Greenhouse gas abatement strategies for animal husbandry
ABSTRACT Agriculture contributes significantly to the anthropogenic emissions of non-CO2 greenhouse gases methane and nitrous oxide. In this paper, a review is presented of the agriculture related sources of methane and nitrous oxide, and of the main strategies for mitigation. The rumen is the most important source of methane production, especially in cattle husbandry. Less, but still substantial, amounts of methane are produced from cattle manures. In pig and poultry husbandry, most methane originates from manures. The main sources of nitrous oxide are: nitrogen fertilisers, land applied animal manure, and urine deposited by grazing animals. Most effective mitigation strategies for methane comprise a source approach, i.e. changing animals’ diets towards greater efficiencies. Methane emissions, however, can also be effectively reduced by optimal use of the gas produced from manures, e.g. for energy production. Frequent and complete manure removal from animal housing, combined with on-farm biogas production is an example of an integrated on-farm solution. Reduced fertiliser nitrogen input, optimal fertiliser form, adding nitrification inhibitors, land drainage management, and reduced land compaction by restricted grazing are the best ways to mitigate nitrous oxide emissions from farm land, whereas, management of bedding material and solid manure reduce nitrous oxide emissions from housing and storage. Other than for methane, mitigation measures for nitrous oxide interact with other important environmental issues, like reduction of nitrate leaching and ammonia emission. Mitigation strategies for reduction of the greenhouse gases should also minimize pollution swapping.
- SourceAvailable from: Sanjay Kumar[Show abstract] [Hide abstract]
ABSTRACT: Thirty-five available feeds were fermented in vitro in order to investigate their soluble total organic carbon (TOCs) and methane (CH4) production rate. A fermentation reactor was designed to capture the CH4 gas emitted and to collect liquor from the reactor during in vitro fermentation. The results showed that CH4 production rate greatly varied among feeds with different ingredients. The lowest CH4-producing feeds were corn gluten feed, brewer's grain, and orchard grass among the energy, protein, and forage feed groups, respectively. Significant differences (p<0.05) were found in digestibility, soluble total organic carbon (TOCs), and CH4 emissions among feeds, during 48 h of in vitro fermentation. Digestibility and TOCs was not found to be related due to different fermentation pattern of each but TOCs production was directly proportional to CH4 production (y = 0.0076x, r(2) = 0.83). From this in vitro study, TOCs production could be used as an indirect index for estimation of CH4 emission from feed ingredients.Asian Australasian Journal of Animal Sciences 04/2012; 25(4):496-501. · 0.64 Impact Factor
Dataset: IJET2013 Vol10 Issue1 22-26
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ABSTRACT: A structured, pre-tested and peer-reviewed questionnaire was used for collecting data pertaining to location, stock type and density, husbandry methods, feed sources, water sources for farm use and waste disposal methods, from 19 farms situated in 4 local government areas of Ogun State, Nigeria. Of the farms 58% practiced mixed animal husbandry consisting of poultry birds, large and small ruminants, swine, rabbits and fish, while the remainder (42%) raised only chickens. The results also showed that 26% of the farms sun-dried and burned animal manure, 21% converted animal wastes into slurry that was flushed into nearby streams and rivers, 37% used the wastes as manure on farmlands or dumped them in bushes, garbage sites or open wastelands, while 16% of the farms practiced a combination of all these methods. It is concluded that animal waste management by poultry farmers in the state is inefficient, implying inadequate awareness of the potential negative impact of poor handling of animal wastes in the environment. There is a need for further studies to assess the magnitude of the risk posed to the environment, livestock and human health by poor animal waste management practices in the area.Journal of Food Agriculture and Environment 11/2011; 9(3&4):643-645. · 0.44 Impact Factor
Greenhouse gas abatement strategies for animal husbandry
Gert-Jan Montenya,*, Andre Banninkb, David Chadwickc
aWageningen University and Research Centre, Agrotechnology and Food Innovations,
Livestock Environment, P.O. Box 17, 6700 AA Wageningen, The Netherlands
bWageningen University and Research Centre, Department of Nutrition and Food,
Animal Science Group, Lelystad, The Netherlands
cInstitute of Grassland and Environmental Research, North Wyke Research Station, Okehampton, Devon, UK
Available online 26 October 2005
Agriculture contributes significantly to the anthropogenic emissions of non-CO2greenhouse gases methane and nitrous oxide. In this
paper, a review is presented of the agriculture related sources of methane and nitrous oxide, and of the main strategies for mitigation. The
rumen is the most important source of methane production, especially in cattle husbandry. Less, but still substantial, amounts of methane are
produced from cattle manures. In pig and poultry husbandry, most methane originates from manures. The main sources of nitrous oxide are:
nitrogen fertilisers, land applied animal manure, and urine deposited by grazing animals. Most effective mitigation strategies for methane
comprise a source approach, i.e. changing animals’ diets towards greater efficiencies. Methane emissions, however, can also be effectively
reduced by optimal use of the gas produced from manures, e.g. for energy production. Frequent and complete manure removal from animal
housing,combinedwithon-farmbiogasproductionisanexample ofanintegratedon-farmsolution.Reducedfertiliser nitrogeninput,optimal
to mitigate nitrous oxide emissions from farm land, whereas, management of bedding material and solid manure reduce nitrous oxide
emissions from housing and storage. Other than for methane, mitigation measures for nitrous oxide interact with other important
environmental issues, like reduction of nitrate leaching and ammonia emission. Mitigation strategies for reduction of the greenhouse gases
should also minimize pollution swapping.
