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| Titel |
Role of soil mineral components in the stabilization of organic matter in Umbric Ferralsols of South Brazil |
| VerfasserIn |
Marta Velasco-Molina, Anne E. Berns, Felipe Macías, Heike Knicker |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250080697
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| Zusammenfassung |
| Climatic conditions of subtropical and tropical regions support fast carbon (C)
mineralization, and thus an accelerated degradation of soil organic matter (SOM) if compared
to temperate region (Sánchez & Logan, 1992). However, even in those regions, there
are still soil horizons that show notable C accumulation. Examples for the latter
are umbric horizons in typical tropical soils, such as Ferralsols. The occurrence
of this soils with thick umbric epipedons (-¥ 100 cm thickness) in areas of South
Brazil is a paradox, that still needs a better understanding (Marques et al., 2011), in
particular since the processes that are responsible for the thickness and darkness of the
umbric horizons are of special interest with respect to the role of soils as carbon
sink.
One major contributor to SOM stabilization represents the soil mineral phase.
Therefore the main goal of this work its to study the impact of this factor on the SOM
sequestration in Umbric Ferralsols from Atibaia, Campinas (São Paulo State) and Chapecó
(Santa Catarina State) developed under different environmental conditions. With this
objective the mineral fractions have been isolated by selective extraction of iron and
aluminium oxides with different extracting solutions (sodium pyrophosphate, ammonium
oxalate and dithionite-citrate-bicarbonate solution) and related to SOM quality and
quantity.
The latter was studied by the use of solid-state cross polarisation (CPMAS) 13C NMR
spectroscopy after demineralization with hydrofluoric acid (Gonçalves et al., 2003).
Quantification of the NMR spectra was performed by integration of the respective chemical
shift regions under consideration of the contribution of spinning side bands. For our study the
following regions were distinguished (Knicker & Lüdemann, 1995): alkyl C (0-45 ppm),
N-alkyl C (45-60ppm), O-alkyl C (60-110 ppm), aryl C (110-160 ppm), carbonyl C (160-245
ppm).
Preliminary results show that, the minimum vertical variation of total Fe into the profile is
classical in Ferralsols and the behavior of Al points to the high presence of gibbsite in the
clay fractions of the deeper horizon of the Campinas soils. The (AlP+FeP)/C ratios, obtained
after extraction of the Al and Fe forms with a sodium pyrophosphate solution, were above
0.03 throughout the studied profile. According to Nierop et al. (2002) this points towards the
existence of organic-metallic compounds. Most tentatively, they precipitated due to saturation
of adsorption site.
The solid-state 13C NMR spectra of the Chapecó samples showed that the preserved
organic C is dominated by a alkyl C in lipids and amino acids (45 - 0 ppm). Other major
intensities are observed between 110 and 45 ppm, in the region of O/N-alkyl C
(carbohydrates, amino acids) and carboxyl C (220 to 160 ppm). The missing of a clear signal
in the region between 160 and 110 ppm (signal derives from aromatic or olefinic C)
indicates that in this soil lignin has minor contributions to its aromatic C content. |
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