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| Titel |
The annual ammonia budget of fertilised cut grassland – Part 2: Seasonal variations and compensation point modeling |
| VerfasserIn |
C. R. Flechard, C. Spirig, A. Neftel, C. Ammann |
| 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 ; 7, no. 2 ; Nr. 7, no. 2 (2010-02-08), S.537-556 |
| Datensatznummer |
250004488
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| Publikation (Nr.) |
 copernicus.org/bg-7-537-2010.pdf |
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| Zusammenfassung |
| The net annual NH3 exchange budget of a fertilised, cut
grassland in Central Switzerland is presented. The
observation-based budget was computed from semi-continuous
micrometeorological fluxes over a time period of 16 months and
using a process-based gap-filling procedure. The data for
emission peak events following the application of cattle
slurry and for background exchange were analysed separately to
distinguish short-term perturbations from longer-term
ecosystem functioning. A canopy compensation point model of
background exchange is parameterised on the basis of measured
data and applied for the purposes of gap-filling. The data
show that, outside fertilisation events, grassland behaves as
a net sink for atmospheric NH3 with an annual dry
deposition flux of −3.0 kg N ha−1 yr−1,
although small NH3 emissions by the canopy were measured
in dry daytime conditions. The median Γs ratio in
the apoplast (=[NH4+]/[H+]) estimated from
micrometeorological measurements was 620, equivalent to
a stomatal compensation point of
1.3 μg NH3 m−3 at
15 °C. Non-stomatal resistance to deposition Rw was
shown to increase with temperature and decrease with surface
relative humidity, and Rw values were among the highest
published for European grasslands, consistent with
a relatively high ratio of NH3 to acid gases in the
boundary layer at this site. Since the gross annual NH3
emission by slurry spreading was of the order of
+20 kg N ha−1 yr−1, the fertilised grassland
was a net NH3 source of
+17 kg N ha−1 yr−1. A comparison with the few
other measurement-based budget values from the literature
reveals considerable variability, demonstrating both the
influence of soil, climate, management and grassland type on
the NH3 budget and the difficulty of scaling up to the
national level. |
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