Spatial Variability Of Water Stable Aggregates On Ephemeral Gully Soil Of Pinus Massoniana Artificial Forest In Southern Red Soil Region

The red soil hilly region of South China is one of the most serious areas of soil erosion in China.Ephemeral gully erosion is one of the main forms of soil erosion in Pinus massoniana artificial forest.Soil texture,soil structure and soil erodibility are important factors affecting soil erosion.Soil structure is the decisive factor of soil anti-corrosion ability,soil particle fractal parameters can better reflect soil texture traits,the stability of agglomerates is closely related to soil erodibility,which is an important basis for quantitative evaluation of soil erosion.The spatial difference of water-stable aggregates in the ephemeral gully of Pinus massoniana forest in the red soil hilly region of South China is studied,which not only helps to explore the influence of ephemeral gully erosion on soil water-stable aggregates in the red soil hilly region,but also the Pinus massoniana forest in the red soil hilly region.The management of water and soil erosion provides scientific and technological support and has very important theoretical and practical significance.In this paper,the topsoil of the underlying ephemeral gully in the red soil hilly area was taken as the research object,the ephemeral gully survey and soil characteristics analysis in the field,and the fractal model was used to analyze the fractal dimension characteristics of the topsoil soil particle mass;the indoor spatial(dry sieve + wet sieve)test was used to study the spatial distribution of water-stable aggregates in the topsoil soil;based on the EPIC model,the soil erodibility K value was estimated,the spatial distribution of soil erodibility index in different parts of ephemeral gully was analyzed,and the influence of ephemeral gully erosion on topsoil soil aggregates was determined,The main results of this study are as follows:(1)Fractal characteristics of topsoil soil in ephemeral gully of Pinus rmassoniana forest.The topsoil of the ephemeral furrow has high grain gravel content and serious soil coarsening.The fractal dimension D value is between 2.30 and 2.57,showing weak variability.Fractal dimension was positively correlated with the content of silt and clay,and positively correlated with the content of coarse sand,coarse sand,medium sand and fine sand,and negatively correlated with the content of coarse gravel and fine gravel.In the direction of the cross slope,the fractal dimension of topsoil soil particles is represented by the bottom of the gully>the gully slope>the edge of the gully,and the bottom of the gully is significantly larger than the gully slope and the gully edge;the direction of longitudinal slope,as the length of the trench increases,the trend of fractal dimension is not obvious.(2)Spatial distribution of soil water-stable aggregates.Soil water-stable aggregates decrease first,then increase,then decrease and then increase.The diameter is<0.50 mm,the content of 2.00-5.00 mm is more,the content of>5.00 mm is the least,the content of>0.25 mm is 70%or more of the total content;the average weight diameter(MWD)and the geometric mean diameter(GMD)are 1.10?2.76 respectively.Mm and 0.41?1.55 mm.In the direction of the cross slope,the soil water stable aggregates of the gully slope,the groove edge and the bottom of the gully are significantly different;the direction of longitudinal slope,with the increase of the top distance of the slope,the soil water-stable aggregates showed significant spatial differences:the content of>0.25 mm aggregates showed a normal distribution,and the bottom of the trench increased significantly with the length of the trenches.The edge is decreasing.(3)Spatial distribution of soil erodibility K value.The erodibility K value of the ephemeral gully topsoil soil is between 0.023 and 0.047,with an average value of 0.042,showing moderate variation.The K value was significantly positively correlated with the content of coarse gravel and fine gravel,and was significantly negatively correlated with the content of very coarse sand,coarse sand and medium sand.It was significantly negatively correlated with the content of powder and clay,and the content of organic matter,The fractal dimension was negatively correlated and the soil bulk density was positively correlated.In the direction of the cross slope,the overall value of K is the bottom of the gully<gully slope<the edge of the gully;the direction of the longitudinal slope increases with the top of the slope,and the K value of different parts fluctuates.(4)The relationship between soil water-stable aggregates and soil erodibility K value.There was a significant positive correlation between the K value and the soil water-stable agglomerate content of 2.00-1.00 mm in diameter,and a significant positive correlation with the soil water-stable aggregate content of 5.00?2.00 mm,0.50?0.25 mm and>0.25 mm.The content of water-stable agglomerates in<0.25 mm soil was significantly negatively correlated.In the direction of the cross slope,the soil water-stable agglomerate content and the erodibility K value of the diameter>0.25 mm are represented as the bottom of the gully>the gully slope>the gully edge;the direction of longitudinal slope,with the increase of distance from the head,the content of water-stable agglomerate and the value of erodibility of soil with different diameters>0.25 mm showed a slight decrease trend.All of the above indicate that the water-stable agglomerates in the ephemeral gully topsoil are closely related to the erodibility K value.The research results can provide scientific guidance for the improvement of soil structure and soil properties of ephemeral gully in the red soil hilly region,as well as the treatment of ephemeral gully soil erosion and the construction of ecological environment.