Extraction And Characterization Of Soil Humic Substances From Arid And Semi-arid Grasslands In China

With the influence of abnormal climate and irrational human activities, the land of arid and semi-arid regions in our country is growing, which lead to land desertification、grassland degradation and land pollution a series of problems. Soil humic substance provide nutritions for the growth of plants and microorganisms, its content and quality directly decides the nutrition of soil. Some investigation showed that the soil humic substance show absorption with soil heavy metals and organic pollutants, participate in the migration and cumulation in the soil, it is of great significance in the field of soil interface chemistry.To understand the regional environment issue, in this study, we selects Inner Mongolia to gansu province as the research object, Humic substance was extrated by the method of intenational humic subatance society. Structure characteristics of humus samples was analyzed by Uv/visible spectrum Fourier infrared spectrum and XPS spectra technique. Acid-base titration method was choosed to analysis the content of- COOH and Ar- OH functional group in the molecule.The experimental results show that:Soil humic substance content is influenced by regional aridity index, which increased along with the aridity index, while aridity index as low as 0.15, its useless to divided humic substance from the soil.The ratio of E4/E6 and E2/E3 caculatefrom Uv/visible indicate that there is a threshold about change of molecular weight and aromaticity with the aridity index fo humic acids, that is 0.53. Aridity index between from 0.17 to 0.53, molecular weight and aromaticity increasing. Once over the point, the change is opposite. However, molecular weight and aromaticity have nothing relationship with the aridity index.Humic acid and fulvic acid surface elements are mainly nitrogen、nitrogen carbon and oxygen(except for hydrogen), the content of this element are3.32-5.79% 62.98-71.08% and 25.68-35.38%, respectively. The ratio of(O+N)/C value increases with aridity index for humic substance; the ratio of(O+N)/C value change with aridity index existsa critical value(AI=0.32). Under the critical value the polarity and oxygen content of fulvic acid is proportional to the aridity index, the dry index exceeds 0.32, fulvic acid sample polarity and oxygen content decreased with increasing regional aridity index.Carbon in the humic substance Carbon in the form of seven kinds of chemical form and binding energies are: aromatic carbon C-C/C-H(282.5e V), alkyl carbon C-C/C-H(283e V), C-C(283.5e V), C(O)O-O(284.4e V), C=O(285.6e V), C(O)N(286.45 e V), C(O) O(287.1e V); Three chemical forms of nitrogen in the soil humus and binding energies: NH2(397.8e V), NR3+(399.1e V) and NO2(400.5 e V). The form of oxygen in the soil chemical form and binding energies: C=O(529.5e V) and C-O(530.5e V).Within the study area, the carboxylic content in humic acid molecules around 3.24-4.79mmol/g, the content of phenolic hydroxyl at about 0.16-0.34 mmol/g. Fulvic acid carboxylic content about 5.96-5.96 mmol/g, The content of phenolic hydroxyl at about 0.12-5.44 mmol/g, carboxylic groups in the same sample fulvic acid molecules are higher than humic acid substances. Humic acid and fulvic acid molecular carboxylic and phenolic hydroxyl content change has nothing to do with regional aridity index.