Study On The Distribution Characteristics Of Topsoil Organic Carbon And Its Effect Factors On The Urban-rural Gradient

Soil organic carbon pool can affect global climate change and the global carbon balance by its tiny variations.With the rapidly development of the society,the city has an increasingly changes and influences on the environment.There are more agricultural and natural land converted into urban land.It not only changes the urban ecological environment type,but also affects the chemical and physical properties of soil and the characteristics of surface vegetation coverage.There had largely changed of soil organic carbon content.Therefore,the study on the organic carbon content of urban soil has an great significance to understanding the impact of human activities on soil organic carbon storage.This study was based on the remote sensing and GIS.Principal components analysis was used to build the multiple linear regression model to quantify urban,suburb,rural of Kunming.The result shows the difference of landscape distribution on the urban-rural gradient of Kunming.It can provide scientific bases for city planning and construction.Based on the partitioning results of urban-rural gradient,this article set continuous urban-rural fringes in the study area.And the characteristics of urbanization indicators on the belts are analyzed.Finally,we took soil sampling on the belts in the study area,and tested soil bulk density,soil moisture content,soil organic carbon content,total nitrogen,total phosphorus,total potassium,pH and soil texture.In this paper,we analyzed the distribution characteristics of topsoil organic carbon content and density on the urban-rural gradient,and estimated the topsoil organic carbon storage,and analyzed the soil physical and chemical properties how to effect on topsoil organic carbon content.The results shown that:(1)The topsoil organic carbon content on the urban-rural gradient followed the order of rural>urban>suburb,the topsoil organic carbon in rural area was 1.376 times and 3.063 times than that in urban and suburb soils respectively.The variation coefficient of topsoil organic carbon content in all area was larger.Urban is the largest among them and it's variation coefficient was 84.078%,this indicated that the spatial distribution of soil organic carbon was extremely unbalanced in urban,and the influence by personal factors were more than suburb and rural.(2)The topsoil organic carbon density on the urban-rural gradient followed the order of rural>urban>suburb.The organic carbon density of rural was 8.473kg/m~2,which was 1.343 times and 2.943 times compared to urban and suburb soils respectively.The variation coefficient of topsoil organic carbon density have been presented a stronger spatial variation of urban,suburb and rural areas.(3)The topsoil organic carbon reserves in the study area were about 10.186Tg,rural has the largest topsoil organic carbon reserves was 9.975Tg,urban and suburb topsoil contained 0.136Tg and 0.074Tg respectively.The topsoil organic carbon reserves of rural account for 97.929%of the total area soils,urban and suburb were about 1.352%and 0.726%respectively.(4)The total nitrogen content on the urban-rural gradient was shown that:rural>urban>suburb,and it has significant positive correlation with SOC.The total phosphorus content shown that:urban>rural>suburb,and it also has positive correlation with SOC.The total potassium content shown that:urban>suburb>rural,and it hasn't relationship with SOC.The soil pH in the study area was mainly neutral and alkaline,it also hasn't relationship with SOC.There have four soil texture types in the study area sandy,it is mainly about loam,silt,loam and sandy silt,the highest topsoil organic carbon content was in the loam,but sandy silt has the lowest.There have remarkably different of topsoil organic carbon content between silt and loam,as same as it among loam,silt,sandy silt and sandy loam,but it didn't have difference among silt,sandy silt and sandy loam.(5)The influence of human activities on topsoil organic carbon content is mainly through changing the land use patterns,agricultural management measures and production and way of life.Those human activities can affect vegetation types and the input and out put of various nutrient elements and organic substances in soil,it can affect the organic carbon content in soil.The influence of human activities on soil organic carbon content is more complex,it can release the content of soil organic carbon by unreasonable land use,it also can increase the content of topsoil organic carbon by the grain for green project,adequate irrigation and fertilization.