Structural Characteristics of Humic Acids Extracted from Woody Composts by Two-Step Composting Process

Abstract

Humic acids (HAs) extracted from woody composts by a two-step fermentation procedure (lignin degradation as the 1st step and humification as the 2nd step) were analyzed by a number of chemical (elemental and functional groups analysis) and spectroscopic methods (UV and VIS, and 1H-NMR). Lignin degradation through the 1st step fermentation led to a more complex configuration, a larger amount of functional groups containing oxygen and a lower value of H/C ratio in the HAs after humification, indicating the acceleration of humification. The differences between the humic acids from woody composts obtained after fermentation of wood powders by the lignolytic fungi, Coriolus versicolor, and by the strain IZU-154 were as follows: (1) HAs from the products of fermentation by C. versicolor contained a larger amount of oxygen and showed a higher O/C value than the HAs from the products of fermentation by IZU-154. (2) The content of the OH groups in the HAs from the products of fermentation by C. versicolor was lower than that of the groups in the HAs from the products of fermentation by IZU-154. (3) The difference absorption spectrum between pH 12.4 and pH 7.0 of the HAs from the products of fermentation by C. versicolor was broader than that of the HAs from the products of fermentation by IZU-154. (4) The content of OCH3-H was higher while that of lactone-H, aliphatic side chain-H, and aromatic-H was lower in the HAs from the products of fermentation by C. versicolor than in the HAs from the products of fermentation by IZU-154. These differences were attributed to the difference in the lignolytic and oxidative activities for the woody material between the two strains. © 1992, Japanese Society of Soil Science and Plant Nutrition. All rights reserved.