Whole-year-round Observation of N 2 O Profiles in Soil: A Lysimeter Study

Abstract

Despite many studies of the N2O emission, there is a lack of knowledge on the role of subsoil for N2O emission, particularly in sandy soils. To obtain insight into the entrapment, diffusion, convection and ebullition of N2O in the soil, the N2O concentration in the soil atmosphere was measured over a period of 1 year in 4 lysimeters (agricultural soil monoliths of
1 m2 × 2 m) at 30, 50, 80, 155, and 190 cm depth with altogether 86 gas probes. Additionally the N2O emission into the atmosphere was measured in 20 closed chambers at the soil surface. Concurrently the soil temperature and
soil water content were recorded in order to quantify their effects on the fate of N2O in the soil. Results of the continuous measurements between January and December 2006 were: N2O concentrations were highest in the deeper soil; maximum concentration was found at a depth of 80 cm, where the water content
was high and the gas transport reduced. The highest N2O concentration was recorded after ‘special events’ like snowmelt, heavy rain, fertilization, and grubbing. The combination
of fertilization and heavy rain led to an increase of up to 2,700 ppb in the subsoil.

Full text

Whole-year-round Observation of N
2
O Profiles
in Soil: A Lysimeter Study
S. Reth &W. Graf &O. Gefke &R. Schilling &
H. K. Seidlitz &J. C. Munch
Received: 15 January 2007 / Accepted: 28 September 2007 / Published online: 23 November 2007
#Springer Science + Business Media B.V. 2007
Abstract Despite many studies of the N
2
O emission,
there is a lack of knowledge on the role of subsoil for
N
2
O emission, particularly in sandy soils. To obtain
insight into the entrapment, diffusion, convection and
ebullition of N
2
O in the soil, the N
2
O concentration in
the soil atmosphere was measured over a period of
1 year in 4 lysimeters (agricultural soil monoliths of
1 m2 × 2 m) at 30, 50, 80, 155, and 190 cm depth
with altogether 86 gas probes. Additionally the N
2
O
emission into the atmosphere was measured in 20
closed chambers at the soil surface. Concurrently the
soil temperature and soil water content were recorded
in order to quantify their effects on the fate of N
2
Oin
the soil. Results of the continuous measurements
between January and December 2006 were: N
2
O
concentrations were highest in the deeper soil;
maximum concentration was found at a depth of
80 cm, where the water content was high and the gas
transport reduced. The highest N
2
O concentration was
recorded after ‘special events’like snowmelt, heavy
rain, fertilization, and grubbing. The combination of
fertilization and heavy rain led to an increase of up to
2,700 ppb in the subsoil.
Keywords Lysimeter .N
2
O.Concentration
1 Introduction
Nitrous oxide (N
2
O) is one of the greenhouse gases
classified by the Kyoto Protocol (UNFCCC 1992)and
contributes 6% to the global warming (IPCC 2001).
Furthermore N
2
O is partly responsible for the destruc-
tion of the stratospheric ozone layer (Crutzen 1981). In
the atmosphere N
2
O has a long residence time of about
120 years, resulting in a global warming potential 310
times larger than that of CO
2
(IPCC 1996).
In this context the exchange of N
2
O between soils,
vegetation, and the atmosphere is an important topic
of ecological research. Although there are numerous
studies of N
2
O emissions (e.g. Butterbach-Bahl et al.
2002; Flessa et al. 1998), most of them concentrate on
the soil–atmosphere interface (i.e. at a depth of
≤40 cm), investigate the controlling factors for N
2
O
emissions there (e.g. Luo et al. 1998; Simek et al.
2004; Teepe et al. 2000), and do not consider the
possible sources in subsoil.