# 2005 Elsevier B.V. All rights reserved.
Keywords: Agriculture; Livestock production; Environment; Mitigation; Climate change; Manure; Fertiliser; Animal husbandry
Global atmospheric concentrations of the most important
greenhouse gases carbon dioxide (CO2), methane (CH4) and
nitrous oxide (N2O) have increased significantly within the
last 150 years. Stabilisation at today’s levels and even
reduced concentrations, necessary to reduce climate change
and corresponding effects, would require significant reduc-
tions in emissions of those gases (IPCC, 2001). These
reductions are to be brought about through adoption of
mitigation measures from all sectors, e.g. industry,
agriculture, energy and households. Agriculture contributes
significantly to total greenhouse gas (GHG) emissions.
Approximately 20 and 35% of the global GHG emissions
originate from agriculture. These figures are 40 and >50%
of the anthropogenic emissions of CH4 and N2O,
respectively (IPCC, 2001). Most important agriculture
related CH4sources are animals and their excreta (manure),
whereas, most of the N2O is produced in the field (manure
excreted during grazing, chemical fertilisers), and from
animal houses where straw or litter is used (Freibauer and
Kaltschmitt, 2001). The Kyoto protocol specifies that each
complying country should provide adequate methods and
instruments to quantify, monitor and verify GHG emissions
and their reductions. In this paper, we present a summarised
overview of the range of approaches for reducing emissions
of CH4and N2O from the various sources in the agricultural
Agriculture, Ecosystems and Environment 112 (2006) 163–170
* Corresponding author.
E-mail address: email@example.com (G.-J. Monteny).
0167-8809/$ – see front matter # 2005 Elsevier B.V. All rights reserved.
sector, particularly from livestock systems, with a focus on
European farming practices.
2. Sources and processes
Methane and N2O originate from different cycles.
Methane is usually produced following the degradation of
whereas, N2O is related to the nitrogen (N) cycle with
chemical fertilisers and manures as the most important
The rumen is the most important site of CH4production
in ruminants (breath), whereas, in monogastric animals, like
pigs, CH4is mainly produced in the large intestine (flatus).
Animal manures, stored indoors in sub-floor pits or
outdoors, are also relevant CH4sources, since conditions
usually favor methanogenesis in both slurry and solid
manure heaps (Husted, 1994). Monteny et al. (2001) found
the following data for CH4 produced from enteric
fermentation and from manure, respectively, for various
animal species (Table 1).
Enteric fermentation is the most important source
(approximately 80%) of CH4in dairy husbandry, whereas,
most (70%) of the CH4on pig and poultry farms originates
from manures. The wide range in the total CH4emission
from dairy cows is caused by differences in diets and
housing systems (lower values for tying stalls; greater
emissions from cubicle houses; Groot Koerkamp and Uenk,
2.1.1. Enteric fermentation
The rate of CH4produced from enteric fermentation in
dairy cows depends greatly on the level of feed intake, the
quantity of energy consumed (see IPCC, 1997), and feed
composition. The three most important factors are: (1) rate
of organic matter (OM) fermentation; (2) type of volatile
fatty acids (VFA) produced, which strongly determines the
excess of hydrogen [H] produced in the gastrointestinal tract
and the need for CH4 production as a sink of excess
hydrogen, and (3) efficiency of microbial biosynthesis.
220.127.116.11. Factor1. Therate of OM fermentation is strongly
influenced by level of feed intake and the degradation
characteristics of the carbohydrate fraction. For example,
Mills et al. (2001) demonstrated, in a theoretical study,
that CH4production was reduced from 6.6 to 6.0% of the
gross energy (GE) consumption by dairy cows when the
dry matter intake of a 1:1-ratio of grass silage and
concentrate diet was increased from 10 to 24 kg per day.
