Comparison of degradation state and stability of different humic acids by means of chemolysis with tetramethylammonium hydroxide

In the chemolysis products of extracted humic acids (HAs) and tetramethylam monium hydroxide, different compounds can be identified which allow a descr iption of the sources of soil organic matter (SOM). It is possible to draw conclusions concerning stability, degree of intramolecular cross-linking an d degradation of aliphatic and lignin components from the distinctive produ ct ratios. The ratio of lignin derived acidic phenolic derivatives and thei r analogous aldehydes and the ratio of phenylpropenoic acids and analogous benzoic acids provide comparably good parameters for the characterization o f the state of degradation of lignin compounds to relatively stable HA buil ding blocks. Regarding the aliphatic chemolysis products, alpha,omega-dicar boxylic acid and methoxy fatty acid contents indicate an intramolecular cro ss-linking state within the HA molecules and the degree of stable aliphatic constituent parts. High contents of unsaturated fatty acids can be conside red as an indicator of an easy degradable humic skeleton because with their double bonds they represent active sites for further transformations. The suitability of the carbon preference index as an indicator of a biogenic ca rbon source can be confirmed. It is remarkable how the results obtained fro m extracted humic acids are in accordance with the expectations for the dif ferent SOMs derived from land use.