Modelling the transformation of organic materials in soil with nuclear magnetic resonance spectra

Changes in the carbon (C) and nitrogen (N) compartments that result from the addition of organic material (OM) to the soil are predicted by the transformation of added OM (TAO) model with three parameters: very labile (P-L) and stable (P-S) fractions of the OM and the rate of remineralization (k(remin)) of nitrogen immobilized by microorganisms. We propose relations between P-L, P-S, k(remin) and various chemical groups in the OM identified by their C-13 nuclear magnetic resonance (NMR) spectra. The aromatic content increased the predicted P-S in accordance with published results. The O-aromatic content also increased P-S, but much less so than the aromatic content. The carboxyl content decreased P-S and increased P-L as in the TAO model based on infrared spectrometry. The carbonyl content decreased P-L, whereas di-O-alkyl increased P-L. The chemical composition of the population of decomposer organisms did not appear to be homeostatic, but was related rather to the composition of the substrate: k(remin) was positively correlated with the carboxyl and di-O-alkyl content and negatively correlated with the alkyl content. Solid state C-13 NMR spectroscopy gave better predictions of the transformations that resulted from adding OM than biochemical fractionation and near infrared reflectance spectrometry (NIRS). It is fast and non-destructive and provides new insights into the processes that control decomposition for research into waste recycling, agro-ecology and climate change. HighlightsLinking decomposition of organic materials in soil to NMR measurements. First mathematical model of decomposition based on NMR spectra. Stability of the OM depends on the chemical groups and the inorganic N supply. NMR is a promising tool for monitoring ecosystem changes and soil-air exchanges