Many parameters were found to control the
production and the emissions of N
2
O, such as the
soil moisture (Huetsch et al. 1999; Weier et al. 1993),
the soil compaction (Ruser et al. 2006), the soil
temperature (Flessa et al. 2002; Kamp et al. 1998),
Water Air Soil Pollut: Focus (2008) 8:129–137
DOI 10.1007/s11267-007-9165-3
DO09165; No of Pages
S. Reth (*):W. Graf :O. Gefke :R. Schilling :
H. K. Seidlitz :J. C. Munch
Department of Environmental Engineering,
Institute of Soil Ecology, GSF –National Research
Center for Environment and Health,
Ingolstädter Landstrasse 1,
85764 Neuherberg, Germany
e-mail: sascha.reth@gsf.de

and the nitrogen availability (Silgram et al. 2001;
Wrage et al. 2004). Additionally, the N
2
O production
and emission are influenced by meteorological events
such as rainfall and snowmelt (Brumme et al. 1999;
Potter and Klooster 1998), freezing and thawing
(Kamp et al. 1998; Rudaz et al. 1999; Sharma et al.
2006), and by anthropogenic activities, for instance
tillage (Ball et al. 1999), fertilization (Akiyama et al.
2000; Huetsch et al. 1999), irrigation (Ruser et al.
2006; Sanchez et al. 2001), manure additions (Stevens
and Laughlin 2001; Stevens and Laughlin 2002), and
liming (Gebauer et al. 1998).
Only few investigations determined soil gas con-
centrations and their formation in deeper soils. Van
Groenigen et al. (2005) report a N
2
O soil profile
down to 90 cm depth, and Russow et al. (2002) down
to 250 cm. Many of these investigations were
performed under standardized conditions in the
laboratory (Castle et al. 1998; Mergel et al. 2001).
Concentrations of N
2
O in soil air are extremely
variable over space and time (see e.g. reviews of
Clough et al. 2001; Heincke and Kaupenjohann
1999). This applies also for the N
2
O fluxes from the
soil to the atmosphere (Reth et al. 2005; Schürmann
et al. 2002). It is essential to characterize and to
model the processes involved in the production and
consumption, and the transport of N
2
O. A number of
simulation studies of N
2
O production and transport
through the soil profile have been published (e.g.
Chatskikh et al. 2005; Hosen et al. 2000). In a case
study (Guo et al. 2003) the denitrification potential in
the soil decreases from 30 to100 cm depth and increases
again below the 100 cm depth. Contrasting results are
discussed by Heincke and Kaupenjohann (1999), taking
into account that the total number of viable bacteria
and the number of the denitrifying bacteria decreased
exponentially with depths down to 150 cm.
Up to now only little information is available on
the distribution and the dynamics of N
2
O within the
soil and the water unsaturated zone. Our lysimeter
study contributes to fill this gap. We measured
vertical N
2
O profiles in four soil monoliths and
analyzed the influence of environmental factors and
of anthropogenic activities on the N
2
O production in
soil monoliths with a depth of 200 cm. The high
temporal resolution and the coverage of a whole
annual cycle make these data unique and demonstrate
the excellence of well-equipped lysimeters for in situ
studies of N
2
O emissions.
2 Methods
2.1 Research Field
The lysimeter station with 48 lysimeters is located just
north of Munich, Germany (48° 13’24 N, 11°35’48 O,
and 490 m absolute altitude). The lysimeters –a close-
to-nature experimental setup –are located in the
middle of a 1 ha cultivated area with defined crop
rotation (oat–mustard–wheat). All lysimeter vessels
are made of stainless steel cylinders (V4A) with an area
of 1 m
2
each and a height of 2 m. For an accurate
determination of the water balance the lysimeters are
positioned on 3 high precision load cells (Fig. 1) with
a resolution of 100 g. The outflow of the lysimeters is
collected in weighable seepage vessels to analyze the
dynamics and chemistry of leaching losses. In order
to analyze the heterogeneity of the water flow in the
unsaturated zone and special forms of leachate (e.g.
bypass flow), 4 lysimeters have segmented drain
plates with 8 separated outflows.
The lysimeters are equipped with tensiometers,
TDR probes, and temperature sensors at five depths
(30, 50, 80, 155 and 190 cm). Additionally, suction
cups and soil gas samplers were installed. Climate
data are continuously recorded at a meteorological
station within the lysimeter station.
2.2 Soil Monoliths
The four lysimeters used in this study were mono-
lithically excavated 1995 at Hohenwart, Germany
(48°34.88 N, 11°24.16 E). The soil is anAric Anthrosol,
soil physical parameters are given in Table 1.
