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| Titel |
Quantifying denitrification losses from a sub-tropical pasture in Queensland/Australia - use of the 15N gas flux method |
| VerfasserIn |
Johannes Friedl, Clemens Scheer, Daniel Warner, Peter Grace |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250090584
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| Publikation (Nr.) |
 EGU/EGU2014-4838.pdf |
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| Zusammenfassung |
| The microbial mediated production of nitrous oxide (N2O) and its reduction to dinitrogen
(N2) via denitrification represents a loss of nitrogen (N) from fertilised agro ecosystems to
the atmosphere. Although denitrification remains a major uncertainty in estimating N losses
from soils, the magnitude of N2 losses and related N2:N2O ratios from soils are largely
unknown due to difficulties measuring N2 against a high atmospheric background. In order to
address this lack of data, this study investigated the influence of different soil moisture
contents on N2 and N2O emissions from a sub-tropical pasture in Queensland/Australia using
the 15N gas flux method.
Intact soil cores were incubated over 14 days at 80% and 100% water filled pore
space (WFPS). Gas samples were taken up to six times per day after application of
15N labelled nitrate, equivalent to 50 kg N ha-1 and analysed for N2 and N2O by
isotope ratio mass spectrometry. Fluxes were calculated assuming non-random 15N
distribution in the headspace according to Mulvaney and Kurtz (1984) using the
labelled pool of nitrate estimated from N2O measurements (Stevens and Laughlin
2001).
The main product of denitrification in both treatments was N2. N2 emissions
exceeded N2O emissions by a factor of 1.3 ± 0.3 at 80% WFPS and a factor of 3
± 0.8 at 100% WFPS. The total amount of N-N2 lost over the incubation period
was 13.5±1.0 kg N ha-1 at 80% WFPS and 21.8±1.8 kg ha-1 at 100% WFPS
respectively. Over the entire incubation period, N2 emissions remained elevated
at 100% WFPS, showing high variation between soil cores, while related N2O
emissions decreased. At 80% WFPS, N2 emissions increased constantly over time
showing significantly higher values after day five. At the same time, N2O fluxes
declined. Consequently, N2:N2O ratios rose over the incubation period in both
treatments.
Overall denitrification rates and related N2:N2O ratios were higher at 100% WFPS
compared to 80% WFPS, confirming WFPS as a major driver of denitrification. This study
highlights denitrification as a major pathway of N loss for sub-tropical pasture systems with a
substantial amount of applied fertiliser lost as N2 at high WFPS. The 15N gas flux method
proved an effective tool in assessing N losses from fertilised soils. However, its suitability to
determine N2 fluxes from soils with lower denitrification rates needs to be confirmed in future
studies. The high variation between soil cores emphasises the need for field measurements
with a high spatial and temporal resolution in order to capture the dynamics of N2
emissions.
Mulvaney, R. L. and L. T. Kurtz. 1984. "Evolution of Dinitrogen and Nitrous Oxide from
Nitrogen-15 Fertilized Soil Cores Subjected to Wetting and Drying Cycles1." Soil Sci. Soc.
Am. J. 48 (3): 596-602. https://www.soils.org/publications/sssaj/abstracts/48/3/596. doi:
10.2136/sssaj1984.03615995004800030026x.
Stevens, R. J. and R. J. Laughlin. 2001. "Lowering the detection limit for dinitrogen
using the enrichment of nitrous oxide." Soil Biology and Biochemistry 33 (9):
1287-1289. http://www.sciencedirect.com/science/article/pii/S0038071701000360. doi:
http://dx.doi.org/10.1016/S0038-0717(01)00036-0. |
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