Sleutel, Steven and Leinweber, Peter and Begum, S.A. and Kader, Md. Abdul and De Neve, Stefaan (2009) Shifts in soil organic matter composition following treatment with sodium hypochlorite and hydrofluoric acid. Geoderma, 149 (3-4). pp. 257-266. ISSN 0016-7061
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Abstract
A renewed interest in chemical fractionation of soil organic matter (SOM) originates from the premise that it
enables to isolate labile SOM from SOM protected through mineral binding and recalcitrant SOM. Both selective
removal of labile non-bound SOM through oxidation or hydrolysis as well as selective removal of minerals and
attached SOM are often applied. Molecular-level SOM characterization by means of temperature resolved
Pyrolysis-Field Ionization Mass Spectroscopy analysis (Py-FIMS) was used here as an approach to obtain insight
into the fate of SOMuponwet chemical treatment with regard to composition and thermal stability. The applied
sequential chemical treatment with 6% NaOCl and 10% HF yielded similar sizes in stable SOM fractions between
sandy semi-native heathland and cultivated cropland soil pairs (i.e. NaOCl resistant OC: 12.3–15.0 g C kg−1 and
NaOCl+HF resistant OC: 2.6–5.3 g C kg−1). Py-FIMS spectra of bulk SOM in both heathland–cropland soil pairs
were dominated by signals assigned to lipids, alkylaromatics and sterols. Difference spectra and thermograms
showed selective loss of signals from sterols, lignin dimers and thermolabile lipids. This matches advancing SOM
decomposition as derived from previously reported gradients in SOM composition as decomposition proceeds
fromplantmaterial over particulate organicmatter (OM) to SOMin silt and clay particle sizes. However, increased
ion intensity attributed to carbohydrates, peptides and short-chained lipids after NaOCl treatment indicates that
biologically labile SOM components were also enriched, and they may possibly have been protected through
mineral binding or encapsulation in macromolecular OMstructures. Subsequent HF treatment yielded increased
volatilization in the thermostable region for mass signals tentatively assigned to phenols and lignin monomers
and of heterocyclic N-containing compounds and thermostable alkylaromatics. The resistance to chemical
treatment of the latter two components matches with their hypothesized structural function in macro OM
molecules. However, even for the sites investigated here, with a very similar soil texture, climate, land-use,
drainage and contents of pedogenic oxides, contrasting and not readily explainable results were found for other
SOMconstituents. Therefore, chemical fractionations seemto yield very site specific and less distinct patterns and this study demonstrated that derivation of useful information regarding SOM stabilization mechanisms from such experiments is by no means straightforward.
| Item Type: | Journal Article |
|---|---|
| Subjects: | S Agriculture > S Agriculture (General) |
| Divisions: | Faculty of Business and Economics (FBE) > School of Agriculture and Food Technology |
| Depositing User: | Md. Abdul Kader |
| Date Deposited: | 28 Feb 2019 03:41 |
| Last Modified: | 28 Feb 2019 03:41 |
| URI: | https://repository.usp.ac.fj/id/eprint/11166 |
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