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| Titel |
Positive feedback of crop residue incorporation on dissolved organic carbon
contents under anaerobic conditions in temperate rice paddy soils |
| VerfasserIn |
Daniel Said-Pullicino, Marcella Sodano, Chiara Bertora, Cristina Lerda, Dario Sacco, Luisella Celi |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250127779
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| Publikation (Nr.) |
 EGU/EGU2016-7689.pdf |
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| Zusammenfassung |
| Rice paddy soils are generally characterized by large concentrations and fluxes of DOC in
comparison to other ecosystems. Our recent studies have shown that the combination of
relatively high pore-water DOC concentrations under anoxic soil conditions (>10-20
mg C l−1) and important percolation fluxes of water during field flooding may
contribute significant organic C inputs into the subsoil (18-51 g C m−2) over the
cropping season. Crop residues incorporated into the soil after harvest represent the
main input of organic C into paddy soils, returning about 200-300 g C m−2 y−1 in
single-cropped rice paddies. The anaerobic decomposition of these residues may
supply important amounts of DOC to soil pore waters. Moreover, the supply of
electron donors with the input of residue-derived labile OM may further increase DOC
contents by stimulating the microbially-catalyzed reductive dissolution of Fe and Mn
oxyhydroxides under anoxic conditions, and release of DOC previously stabilized on the
mineral matrix (i.e. positive feedback). This could have important implications
on organic C inputs into the subsoil as well as substrate availability for methane
production.
We therefore hypothesized that crop residue management practices that influence
the amount of labile organic matter present in the soil at the time of field flooding
may strongly influence soil solution DOC concentrations as well as the positive
feedback on the release of soil-derived DOC. We tested this hypothesis at field-scale by
evaluating variations in the contents and quality of DOC above and beneath the
plough pan over the cropping season as a function of crop residue management
practices involving: tillage and crop residue incorporation in spring (SPR), tillage and
crop residue incorporation in spring, dry seeding and 1 month delayed flooding
(DRY), tillage and crop residue incorporation in autumn (AUT), and straw removal
after harvest and tillage in spring (REM). Moreover, we linked changes in DOC
concentrations to the reductive dissolution of Fe and Mn oxyhydroxides and methane
emissions.
Results evidenced that highest DOC concentrations in the topsoil (up to 40
mg C l−1) were obtained when crop residues were incorporated in proximity of
field flooding (i.e. SPR), while lowest contents (up to 20 mg C l−1) were observed
with post-harvest removal of rice straw (i.e. REM). The former also resulted in an
important increase in DOC concentrations below the plough pan suggesting an
important transfer of organic C into the subsoil with respect to the other treatments.
Incorporation of crop residues in spring also enhance the reductive dissolution of Fe and
Mn oxyhydroxides evidenced by a rapid release of reduced Fe and Mn in the soil
solution and transport along the soil profile. This was also linked to an increase in the
aromatic character of the DOC suggesting an important contribution of soil-derived
organic C to the DOC pool. Methane emissions were moreover strongly linked to
DOC concentrations in the topsoil, however we do not have direct evidence of a
positive feedback of residue incorporation on soil-derived methane production. |
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