this area.The main results are as follows:(1)Root system can effectively enhance the anti-erodibility of both soils,and the enhancing effects are as follows: vetiver grass> white clover> ryegrass.However,there are differences between the effects the same plant roots cause on different types of soil's antierosion: vetiver has the same effects on yellow brown soil and brown red soil;the effect of white clover on yellow brown soil is stronger than that on brown red soil,and the effects of rye grass are opposite to that of white clover;(2)Among the factors of root parameters,root length density(RLD),root mass density(RMD),root area ratio(RAR),total root area(Stotal)and root mean diameter(Dmean),RLD is the most important in affecting soil erodibility,and it can better simulate the both soils' erodibility characteristic;RMD and RAR also share the key functions.RSD decreases exponentially corresponding with RLD and RAR,and logarithmically with RMD.There is a significant correlation between RSD and all root parameters(P<0.05);(3)The soil physical properties changed with the time,and the soil bulk density increased first and then decreased slightly.When the soil porosity was correspondingly changed,the MWD of water stable aggregates increased slowly.Soil erodibility was significantly correlated with soil bulk density and soil porosity(P <0.05),and was significantly correlated with <0.25 mm and> 2 mm water stable aggregates,while not correlated with other diameters(P> 0.05).It was also significantly correlated with RLD,RMD and RAR(P <0.05);(4)The enhancement effects of plant root system on two types of soil's erodibility can be better simulated by WEPP model with RLD.And the correlation coefficient R2 between RLD and the nonlinear regression equation of two kinds of soil Dc is above 0.93,equations of two soils are respectively,Dc=0.002exp(-0.036*RLD)(?-1.145)and Dc=0.002exp(-0.040*RLD)(?-1.562).We can see the critical shear force relationship is yellow brown soil < red brown soil,which indicates that the yellow brown soil is more likely to be eroded than red brown soil in this area;(5)Under the same shear force,the sediment content decreased with seasons,and the difference between areas of different sowing density was significant(except 20 and 30 g/m2).During the same testing period,the early sediment content increased rapidly,while in the latter period,it remained basically balanced or increased slowly;(6)The improvement of soil erosion by root increased with the increase of sowing density.The erodibility coefficient Kr of each grass sample decreased with the increase of density.When the density was more than 20 g/m2,Kr remained basically unchanged,indicating that the suitable sowing density of plant was 10 ~ 20 g/m2.In summary,the plant roots can affect the soil physical properties to enhance soil erosion resistance.And vetiver is more suitable in that area while the suitable sowing density of fibrous root system grasses is 10 ~ 20 g/m2.Therefore,appropriate grass and planting density should be chosen to play the best ecological and economic benefits.