Decomposition of organic residues in soil: experimental technique and spectroscopic approach

DRIFT (diffuse reflectance infrared Fourier-transform) spectroscopy was used to follow the early transformations that take place after the incorporation of organic materials in soil. Alfalfa (A), dried maize (DM), laboratory-composted maize (CM), and two commercial composts (YWC and MWC) confined into fiberglass bags were incubated in sand with and without planting with lettuce. DRIFT spectra of these materials before and after incubations were correlated with CO2-C evolution and mass, carbon and nitrogen balances. Spectra obtained by successive subtractions allowed us to distinguish between the main classes of biochemical compounds (cellulose, lignin, polypeptides, pectins) and to study their degradation during incubation. Quantitative spectroscopic determination of lignin showed a relative enrichment in the incubated materials. This experimental approach can be applied to studies on the degradation pathway of green manure materials like A, DM and CM but seems less appropriate for commercial composts.