| Land is a non-renewable resources,as an important material basis of the human survival and development,has the characters such as the quantitative finity,space location fixity,characteristic regional differences and function permanence.But with the urbanization and industrialization,the transformation to systems of earth's which hold by human,has been more extensive and profound.Unreasonable land use patterns not only led to deterioration of the ecological environment,but also the disorder development has seriously restricted the sustainable development of society and economy.Soil erosion problem is one of China's major ecological environmental problems and the Sichuan basin hilly region located in the upper reaches of the Yangtze River is one of the most serious regions.The soil erosion area account for the 65%～70%of the overall land.The non-protection farming measures and over cutting not only damaged the soil structure, reduced soil fertility,but also exacerbated the local and surrounding areas of ecological environment worsening,and soil erosion restrict the region's healthly social and economic development in a great degree.Since the 1980s,fractal geometry as an effective methods to descript irregular shape has been used in soil science to solve many difficult and impossible questions that can't solved by the traditional methods.Many results show that soil is a self similar system with typical fractal character,and the soil particle size,the particle surface,the particle bulk,the particle pore have the self-similar in statistical sense.In other words,the part and whole has the same statistical distribution which would described by fractal dimension.Therefore, It has an important theoretical value and practical significance to study soil particle in this region with fractal theory in order to improve soil structure,soil texture situation and govern soil erosion.This paper take the example of neijiang city in hilly region,results based on the field sampling and laboratory analysis show that:(1) The fractal dimension of 186 soil samples are between 2.794 to 2.996,the Average fractal dimension of J2z,J3s,J3p,J2s are 2.9325,2.9170,2.9086,2.9306(A&Zmodel), 2.8135,2.7764,2.7550,2.8130(YPL model).It shows J2z＞J2s＞J3s＞J3p.Under different use methods,soil particles fractal dimension has obvious characteristics of differentiation.It shows woodland＞farmland＞grassland,its average fractal dimension is 2.9341＞2.9261＞2.9019 (A&Z model),2.8168＞2.7993＞2.7401(YPL model).On the different slope,soil particles fractal dimension shows a lower altitude with the increasing trend,and make the result from the test data that:top of the hill is minimum,middle of the hill is second,the largest is the feet of hill.its fractal dimension is 2.9066～2.9341(A&Z model),2.7504～2.8206(YPL model).(2) A significant negative correlation is between soil particles fractal dimension and sand content,a significant positive correlation is between soil particles fractal dimension and silt,clay content;the correlation analysis indicates that a significant positive correlation between soil particles fractal dimension and fine particulate matter the particle size of less than 0.05mm,and that fractal dimension is a good indicator of the soil texture.(3) Soil particles fractal dimension and soil organic matter content has significant correlation,that is the higher the organic matter content,the greater the fractal dimension. The organic matter content of woodland,grassland are 16.47 Kg.m-1 and 14.00 Kg.m-1, fractal dimension is 2.934(A&Z model),2.817(YPL model) and 2.902(A&Z model), 2.740(YPL model).They are higher than the farmland which is 13.48 Kg.m-1,2.926 (A&Z model),2.799(YPL model).(4) Under the analysis of variation,the soil particles fractal dimension of the spatial distribution has a trend such as the contour lines of Hill.Bottom of the hill and the gully has high-value,middle of the hill and top has low-value,and its value is from 2.794～2.858 to 2.966～2.996.(5) According to soil parent material,land use,landscape position,we could know that A&Z model obtained the surface of the soil particles fractal dimension is greater than Pei-Ling Yang model obtained the soil particle size distribution of fractal dimension. Because A&Z model is based on the relationship between soil porosity,soil particle and fractal theory,and derived by integration,Pei-Ling Yang model is on the assumption that the mass density of soil particle is a constant,and it does not conside different soil particle based on the different shape,so A&Z model is greater than Pei-Ling Yang model.(6) Soil particles fractal dimension as one of the attributes of soil can also reflect the characteristics of the soil fertility.The study results show the linear relationship between soil fertility indicators and the fractal dimension of the soil particle size distribution,the fractal dimension of the surface of the soil particles.F-test results show that the regression equation has been to 1%level(F0.01=7.01)which means the soil particles fractal dimension can be a factor that appraise soil fertility characteristics.
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