Characterization of Nitrogen in Plant Composts and Native Humic Material by Natural-Abundance 15N CPMAS and Solution NMR Spectra

TL;DRAbstract

Soil organic matter (SOM) provides one of the major deposits for carbon and nitrogen on the surface of the Earth. It is continuously produced, mainly from dead plant material, by composting and humification processes. During these processes microorganisms thoroughly convert the starting material, which consists mostly of insoluble lignocelluloses. The end products of these processes in average middle-European soils, that contain typically 1 to 5% w/w of organic material, are clay–SOM complexes which are insoluble in all the usual organic and inorganic solvents. The standard aqueous sodium hydroxide extraction procedure dissolves at most 40% of the total organic carbon in all the soils tested by our group. The insoluble majority, the humin fraction, remains as poorly defined aluminosilicate- SOM complexes. During the decomposition and conversion processes the carbon to nitrogen ratio–decreases. Compared to the starting material, SOM is enriched in nitrogen. Under natural conditions, i.e

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