E. Hartung and G.-J. Monteny
E 62
Methane (CH4) and Nitrous Oxide (N2O) Emissions
from Animal Husbandry
1
2
Eberhard Hartung and Gert-Jan Monteny
Universität Hohenheim, Institut für Agrartechnik, Stuttgart
2
Institute of Agricultural and Environmental Engineering (IMAG), Wageningen
1
The greenhouse gases methane (CH4) and nitrous oxide (N2O) contribute
to global warming. N2O also affects the ozone layer. The most important
sources of greenhouse gas emissions in agricultural animal husbandry
are the animals, animal houses (indoor storage of animal excreta), the
outside storage of manure and slurry and their treatment (e.g. composting), as well as the spreading of manure and chemical fertilizers. The
source of methane emissions from animal husbandry is largely endogenous. Nitrous oxide, however, is mainly produced and emitted during the
storage and treatment of animal excreta, as well as after spreading.
Although in many countries emphasis is already being placed on the reduction of environmental pollution caused by nutrients, ammonia emission and odour nuisance, the reduction of the emission of greenhouse
gases will become equally important in the near future to meet integrated sustainability criteria (Kyoto agreement). While ammonia- and
odour emissions affect farmers directly, it is currently not absolutely necessary to reduce greenhouse gas emissions because no laws governing this
field have been enacted yet. As compared with ammonia emission, only a
few data regarding the emission of CH4 and N2O from animal husbandry
are available in the literature. In addition, these values can be used only to
a very limited extent. The literature summarized below shows that reliable
data regarding CH4 emissions are more or less available only for animal
housing systems. There are virtually no data for N2O, mainly because the
measurement of N2O concentrations sometimes causes considerable difficulties (detection limits of continuously working measuring instruments,
e.g. IR spectrometer).
There is a large variation in the emissions rates stated in the literature,
which must mainly be attributed to the large number of parameters (e.g.
temperature, substrate) that determine the emission of greenhouse gases.
For this reason, some normative values, e.g. those used in national and
international emission budget calculation, may have to be revised frequently based on the outcome of experimental research. As knowledge
about source-specific emission rates grows, there is an increasing need
for a more detailed description of the emission factors used in national
emission budget calculations and of the parameters which influence
them.
Keywords
Methane, nitrous oxide, emission rates, daire cow keeping, pig keeping, poultry keeping
Introduction
Are farmers interested in greenhouse gas
emissions from their livestock operations?
The answer is definitely ”No”. Farmers
face other problems which are much more
urgent for them, such as product prices
(economy of animal production), as well
as legal requirements regarding nutrient
management (Fertilizer Decree) and the
reduction of odour and ammonia
emissions. However, the conditions are
changing: the reduction of the emission
and input of greenhouse gases such as
CH4, N2O, and CO2, as well as the
mitigation of their negative effects are
gaining in importance in national and
international politics and are waiting for
legislative implementation.
Because of the importance of the nitrogen
(N) and carbon (C) cycle in biological
systems, the emission of gaseous reaction
products such as methane (CH4) and
nitrous oxide (N2O) during these
biochemical processes is unavoidable.
However,
human
activities
like
agriculture have led to a higher C- and Ninput and thus to an increase in the
emission of methane and N2O and,
ultimately, to the intensification of global
warming. The global warming potential
(GWP) of CH4 and N2O is estimated to be
20 times (methane)(IPCC, 1992 [1]) or
even 300 times (N2O) (Olivier et al., 1998
[2]) the GWP of carbon dioxide (CO2) (in
relation to the mass and a time horizon of
100 years). Furthermore, N2O emissions
contribute to the depletion of ozone in the
stratosphere, which is caused by the
stratospheric conversion of N2O to NO
(Olivier et al., 1998 [2])
According to current estimates, the global
emission of CH4 and N2O amounts to 535
(Houghton et al., 1996 [3]) and 17.7 MT
(Kroeze et al., 1999 [4]; 1 MT = Tg = 1012
g) respectively. Subak et al (1993) [5] estimated that 103 MT of the man-induced
CH4 emissions originate from livestock
production. The emission of N2O from
anthropogenic sources amounts to ca. 8.0
MT per year. Of these, ca. 6.2 MT are attributed to livestock production (Kroeze
et al., 1999 [4]). Olivier et al. (1998) [2]
emphasize that fertilizer consumption and
animal excreta are equally important as
the largest contributors to agricultural
N2O emissions. Many authors mention
that the greatest uncertainties in the
greenhouse gas emission data (e.g. IPCC,
1992 [1] Subak et al, 1993 [5]; Houghton
et al., 1995 [3]) are mainly caused by insufficient knowledge about the sourcespecific emission factors.