2.3 Soil Emissions
Measurements were carried out from January 1st to
December 31st, 2006. From January 1st to May 30th,
2006 the measurements were performed at one
lysimeter, thereafter at four lysimeters. The measure-
ments were performed weekly in the winter months
and up to eight times a day in the summer months.
The measuring system to determine gas emissions
from the soil surface consists of cylindrical steel
chambers (height 80 mm, diameter 127 mm) with lids
attached during the measurement. The basic rings of
the chambers were inserted 20 mm into the soil. The
chambers were set between the cropping rows and
130 Water Air Soil Pollut: Focus (2008) 8:129–137

weed (if present) was removed from the interiors. The
increase of the soil temperature during the collection
of the gas sample was less than 1 K. Gas samples of
the ambient air were collected at the beginning of
each measurement. Twenty minutes after closing the
chambers, the gas inside the chambers was collected
using evacuated 100 ml glass flasks. N
2
O efflux was
determined from the slope of the concentration
increase inside the chamber within 20 min. By a test
series the best closing interval was determined at
20 min. Longer intervals yield to an underestimation
of the emissions and shorter intervals increase the
uncertainty of result.
To estimate the sampling and instrumental error of
the method, 10 bottles were filled with gas of ambient
air and the N
2
O concentrations were measured. From
that, the uncertainty of the reported values is about
7 ppb, about 2% of the ambient N
2
O concentration.
2.4 Soil Gas Concentration Measurements
The probing system for collecting soil air aliquots
consists of thin steel tubes (lengths 350 mm, inner
diameter 2 mm), inserted into the soil through lids in
the lysimeters vessels at an angle of 20°. The
sampling orifice of the tube was covered with a
Gore-Tex®-membrane. To avoid a rapid gas flow
Fig. 1 Schematic diagram
of a lysimeter at the GSF
research station with com-
plete equipment: (1) sur-
rounding field, (2) closed
chamber for gas measure-
ments, (3) tensiometer, (4)
soil monolith, (5) TDR-
probe, (6) gas tube, (7) filter
layer, (8) load cells for
precision weighting, (9) tef-
lon tube, (10) support, (11)
evacuated gas vessel, (12)
data-logger, (13) Linde
Plastigas®bags, (14) out-
flow, (15) seepage tank,
(16) precision load cell of
the seepage tank, (17)
weighting display
Table 1 Soil physical parameters of the investigated soil at the
beginning of the experiment 1995 (slightly modified from
Kühn 2004)
Horizon Texture Clay % dry
weight
Silt % dry
weight
Sand % dry
weight
Ap Sl
3
13 19 68
MSl
3
92170
Bv1 Sl
2
51481
Bv2 S 1 4 95
Water Air Soil Pollut: Focus (2008) 8:129–137 131

from the soil we used a small orifice of 6.28 mm2.
Altogether 86 gas probes were installed in the 4
lysimeters. To collect gas samples, evacuated gas
vessels (4 mbar) with a volume of 100 ml were
connected to the tubes. The sampling bottle was filled
within 150 h. All gas samples were analyzed using an
automated probing gas chromatographic system (GC
14A, Shimadzu, Duisburg, Germany) with a 63Ni
electron capture detector (ECD), as described by
Loftfield et al. (1997), and Ruser et al. (2001).
3 Results
The time series of the N
2
O emissions at the surface
and the N
2
O concentrations at 30, 50, 80, 155, and at
190 cm depth in the soil air of the four lysimeters are
presented in Fig. 2. The N
2
O concentrations were
highest in 50 and 80 cm depth; in the latter also the
highest concentration at all (2,900 ppb) was mea-
sured. The lowest concentrations occurred in the
uppermost horizon (30 cm) close to the atmosphere
and in the deepest horizon (190 cm). In the horizons
with the highest concentrations (50 and 80 cm) we
also observed the highest N
2
O variability (Table 2).
At all depths deviations of the N
2
O concentration to
elevated values were observed, possibly the response
to soil treatment.
During the winter months the N
2
O emissions were
very low, less than 0.1 nmol N
2
Om
−2
s
−1
because of
the low soil temperature. With increasing soil tem-
perature also the N
2
O emission and the N
2
O
fluctuation increased (Fig. 2). (The fairly constant
winter emissions are the reason for less frequent
measurements in the winter).
