Soil Organic Matter

The successful recording of NMR signals nearly 70 years ago started the development of one of the most powerful experimental methods for the elucidation of molecular-level structures. As a noninvasive technique, NMR spectroscopy can be used for the chemical characterization of individual compounds and bulk chemical composition as well as for the examination of reaction kinetics and physicochemical properties of certain molecular domains. In environmental sciences, the application of NMR spectroscopy had a major impact on further developments as it could tackle problems and questions that previously were difficult to answer. In the following, an overview is given on how the introduction of NMR spectroscopy into soil science altered the view about the structure of soil organic matter (SOM) and the mechanisms involved in its stabilization. While former humification pathways were mainly based on the idea that monomers derived from degraded biopolymers recondensate into recalcitrant macrogeopolymers, modern concepts recognize the survival of partially degraded biopolymers because of physical and chemical protection mechanisms. Although a great deal of information was already obtained by common one-dimensional NMR techniques, advanced two-dimensional (2-D) NMR techniques are now available and first applications to geochemical samples promise to further open a door toward an improved understanding of SOM dynamics.