This paper describes the processes which
cause, and the factors which influence, the
levels of CH4 and N2O emissions from
animal housing systems and facilities for
the storage of animal excreta. Because of
Agrartechnische Forschung 6 (2000) Heft 4, S. E 62-E 69
the significant difference between ”data”
and ”reliable data”, the criteria for
scientific investigations and the collection
of emission data will be discussed first,
followed by the results of a literature
survey on the emission levels of nitrous
oxide and methane from different animal
species and husbandry systems, as well as
from the storage of animal excreta. The
emission levels listed below are mainly
the result of German and Dutch
investigations. Since the marginal
parameters indicated in the literature were
not always sufficient for the use of one
common unit for all emission factors (e.g.
kg emission per livestock unit (LU) and
day), different reference quantities are
employed to describe some of these
factors.
Processes and Influencing Factors
The nitrogen (N) and carbon (C) cycle are
closely related in plant production because both play a decisive role in carbohydrate production through photosynthesis. The greenhouse gases methane (CH4)
and nitrous oxide (N2O) are both produced in the C and the N cycle. Methane
is mainly a primary reaction product of
the anaerobic bacterial fermentation of
easily degradable organic compounds
(carbohydrates) present in feed but also in
already digested food (excreta). Nitrous
oxide, however, is generally not produced
from any basic N component of feed or
digested food (excreta), but it is formed
during nitrification (an oxygen consuming
process) and denitrification. It is therefore
considered to be a secondary reaction
product of the primary N compounds.
Methane
Methane production is a result of the anaerobic degradation chain of organic substance. The organic polymers (cellulose,
starch, protein, fats, etc.) are mainly degraded to CO2, H2, and short chain carboxylic acids by a complex community of
anaerobic microbes. This degradation
process comprises the three steps of hydrolysis, fermentation, and acetogenesis.
In the final step of methanogenesis, the
above-mentioned degradation products
are converted into methane with its specific characteristic of water insolubility
(Wellinger et al., 1991 [6], Hüther, 1997
[7]). Important prerequisites for methane
formation are the absence of oxygen, absolute darkness, and a redox potential of
less than -300 mV. The quantity and the
degradability of the organic substance, the
temperature, the pH value, the C/Nrelation, and the water content of the substrate exert an important influence on
methane formation (Amon et al., 1998
[8], Hüther, 1999 [9]). Methane production can be impaired by inhibitors (such
as ammonia) or by substances which have
a toxic effect on the methane bacteria
(such as hydrogen sulphide).
In agricultural animal production, there
are two main methane sources: digestion
in the first stomach of the ruminants and
excrement. Under quantitative aspects, the
most important source is fermentation in
the rumen, during which the unavoidable
formation of methane acts as a hydrogen
absorber, which is necessary for the fermentation process (Finger, 1999 [10]).
The methane thus produced in the rumen
is discharged during eructation through
the oesophagus (Menke and Huss, 1987
[11]). In contrast, pigs (monogastric animals) release methane mainly through
flatulence. The amount of methane produced by the animals is generally dependent upon the species and the size of the
animals, the feed intake, and the digestibility of the food (food composition)
(Wilkerson et al., 1994 [12]). Extensive
empirical studies on this topic are available in the literature, which will not be
discussed in more detail here. As a result,
they express the influencing factors in estimating functions (cf. table 2) and hence
enable the methane production at the animal level to be calculated or estimated (cf.
chapter 3.2.1).
Methane production from animal excrement stored inside or outside exhibits
similarities with the formation processes
of methane in the animal (Zeeman, 1991
[13]) even though there are also differences. The most important similarity is
that the same bacteria are responsible for
methane production. Differences exist
with regard to the temperature (inside
room temperature in contrast to fermenter
temperature and the body temperature of
the animals), the homogeneity of the substrate (storage: inhomogeneous mixture;
rumen and fermenter: homogeneous
mixture), the kind of availability, and the
degradation degree of the carbohydrates.
The most important factors which directly
influence the intensity of methanogenesis
are the quantity and the degradability of
the organic substance and the temperature. The pH optimum ranges from between 6.7 and 7.4 (Hüther, 1999 [9]).