Concomitantly with the N
2
O concentration rise the
highest emissions at the surface occurred after special
events: heavy rain, grubbing, and fertilization. The
highest emissions (values up to 0.8 nmol N
2
Om
−2
s
−1
)
were measured after fertilization with a NPK fertilizer
(event 4 in Fig. 2) and after grubbing and seeding
(event 5). The concentration in the soil air increased up
to 900% compared to the ambient concentration during
the course of such a fertilization event with concurrent
heavy rain (>20 mm/day). The increase period lasted
about 2 weeks.
The spatial variability of both, the emissions and
the N
2
O soil air concentrations, was high. The relative
variability (standard deviation/mean concentration) of
the N
2
O emission was between 55 and 92%. The
relative variability of the soil N
2
O concentrations,
calculated separately for each depth and each lysim-
eter, was in the range from 10 to 30%. There was no
N2O (ppb)
Date
N2O (ppb)
N2O flux
(nmol s-1 m-2)N2O (ppb)N2O (ppb)
30 cm
50 cm
80 cm
155 cm
190 cm
Event 1 2 345
N2O (ppb) P (mm/d)
01.01.06 01.04.06 01.07.06 01.10.06 01.01.07
0
1000
2000
3000
0
1000
2000
3000
0
1000
2000
3000
0
1000
2000
3000
0
1000
2000
3000
0
0.5
1
0
15
30
b
c
d
e
f
g
a
Fig. 2 a Time series of the precipitation amount from January
1st to December 31st, 2006. bN
2
O emissions at the surface of
the lysimeters and the N
2
O concentrations in the soil air of the
lysimeters 1 to 4 at the indicated depths from (c) to (g). For
each depth and each lysimeter only the maximal values are
shown. In each cluster the individual concentrations are shown
by bars (the values of lysimeters 1 to 4 from left to right). The
dates of events which increased the N
2
O concentrations at least
in some depths and some lysimeters are marked [1: snow
melting, 2: grubbing and seeding of wheat, 3: fertilization with
NPK (18 kg ha
−1
,24kgha
−1
,18kgha
−1
), 4: fertilization with
NPK (18 kg ha
−1
,24kgha
−1
,18kgha
−1
], 5: grubbing and
seeding of mustard
132 Water Air Soil Pollut: Focus (2008) 8:129–137

difference in the variability within and between the
lysimeters.
The N
2
O soil gas content within and outside the
event periods versus soil temperature are shown in
Fig. 3and versus soil water content in Fig. 4.Whereas
at the same time and equal depths the soil temperatures
in the four lysimeters were very similar, the soil water
contents differed up to 30% between the lysimeters.
The N
2
O concentrations and the soil gas emissions
showed no significant increase with increasing soil
temperature. But in some lysimeters and at some depths
the N
2
O concentration and the soil water content are
positively correlated. The small changes of the soil
water content at the individual measurement points
below the 30 cm depth might prevent a significant and
positive correlation at the other measuring points.
4 Discussion
Contrary to several other studies (e.g. Granli and
Bockman 1994; Ruser et al. 2006) we observed no
positive dependence of N
2
O emissions on the mois-
ture and temperature in the topsoil. In the subsoil, in
only one case, a weak positive correlation between
soil temperature and N
2
O concentrations was ob-
served. But we also found negative correlations. This
is in contrast to the expectations for denitrification
processes: Higher soil temperatures should enable
higher formation of N
2
O via denitrification, but could
also lead to a reduced nitrification (Reth et al. 2005).
Apparently, other parameters not considered in this
study influence the production and consumption of
N
2
O in the four lysimeters.
Soil gas samples taken at the same time and depth
but at different horizontal positions displayed a high
spatial variability of the N
2
O concentrations and
indicate high soil heterogeneity. As mentioned in
several studies for the lower soil (e.g. Griffiths 1994;
Hesselsøe et al. 2001) the variability, in the upper as
well as in the deeper soil, could be explained by the
existence of ‘hot spots’in the soil matrix.
