Electron spin resonance spectroscopy of commercial HUMIC acids in comparison with natural HUMIC acids extracted from soil and some naturally decomposed agriculture wastes

الملخص EN

Concentration of free radicals, g-values, and line widths of the ESR spectra were determined for three commercial humic acids used for agriculture in Egypt and compared with three natural humic acids extracted from soil and two decomposed agricultural wastes including olive mill solid residual and rice straw - cattle manure mixture.

The natural regional soil humic acid shows lower free electron contents.

The calculated free radical contents of the commercial humic acids were found to be abnormally higher than not only the studied natural humic acids but also than the cited literature humic acids originated from different sources.

All the g-values indicate semiquinonic radical moieties associated with an aromatic network or a semiquinone radical unit conjugated to aromatic rings of different type.

Higher g- values recorded for the studied humic acids indicate oxygen-centered radicals.

The relations govern the line-width and g-value, the line-width and the shape of the esr signal, spin concentration and %O, spin concentration and % H, spin concentration and absorbance at 465 nm., spin concentration and atomic C/H ratios are more significant in case of natural humic acids extracted from soil and the two composts but not in case of commercial humic acid.

This indicates that the two humic acids classes are basically different in their structures.