Nitrous oxide
In contrast to CH4, N2O is not directly
produced from compounds that are primarily present in feed or slurry/manure,
but it is a secondary reaction product.
Details of the processes and process conditions of N2O production are in general
poorly understood (Ambus, 1998 [14];
Firestone and Davidson, 1989 [15]) and
E 63
are probably significantly more complex
than those that govern CH4 production.
Before
N2O
is
emitted
from
slurry/manure, urea must be ammonified
first, i.e. broken down (either directly in
urine from animals or indirectly, through
the conversion of uric acid to urea, in excreta from birds). The ammonification
process is well understood and described
for urine (Monteny and Erisman, 1998
[16]) and uric acid (Groot Koerkamp and
Elzing, 1996 [17]) excreted by cattle/pigs
and poultry, respectively. The ammonium
that is produced is transformed by nitrifying bacteria if the supply of oxygen is
sufficient (nitrification; Equation 1).
Nitrosomonasspp .
Nitrobacterspp
NH 4+ 

→ NO2− 
→ NO3−
[1]
Under optimal conditions, nitrification
does not lead to the formation of nitrous
oxide as an intermediate product. Only if
little oxygen is available is it produced as
a consequence of the reduction of oxidized nitrogen compounds (NH2OH, NO2;
Sibbesen et al, 1993 [18]). Furthermore,
high NH3 concentrations and low C-to-N
ratios affect the bio-chemical transformation of ammonium to nitrite/nitrate and
thus promote the production of N2O.
The denitrification process (Equation 2)
takes place in treated slurry (e.g. nitrification of ammonium by oxidation/aeration
or in soils where nitrate from chemical
fertilizers is potentially transformed to
nitrogen gas with N2O as one of the intermediate products):
NO3− → NO 2− → NO → N 2 O → N 2
[2]
As regards N2O production in soils, and
presumably also in other on-farm subsystems, critical factors for denitrification
are the presence (or rather: lack) of denitrifiers, which represent a large spectrum
of heterotrophic bacteria, oxygen, nitrite
and nitrate, and easily oxidizable organic
matter (C-source for bacteria; Firestone
and Davidson, 1989 [15]). Groenestein
and Van Faassen (1996) [19] studied the
N2O production in pig housing systems
where a mixture of excreta and litter, the
so-called deep litter system, was treated
with additives in order to immobilize
ammonium through the growth of bacteria. They reported on very high potential
for N2O production, which is mainly
caused by poor O2 availability in the
compacted deep litter.
E. Hartung and G.-J. Monteny
E 64
Greenhouse Gas Emissions from
Animal Husbandry
Greenhouse gases are produced at any
stage of the nutrient cycle on farms, although the number of the CH4 and N2O
sources and their magnitude vary significantly, as described above. The chemical
and physical properties of the gases involved (e.g. low water solubility) promote
easy volatilization into the ambient air
immediately after formation. Therefore,
no accumulation in liquids (e.g. in the digestive system or slurry/manure) must be
expected. This is a decisive difference as
compared with other gaseous pollutants
like ammonia, whose water solubility is
relatively high depending on the temperature and the pH value and which can
hence be reduced before volatilization
(Monteny and Erisman, 1998 [16]). The
following chapter first provides an overview of the requirements governing
measurement methods and instruments for
the quantification of greenhouse gases
and gaseous pollutants from agriculture
and the determination of emission factors.
Afterwards, the results of a literature survey on CH4 and N2O emissions from
animal husbandry are presented.
Requirements for Measurement Methods and Instruments for the Quantification of Emission Levels
The emission of gases and odour from
livestock facilities exhibits a wide range of
diurnal and seasonal variation (Keck, 1997
[20], Hartung et al., 1998 [21]). Minimum
requirements for the measurement of
emissions were formulated by Hartung
(1995) [22] and Jungbluth and Büscher
(1996) [23]:
Continuous measurement of ventilation
rates and gas concentrations,
- Long-term
experiments
for
the
description of diurnal and seasonal
effects.
-
Amon et al. (1998) [8] call for continuous
measurements with highly precise
instruments which must be repeated in
different seasons. Only measurements
carried out continuously over several
seasons provide reliable data for the
calculation of the emissions caused by
different housing systems or production
processes (table 1). Setting such high
requirements also means that about 80 %
of the publications do not provide a
suitable basis for the calculation of
emission levels.