The variation of the water content (ϑ)atthe
individual measuring positions below the 30 cm depth
(dϑ=1.5–7.3% [16.7%], the value in brackets is
questionable) was small but may cause the observed
N
2
O concentration changes. So at some of the
individual measurement points a positive correlation
between the N
2
O concentrations and the soil moisture
was observed. Additionally, the variation of the water
content at the site of the N
2
O production may be
higher than indicated by the values of the TDR
probes. The TDR probes and the soil gas samplers in
the same depth are 20–50 cm apart and the soil gas
therefore was not necessarily sampled from the space
where the TDR probes are installed; and the hetero-
geneity in the water content was high. This heteroge-
neity was observed during the installation of the gas
probes. The soil was water saturated at one position,
while it was dry at another position at the same depth.
Possibly the measured N
2
O concentrations and the
water contents are not related to each other, possibly
variations of the N
2
O concentrations are caused
additionally by the influence of other factors.
After events like heavy rain, snow melt, fertilization,
and soil cultivation, the N
2
O concentration increased
much more in the deeper soil than in the topsoil. This
corresponds to a typical diffusion profile. In our study
soil working and fertilization triggered the highest
formation of N
2
O. Former accelerates the aggregate
turnover and rise the nutrient availability, as described
by Grandy and Robertson (2006), and the fertilization
directly increased the nitrate in the soil water.
In this study we observed two fertilization events
(event 3 and 4), both followed by heavy rain (>20 mm/
day) and an increase of the N
2
O concentration in the
soil air. Highest response was recorded in 80 cm depth,
which mainly is caused by a transport of nitrate with
rain water. Similar effects were observed after soil
working (event 2 and 5). During 2 weeks after the
cultivation of the soil, there was no precipitation and
accordingly no nutrient transport and no additional
N
2
O production occurred. Short time after a heavy rain
event the N
2
O concentration in the 80 cm depth rose
up to 2,900 ppb by more than 900%.
This demonstrates that the availability of NO
3
enables high N
2
O production/consumption and high
Table 2 N
2
O concentration in the soil air of 4 lysimeters at
four depths: mean values and standard deviation (1σ) of the
observations in 2006
Soil depth [cm] N2O [ppb]
30 385± 100
50 430± 171
80 419± 207
155 372± 160
190 374± 81
Water Air Soil Pollut: Focus (2008) 8:129–137 133

N
2
O concentrations. However, unfavourable denitri-
fication conditions may limit or prevent the N
2
O
production. This may explain that both high and low
N
2
O concentrations were measured at the same time
only a few centimetres apart.
Outside the event periods the N
2
O depth profile
had a slight maximum in 50 and 80 cm depth. This
could be explained as a diffusion profile with N
2
O
production in the 50 and 80 cm depths. This
observation is also in line with the study of Guo
et al. (2003). They explain the increase of N
2
O
concentration at deeper depths with an increasing
denitrification potential. In several studies similar
explanations are given (see the review of Clough
et al. 2001), also under the consideration of the transport
of dissolved N
2
O in the leachate of a wetting fronts.
There seems to be no link between the soil gas
formation and the emissions. This could be caused by
a time lack between the measurements of the gas
concentrations in the soil and the measurement of the
N2O (ppb)
(190cm depth)
N2O (ppb)
(155cm depth)
N2O (ppb)
(80cm depth)
N2O (ppb)
(50cm depth)
N2O (ppb)
(30cm depth)
N2O flux
(nmol s-1 m-2)
Soil temperature (°C)
Lysimeter 13 Lysimeter 14 Lysimeter 15 Lysimeter 16
0 15 30 0 15 30 0 15 30 0 15 30
0
1000
2000
0
1000
2000
0
1000
2000
0
1000
2000
0
1000
2000
0
0.5
1
r2= 0.09
r2= 0.18
r2= 0.09 r2= 0.03 r2= 0.22
r2= 0.18
r2= 0.20
Fig. 3 N
2
O emissions at
the surface of the lysime-
ters and the N
2
O concentra-
tions in the soil air of the
lysimeters at the indicated
depths versus soil tempera-
ture. Triangles represent the
fluxes and concentrations,
which are influenced by a
special event. The circles
represent all other data out-
side these periods. If the
correlation of the data out-
side the event periods is
significant on the 95% level,
the regression coefficient is
given
134 Water Air Soil Pollut: Focus (2008) 8:129–137

emissions. After 7 days of an injection of
15
N
14
NO in
the 155 cm depth, the labelled N
2
O was detected at
the soil surface (data not shown). Diffusion models
could help to link between the two measurements.
