Soil Erosion Resistance Of Typical Farmland And Grassland In Ya’an City

Soil erosion is a worldwide environmental problem.It is an important cause of soil degradation and reservoir sedimentation,which seriously restricts the development of social economy.There are abundant rainfall and wide slope farmland,many reservoirs,and serious soil erosion in Ya’an.Therefore,it is of great significance to carry out the study of soil erosion for soil and water conservation and promoting the sustainable development of social economy in Ya’an City.In this study,ryegrass grassland,alfalfa grassland,cornfield,and bare land were taken as the research object.Soil physical and chemical properties,root weight density and soil detachment capacity under different water flow shear stress were measured in different plots in a 30-days cycle from March to October.Soil erosion resistance（soil rill erodibility and critical shear stress）was calculated using the linear regression method,and the influence mechanism of soil detachment capacity was analyzed.The multiple stepwise regression method was used to determine the main influencing factors of soil erosion resistance temporal variation,and several prediction equations for the temporal variation of soil erosion resistance were conducted.The main conclusions of this study are as follows:（1）The particle sizes of soil water-stable aggregates>5 mm and<0.25 mm varied greatly in different plots.The soil organic carbon content was generally stable and higher in spring.Soil bulk density decreased first and then increased slowly.The soil cohesion of ryegrass,alfalfa and corn plots decreased first,then increased and stabilized after July,bare land decreased first and then increased.The root weight density of ryegrass,alfalfa and corn increased first and stabilized after July.（2）Soil detachment capacity was affected by hydrodynamic conditions.With the increase of flow velocity,steam power and unit steam power,soil detachment capacity increased as a power function relationship,and it increased linearly with the increase of water flow shear stress.Soil detachment capacity was also affected by soil physical and chemical properties and roots.It was significantly negatively correlated with water stability macroaggregate content,(R_0.25),mean weight diameter of water stability aggregate（MWD）,geometric mean diameter of water stability aggregate（GMD）,soil organic carbon content（SOC）,soil bulk density（BD）,soil cohesion（SC）and root weight density（RWD）,and significantly positively correlated with fractal dimension of soil water stability aggregates（D）and percentage of aggregate disruption（PAD）.Stream power,soil cohesion,mean weight diameter of soil water stability aggregates,and root weight density could be used to simulate the soil detachment capacity well,and the coefficient of determination of the simulation equation was 0.952.（3）There was a significant temporal variation in soil erosion resistance in those experimental plots.The soil rill erodibility of rye grassland,alfalfa grassland,cornfield and bare land fluctuated in 0.00160～0.0127,0.00161～0.0598,0.00173～0.0668,0.00167～0.110s/m,respectively,and the average values were 0.00360,0.0121,0.0118,0.0547 s/m,respectively.The soil critical shear stress of rye grassland,alfalfa grassland,cornfield and bare land fluctuated in 4.34～5.38,4.30～5.15,4.60～5.38,3.86～5.01 Pa,respectively,and the average values were 4.95,4.85,5.05,4.72 Pa.Ploughing led to a sharp increase in soil rill erodibility in those plots,then followed by a continuous decline.At the end of the experiment,the soil rill erodibility of the rye grassland was relatively stable,and the soil rill erodibility value of the alfalfa grassland and cornfield increased slightly.The soil critical shear stress of those experimental plots decreased sharply after ploughing,and then showed a fluctuating upward trend.（4）Correlation analysis showed that soil rill erodibility was significantly negatively correlated with R_0.25,MWD,GMD,SOC,BD,SC and RWD,and significantly positively correlated with D and PAD.With the increase of R_0.25,MWD,GMD,BD,SC,RWD,soil rill erodibility decreased exponentially,with the increase of SOC,soil rill erodibility decreased as a power function,while with the increase of D and PAD,soil rill erodibility increased exponentially.The results of stepwise regression analysis showed that the temporal variation of soil rill erodibility of the experimental plots could be simulated by SC,MWD,and RWD.Soil critical shear stress was significantly positively correlated with R_0.25,MWD,GMD,BD,SC,and RWD,and significantly negatively correlated with D and PAD,but had no significant correlation with SOC.With the increase of R_0.25,MWD,GMD,BD,SC and RWD,soil critical shear stress increased as a power function,and with the increase of D and PAD,soil critical shear stress decreased as a power function.The results of stepwise regression analysis showed that soil critical shear stress could be simulated by SC and RWD.