Very expensive measuring instruments,
which often cannot be purchased two- or
threefold, are one essential prerequisite
for the postulated requirements to be met.
This leads to the dilemma that, under
practical conditions, measurements with
highly accurate instruments can usually
be taken only at a few selected locations.
Therefore, the number of measurements
from the same farm or production system
is often very low.
Literature Survey on Greenhouse Gas
Emissions
With regard to the literature data concerning CH4 emissions from livestock, a
distinction can be made between measurements at the animal level (respiration
chambers) and measurements at the system level (animal houses, storage). Data
at the animal level are generally gained in
respiration chamber experiments, whereas
system level data are mainly collected
during emission measurements in animal
facilities.
Animal level
As regards greenhouse gas emissions
from animals (i.e. their digestive system),
only a few data are available, which are
usually limited to CH4. Kroeze (1998)
[24] reports that the percentage of N2O
released by the animals is still unknown
and can probably be neglected, at least at
the national level. Data on CH4 emissions
from cattle are summarized in table 2.
These data are mainly the result of fee-
ding trials in respiratory chambers. The
CH4 emitted originates from breath and
flatus.
The data in Table 2 show that cattle produce substantial amounts of CH4, which
vary depending on the lactation stage and
the age. The variation in the formation of
CH4 reported by the authors is most likely
caused by differences in diet or the (climatic) conditions during the trials (under
laboratory- and practice conditions). The
quantity of CH4 emitted ranges between
5.2 and 6.5% of the Gross Energy (GE)
intake (Table 2; and Pelchen et al., 1998
[29]). Corre and Oenema (1998) [30],
however, reported that the amount of CH4
produced by cattle roughly equals 10% of
the digestible feed intake.
In monogastric animals, like pigs and
poultry, microbial fermentation only occurs in the large intestine, with an estimated CH4 production of less than 1% of
the digestible feed intake (Corre and Oenema, 1998 [30] or approximately 0.6%
of the gross energy intake (Crutzen et al.,
1986 [26])).
Houses
Cattle
Table 3 summarizes the measured CH4
emissions from housing systems for cattle. The CH4 emissions originate from
both the animals and the excrement stored
indoors.
Table 1: Requirements governing the methods and the equipment for the quantification of greenhouse gases and gaseous pollutants from agriculture (Amon et al., 1998 [19])
Requirements
Reasons
•
Simultaneous measurement of NH3, CH4 •
and N2O
•
Registration of the entire production chain
•
Emission measurements in practice
•
Sampling area as large as possible
•
Continuous, highly accurate measurement
of NH3, CH4, and N2O
•
Simultaneous measurement
concentration and air flow rate
of
gas
Improvement of the overall environmental
compatibility of agricultural production
processes
•
Data close to reality
•
Emitting substrates are inhomogeneous
•
Diurnal and seasonal variation of emission
rates
•
Calculation of the emission rate (quantity
of gases emitted)
Table 2: CH4 emissions (g LU-1 d-1) from dairy cows and heifers (animal level)
Animal species
Dairy cow,
lactating
Emission
260-290
260
257
268
Dairy cow,
dry period
Heifer (6-24
months)
130-160
Notes
Author
24 h respiration trials with two ani- Brose et al., 1999 [25]
mals each
methane yield = 5.5 % of BE
Crutzen et al., 1986 [26]
153 respiration trials,
Kirchgessner et al., 1991
[27]
M = ∅ 17 kg/d, W = ∅ 583 kg
Holter and Young, 1992
methane yield = 5.2 % of BE;
[28]
LM = ∅ 559 kg
139
24 h respiration trials with two ani- Brose et al., 1999 [25]
mals each
methane yield = 5.5 % of BE;
Holter and Young, 1992
[28]
LM = ∅ 633 kg
140
methane yield = 6.5 % of BE
Crutzen et al., 1986 [26]
BE: gross energy intake [MJ], GV: livestock unit = 500 kg, M: dairy performance [kg/d], LM: animal weight [kg]
Agrartechnische Forschung 6 (2000) Heft 4, S. E 62-E 69
The data in Table 3 illustrate that CH4
emissions from cattle houses range from
between 120 and 390 g LU-1 d-1, with
somewhat greater values for dairy cows in
loose housing systems (cubicle houses).
This range of data is comparable with the
range of CH4 emissions used as normative
values for dairy cattle in the Netherlands
(63 – 102 kg year-1 per animal, corresponding to 173 – 279 g d-1 per animal)
(Van Amstel et al., 1993 [37]). The highest CH4 emissions occur during feeding
and rumination (Brose et al., 1999 [25]).