5 Conclusions
The N
2
O production in the soil is highly variable in
space and time. The variability is much higher at 50
and 80 cm depth than in the upper 30 cm, where N
2
O
is coupled to the atmosphere. Special events were
identified as key factors to influence spatial and
temporal variation of the soil N
2
O production and
consumption. Future measurements with high spatial
resolution are necessary to improve our understanding
of the high heterogeneity of the N
2
O formation in the
soil matrix and to get more information on the
seasonality of the N
2
O production and consumption
in the soil. Further efforts should focus on the
E
Water content (%)
Lysimeter 13 Lysimeter 14 Lysimeter 15 Lysimeter 16
0 15 30 45 0 15 30 45 0 15 30 45 0 15 30 45
0
1000
2000
0
1000
2000
0
1000
2000
0
1000
2000
0
1000
2000
0
0.5
1
r2= 0.13 r2= 0.06
r2= 0.30 r2= 0.05 r2= 0.16
r2= 0.10 r2= 0.05 r2= 0.21
r2= 0.05 r2= 0.06 r2= 0.18
r2= 0.50
N2O (ppb)
(190cm depth)
N2O (ppb)
(155cm depth)
N2O (ppb)
(80cm depth)
N2O (ppb)
(50cm depth)
N2O (ppb)
(30cm depth)
N2O flux
(nmol s-1 m-2)
Fig. 4 N
2
O emissions at
the surface of the lysime-
ters and the N
2
O concentra-
tions in the soil air of the
lysimeters at the indicated
depths versus soil water
content. For details see
Fig. 3
Water Air Soil Pollut: Focus (2008) 8:129–137 135

combination of N
2
O formation in deeper soil and the
emissions, allowing for the time lack.
References
Akiyama, H., Tsuruta, H., & Watanabe, T. (2000). N
2
O and NO
emissions from soils after the application of different
chemical fertilizers. Chemosphere Global Change Science,
2, 313–320.
Ball, B. C., Parker, J. P., & Scott, A. (1999). Soil and residue
management effects on cropping conditions and nitrous
oxide fluxes under controlled traffic in Scotland; 2.
Nitrous oxide, soil N status and weather. Soil and Tillage
Research, 52, 191–201.
Brumme, R., Borken, W., & Finke, S. (1999). Hierarchical
control on nitrous oxide emission in forest ecosystems.
Global Biogeochemical Cycles, 13, 1137–1148.
Butterbach-Bahl, K., Gasche, R., Willibald, G., & Papen, H.
(2002). Exchange of N-gases at the Hoglwald Forest –A
summary. Plant Soil, 240,117–123.
Castle, K., Arah, J. R. M., & Vinten, A. J. A. (1998).
Denitrification in intact subsoil cores. Biology and
Fertility of Soils, 28,12–18.
Chatskikh, D., Olesen, J. E., Berntsen, J., Regina, K., &
Yamulki, S. (2005). Simulation of effects of soils, climate
and management on N
2
O emission from grasslands.
Biogeochemistry, 76, 395–419.
Clough, T. J., Stevens, R. J., Laughlin, R. J., Sherlock, R. R., &
Cameron, K. C. (2001). Transformations of inorganic-N in
soil leachate under differing storage conditions. Soil
Biology and Biochemistry, 33, 1473–1480.
Crutzen, P. J. (1981). Atmospheric chemical processes of the
oxides of nitrogen, including nitrous oxide. In C. C.
Delwiche (Ed.) Denitrification, nitrification and atmo-
spheric nitrous oxide (pp. 17–45). New York: Wiley.
Flessa, H., Potthoff, M., & Loftfield, N. (2002). Greenhouse
estimates of CO
2
and N
2
O emissions following surface
application of grass mulch: Importance of indigenous
microflora of mulch. Soil Biology & Biochemistry, 34,
875–879.
Flessa, H., Wild, U., Klemisch, M., & Pfadenhauer, J. (1998).
Nitrous oxide and methane fluxes from organic soils under
agriculture. European Journal of Soil Science, 49,327–335.
Gebauer, G., Hahn, G., Rodenkirchen, H., & Zuleger, M.
