Assessing the extent of decomposition of natural organic materials using solid-state 13C NMR spectroscopy

Baldock, J.A., Oades, J M., Nelson, P.N., Skene, T.M., Golchin, A., and Clarke, P. (1997) Assessing the extent of decomposition of natural organic materials using solid-state 13C NMR spectroscopy. Australian Journal of Soil Research, 35 (5). pp. 1061-1083.

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Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy has become an important tool for examining the chemical structure of natural organic materials and the chemical changes associated with decomposition. In this paper, solid-state 13C NMR data pertaining to changes in the chemical composition of a diverse range of natural organic materials, including wood, peat, composts, forest litter layers, and organic materials in surface layers of mineral soils, were reviewed with the objective of deriving an index of the extent of decomposition of such organic materials based on changes in chemical composition. Chemical changes associated with the decomposition of wood varied considerably and were dependent on a strong interaction between the species of wood examined and the species composition of the microbial decomposer community, making the derivation of a single general index applicable to wood decomposition unlikely. For the remaining forms of natural organic residues, decomposition was almost always associated with an increased content of alkyl C and a decreased content of O-alkyl C. The concomitant increase and decrease in alkyl and O-alkyl C contents, respectively, suggested that the ratio of alkyl to O-alkyl carbon (A/O-A ratio) may provide a sensitive index of the extent of decomposition. Contrary to the traditional view that humic substances with an aromatic core accumulate as decomposition proceeds, changes in the aromatic region were variable and suggested a relationship with the activity of lignin-degrading fungi. The A/O-A ratio did appear to provide a sensitive index of extent of decomposition provided that its use was restricted to situations where the organic materials were derived from a common starting material. In addition, the potential for adsorption of highly decomposable materials on mineral soil surfaces and the impacts which such an adsorption may have on bioavailability required consideration when the A/O-A ratio was used to assess the extent of decomposition of organic materials found in mineral soils.

Item ID: 19770
Item Type: Article (Research - C1)
ISSN: 1446-568X
Keywords: composts, forest litter, peat, soil organic matter, wood, chemical, composition
Date Deposited: 12 Jun 2012 07:01
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0503 Soil Sciences > 050304 Soil Chemistry (excl Carbon Sequestration Science) @ 40%
04 EARTH SCIENCES > 0402 Geochemistry > 040204 Organic Geochemistry @ 20%
05 ENVIRONMENTAL SCIENCES > 0503 Soil Sciences > 050301 Carbon Sequestration Science @ 40%
SEO Codes: 96 ENVIRONMENT > 9614 Soils > 961402 Farmland, Arable Cropland and Permanent Cropland Soils @ 50%
96 ENVIRONMENT > 9614 Soils > 961403 Forest and Woodlands Soils @ 50%
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