| Since the implementation of the project of returning farmland to forest in 1999,the vegetation coverage of the Loess Plateau has increased significantly,which has effectively curbed soil erosion in the region,and the basic properties and structural characteristics of soil have also been significantly improved.Soil structure is the basis of maintaining soil function,which plays an important role in the movement of soil water,gas,nutrients and microbial activities.In this paper,Wangdonggou small watershed in Changwu County of Shaanxi Province in the Southern Loess Plateau was taken as the research area,and four planting areas,namely,wasteland(HD),farmland(NT),orchard(GY)and Robinia pseudoacacia(CH),were covered for 0-500 cm.The response of soil physicochemical properties to different vegetation types was analyzed.The CT scanning images were processed by Image J software to quantitatively characterize the distribution of soil pore structure(porosity,number of pores)and the variation of related parameters of morphological characteristics(roundness,connectivity,fractal dimension,etc.),and the relationship between soil physicochemical properties and soil pore structure was analyzed The relationship between the two structures can provide theoretical basis and scientific guidance for the sustainable development of watershed vegetation construction.The main results are as follows:(1)There were significant differences in soil physical and chemical properties between HD,NT,GY and CH(P<0.05).The soil particle composition of four types of plots in the study area was silt(55%-60%)> clay(32%-36%)> sand(8%-9%),indicating that the soil in the study area was silt clay loam;0-500 The saturated hydraulic conductivity decreased with the increase of soil depth in cm profile,which was GY>CH>NT>HD;the change trend of soil bulk density and saturated hydraulic conductivity was opposite,which was HD>NT>GY>CH;the soil water content of HD,NT and GY fluctuated from top to bottom,and the change trend was obvious,and the difference of CH water content between adjacent soil layers was small and the average water content was small(9.5%)was significantly lower than that of other vegetation types.(2)The results show that the visual analysis results of CT scanning are consistent with the quantitative analysis results of soil pore structure characteristic parameters.In the two-dimensional scale,the porosity and pore number of HD,NT and GY soil decreased significantly with the increase of soil depth,while the porosity decreased with the increase of CH,in which NT had the highest pore number,but the porosity was significantly lower than HD,GY and CH;in the vertical direction,the pore morphology characteristics such as roundness and pore equivalent diameter showed a fluctuating trend,and the average roundness was about 0.64.The results showed that the soil pore morphology was regular and close to round;the change trend of equivalent pore size and soil porosity was the same,and the vegetation root increased the equivalent diameter of soil pore while increasing soil pore,and the macropore of 100-500 μm accounted for 40%-60% of all pores,and the micropore of 0-30 μm was the least.Similar to the results of two-dimensional scale,with the increase of soil depth,the number of soil pores first increases and then decreases in three-dimensional scale.The average porosity of GY and CH is higher than that of HD and NT,and the fractal dimension of pores is at a high level(2.80-2.96),while the anisotropy of pores is low(0.05-0.3).The soil pore network is complex but the pore shape is regular.(3)Correlation analysis showed that soil fractal dimension was significantly positively correlated with soil total nitrogen content(P<0.05),soil pore anisotropy was significantly positively correlated with organic matter content(P<0.01),and there was a strong correlation between soil pore connectivity and porosity Other soil structure parameters have significant effects on soil physical and chemical properties,which can comprehensively reflect the soil structure. |
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