(1998). Effects of acid irrigation and liming on nitrate
reduction and nitrate content of Picea abies (L.) Karst. and
Oxalis acetosella L. Plant Soil, 199,59–70.
Grandy, S. A., & Robertson, P. G. (2006). Initial cultivation of
a temperate-region soil immediately accelerates aggregate
turnover and CO
2
and N
2
O fluxes. Global Change
Biology, 12, 1507–1520.
Granli, T., & Bockman, O. C. (1994). Nitrous oxide from
agriculture. Norwegian Journal of Agricultural Sciences,
12,7–127.
Griffiths, B. S. (1994). Microbial-feeding nematodes and
protozoa in soil: Their effects on microbial activity and
nitrogen mineralization in decomposition hotspots and the
rhizosphere. Plant and Soil, 164,25–33.
Guo, H., Li, G., Zhang, X., Yan, F., Zhang, D., & Lu, C.
(2003). Spatial research of denitrification and nitrification
potential of agricultural soils in relation to fertilization
practice. Proceedings of the 2003 International Sympo-
sium on Water Resources and the Urban Environment (pp.
179–185).
Heincke, M., & Kaupenjohann, M. (1999). Effects of soil
solution on the dynamics of N
2
O emissions: A review.
Nutrient Cycling in Agroecosystems, 55, 133–157.
Hesselsøe, M., Pedersen, A., Bundgaard, K., Brandt, K. K., &
Sørensen, J. (2001). Development of nitrification hot-spots
around degrading red clover (Trifolium pratense) leaves in
soil. Biology and Fertility of Soils, 33, 238–245.
Hosen, Y., Tsuruta, H., & Minami, K. (2000). Effects of the
depth of NO and N
2
O productions in soil on their emission
rates to the atmosphere: Analysis by a simulation model.
Nutrient Cycling in Agroecosystems, 57,83–98.
Huetsch, B. W., Wang, X., Feng, K., Yan, F., & Schubert, S.
(1999). Nitrous oxide emission as affected by changes in
soil water content and nitrogen fertilization. Journal of
Plant Nutrition and Soil Science, 162, 607–613.
IPCC (1996). Climate change (1995). The science of climate
change. Cambridge, UK: Cambridge University Press.
IPCC (2001). Climate Change (2001). The scientific basis.
Cambridge, UK: Cambridge University Press.
Kamp, T., Steindl, H., Hantschel, R. E., Beese, F., & Munch, J. C.
(1998). Nitrous oxide emissions from a fallow and wheat
field as affected by increased soil temperatures. Biology and
Fertility of Soils, 27,307–314.
Kühn, S. S. (2004). Bedeutung der leistung mikrobieller
lebensgemeinschaften beim umsatz und abbau von iso-
proturon in böden und möglichkeiten zur steuerung des
in-situ-pestizidabbaus. Institut für Bodenökologie, GSF-
Forschungszentrum für Umwelt und Gesundheit, Technischen
Universität München, 183 pp.
Loftfield, N., Flessa, H., Augustin, J., & Beese, F. (1997).
Automated gas chromatographic system for rapid analysis
of the atmospheric trace gases methane, carbon dioxide,
and nitrous oxide. Journal of Environmental Quality, 26,
560–564.
Luo, J., Tillman, R. W., White, R. E., & Ball, P. R. (1998).
Variation in denitrification activity with soil depth under
pasture. Soil Biology and Biochemistry, 30, 897–903.
Mergel, A., Kloos, K., & Bothe, H. (2001). Seasonal fluctua-
tions in the population of denitrifying and N
2
-fixing
bacteria in an acid soil of a Norway spruce forest. Plant
and Soil, 230, 145–160.
Potter, C. S., & Klooster, S. A. (1998). Interannual variability in
soil trace gas (CO
2
,N
2
O, NO) fluxes and analysis of
controllers on regional to global scales. Global Biogeo-
chemical Cycles, 12, 621–635.
Reth, S., Hentschel, K., Drössler, M., & Falge, E. (2005).
DenNit –Experimental analysis and modelling of soil
N2O efflux in response on changes of soil water content,
soil temperature, soil pH, nutrient availability and the time
after rain event. Plant Soil, 272, 349–363.