The emission levels are mainly influenced
by the animal weight, the diet, and the
milk yield. Furthermore, details of the
housing system design (e.g. air conduction, type of flooring, type and dimensions of manure removal and storage of
excrement) play a role. The large number
of influencing factors shows that realistic
normative values for the calculation of
CH4 emissions (e.g. in national studies or
emission inventories) should be differentiated with regard to housing systems, besides the already stated need for differentiation according to the age of the animals, the type of feed, the diet, the feeding level and the lactation stage.
A comparison of the data listed in Table 2
(animal level) and Table 3 (system level)
shows that CH4 emitted from the respiratory system of the cows accounts for the
largest part of the CH4 emissions from
cow houses. This is confirmed by data reported by Kinsman et al. (1995) [31], who
attributes less than 10% (21 g d-1 LU-1) of
the total CH4 emission from a tying stall
for dairy cows to the manure stored indoors. However, it is very difficult to
measure the percentage of the CH4 emission caused by manure and animals.
Data about the specific CH4 production
from animal excreta (1.3 kg CH4 per
tonne of cattle excreta; Van Amstel et al.,
1993 [36]) and data about the volumes of
slurry produced in cow houses (16 tonnes
of excreta per year; Van Eerdt, 1998 [37])
lead to the assumption that the CH4 production from manure stored in dairy cow
houses would amount to approximately
21 kg year-1 per animal (57 g d-1 per animal if the animals spend 365 days per
year indoors). This is about 20% of the
CH4 produced during the entire fermentation process and substantially more than
the figure reported by Kinsman et al.
(1995) [31]. This discrepancy clearly
shows that there is a need for additional,
more specific data for methane emission
from cattle stalls.
As regards N2O emissions from cattle
housing systems, only very few data are
available, mainly because the accurate
measurement of ventilation rates in naturally ventilated houses is difficult, time
consuming, and requires extensive
equipment and because the N2O concentrations are very low (detection limit and
accuracy of the gas sensors). These data
are summarized in table 4: Amon et al.
(1998) [8] reported no difference in N2O
emission between tethered housing with
solid and liquid manure. At higher temperatures, an increase in N2O emissions
from deep litter systems was recorded.
Only deep litter systems with straw seem
to produce significant quantities of N2O,
which is most likely caused by nitrification and denitrification in the litter bed
(equation 1 and 2). Slurry systems, however, produce no or only little N2O because slurry generally contains neither
nitrate nor nitrite which could be degraded through denitrification in anaerobic areas (Hüther, 1999 [9]). Sneath et al.
(1997) [33] also reported very low N2O
emissions at the detection threshold of the
measuring instrument.
Pigs
Numerous studies have been conducted
on greenhouse gas emissions from pig
housing systems (table 5).
Similar to deep litter stalls for cattle, significant N2O emissions from pig husbandry exclusively originate from deep
E 65
litter- or compost systems. Methane,
however, is emitted by all pig housing
systems. Excrement temporarily stored
indoors is the main source of methane
emissions. The quantity of methane emitted by the animal itself should not be neglected because it may amount to up to 8 l
of CH4 per pig and per day (Ahlgrimm
and Bredford, 1998 [41]). The amount of
methane emitted from stalls for fattening
pigs is influenced by the diet (digestibility), the daily weight increase of the animals, the temperature, and the kind of
housing system (Ahlgrimm and Bredford,
1998 [41], Hüther, 1999 [9]). The data in
Table 5 show great variation. With regard
to CH4, this is mainly caused by the different animal species and housing systems. Methane emissions from fattening
pigs range between 1.5 and 11.1 kg per
animal place per year, whereas emissions
of 21.1 and 3.9 kg per animal place per
year were reported for sows and weaners,
respectively. Hahne et al. (1999) [38]
found higher CH4 emissions in autumn
and winter when the air exchange rates
are lower. They suggested that the CH4
production might be influenced by the
availability of oxygen over the emitting
surfaces.
