Experimental Study On The Effects Of Seasonal Freeze-thaw On Soil Erodibility

The middle reaches of the Yellow River is located in the temperate mid-latitude regions,which belongs to the moderate freezing and thawing zone.The amount of soil loss during the thawing period of the frozen soil in this area accounts for more than 50% of the annual soil loss,which is a typical area to study the change of soil erodibility under seasonal freeze and thaw.In this study,seasonal freeze-thaw area of typical aeolian sandy soil,cinnamon soil,dark loessial soil,loessial soil as an example,through indoor simulated freeze-thaw test,the effects of seasonal freezing thawing on soil erodibility were studied by observing the changes of soil physical and chemical properties under freeze-thaw conditions,and through the EPIC soil erosion model to estimate soil erodibility K values,quantitative analysis of freeze thaw effects on soil anti erodibility,construction of soil erodibility K relationship before and after freeze and thaw,to investigate the soil erodibility of freeze and thaw response mechanism.The study laid the foundation for the study on the mechanism of soil erosion of the sloping farmland in the freeze-thaw process,and provided a theoretical basis and scientific guidance for the prevention and control of soil erosion in seasonally frozen soil.The major conclusions are as follows:(1)Seasonal freezing and thawing significantly affected the physical and chemical properties of soil,and the degree of influence was related to the numbers of freeze-thaw cycles,the initial soil moisture content and soil depth.The changes of soil moisture content,soil porosity,soil bulk density,clay content,sand content,micro aggregate content,soil aggregation,dispersion rate,soil hardness and soil shear strength,organic matter content of aeolian sandy soil,cinnamon soil,dark loessial soil and loessal soil were significant different between 1~9 freeze-thaw cycles(P<0.05),and after9 cycles,the change amplitude decreased,the freeze-thaw cycle between the difference was not significant(P>0.05);The change of physical and chemical properties of soil with high moisture content was more obvious than that of low moisture content in the process of freeze-thaw cycles,the results showed that the response of soil with high water content to the freeze-thaw action is more severe;The physical and chemical properties of the surface soiland the deep soil were significantly different(P<0.05),and the freeze-thaw damage to the surface soil(0~5 cm)was the most serious.(2)Seasonal freeze-thaw cycles significantly increased soil erodibility,and the degree of soil erodibility was mainly affected by the number of freeze-thaw cycles and soil types.The soil erodibility K value showed an increasing trend in the process of freeze-thaw cycles,the aeolian sandy soil,cinnamon soil,loessial soil erodibility K value and the number of freeze-thaw cycles(1~15)showed logarithmic function;aeolian sandy soil erodibility changed greatly in the process of 1~5 freeze-thaw cycles,and the soil erodibility of aeolian sandy soil was increased by 0.0376 [t ha h/(ha MJ mm)] after freeze thaw,compared with unfrozen soil,it increased by 19.00%,after 15 freeze-thaw cycles,the aeolian sandy soil erodibility increased by 20.55%;The cinnamon soil and loessial soil erodibility increases greatly in the process of freeze-thaw cycles(1~9),cinnamon soil,loessial soil erodibility were increased by 7.37%,9.45% after 9 cycles,and after 15 cycles of freeze-thaw,the soil erodibility were increased by 10.57%,11.79%;The dark loessial soil erodibility had no obvious change rule in the freeze-thaw process,but with the increase of the number of freeze-thaw cycles,the overall showed a certain increasing trend,dark loessial soil erodibility increased by 2.77% after 15 freeze-thaw cycles;The soil erodibility K value after freezing and thawing is about 1.173 times of the unfrozen soil erodibility K value,that: K freez-thaw =1.173 K unfrozen.(3)Seasonal freeze-thaw action destructed soil aggregates,reduced the degree of aggregation of soil,soil clay content,soil bulk density,generalized soil structure index and soil physical properties,on the other hand,the increased soil organic matter content,sand content,silt content,median grain diameter(d50),and soil dispersion rate,through these two aspects.The soil erodibility K showed different degrees of increase,through these two aspects,the soil erodibility K increased in different degrees.The freeze-thaw cycle significantly reduced soil clay,increase soil sand content,reduce the particle size of micro aggregates and the particle size of micro aggregates increased,leading to soil desertification,soil aggregation degree decreased,the dispersion rate increases;Freeze-thaw cycle significantly reduced soil bulk density,soil hardness and soil shear strength,increased soil moisture,soil porosityand organic matter content,thus reduced the ability of soil to resist external force of destruction;The limiting factor for soil erodibility after freeze-thaw cycles aggregate content influence thawing,clay content,sand content,silt content,followed by the content of soil organic matter,soil bulk density and porosity;The limiting factor for the influence of the soil erodibility after freeze-thaw cycles were soilaggregate content,followed by clay content,sand content,silt content,followed by third,soil organic matter content,soil bulk density and porosity;The factors affecting soil erodibility in seasonally freeze-thaw area can be generalized as follows: soil texture and organic matter factor,soil aggregation factor,soil three phase structure factor.