Rudaz, A. O., Walti, E., Kyburz, G., Lehmann, P., & Fuhrer, J.
(1999). Temporal variation in N
2
O and N
2
fluxes from a
permanent pasture in Switzerland in relation to manage-
ment, soil water content and soil temperature. Agriculture,
Ecosystems and Environment, 73,83–91.
136 Water Air Soil Pollut: Focus (2008) 8:129–137

Ruser, R., Flessa, H., Russow, R., Schmidt, G., Buegger, F., &
Munch, J. C. (2006). Emission of N
2
O, N
2
and CO
2
from
soil fertilized with nitrate: Effect of compaction, soil
moisture and rewetting. Soil Biology and Biochemistry,
38, 263–274.
Ruser, R., Flessa, H., Schilling, R., Beese, F., & Munch, J. C.
(2001). Effect of crop-specific field management and N
fertilization on N
2
O emissions from a fine–loamy soil.
Nutrient Cycling in Agroecosystems, 59, 177–191.
Russow, R., Knappe, S., & Neue, H.-U. (2002). The N2O
content of soil air at different depths as well as its related
content in and transport by seepage in lysimeter soils. In
Non-CO
2
greenhouse gases: Scientific understanding,
control options and policy aspects (pp. 151–152). Rotter-
dam, The Netherlands: Millpress.
Sanchez, L., Diez, J. A., Vallejo, A., & Cartagena, M. C. (2001).
Denitrification losses from irrigated crops in central Spain.
Soil Biology & Biochemistry, 33, 1201–1209.
Schürmann, A., Mohn, J., & Bachofen, R. (2002). N
2
O
emissions from snow-covered soils in the Swiss Alps.
Tellus B, 54, 134–142.
Sharma, S., Szele, Z., Schilling, R., Munch, J. C., & Schloter,
M. (2006). Influence of freeze-thaw stress on the structure
and function of microbial communities and denitrifying
populations in soil. Applied and Environmental Microbi-
ology, 72, 2148–2154.
Silgram, M., Waring, R., Anthony, S., & Webb, J. (2001).
Intercomparison of national & IPCC methods for estimat-
ing N loss from agricultural land. Nutrient Cycling in
Agroecosystems, 60, 189–195.
Šimek, M., Elhottova, D., Klimes, F., & Hopkins, D. W.
(2004). Emissions of N
2
OandCO
2
, denitrification
measurements and soil properties in red clover and
ryegrass stands. Soil Biology and Biochemistry, 36,9–21.
Stevens, R. J., & Laughlin, R. J. (2001). Cattle slurry affects
nitrous oxide and dinitrogen emissions from fertilizer
nitrate. Soil Science Society of America Journal, 65,
1307–1314.
Stevens, R. J., & Laughlin, R. J. (2002). Cattle slurry applied before
fertilizer nitrate lowers nitrous oxide and dinitrogen emis-
sions. Soil Science Society of America Journal, 66, 647–652.
Teepe, R., Brumme, R., & Beese, F. (2000). Nitrous oxide
emissions from frozen soils under agricultural, fallow and
forest land. Soil Biology & Biochemistry, 32, 1807–1810.
UNFCCC (1992). Kyoto protocol to the United Nations
Framework Convention on climate change. Bonn:
UNFCCC Sekretariat.
VanGroenigen,J.W.,Georgius,P.J.,VanKessel,C.,
Hummelink, E. W. J., Velthof, G. L., & Zwart, K. B.
(2005). Subsoil 15N-N2O concentrations in a sandy soil
profile after application of 15N-fertilizer. Nutrient Cycling
in Agroecosystems, 72,13–25.
Weier, K. L., Doran, J. W., Power, J. S., & Walters, D. T. (1993).
Denitrification and the dinitrogen/nitrous oxide ration as
effected by soil water, available carbon, and nitrate. Soil
Science Society of America Journal, 57,66–72.
Wrage, N., Lauf, J., del Prado, A., Pinto, M., Pietrzak, S., &
Yamulki, S. (2004). Distinguishing sources of N2O in
European grasslands by stable isotope analysis. Rapid
Communications in Mass Spectrometry, 18, 1201–1207.
Water Air Soil Pollut: Focus (2008) 8:129–137 137