Table 3: CH4 emission (g LU-1 d-1) from cattle housing systems (system level)
Housing system
Dairy cows in tying stall
Emission
Notes
Author
327
120
emission from animals only
four 24 h measurements each in
the summer and the winter, emission from animals and excrement,
volume flow measurement through
CO2 balance
for slurry and manure system
Kinsman et al., 1995 [31]
Groot Koerkamp und
Uenk, 1997 [32]
194
Dairy cows in
loose housing
320
265
200-250
267-390
Amon et al., 1998 [8]
emission from animals and excre- Sneath et al., 1997 [33]
ment, average of 12 days in April,
volume flow measurement with tracer gas
see above
Groot Koerkamp und
Uenk, 1997 [32]
emission from animals and excreJungbluth et al., 1999 [33]
ment, measurement over the course of one year, volume flow measurement with measuring fans
emission from animals and excreSeipelt et al., 1999 [35]
ment, volume flow measurement
with tracer gas, random measurements
Fattening bulls
on slats
147
s.o.
Groot Koerkamp und
Uenk, 1997 [32]
Beef cattle on
slats
121
s.o.
Groot Koerkamp und
Uenk, 1997 [32]
Table 4: N2O emission (g LU-1 d-1) from cattle housing systems
Housing system
Notes
Author
tying stall
0.62
Yearly average; seasonal influence
Amon et al., 1998 [8]
deep litter (straw)
2.01
summer data
Amon et al., 1998 [8]
loose housing
system
1.6
0.8
Average of 18 measurements
Jungbluth et al., 1999 [34]
Sneath et al., 1997 [33]
E 66
The variation in the N2O emissions is
mainly caused by the kind of housing
system (no data available for sows and
weaners). Fattening pigs kept on partly or
fully slatted floors (slurry-systems) emit
very little N2O (0.02 - 0.31 kg per animal
place per year), whereas higher emissions
(1.09 - 3.73 kg per animal place per year)
were reported for fatteners in deep litter
and compost systems (Groenestein and
Van Faassen, 1996 [19]). At present, no
reliable data are available for sows and
rearing pigs.
E. Hartung and G.-J. Monteny
Table 5: CH4 and N2O emissions (kg per animal place per year) from pig housing systems
Animal species/
housing system
Fattening pigs on fully
slatted floors
Fattening pigs on partly
slatted floors
Outdoor Storage of Animal Excrement
Greenhouse gas emissions from outdoor
manure and slurry storage show analogies
to those from indoor storage. This means
that manure alone must be expected to
emit both CH4 and N2O, while slurry only
causes CH4 emissions.
In order to quantify the gas emissions
from storage containers and the factors
that influence them, most authors use
closed laboratory-size storage containers
(with a volume of 0,05 to 1,5 m³) or opendynamic chambers of different size,
which are placed on the emitting surface
such that they partly or entirely cover it.
This is one reason why only very few
meaningful data for CH4 emissions
caused by outdoor slurry storage are
available. Williams and Nigro (1997) [50]
(table 7) report on methane emissions of
24 – 47 g per m3 of cattle slurry per day
(semicommercial size). These figures
N2O
2.8 – 4.5
0.15
-
0.02 - 0.04
0.15
4.2
0.02
11.1
Fattening pigs on fully or
partly slatted floor without
straw
Poultry
The CH4 and N2O emissions from housing
systems for laying hens (table 6) vary
greatly and must be judged very critically
because the measured concentrations were
very low (sometimes only slightly above
the ambient concentration of N2O). In
general, floor husbandry systems for laying hens seem to emit more N2O than
battery cages or aviary systems, which is
mainly caused by the presence of material
(e.g. wood shavings, straw, litter) on the
floor. Reliable CH4 and N2O emission
data for other kinds of poultry such as
broilers, turkeys, ducks etc. and for
housing systems with natural ventilation
(e.g. Louisiana stalls) are not yet available.
Gas emission values for poultry are low
when compared with emissions from cattle and pigs, which is mainly caused by
the considerably lower body weight of the
hens. If the body weight of one laying hen
is assumed to be 2.5 kg, one LU would
correspond to approximately 200 hens,
and the N2O emission established by
Sneath et al. (1996) [48] would amount to
ca. 0.042 kg per animal place and per
year.
