PhD Thesis, 2010 - University College Cork

Nitrous oxide flux dynamics of grassland undergoing afforestation
Intra annual variation of the rainfall was well reflected in the WFPS time series.
Both Figure 5.2a and the Table 5.2 show that summer 2008 lacked the typical dry
period of any significant duration. The summer rainfall of 2008 exceeded the average
value for the previous four years by 31%. Since spring and summer are the main
seasons of fertiliser applications and cattle grazing, deviations from the long-term
averaged values during those seasons play an important role in the annual sums of the
N 2 O emission.
Table 5.2 Meteorological information by quarters and years. The first letters of the months are
used to indentify the quarter. Values marked with asterisk were averaged over the periods that
included a prolonged gap period. The upper value in the quarterly cell is total rainfall and the
lower value is average soil temperature.
Year
2004
2005
2006
2007
2008
Rainfall (mm) and temperature (°C) by
quarters
JFM AMJ JAS OND
394.8
5.3
415.4
6.0
332.6
-
483.6
6.2
513.8
6.3
254.8
10.1
302.6
9.9
261.6
10.3
296.6
10.7
243.0
9.7
373.6
13.2
313.2
13.8
364.8
13.9
326.8
13.2
452.3
13.2
407.0
8.1
586.4
8.3
637.6
8.7
379.6
9.5
369.5
8.1
Annual
rainfall, mm
Annual
temperature,
°C
1430.2 9.3
1617.6 9.7*
1596.6 11.1*
1489.0 9.9
1578.6 9.3
The intensity of the nitrous oxide flux is shown in Figure 5.2c and was typically
higher during the months of April–October when most of the agricultural activity
occurs (including N fertilisation – both mineral and slurry application and silage
harvesting). In the winter months, the N 2 O flux intensities are usually much lower,
which is related to the lack of fertiliser application as well as frequently saturated soil
moisture conditions at the site. The emission peaks occur often as a result of coinciding
rainfall and fertiliser application.
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