Evaluation of humus quality of forest soils with two extraction methods

Extraction method as one of the most important steps of the study of humic substances quality can affect the results. In this study three types of forests with different ages and vegetation were chosen to study the different extraction methods on the quality of extracted humic substances. A virgin forest, Bald Cypress forest and Eastern Cottonwood forest in the north of Iran were chosen. Some physical and chemical properties of soil samples were measured. The soil samples were extracted with NaHCO3 and Hot Water Percolation method. The quality of organic carbon in both kinds of extracts was studied using spectroscopy method. The E2:E3, E4:E6 ratios and URI were estimated. There were some differences in physical and chemical properties between different samples. Bald Cypress forest had the maximum amount of clay fraction in its texture. Also this samples contained the highest value of soil organic carbon. Virgin forest showed the maximum amount of total soil nitrogen which is probably related to the species of its vegetation. The minimum C:N ratio as a humification factor was observed in virgin forest sample. The organic compounds which extracted with NaHCO3 and Hot Water were different. The results indicated the presence of humic acid (HA) in all of samples which were extracted with NaHCO3 solution, however, Hot Water extracts contain compounds with fulvic acid (FA) properties. According to our results Hot Water Percolation is an appropriate method for extracting organic compound with more activity, simple structure, less carbon and low molecule weight (MW).