CH4
Fattening pigs on deep
litter/compost
Fattening pigs on straw
Fattening pigs on a straw
flow system
Author
Hahne et al., 1999 [38]
Kaiser, 1999 [39]
Stein, 1999 [40]
Sneath et al., 1997 [33]
Groot Koerkamp and Uenk,
1997 [32]
1.5 - 3
-
-
0.15
0.31
-
1.9 – 2.4
-
2.48 - 3.73
-
0.59 – 3.44
1.55 – 3.07
1.43 – 1.89
1.09
-
0.05
0.9 – 1.1
-
Ahlgrimm and Bredford, 1998
[41]
Hoy et al., 1997 [42]
Thelosen et al., 1993 [43]
Döhler, 1993 [44]
Groenestein and Van Faassen, 1996 [19]
Hoy, 1997 [45]
Kaiser, 1999 [39]
Stein, 1999 [40]
Thelosen et al., 1993 [43]
Kaiser, 1999 [39]
Ahlgrimm and Bredford, 1998
[41]
Hesse, 1994 [46]
-
1.6 – 2.4
Sows
21.1
-
Groot Koerkamp and Uenk,
1997 [32]
Weaners
3.9
-
Groot Koerkamp and Uenk,
1997 [32]
Table 6: CH4 and N2O emissions (kg per animal place per year) from poultry facilities
Animal species/
housing system
CH4
N2O
Laying hens, floor system
with straw
0.076
0.017
Mennicken, 1998 [47]
Laying hens, floor system
with wood shavings
0.254 – 0.383
0.043 – 0.079
Mennicken, 1998 [47]
Laying hens, floor system
with ¾ straw and ¼ wood
shavings
0.34
0.155
Mennicken, 1998 [47]
Laying hens in battery cages /
aviary systems
-
0.95 g h-1 LU-1
Sneath et al., 1996 [48]
Laying hens in battery cages /
aviary systems
not detectable
0.02 – 0.15
g h-1 LU-1
Neser et al., 1997 [49]
Laying hens in battery cages
0.06
-
Laying hens on a floor system
not detectable
0.05 – 0.35
g h-1 LU-1
Laying hens in a free range
system
0.06
-
Groot Koerkamp and Uenk,
1997 [32]
Broilers on litter
0.02
-
Groot Koerkamp and Uenk,
1997 [32]
roughly tally with the results of measurements by Sommer et al. (1999) [51].
During both measurements, no nitrous
oxide emissions were detected. This
mainly seems to be caused by the lack of
substrates (e.g. nitrate, degradable carbon)
and oxygen under storage conditions. Trials by Hüther (1999) [9] with cattle slurry
showed that methane emissions from
containers with artificial floating layers
increased during the first days and then
Author
Groot Koerkamp and Uenk,
1997 [32]
Neser et al., 1997 [49]
dropped back to a low level. Over the
course of the last trial month (entire trial
period: 120 days), CH4 release increased
again. In contrast, methane emissions
from containers without artificial covering
remained at relatively the same level.
Manure from pig husbandry emits N2O
because of the nitrification and denitrification of nitrogen compounds. Sibbesen
and Lind (1993) [18] reported 0.3 g of
N2O per day per m2 of farm yard manure
Agrartechnische Forschung 6 (2000) Heft 4, S. E 62-E 69
stored under summer conditions, whereas
Sommer et al. (1999) [51] found N2O
emission rates of 0.73 g per day per m3 of
cattle slurry during summer storage. Both
values indicate that N2O emissions from
storage cannot be neglected and need
further attention.
To reduce NH3 emission from liquid manure containers, storage facilities should
be covered if possible and/or feature a
sufficiently stable floating layer. However, as Ross et al. (1999) [52] and Hüther
(1999) [9] report, measurements have
shown that the volatilization of CH4 and
N2O from laboratory-size slurry containers (0,5 m³) may increase dramatically if
they are covered with different materials
(table 8).
These findings at a laboratory scale indicate that any kind of straw covering provides suboptimal conditions for both nitrification and denitrification and therefore
increases the production of CH4 and N2O
(Ross et al, 1999 [52]; Hüther, 1999 [9]).
In contrast to results of trials conducted
under laboratory conditions, Ross et al.
(1999) [52] found that, under full-scale
conditions (farm manure pits), straw covers may also reduce CH4 and N2O emissions (table 9). However, these results
were gained under winter conditions
when CH4 and N2O emission rates are
about 50 % lower than under summer
conditions. This might indicate that the
slurry temperature is one main factor that
influences N2O emissions and that this effect compensates for that of the straw
cover. Additionally, it must be taken into
account that the summer data were gained
using laboratory storage containers (0,5
m³), which were closed for one hour during the measurements, while the winter
data were collected with the aid of measuring chambers floating on the slurry (table 9). Hüther (1999) [9] established that
the amount of the emissions is not dependent on the slurry volume, but only on
the thickness and consistency of the
floating cover. In other words: the thicker
the floating layers that developed, the
higher the N2O emissions.
