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| Titel |
Closed-loop 15N measurement of N2O and its isotopomers for real-time
greenhouse gas tracing |
| VerfasserIn |
Johanna Slaets, Leopold Mayr, Maria Heiling, Mohammad Zaman, Christian Resch, Georg Weltin, Roman Gruber, Gerd Dercon |
| 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 |
250133372
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| Publikation (Nr.) |
 EGU/EGU2016-13976.pdf |
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| Zusammenfassung |
| Quantifying sources of nitrous oxide is essential to improve understanding of the global N
cycle and to develop climate-smart agriculture, as N2O has a global warming potential 300
times higher than CO2. The isotopic signature and the intramolecular distribution (site
preference) of 15N are powerful tools to trace N2O, but the application of these
methods is limited as conventional methods cannot provide continuous and in situ
data. Here we present a method for closed-loop, real time monitoring of the N2O
flux, the isotopic signature and the intramolecular distribution of 15N by using
off-axis integrated cavity output spectroscopy (ICOS, Los Gatos Research). The
developed method was applied to a fertilizer inhibitor experiment, in which N2O
emissions were measured on undisturbed soil cores for three weeks. The treatments
consisted of enriched urea-N (100 kg urea-N/ha), the same fertilizer combined with the
nitrification inhibitor nitrapyrin (375 g/100 kg urea), and control cores. Monitoring the
isotopic signature makes it possible to distinguish emissions from soil and fertilizer.
Characterization of site preference could additionally provide a tool to identify different
microbial processes leading to N2O emissions. Furthermore, the closed-loop approach
enables direct measurement on site and does not require removal of CO2 and H2O.
Results showed that 75% of total N2O emissions (total=11 346 μg N2O-N/m2) in
the fertilized cores originated from fertilizer, while only 55% of total emissions
(total=2 450 μg N2ON/m2) stemmed from fertilizer for the cores treated with
nitrapyrin. In the controls, N2O derived from soil was only 40% of the size of the
corresponding pool from the fertilized cores, pointing towards a priming effect
on the microbial community from the fertilizer and demonstrating the bias that
could be introduced by relying on non-treated cores to estimate soil emission rates,
rather than using the isotopic signature. The site preference increased linearly over
time for the cores with fertilizer and those with nitrapyrin, but the increase was
stronger for the fertilized cores: during the first 10 days of the experiment, theses cores
showed a more negative site preference than the cores with inhibitor, while during
the last 10 days, the site preference for the fertilized cores was more positive than
that of the inhibitor. This change indicates that the site preference of 15N can be
used to distinguish the processes of nitrification and denitrification, the former
having been supressed by nitrapyrin in the cores treated with the inhibitor. Low
enrichment levels (5% atomic excess in this study) sufficed in order to separate emissions
from soil and fertilizer, making the proposed closed-loop approach a cost-effective
and practical tool to obtain a continuous, in situ characterization of N2O sources. |
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