Effects Of Land Use On Soil Quality In Fragile Grassland Area

Land use is the process that human beings use the characteristics of land to meet their own needs.Land use and land use change can lead to changes in soil environment and soil quality.Because of the temporal and spatial differentiation of soil quality,it is necessary to compare two or more phase changes in order to get better understanding of the nature and mechanism of soil quality change.This thesis carried out following studies taking the fragile grassland region as the study area,which is located in middle-southern part of Siziwang Banner,Inner Mongolia and is consists of 8 towns and 54 villages(communities): Firstly,this thesis quantitatively analyzed the change of land use structure and its spatial distribution patterns by utilization of quantitative geography methods and GIS technologies based on interpreted satellite remote sensing data acquired in 1987 and 2013 respectively.In the next step,it analyzed the soil quality data by utilization of IBM SPSS and Microsoft Excel software based on collation of existing soil investigatio n data,field investigation for soil sampling and laboratory analysis,then quantitatively evaluated the soil quality change using relative soil quality index.Finally,it implemented spatial interpolation of soil quality indices using multiquadric radial basis function by application of geostatistical functions of ArcGIS software.On the above basis,it also completed spatial overlay and correlation analysis for changes of land use and soil quality.The final results are as follows:(1)The area of cropland and grassland decreased,and the area of industry and mining store land,water body and water conservancy facilities,residential land increased obviously,and the area of unused land increased a little during the period from 1987 to 2013 in the first grade land use types.The area of shrubland increased greatly during above same period in the second grade land use types.Cropland,woodland(it was mainly forestry in 1987 and was mainly shrubland in 2013 respectively)and grassland which as main land use types in the study area had larger proportion of the area,and their spatial distribution pattern shows that there are shrubland or grassland on the periphery of cropland with different sizes,thus there were few of large extent cropland area.27 years of land use made the land use structure more rational and performance following characteristics: the degree of diversification of land use types was on the medium to upper level,the land use combination type was relatively abundant,the overall level of land use degree was relatively high,and affected by topography,altitude and effort level of human productivity cropland and woodland had relatively prominent location significance.The main drivers of land use change include precipitation,population change,industrial distribution and land use policies etc.(2)During this period of 27 years,mean values and variation coefficients of six indices for reflecting of soil quality had obvious changes,among which,clay content,organic matter content and total nitrogen content had significantly increased mean value,and total phosphorus content,total potassium content and p H value had significantly decreased mean values.The variation coefficient of total potassium content and p H value are less than 10%,and belonging to weak variation,the variance coefficients of other indices were between 10%-100%,belonging to moderate variation.The spatial variation of soil quality indexes is very obvious.Spatial changes of all of the soil quality indices were very obvious.Mean value of soil quality index was 57.34 in 1987 and was 61.26 in 2013 respectively,and soil quality changes for all of the soil quality grades were obvious during the period of 27 years,among of them,the proportion of soil in fourth grade decreased significantly,the proportion of soil in the first and second grades increased obviously,but the third grade soil increased slightly,as a whole,the quality of soil showed a trend of improvement.The spatial changes of soil quality were also obvious in the 27 years period,distribution of the best soil quality extended in north direction to form a strip based on the original basis in southeastern part of the study area,then grade second and grade third soil regions formed interphase distribution pattern in the following region of the study area,the fourth grade of soil region just had few distribution area in southwestern part of the study area.(3)Land use had a significant impact on soil quality.Cropland,woodland,shrubland,and grassland had greatly improved soil quality as a whole.There had been a marked improvement of soil quality between changes of land use types such as cropland,woodland,shrubland and grassland,except that change category of from woodland to cropland lead to degradation of soil quality obviously.Nested structure and spatial pattern between cropland,woodland(shrubland)and grassland had a direct impact on the improvement of the comprehensive quality of the soil.