Although CH4production increases almost linearly with a
higher feed intake, the fraction of consumed GE lost as
CH4reduces. This effect is partly a consequence of a
reduction in lower rumen digestibility with increased feed
intake (factor 1), and partly a consequence of shifts in the
rumen fermentation pattern and the type of VFA produced
18.104.22.168. Factor 2. Bannink et al. (2000), recently updated
coefficients for the production of VFA from different types
of substrate fermented in the rumen of specifically lactating
cows. With these new coefficients, Mills et al. (2001)
demonstrated that replacing sugars by starch in concentrate
reduced the total CH4production by 14.7%. Also, the rate of
fermentation of OM in the rumen (see Section 22.214.171.124) is
known to affect the type of VFA produced. When the
production rates rise and rumen pH drops, a shift occurs
towards more production of propionate, mainly because of
shifts in the abundance of species of micro-organisms
present in the gastrointestinal tract. As an alternative to the
production of CH4, also propionate acts as a sink of [H] and
consequently less CH4will be produced per unit of OM
fermented (Pitt et al., 1996; Baldwin, 1995). Since high-
yielding cows have a higher intake of dry matter (which is to
be expected to result in low rumen pH), the effect of
expected to be even larger.
126.96.36.199. Factor 3. Current feed evaluation systems assume
a rather constant figure for the efficiency of microbial
synthesis (e.g. 150 g of protein per kg of OM fermented;
Dutch protein evaluation system). However, Dijkstra et al.
(1992) demonstrated that environmental conditions in the
rumen have a major impact on this efficiency.Hence, dietary
measures and their consequences for rumen fermentation
conditions may also have a large impact on the efficiency of
microbial growth achieved and, consequently, on the
quantities of OM converted into VFA and CH4produced.
Although microbialbiosynthesis also acts asa sink or source
of [H], depending on ammonia or amino acids used as a
nitrogen source (Benchaar et al., 1998; Mills et al., 2001),
this affects rumen [H] balance much less than the type of
VFA produced (factor 2) and the quantity of OM converted
into VFA (factors 1 and 3 combined). For reviews on the
and Dijkstra et al. (1996).
The above factors are also relevant to digestion in
monogastric animals (e.g. pigs), although normally most of
the feed ingested will be digested enzymatically instead of
fermentatively. Only in the large intestine fermentation
G.-J. Monteny et al./Agriculture, Ecosystems and Environment 112 (2006) 163–170164
Typical absolute and relative CH4emissions from enteric fermentation and
manure (Monteny et al., 2001)
Total (kg CH4per
year per animal)
Contribution of enteric
(flatus) CH4production becomes substantial, in particular
when carbohydrates fed are enzymatically indegradable and
therefore end up undegraded in the large intestine. Although
the precise fermentation conditions in the largeintestinewill
be different from those in the rumen, the same principles of
microbial fermentation and CH4production hold. Bakker
(1996) found, in experiments with pigs (maize starch
replacement by products with a high content of fermentable
carbohydrates), that some 10% of the GE digested in the
large intestine was retrieved as CH4, ranging from 0.5 to
1.9% of GE consumed. Therefore, the digestive process in
pigs generates at the most 1/3 (up to 2% of GE intake) of the
CH4produced in ruminants (up to 7% of GE intake; Pelchen
et al., 1998; IPCC, 1997; Mills et al., 2001), but it may still
be considered substantial when diets with a high content of
fermentable carbohydrates instead of starch-rich feed
ingredients are fed.
2.1.2. Animal manure
Fermentation of manure (digestion), both solid and
liquid, is an anaerobic process (absence of oxygen). It has
some similarities with enteric fermentation, and is described
in detail, e.g. by Burton (1997) and Møller (2001). In brief,
the fermentation process runs in two steps:
(a) Fast growth of acidogenic bacteria, active in a wide
temperature range (3–70 8C) with an optimum at 30 8C.
Intensive mixing of substrate and bacteria producing
organic acids, [H], and CO2.
(b) Specific methanogenic bacteria (psychrophilic, <20 8C;
mesophilic, 20–40 8C; thermophilic, >40 8C) produce
CH4from organic acids.
Methane production from animal manure (also known as
biogas) increases with temperature, and with increased
biodegradability of the manure (or the combination of
manure and by-products; see e.g. Wulf et al., 2005).
Although digestion at higher temperatures generates more
CH4, the costs of energy needed for additional heating have
to be considered in the choice of the optimal reactor. The
quality of the substrate greatly determines CH4production.
