Short communication
Nitrous oxide emissions from frozen soils under agricultural,
fallow and forest land
R. Teepe*, R. Brumme, F. Beese
Institute of Soil Science and Forest Nutrients, University of GoÈttingen, BuÈsgenweg 2, 37077 GoÈttingen, Germany
Accepted 15 March 2000
Abstract
In a ®eld study, N2O emissions were measured in an agricultural, a fallow, and a forest system once a week from December
1995 to November 1996. Elevated N2O emissions were detected during periods of both soil freezing and soil thawing. The
dynamics of the N2O winter emissions were in¯uenced by the changes in soil temperatures. The highest emission rates were
observed during soil thawing. The N2O emissions during the entire winter period (December 1995 to March 1996) amounted to
2.8, 1.3, and 0.7 kg N2O±N for the agricultural land, fallow and forest, respectively, and contributed to 58, 45 and 50% of the
annual N2O emissions from these systems. Dierences in the winter emissions among the three sites could not be explained by
means of nitrate concentration but rather by water-®lled pore space (WFPS). Additionally, the upper organic layers of the forest and the grass vegetation of the fallow site delayed the time of soil freezing and reduced the depth of frost penetration. Both WFPS and vegetation control the N2O emissions in winter.72000 Elsevier Science Ltd. All rights reserved.
Keywords:Nitrous oxide emissions; Soil freezing; Soil thawing; Land use
Nitrous oxide is a still increasing tropospheric green-house gas (IPCC, 1994) and is additionally involved in the destruction of ozone in the stratosphere (Crutzen, 1981). The soil of terrestrial ecosystems is an
import-ant source of N2O (Bouwman, 1994). High N2O
emis-sions during the winter demonstrate their importance
for reliable estimation of annual N2O budgets (Flessa
et al., 1995; Wagner-Riddle et al., 1997; Papen and Butterbach-Bahl, 1999; Brumme et al., 1999). In this
study, we quanti®ed N2O emissions over the winter
from three adjacent sites (arable agricultural, a fallow and forested land) and discuss the eects of these dierent land uses on the gas ¯uxes.
The study sites were located within close proximity to each other in Central Germany. The local climate and parent soil characteristics of the three sites were very similar. The soil was an imperfectly drained loam
with silt as the dominant textural component. The land use and management histories of the sites resulted in dierent properties of bulk density, pH and concen-trations of organic-C and total-N (Table 1). The agri-cultural site was sown with oil seed rape in August 1995 after the winter barley had been harvested and
was fertilized with 200 kg N haÿ1 yrÿ1 in 1995 and
195 kg N haÿ1 yrÿ1 in 1996. The fallow, which was
last cultivated in 1987, was covered with grass. The
forest site was a 32-year-old oak-forest (Quercus
pet-rea). As a consequence of the acidic soil conditions
pH4:2), the upper organic layer had developed into
a moder humus to a depth of 4 cm.
The N2O emissions of each site were measured for 1
year once a week from December 1995 to November 1996 using the closed chamber method (Matthias et al., 1980). Sampling was carried out over three periods: early winter, the following period of freezing air tem-peratures from December 1995 to March 1996, and the growing season from April 1996 to November
1996. Five chambers (area 0.25 m2, volume 20 l) were
Soil Biology & Biochemistry 32 (2000) 1807±1810
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* Corresponding author. Tel.: 393508; fax: +49-551-393310.
randomly placed on each site. The gas samples were collected in evacuated glass bottles and analysed in the laboratory with a gas chromatographic system (Loft-®eld et al., 1997). Soil and air temperature were measured on each gas sampling date. Soil moisture
and extractable NO3ÿ concentrations in the soil were
investigated six times during the winter.
