Characteristic of Molecular Weight-Fractions of Soil Organic Matter from Calcareous Soil and Yellow Soil

Soil organic matter (SOM), along with the rock weathering, originating from residues of animals, plants and microorganisms involved in soil formation evolution. The stability SOM could directly produce an effect on carbon sequestration. To elucidate characteristics karst areas at molecular structure level, this study, humic acids (HA), as major proxy SOM, were extracted, purified, ultra-filtrated. HA calcareous fractionated into five size fractions, while yellow separated eight fractions. Via analysis potentiometric titration, FTIR, CPMAS 13C NMR, results showed some common features, whereby compared bigger smaller fractions have much lower contents aliphatic carbon, but higher aromatic carboxyl groups, ketonic phenolic hydroxyl total acidity, which indicates that are more soluble well degradable than ones. It was distinct that, soil, negative correlations between acidic functional groups’ oxygen found, suggesting mainly located group carbohydrates instead groups rings, confirming carbohydrate subunits. According to analysis, comparing we presumed polar degradable. However had a larger as, content same layer suggests conservation mechanism is not only resistance also chemical protection forming complexes calcium or/and physical enclosing by hypergene CaCO3 precipitation.