Comparison between the humic acids characteristics of two andisols of different age by: FT-IR and 1H-NMR spectroscopy and py-FIMS

Mt Etna (Italy) is the highest, active volcano in Europe. Thanks to the availability of descriptive documents and maps, it is possible to date the formation of several Etna soils. We evaluated the effect of soil formation age on the composition of the soil organic matter (SOM) and humic acids (HAs) from two Etna andisols of different ages but having the same vegetation (Castanea saliva) and pedogenetic substrate (tephra). The characterization of the SOM and the HAs was carried out by elementary and functional group analysis, UV-visible spectrophotometry, Fourier Transform InfraRed (FT-IR) and 1H-Nuclear Magnetic Resonance ( 1H-NMR) spectroscopies, and Pyrolysis-Field Ionization Mass Spectrometry (py-FIMS). Data showed that the age of the soil cannot be considered as influencing the chemical composition of the SOM. However higher volatilisation temperatures, for some compound classes, indicate the presence of more thermally-stable, organic molecules, therefore a more mature organic matter, or an organic component more greatly bound to the mineral component in the older soil. Finally the HA extracted from old soil contains a lower quantity of aliphatic compounds and a greater quantity of carbohydrate and aromatic molecules than the HA extracted from young soil.