Fingerprinting of soil organic matter composition by attenuated total reflectance – Fourier transform infrared spectroscopy

Fourier transform infrared spectroscopy (FTIR), as a non-destructive method, is a powerful tool that provides insights into SOM functional groups and other soil dynamic properties. This study aims to provide a comprehensive review of the use of FTIR spectroscopy for the spectral characterization of soil constituents, both organic and inorganic, along with a case study evaluating the applicability of Attenuated Total Reflectance - Fourier Transform Infrared Spectroscopy (ATR-FTIR) for SOM characterisation in five Croatian soil types. The investigated soil types were: Luvisol, Regosol acric, Gleysol vertic, Dystric Stagnosol and Chernozem, which differ in various soil indicators, including organic matter content (OM), pH, clay content, total nitrogen (TN), plant available phosphorus (PAL) and potassium (KAL). According to our findings, ATR-FTIR spectroscopy provided insights into the inorganic and organic soil constituents. The FTIR spectra indicated that only the hydrophilic fraction of the SOM of all five soil types analyzed was detected. However, strong absorbance bands attributed to minerals and other inorganic constituents of soils masked (overlapped) the molecular vibrations of distinct SOM constituents, highlighting the need for further sample pretreatment and advanced chemometric modelling techniques to fingerprint SOM composition using ATR-FTIR spectroscopy.