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| Titel |
Linking measurements of biodegradability, thermal stability and chemical composition to evaluate the effects of management on soil organic matter |
| VerfasserIn |
Ed Gregorich, Adam Gillespie, Mike Beare, Denis Curtin, Hamed Sanei, Sandra Yanni |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250107581
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| Publikation (Nr.) |
 EGU/EGU2015-7287.pdf |
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| Zusammenfassung |
| The stability of soil organic matter (SOM) as it relates to resistance to microbial degradation
has important implications for nutrient cycling, emission of greenhouse gases, and C
sequestration. Hence, there is interest in developing new ways to accurately quantify and
characterise the labile and stable forms of soil organic C. Our objectives in this study were to
evaluate and describe relationships among the biodegradability, thermal stability and
chemistry of SOM in soil under widely contrasting management regimes. Samples from
the same soil under permanent pasture, an arable cropping rotation, and chemical
fallow were fractionated (sand: 2000-50 μm; silt: 50-5 μm, and clay: < 5 μm).
Biodegradability of the SOM in size fractions and whole soils was assessed in a
laboratory mineralization study. The chemical composition of SOM was characterized
by X-ray absorption near-edge structure (XANES) spectroscopy at the K-edge
and its thermal stability was determined by analytical pyrolysis using a Rock-Eval
pyrolyser.
The mineralization bioassay showed that whole soils and soil fractions under fallow were
less susceptible to biodegradation than other managements and that sand-associated organic
matter was significantly more susceptible than that in the silt or clay fractions. Analysis by
XANES showed accumulation of carboxylates and strong depletion of amides (protein) and
aromatics in the fallow whole soil. Moreover, protein depletion was most significant in the
sand fraction of the fallow soil. Sand fractions in fallow and cropped soils were, however,
enriched in plant-derived phenols, aromatics and carboxylates compared to the sand fraction
of pasture soils. In contrast, ketones, which have been identified as products of
microbially-processed organic matter, were slightly enriched in the silt fraction of the pasture
soil. These data suggest reduced inputs and cropping restrict the decomposition of
plant residues and, without supplemental N additions, protein-N in native SOM is
significantly mineralized in fallow systems to meet microbial C mineralization
demands.
Analytical pyrolysis showed distinct differences in the thermal stability of SOM among
the size fractions and management treatments; it also showed that the loss of SOM generally
involved dehydrogenation. The temperature at which half of the C was pyrolyzed showed
strong correlation with mineralizable C and thus provides solid evidence for a link between
the biological and thermal stability of SOM. |
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