The winter of 1995/1996 was unusually long in
Germany. Elevated N2O emissions could be observed
during the entire winter period at each site with cumu-lative emissions of 2.8 (agriculture), 1.3 (fallow) and
0.7 (forest) kg N2O±N haÿ1 from December 1995 to
March 1996 (Table 2). The highest N2O emissions
occurred during the thaw period in March (Fig. 1) and was ®rst evident at the forest site in the beginning of March, followed by the fallow and the agricultural site. The dierent times for the onset of the thawing peaks of gas emissions may be explained by an ice layer at the agricultural site and the fallow land, which was formed as a result of melting snow and its sub-sequent freezing. This created an ice crust which may have acted as a gas diusion barrier. This ice layer was not observed at the forest site.
All of the three sites emitted N2O during soil
freez-ing at the end of January. Although air temperatures
decreased to ÿ108C, and soil thawing can de®nitely be
excluded during this time, we measured N2O emission
rates of 16 (forest), 25 (fallow), and 60 (agricultural land) mg N2O±N mÿ2 hÿ1. Similar emissions of N2O
during soil freezing have been detected in other studies (Kaiser and Heinemeyer, 1996; RoÈver et al., 1998; Kai-ser et al., 1998; Papen and Butterbach-Bahl, 1999). We
have attributed these N2O ¯uxes during soil freezing to
microbiological activity in unfrozen soil water located in a thin water ®lm at the soil matrix (Teepe et al.,
2000). The ¯uctuation of N2O emissions during soil
freezing is controlled by temperature. For example,
N2O emissions at the beginning of February peaked
together with soil temperature although soil surface
temperature did not exceed 08C (Fig. 1). We assume
that this peak emission is due to thawing processes in the subsoil. In a laboratory investigation with undis-turbed soil columns from the agricultural site we
observed the same response of the N2O emission rates.
After subsoil thawing the N2O emissions increased
although the top soil was still frozen (Teepe et al., 2000).
The NO3ÿ concentrations in the soil were very low
during winter (Table 2), although high N2O emissions
could be measured at each site. It is unclear whether
the dierent N2O winter emissions can be explained by
the dierence in these low NO3ÿ concentrations. As a
consequence of only sampling six times during the win-ter we may have missed the increase in N mineraliz-ation which has been observed by Groman et al. (2000) in frozen soils. However, the average water-®lled pore space (WFPS) in the top 0±5 cm of soil was
positively correlated with the total N2O winter
emis-Table 1
Texture and chemical soil properties, bulk density dB), and pore space (PV) of the investigated agricultural, fallow, and forest sitesa
Site Depth (cm) Clay (%) Silt (%) Sand (%) dB(g cmÿ3) PV (%) pH (H2O) Corg. (%) Nt (%)
Agricultural 0±20 21 44 35 1.27 51.1 7.3 1.1 0.12
35±40 22 43 35 1.69 35.3 ND ND ND
aNt= totalNcontent, ND = no determination.
Table 2
Total N2O emissions (standard error of the mean (SEM) withn5), average NO3ÿconcentration and average water-®lled pore space (WFPS) at
two depths from the three sites in the winter period (December 1995 to March 1996) and in the vegetation period (April 1996 to November 1996)
Agricultural land Fallow Forest
Winter period Vegetation period Winter period Vegetation period Winter period Vegetation period N2O±N (kg ha
R. Teepe et al. / Soil Biology & Biochemistry 32 (2000) 1807±1810
sions indicating the importance of oxygen diusion as
a regulator for N2O emissions in winter which is in
agreement with Groman and Tiedje (1991). They showed that the denitri®cation rate in a loamy soil was negatively correlated to the air ®lled porosity.
An additional explanation for the dierent N2O
win-ter emissions among the sites is probably the dierent onset time of soil freezing and dierent depth of frost penetration. The soil froze ®rst in the rape ®eld which had only a sparse covering of small plants. The closed vegetation cover of grass on the fallow, and the surface organic layer at the forest site, caused a delayed soil
Fig. 1. Average N2O-¯ux with standard deviation n5of the rape (A), fallow (B), forest sites (C) with soil temperature (at 5 cm of depth;
depth of forest including humus layer) and average daily air temperature and precipitation at the nearby weather station (D).
freezing of about 3 and 4 weeks. At the end of January the soil temperature at the agricultural site fell below
08C to a depth of 40 cm, whereas in the forest only
the upper 20 cm of the pro®le were frozen. Numerous studies described that frost penetration is inversely linked to the amount of organic litter and therefore, in¯uenced by the vegetation type (Edwards and Cres-ser, 1992). Delayed soil freezing and deeper frost pen-etration may have reduced the winter emissions from the fallow and forest site compared to the agricultural site.