Amon et al. (1999) [53] compared CH4
and N2O emissions from the solid and the
liquid manure of a tying stall for dairy
cattle (table 10) and found virtually no
difference between these two manure
systems. Aerobic manure composting allows the emission of greenhouse gases
during manure storage to be reduced efficiently. However, this requires a good
composting process with sufficient oxygen supply in the clamp, which, on the
other hand, leads to the emission of large
quantities of ammonia (Amon et al., 1999
[53]).
E 67
Table 7: CH4 emission rates during simulated uncovered storage of slurry (g CH4 per day per m3 of
slurry) at different temperatures (Williams and Nigro, 1997 [50])
4
Temperature (oC)
11
18
25
Cattle slurry
18
36
61
130
Pig slurry
6
4
46
29
Table 8: CH4 and N2O emissions (mg m-² h-1) from storage facilities for pig- and dairy cattle manure
and their reduction (in %, compared to uncovered) through various types of chopped straw covering
(laboratory scale; Ross et al., 1999 [52])
Slurry type/Type of covering
Pig manure:
Without covering
20 cm of barley straw
Straw mixed with slurry
Long straw
Triticale
Cattle manure:
Without covering
With covering
CH4
N2O
196
+ 55
+6
+ 82
+ 62
0.67
+ 42
+ 878
+ 1258
+ 199
64
+ 113
0.78
+87
Table 9: CH4 and N2O emission (mg m-2 h-1) from pig manure in the summer (laboratory scale) and
the winter (full scale; Ross et al., 1999 [52])
Type of manure covering
CH4
N2O
Summer (laboratory scale)
Without covering
With covering
Difference (%)
196
304
+ 55
0.67
0.95
+ 42
Winter (full scale)
Without covering
With covering
Difference (%)
104
17
- 87
0.35
0.30
- 12
Table 10: CH4 and N2O emission (mg LU-1 h-1) from solid and liquid dairy cattle manure (Amon et
al., 1999 [53])
Type of manure covering
CH4
N2O
solid manure (farm yard manure)
8100
25.8
liquid manure (slurry)
8100
25.4
Concluding Remarks
The formation and emission of CH4 and
N2O from sources in animal husbandry
are a very complex phenomenon. Both
gases are produced during the biological
degradation of nutrients in animal excreta
and, to some extent, their formation is influenced by the same parameters (e.g.
temperature, substrate availability). Besides these similarities, there are also significant differences, mainly with regard to
the conditions under which the gases are
produced. Methane is mainly a primary
product of anaerobic processes, whereas
N2O as a secondary reaction product is
formed in process chains where nitrification and/or denitrification occur.
Only very few precise emission rates of
methane and nitrous oxide from different
animal husbandry systems are available.
Some of the data presented in this paper
show considerable variation, which must
mainly be attributed to the large number
of factors that influence the amount of
methane and nitrous oxide emissions.
Without repeating all the results in detail,
it is possible to say that:
- the measuring method and -equipment
must meet certain minimum requirements with regard to accuracy, measuring periods, and the repetition of measurements,
- CH4 emissions from cattle husbandry
are relatively well known, while for
other animal species and production
systems only very few data are available, which can only be used to a very
limited extent;
- N2O emissions are very difficult to
quantify. Therefore, no reliable data are
available for emission rates from virtually all animal species and production
systems.
E 68
The standard emission factors which are
currently used for national and international emission budget calculations may
have to be adapted to future insights and
newly found cause-effect relations. With
increasing knowledge about the emission
rates from different sources, the necessity
for a more detailed consideration of the
emission factors and the cause-effect relations that characterize them will gain in
importance.
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Authors
Dr. Eberhard Hartung
Universität Hohenheim
Institut für Agrartechnik
Fachgebietes für Verfahrenstechnik in der Tierproduktion und landwirtschaftliches Bauwesen
Garbenstr. 9
70599 Stuttgart
Telefon: +49/(0)711/459-2507
Telefax: +49/(0)711/459-2519
E-mail: [email protected]
Dr. Gert-Jan Monteny
Institute of Agricultural and Environmental
Engineering (IMAG)
POBox 43
6700 AA Wageningen
Niederlande
Telefon: +31/317-476300
Telefax: +31/317-425670
E-mail: G.J.Monteny.imag.dlo.nl