Improvement And Characteristic Curve Of Physical-chemical Combined Grouping Method Of Soil Organic Carbon

In this study,the research on small Karst basin and its soil under different land use is carried out in Chenjiazhai,Puding County,Guizhou province(agricultural land ecosystem and ecosystems of rocky desertification and restoration forms).It comes up with the improvement and perfection based on the study of physical-chemical combined grouping method of Stewart soil organic carbon.In the study,the author draws the characteristic curve of soil organic carbon according to different stabilization and protection mechanism of different compositions in soil organic carbon(SOC)as well as their contents,and discusses on the features of characteristic curve of soil organic carbon for different land uses,with a view to the understanding and re-understanding of the quantity,quality and stabilization of soil organic carbon,and provide some references for its evaluation.The main results are as follows:(1)Based on the Stewart and other grouping methods,it increased the consideration to water-soluble organic carbon,and separated the water-soluble organic carbon components;the unprotected coarse particle components were renamed as coarse particles and crushed agglomerates,further separated by density flotation,dispersion,screening and centrifugal separation as well as acid hydrolysis.The improved physical-chemical combined grouping method of the soil organic carbon had classified the soil organic carbon into six kinds of protection mechanisms,namely,non-protection,physical protection,chemical protection,physical +chemical protection,biochemical protection and physical + chemical + biochemical protection.Compared with the original method,it increases two kinds of protection mechanisms,i.e.,physical+ chemical protection and physical + chemical + biochemical protection.(2)The soil water-soluble organic carbon was determined by potassium permanganate oxidation-colorimetric method.The colorimetric wavelength was 490 nm and the colorimetric time was 2 hours.Soil water-soluble organic carbon content was calculated according to the change of potassium permanganate concentration.The result of the determination of WSOC by potassium permanganate oxidation and colorimetric method was compared with that of TOC.Although the result was lower than those of TOC meter potassium permanganate,there was a good linearrelationship with the results of TOC measurement.The former result after being multiplied by the coefficient 1.28 can be the TOC measured value.(3)Six kinds of organic carbon components were obtained by the improved physical-chemical combined grouping method.Under these five land use methods,the carbon content of soil components had the same trend and the difference was significant,mainly as follows: stable organic carbon components(chemical protection,physical + chemical protection,biochemical protection and physical + chemical + biochemical protection)were the highest,followed by the active organic carbon content,and the organic carbon of physical protection was the lowest,suggesting that the soil organic carbon in this area was mainly stored in stable organic carbon.Active organic carbon,organic carbon of physical protection and stable organic carbon components(chemical protection,physical + chemical protection,biochemical protection and physical + chemical + biochemical protection)in different land use are roughly as: shrub land>plantation> grass>garden>cultivated land,which is consistent with the trend of the total organic carbon content in different land use.The cumulative results of soil organic carbon under different protection mechanisms for different land use showed that the accumulation of soil organic carbon under different protection mechanisms of shrub land were all higher;and the accumulation rules of artificial forest and grassland were basically the same;and the accumulation rules of orchard and cultivated land were basically the same.In terms of the distribution proportion of soil organic carbon,those of stable organic carbon components(chemical protection,physical + chemical protection,biochemical protection and physical + chemical + biochemical protection)were the highest,followed by active organic carbon components,and lowest for the organic carbon components under physical protection.