A comparison of four different raw humus types in Norway using chemical degradations and CPMAS 13C NMR spectroscopy

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Abstract Crust, felty, greasy and granular raw humus were analysed by wet chemical methods and by 13C NMR. The amounts of amino acids, monosaccharides and aliphatic dicarboxylic acids were determined and the yields compared with the 13C NMR spectra. Protein carbon constitutes 9–13%, polysaccharide carbon 8–19% dicarboxylic acids 1–2% and free carboxylic acid groups 2–4% of the total sample carbon. Degradation of greasy raw humus yields half the amount of monosaccharides and twice the amount of aliphatic dicarboxylic acids found in the other raw humus types. This result is confirmed by 13C NMR. Forty to fifty percent of the soil carbon is unaccounted for among the degradation products identified. Based on estimates of 13C NMR data, the unknown part consists of aliphatic carbon, where the C:O ratio ranges between 1 1.1:1 and 1.8:1. All data indicate great similarity between crust and felty raw humus, whereas greasy raw humus differs clearly from those two. Granular raw humus gives approximately the same amount of degradation products as crust and felty raw humus but differs in its 13C NMR spectrum. The relative proportions of all compounds identified, including aliphatic dicarboxylic acids, are approximately constant, indicating a difference in degree rather than kind of the four raw humus types.