Soil Aggregate And Erodibility Of Zigui Mountain Citrus Orchard

Zigui County is one of the important citrus producing areas in China,with a long history of citrus planting.However,the citrus orchard in this area is located in hilly and mountainous areas,and the soil layer is thin.With the extension of planting years and the influence of human management（implementation of terraces）,the aggregate structure and erodibility of surface soil will be changed,thus affecting soil erosion.In this study,typical local orchards（three planting years of 10,20,30 a and two planting measures of natural slope and stone ridge terrace）were selected to analyze the basic physical and chemical properties of soil and the stability of aggregate structure.Correlation analysis and Taylor diagram method were used to clarify the erodibility calculation model suitable for local orange orchards,and the soil K values of different orchards were calculated and compared with the determined estimation model.On this basis,the variation characteristics of soil aggregates and erodibility and their internal relations under the influence of’planting years-stone ridge terrace-terrain slope difference’were comprehensively analyzed.The research results are of great significance to the prevention and control of soil erosion and the protection and utilization of soil in local orchards.The main results are as follows:（1）The soil texture type of citrus orchard in the study area belongs to silty loam.After many years of planting,the p H value of the soil is between 6.5 and 8.5,which is still within the appropriate range.Soil nutrients continue to accumulate,but soil permeability gradually deteriorates.（2）The particle size of soil aggregates in citrus orchards in the study area was mainly>2 mm,followed by the content of macroaggregates with particle size of 2 mm,and R0.25,MWD and GMD all showed 30 a<20 a<10 a,and the stability of aggregates decreased with the increase of years.Among different slope positions,the content of large aggregates in the slope was the highest,and the aggregate structure was the most stable.Among the two planting methods,the content of large aggregates in terraces is greater than that in natural slopes,and the stability index of aggregates is also that terraces are better than natural slopes,indicating that after the implementation of terraces,the terrain changes,which can slow down the degradation of soil structure.（3）The soil erodibility estimation method EPIC model method was selected by Taylor diagram method in this study area.The EPIC model method was used to calculate the variation characteristics of soil erodibility K value in different planting years in the study area.The change rule of K value in natural slope citrus orchards was10 a>30 a>20 a.The soil erosion resistance was enhanced when the planting years were about 20 years,and the soil erodibility K value increased with the planting years continued to extend to about 30 years,and the erosion resistance decreased.In contrast,the soil erodibility K value of terraced citrus orchards with different planting years increased with the extension of planting years,but the change was not obvious and stable.The K value of terraces is lower than that of natural slopes,and the erosion resistance of terraces is stronger.（4）Soil erodibility in the study area is closely related to some soil physical and chemical properties and aggregate structure.There was a significant negative correlation between soil erodibility and silt content,and a significant negatively correlation with sand content（the higher the sand content,the stronger the soil erodibility/the worse the soil erosion resistance）.Soil erodibility K value was negatively correlated with organic matter content.K value was negatively correlated with MWD,GMD and R_0.25 of aggregates,and fractal dimension D was positively correlated with them.