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| Titel |
Combining a coupled FTIR-EGA system and in situ DRIFTS for studying soil organic matter in arable soils |
| VerfasserIn |
M. S. Demyan, F. Rasche, M. Schütt, N. Smirnova, E. Schulz, G. Cadisch |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 5 ; Nr. 10, no. 5 (2013-05-02), S.2897-2913 |
| Datensatznummer |
250018228
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| Publikation (Nr.) |
 copernicus.org/bg-10-2897-2013.pdf |
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| Zusammenfassung |
An optimized spectroscopic method combining quantitative evolved gas
analysis via Fourier transform infrared spectroscopy (FTIR-EGA) in
combination with a qualitative in situ thermal reaction monitoring
via diffuse reflectance Fourier transform infrared spectroscopy (in
situT DRIFTS) is being proposed to rapidly characterize soil organic
matter (SOM) to study its dynamics and stability. A thermal reaction chamber
coupled with an infrared gas cell was used to study the pattern of thermal
evolution of carbon dioxide (CO2) in order to relate evolved gas (i.e.,
CO2) to different qualities of SOM. Soil samples were taken from three
different arable sites in Germany: (i) the Static Fertilization
Experiment, Bad Lauchstädt (Chernozem), from treatments of farmyard
manure (FYM), mineral fertilizer (NPK), their combination (FYM + NPK) and
control without fertilizer inputs; (ii) Kraichgau; and (iii) Swabian
Alb (Cambisols) areas, Southwest Germany. The two latter soils were further
fractionated into particulate organic matter (POM), sand and stable
aggregates (Sa + A), silt and clay (Si + C), and NaOCl oxidized Si + C
(rSOC) to gain OM of different inferred stabilities; respiration was
measured from fresh soil samples incubated at 20 °C and 50%
water holding capacity for 490 days. A variable long path length gas cell
was used to record the mid-infrared absorbance intensity of CO2 (2400
to 2200 cm−1) being evolved during soil heating from 25 to
700 °C with a heating rate of 68 °C min−1 and
holding time of 10 min at 700 °C. Separately, the heating
chamber was placed in a diffuse reflectance chamber (DRIFTS) for measuring
the mid-infrared absorbance of the soil sample during heating. Thermal
stability of the bulk soils and fractions was measured via the temperature
of maximum CO2 evolution (CO2max).
Results indicated that the
FYM + NPK and FYM treatments of the Chernozem soils had a lower
CO2max as compared to both NPK and CON treatments. On average,
CO2max of the Chernozem was much higher (447 °C) as
compared to the Cambisol sites (Kraichgau 392 °C; Swabian Alb
384 °C). The POM fraction had the highest CO2max
(477 °C), while rSOC had a first peak at 265 °C at both
sites and a second peak at 392 °C for the Swabian Alb and
482 °C for the Kraichgau. The CO2max increased after 490 day incubation, while the C lost during incubation was derived from the
whole temperature range but a relatively higher proportion from 200 to
350 °C. In situT DRIFTS measurements indicated decreases in
vibrational intensities in the order of C-OH = unknown C vibration
< C-H < −COO/C =C < C = C with increasing
temperature, but interpretation of vibrational changes was complicated by
changes in the spectra (i.e., overall vibrational intensity increased with
temperature increase) of the sample during heating. The relative quality
changes and corresponding temperatures shown by the in situT DRIFTS
measurements enabled the fitting of four components or peaks to the evolved
CO2 thermogram from the FTIR-EGA measurements. This gave a
semi-quantitative measure of the quality of evolved C during the heating
experiment, lending more evidence that different qualities of SOM are being
evolved at different temperatures from 200 to 700 °C. The
CO2max was influenced by long-term FYM input and also after 490
days of laboratory incubation, indicating that this measurement is an
indicator for the relative overall SOM stability. The combination of
FTIR-EGA and in situT DRIFTS allows for a quantitative and qualitative
monitoring of thermal reactions of SOM, revealing its relative stability, and
provides a sound basis for a peak fitting procedure for assigning
proportions of evolved CO2 to different thermal stability components. |
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