Fractal Characteristics Of Soil Particles And Their Influencing Factors On Different Land Cover Types In The Southern Slope Of Qilian Mountains

Soil solids with different particle sizes constitute soil particles,and their combination ratio directly determines the basic physical properties of the soil,which has an important impact on soil fertility.So,the soil particle is the most important factor affecting soil structure.Different land cover types have different effects on soil remediation and soil and water conservation,which further leads to differences in soil particle composition.The fractal dilension of soil particles can reflect the structure and quality of soil quantitatively.The vulnerability of the soil environment on the southern slope of Qilian Mountain makes it important to quantify the soil structure and quality of this area.And the research results can provide guidance for protecting surface vegetation and increasing the coverage of surface vegetation of the southern slope of Qilian Mountains,which can directly serve the agricultural and animal husbandry production and the vegetation restoration of ecologically fragile areas as well as the rational use and protection of the land.Therefore,it is of great significance for the prevention and control of water and soil erosion.In this paper,we selected the southern slope of Qilian Mountain as the study area and collected the soil samples under different land cover types for the determination of soil particle size,and the fractal dimension of soil particles was calculated to compare the difference of soil particle composition and fractal dimension.Then we discussed the variation of fractal dimension of soil particles in different land cover types in the depth of 0-50 cm soil layers,the change of fractal dimension in geospatial distribution and the main factors affecting the fractal dimension of soil.The main findings are as follows:(1)The average soil particle fractal dimension of 6 land cover types(0-50 cm)on the southern slope of Qilian Mountains was between 2.285 and 2.541.The fractal dimension of soil particles of shrub forest was the highest,and the low coverage grassland has tho lowest fractal dimension of soil particles.The average soil particle fractal dimension of different land cover types from high to low was shrub forest(2.541)>Picea crassifolia(2.528)>high coverage grassland(2.516)>cultivated land(2.502)>Sabina przewalskii(2.463)>low coverage grassland(2.285).(2)The fractal dimension of soil particles of different land cover types showed different variation characteristics with the increase of soil depth.The fractal dimension of soil granules in cultivated land,Sabina przewalskii and Picea crassifolia decreased with the increase of soil depth,and there was a large fluctuation of cultivated land at 20-30 cm.The fractal dimension of soil particles in shrub forest and high coverage grassland varied with the trend of "W" shape and "V" shape in the 0-50 cm soil depth,respectively.The fractal dimension of soil particles at the bottom of shrub forest(40-50 cm)was significantly higher than that at the surface(0-10 cm),while the fractal dimension of high-coverage grassland is slightly higher than that of the bottom.The fractal dimension of low coverage grassland in the soil layers of 0-10 cm,10-20 cm,20-30 cm and 40-50 cm did not change much,but the fractal dimension in the soil layer of 30-40 cm was significantly higher than that in other soil layers.(3)The overall change trend of soil particle fractal dimension in spatial distribution on the southern slope of Qilian Mountains was as follows:on the slope upward,the order of soil particle fractal dimension was North>Northwest>Southwest>West>Southeast>Northeast>East>South.In the altitude gradient,the fractal dimension decreased with increasing altitude.In the latitude and longitude,the fractal dimension decreased gradually from southeast to northwest,and was highest in the southeast and lowest in the northwest.(4)The soil texture of the southern slope of Qilian Mountains was coarse,mainly composed of silt and sand,and the average content of clay was only 6.15%.Soil clay content,silt content and sand content of different land cover types were significantly different(p<0.01).On the whole,the order of the soil clay content of different land cover types was shrub forest>Picea crassifolia>high coverage grassland>cultivated land>Sabina przewalskii>low coverage grassland.The order of the soil silt content was Picea crassifolio>shrub forest>high coverage grassland>cultivated land>Sabina przewalskii>low coverage grassland.The order of the soil sand content was low coverage grassland>Sabina przewalskii>cultivated land>high coverage grassland>shrub forest>Picea crassifolia.The fractal dimension of soil particles was significantly positively correlated with soil clay content and silt content(p<0.01),and it was significantly negatively correlated with soil sand content(p<0.01).(5)There were different degrees of correlation between soil fractal dimension and soil physical and chemical properties on the southern slope of Qilian Mountains.The fractal dimension of soil particles was significantly positively correlated with water content,total porosity,capillary porosity,organic matter,total nitrogen and total carbon(p<0.01),and it was significantly negatively correlated with bulk density(p<0.01),but it had no significant correlation with non-capillary porosity and pH value of soil.