Study on the Profile Distribution and Morphology of Soil Humic Substances in Karst Area of Zunyi City, China

Soil degradation in low soil humus content karst areas is a serious problem. Humus is composed of a series of polymer organic compounds, with no fixed form, therefore it is difficult to study, especially humin. In this study, 13C CP/MAS NMR was used to study the humic acids (HA), fulvic acids (FA), and humin (HM) components in the soil profiles of carbonate rocks and argillaceous rocks in the Northern Guizhou region. Through the vertical distribution of humus in soil, the transformation mechanism among functional groups of humus was studied. The content of HA and FA in the soil of Zunyi New Area was low, and the humification degree was low. FA was the main HA with simple molecules, which were directly related to the surface vegetation in the area. There may have been some genetic relationship between Aliphatic C and Aromatic C, Aliphatic C and Carboxyl C in the same group of humus. In the phylogenetic relationship of HA, FA, and HM, more transformations existed between HA and FA, and between HA and HM, while the transformations between FA and HM were very rare. This study provides an important scientific basis for the theory of the formation and transformation of soil humus in karst area.