Acknowledgements
The authors wish to acknowledge the ®nancial sup-port of the Deutsche Bundesstiftung Umwelt.
References
Bouwman, A.F., 1994. Direct emissions of nitrous oxide from agri-culture soil. Report No. 773994004 National Institute of Public Health and Environmental Protection, Bilthoven, Netherlands. Brumme, R., Borken, W., Finke, S., 1999. Hierarchical control on
nitrous oxide emissions in forest ecosystems. Global Biogeochemical Cycles 13, 1137±1148.
Crutzen, P.J., 1981. Atmospheric chemical processes of the oxides of nitrogen, including N2O. In: Delwiche, C.C. (Ed.),
Denitri®cation, Nitri®cation, and Atmospheric Nitrous Oxide. Wiley, New York, pp. 17±44.
Edwards, A.C., Cresser, M.S., 1992. Freezing and its eect on chemi-cal and biologichemi-cal properties of soil. In: Steward, B.A. (Ed.), Advances in Soil Science, vol. 18. Springer-Verlag, New York, pp. 59±79.
Flessa, H., Dorsch, P., Beese, F., 1995. Seasonal variation of N2O
and CH4 ¯uxes in dierently managed arable soils in southern
Germany. Journal of Geophysical Research 100, 115±124. Groman, P.M., Tiedje, J.M., 1991. Relationships between
denitri®-cation, CO2production and air-®lled porosity in soils of dierent
texture and drainage. Soil Biology and Biochemistry 23, 299±302. Groman, P.M., Hardy, J.P., Nolan, S., Fitzhugh, R.D., Driscoll,
C.T., Fahey, T.J., 2000. Snow depth, soil frost and nutrient loss in a Northern Hardwood Forest. Hydrogical Processes, (in press). IPCC, 1994. Radiative forcing of climate change. The 1994 report of the scienti®c assessment working group of IPCC. Summary for Policy-makers. WMO/UNEP, Geneva, Switzerland.
Kaiser, E.-A., Heinemeyer, O., 1996. Temporal changes in N2
O-losses from two arable soils. Plant and Soil 181, 57±63.
Kaiser, E.-A., Kohres, K., KuÈcke, M., Schnug, E., Heinemeyer, O., Munch, J.C., 1998. Nitrous oxide release from arable soil: im-portance of N-fertilisation, crops and temporal variation. Soil Biology and Biochemistry 30, 1553±1563.
Loft®eld, 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.
Matthias, A.D., Blackmer, A.M., Bremner, J.M., 1980. A simple chamber technique for ®eld measurement of emissions of nitrous oxide from soils. Journal of Environmental Quality 9, 244±251. Papen, H., Butterbach-Bahl, K., 1999. A 3 year continuous record of
N-trace gas ¯uxes from untreated and limed soil of a N-saturated spruce and beech forest in Germany: I. N2O emissions. Journal
of Geophysical Research 104, 18487±18503.
RoÈver, M., Heinemeyer, O., Kaiser, E.-A., 1998. Microbial induced nitrous oxide emissions from an arable soil during winter. Soil Biology and Biochemistry 30, 1859±1865.
Teepe, R., Brumme, R., Beese, F., 2000. Nitrous oxide emissions from soil during freezing and thawing periods. Soil Biology and Biochemistry (accepted).
Wagner-Riddle, C., Thurtell, G.W., Kidd, G.K., Beauchamp, E.G., Sweetman, R., 1997. Estimates of nitrous oxide emissions from agriculture ®elds over 28 months. Canadian Journal of Soil Science 77, 135±144.
R. Teepe et al. / Soil Biology & Biochemistry 32 (2000) 1807±1810
