Study On The Impact Of Wind And Water Combined Erosion On Soil Quality In Mollisols Sloping Farmland With Different Slope Shapes

The Mollisols region in Northeast China is an important production base for commercial crops in China,playing a crucial role in ensuring national food security.Wind and water forces have long been recognized as significant drivers of erosion and degradation in Mollisols.However,research on the combined effects of wind-water erosion on slope erosion patterns and soil quality in Mollisol areas has been relatively limited,thereby constraining the conservation and sustainable utilization of these soils.Therefore,this study focuses on different slope shapes of Mollisols sloping farmland in the Northeast China.By utilizing ¹³⁷Cs nuclide tracing technique and combining statistical analysis,the study elucidates the spatial distribution characteristics of soil erosion-sedimentation,different types of soil erosion,physicochemical properties,and the impact of soil erosion on soil quality.The findings provide scientific evidence for targeted conservation of Black Soil resources.The main conclusions are as follows:（1）Soil ¹³⁷Cs content and soil erosion rates in three different slope shapes,namely straight slopes,convex slopes,and concave slopes,exhibit an alternating trend of"increase-decrease"with increasing slope length.The mean soil erosion rates are as follows:concave slope>convex slope>straight slope.The straight slope(2446.23 t km^-2 a^-1)and convex slope(1965.18 t km^-2 a^-1)are classified as slight or mild erosion,while the concave slope(5375.48 t km^-2 a^-1)experience intense erosion.However,all erosion rates significantly exceed the allowable soil loss of 200 t km^-2 a^-1 the Northeast China Mollisols region.（2）The proportions of wind erosion and water erosion on different slope shapes are essentially the same,and both wind erosion rate and water erosion rate exhibit an alternating trend of"increase-decrease"with increasing slope length.The fluctuation trend of water erosion rate showed apparent hysteresis compared to the wind erosion rate and total erosion rate,with relatively smaller fluctuations.Convex slope and concave slope exhibit minimal fluctuation in water erosion rate.Wind erosion and water erosion primarily occur on the slope shoulders of straight slope,on the slope base of convex slope,and on the middle-lower part of the slope for concave slope.This indicates a certain relationship between the fluctuation trend and occurrence location of wind and water erosion on slope and the slope shapes.（3）The organic matter,total nitrogen,soil specific surface area,and median particle size of different slope shapes exhibit periodic variations with increasing slope length.The mean organic matter content follows the pattern:concave slope>straight slope>convex slope,with coefficient of variation values of 0.09,0.07,and 0.07,respectively,indicating weak variability.The mean total nitrogen content follows the pattern:straight slope>concave slope>convex slope,with coefficient of variation values of 0.12,0.05,and 0.13,respectively.The variability of straight slope and concave slope is moderate,while convex slope shows weak variability.（4）Different types of erosion have varying degrees of impact on soil physical and chemical properties,with water erosion having the greatest impact.The water erosion rates in all three slope shapes are negatively correlated with organic matter and silt content,but positively correlated with sand content.On the other hand,the effects of wind erosion rates on soil physical and chemical properties vary among the three slope shapes,indicating an influence of slope shape.（5）Soil quality assessment indices were constructed based on soil properties such as organic matter（SOM）,total nitrogen（TN）,available nitrogen（AN）,available phosphorus（AP）,available potassium（AK）,and soil particle composition.Soil quality indices were calculated,and the results showed that the soil quality index followed the pattern:straight slope>concave slope>convex slope.The indices exhibited an alternating trend of"increase-decrease"with increasing slope length,and were negatively correlated with soil erosion intensity.Soil quality indices for different slope shapes were classified,and evaluation criteria for soil quality degradation were proposed when soil erosion rates were relatively low(<2500 t km^-2 a^-1),based on low nutrient standards.The soil quality index was lower for straight slope at the slope top and bottom,for convex slope at the slope top,and for concave slope at the slope top,bottom,and depressed areas.When soil erosion rates were higher(>2500 t km^-2 a^-1),the soil erosion rates were higher for straight slope at the slope shoulder and middle,for convex slope at the upper and middle-lower parts of the slope,and for concave slope at the shoulder and upper-middle parts of the slope.This indicates that even when erosion rates are relatively low,quantitative assessment of soil quality is still necessary.