COMPARISONS OF SOIL ORGANIC MATTER AND ITS FRACTIONS BY PYROLYSIS MASS-SPECTROMETRY

Pyrolysis mass-spectra from a sample of the Al-horizon of a soH from southem Spain showed predominant peaks related to furan derivatives similar to those observed from complex polysaccharides in which not only hexoses but aiso pentoses and deoxyhexoses were constituent units. SmaHer peaks. typical for protein materials and phenolic units, were also observed. On the other hand. typical peaks for the methoxyphenols oí lignins were very small and indicated only limited amounts oC undecomposed lignín residues in this soH sample. Peaks related to benzene or toIuene were also very small. Humic acid samples from this soil showed much more prominent signals related to protein materíals, benzene and phenolic derivatives and weaker polysaccharide-related signals than did the entire sample. Typicallignin related peaks were smaIl or insignificant. Spectra from the grey or brown humidic acid fractions were much like those of the parent humic acid. Brown humic acid, however, showed stronger signals for nitrogen and sulphur compounds, indicating a higher content of protein-like materials in this fraction. Prepara-tions of humic acid hydroIyzed by 6 N HCI showed in their pyrolysis products a marked in-crease in phenols and methoxyphenols. In its pyrogram, humin resembled humic acid, but signals for complex polysaccharides were more evident. Lignin-like materials seem not to be higher in this fraction. Hymato-melanic acid showed prominent signals related to polysaccharides and lignin. Pyrograms from the soH polysaccharides showed the characteristic pattern of a complex polysaccha-ride with the presence of fragments from polymers of amino acids or amino sugars. Fulvic acid spectra showed obvious dissimilarities to those from humic acid in that signals for protein, as well as those related to phenols, were low. Depending upon the isolation method, the fulvic acid preparations showed differing signals related to poly-saccharide or phenolic materials