Study On Soil Organic Carbon And Inorganic Phosphorus Form Variation Characteristic Under Different Land Use Pattern In Karst Area

The karst ecosystem in southwest China is very vulnerable because of the special geological conditions and geographical background.The unreasonable interference of human activities lead to the destruction of vegetation,soil erosion,land degradation,a large area exposed bedrock landscape. The soil and epikarst of karst ecosystem are in close contact with lithosphere,atmosphere, hydrosphere and biosphere.To curb the development of rocky desertification and improve soil quality is the key factor to achieve sustainable development in southwest area of China.Returning farmland to forest and afforestation is one of the important ways to increase vegetation coverage.In recent years,the country has carried out a series of returning farmland to forests in karst area,and these activities will inevitably have a direct compact on the nature of the soil.This paper will study on the characteristic of soil anti-erodibility,soil organic carbon,inorganic phosphorus in different defarmland,and the impact of organic carbon,calcium to inorganic phosphorus form,in order to provide a scientific basis for optimization of the returning pattern,protection of soil organic carbon, rational use of phosphate fertilizer.In this study,taking Shi Qing Village of Chongqin as an example,we select the nine land-use types(including defarmland,farmland,forest land etc.),and according to the pedogenetic layer of soil collected 29 soil samples.In laboratory carry out the basic physical and chemical properties analysis,anti-erodibility indicators analysis,active organic carbon analysis,inorganic phosphorus forms analysis,calcium form analysis.Focus on the corrosion resistance of soil,soil organic carbon, inorganic phosphorus in selected land-use types,and the impact of organic carbon,calcium to inorganic phosphorus form.And draw the following major conclusion:1.The soil anti-erodibility and soil active organic carbon are different in different land-use patterns.(1) In study area,the soil anti-erodibility of A layer of defarmland(three kinds) have obvious changes after 3 to 6 years set-aside,but erosion resistance of soil after set-aside range from traditional farmland to Pinus massoniana forest land.Among the three kinds of set-aside pattern,the erosion resistance of soil is highest under camphor+grass.(2) Different from traditional farm land,at set-aside farm land,the erosion resistance of soil in horizon A are higher than horizon B,which show s that set-aside can improve erosion resistance of soil in horizon A faster,especially under the camphor tree + grass pattern.(3) The various kinds of soil profile are not obvious difference between total organic carbon content.The total organic carbon content of the defarmland is equal to the farmland or a very slow increase.These reflect the total organic carbon content of soil is not insensitive to the soil management during a short period(3-6 years).(4) Soil dissolved organic carbon,the active organic carbon content and the active carbon in the proportion of the toal organic carbon have obvious differences between farmland and defarmland, and there also are obvious difference among the different defarmland.These Show that the active organic carbon is sensitive to land use patterns,can reflect the little changes of soil organic carbon.(5) The soil composition of the organic carbon were significantly to the main factor of soil nutrient factors,including the total N,available N,total P,available P.It shows organic carbon is of great significance to nutrient recovery and circulation.(6) In terms of soil organic carbon and corrosion resistance,in karst area the vegetation of natural recovery or returning double-structure pattern is superior to artificial pure forest.2.In karst area the content of the form of inorganic phosphorus have obvious difference,and there also are obvious difference among the land use patterns.(1) In the study area the farmland and parts of defarmland have high contents of total phosphorus, available phosphorus and the forms of inorganic phosphorus.Pinus massoniana land has a low phosphorus content.Compared to the Pinus massoniana,arable land shows strong P accumulation process.Compared to the arable land,defarmland shows the consumption of the process.The content of the inorganic phosphorus also shows difference among the different defarmland.(2) The study found the inorganic phosphorus is the main proportion of total phosphorus.In different forms of inorganic phosphorus,the order of the content is O-P＞Fe-P＞Ca-P＞Al-R(3) Use related coefficient analysis and path coefficient analysis to discuss the relation between every form inorganic phosphorus and available phosphorus draw the conclusion that the order of relative importance of inorganic phosphates forms to the available phosphorus is as follow:Al-P＞Ca₂-P＞Fe-P＞Ca₈-P＞Ca₁₀-P1＞O-P.(4) Most defarmlands have high content of available phosphorus and slowly available phosphorus, the potential capacity of providing available phosphorus for plants is strong.so in terms of phosphorus nutrition,there are the possibility of natural recovery of vegetation and artificial recovery.3.The composition of active organic carbon,total Ca,exchangeable Ca to inorganic phosphorus form have an important impact(1) The composition of organic carbon have a strongly positive correction with the proportion of Ca2-P,Al-P,Ca8-P,Fe-P,and have strongly negative correction with the proportion of O-P,and have weak correction with the proportion of Ca₁₀-P.The result shows soil organic carbon plays an important role to available phosphorus and the proportion of inorganic phosphorus form.(2) The total Ca and exchangeable Ca,especially exchangeable Ca,have strongly negative correction with the proportion of Ca₂-P,Al-P,Fe-P,have strongly positive correction with Ca₁₀-P.The result shows Ca plays an important role to the chemical behavior of soil inorganic phosphorus.