NaOH and Na-Na4P2O7-extractable organic matter in two allophanic volcanic ash soils of the Azores Islands-Quantified pyrolysis-GC/MS data and factor analysis

In a previous paper (Nierop et al. 2005) we described the general results of pyrolysis-GC/MS of the Azores Andosols EUR05 and EUR06. This previous paper was based on visual comparison of pyrolysis-GC/MS results by chemical group. We found that polysaccharide-derived compounds dominated the chemistry of organic matter in these two allophanic Andosols. Three groups of organic compounds that tend to be important in humus of other soils, i.e. moieties derived from lignin, from lipids and from aliphatic biopolymers such as cutin and suberin were relatively scarce. On the other hand, chitin moieties were present in significant amounts, which is rare in most soils. The aforementioned study was based mainly on molecular fragments that are commonly found in pyrolysis-GC/MS results. When we interpreted the mass spectra in more detail, we found a large number of polysaccharide-derived and N-containing fragments that are not commonly identified in pyrolysates of soils. We therefore decided to carry out a more detailed analysis, to quantify the pyrolysis products, and to analyze the quantified results by principal components analysis so that differences that are otherwise not apparent would be made visible. Additionally, this might also bring out differences in NaOH-and Na₄P₂O ₇-extracts that are not evident from visual comparison, and elucidate binding mechanisms in allophanic soils. The present detailed study is based on the same samples and pyrograms as that by Nierop et al. (2005).