Specific pH values and carbon:nitrogen ratios (optimum is
between 13:1 and 28:1) have to be realized. Since digestion
of animal manure is a biological process, the concentrations
of inhibitory compounds like ammonia/ammonium and
sulphides need to be kept low when optimal gas production
2.2. Nitrous oxide
The main sources of N2O are nitrogen fertiliser and
animal manure applications to land, and urine deposition by
released in deep litter systems and from solid manure heaps
(Chadwick et al., 1999). Evensilage clamps may be a source
of N2O. Whereas, CH4is commonly produced from animal
manures, N2O production only takes place under specific
conditions since it results from combined aerobic and
(a) nitrification: transformation of ammonium to nitrate
(b) denitrification: formation of nitrogen gas from nitrate
As a consequence, N2O emission is influenced by the
environmental factors oxygen status, temperature, moisture
content and antecedent soil conditions, which control
enzyme production. Normally, conditions in manure are
strictly anaerobic, and processes (a) and (b) will not occur.
However, when forced and controlled aeration of liquid
manure (‘aerobic treatment’) or solid manure (‘compost-
ing’) is used to achieve removal of OM and nitrogen, and
water (drying), respectively, denitrification occurs after
aeration. Besides these examples of active nitrification/
dentrification, the processes (a) and (b) also happen in a
situation of passive aeration, e.g. in organic housing systems
and systems with enhanced animal welfare where straw or
litter may be introduced. The mixture of manure and straw/
litter, combined with (partial) compaction of the bedding
creates conditions that favor passive aeration, resulting in
uncontrolled nitrification and denitrification (Groenestein
and Van Faassen, 1996). Although ammonia emissions from
significant trade off to N2O (and CH4), resulting in a net
higher N-emission than observed from traditional, liquid
manure based, housing systems.
3. Mitigation options
Methane emission per unit of animal product will be
reduced by any process that increases the ratio of livestock
‘production’ to ‘maintenance’. Thus faster growth, higher
milk yields and shorter dry periods in lactating cows will
lower CH4emissions. Likewise, an increase in the average
longevity of dairy cows (i.e. a greater number of lactations
per lifetime) relative to the period from birth to first calving
(usually 3 years) will reduce CH4loss per unit of milk yield.
Additionally, measures concerning technology (e.g. aerobic
digestion) and management based solutions may be
implemented (Harrison et al., 2003). However, only
mitigations that involve a reduction in the number of
animals would currently register as a reduction in the IPCC
inventory (IPCC, 1997) because this is based on a standard
emission factor. Other forms of mitigation, for example
those based on manipulation ofthe diet, couldproduce ‘real’
reductions in CH4production, but presently these would go
unrecorded in the inventory, unless they indirectly led to a
reduction in livestock numbers.
G.-J. Monteny et al./Agriculture, Ecosystems and Environment 112 (2006) 163–170165
3.1.1. Dietary measures
It is widely recognized that alterations in the diet strongly
affect rumen functioning and the performance of ruminants
(e.g. roughage:concentrate ratio, or the fibre, starch, sugars
and protein content of the feed). Similarly, dietary
composition may strongly affect the supply and subsequent
fermentationofsubstrateinthe largeintestineofpigs aswell
inflow to large intestine). In particular, the fermentative
capacity of the large intestine of pigs is excessive, whereas,
it is considered minor in ruminants in comparison to that of
the rumen. Changes in feeding strategyor farm management
may have a large impact on GHG production by farm
animals. Concerning ruminants, the most effective measures
are (in theory):
(a) increase the level of starch or rapidly fermentable
carbohydrates (soluble carbohydrates and starch in
concentrates), to enhance propionate production, reduce
excess [H] and subsequent CH4formation;
(b) alter the diet concerning feed intake and feed composi-
tion to allow for a higher animal productivity;
(c) reduce [H] by addition of (unsaturated) fat or
stimulation of acetogenic bacteria;
(d) reduction of methanogens or removal of protozoa
(through additives or probiotics).
In practice, only (a) and (b) seem feasible and
applicable in today farming practices. Options (c) (Sauer
et al., 1998) and (d) are either purely theoretical, under
study (cf. Machmu ¨ller, this issue) or may encounter
resistance from consumers (especially (d)). Mills et al.
(2001) demonstrated that changing from an intensive
system with less cows fed ad libitum (9150 kg of 305 days
milk yield) to an extensive system with restricted feeding
of more cows (6100 kg of 305 days milk yield) reduced
CH4production per cow per day with 20%, yet a 21%
increase of the CH4 production of the total herd was
observed. This study illustrated that an evaluation of
dietary measures at the farm level requires first of all a
careful evaluation at the animal (or even rumen) level, and
subsequently an evaluation at the herd level in terms of
herd productivity, nutrient utilization, costs, and similar
characteristics that are important at the farm level.
3.1.2. Housing and storage
Methane is poorly soluble in water. This implies that
produced CH4will instantly emit to the air inside the house.
Hence, possible options to reduce emissions from the house
and (indoor) storage have to focus on:
(a) reduction of gas production through deep cooling of
manure (<10 8C) or a substantial reduction of manure
pH, e.g. via additives;
(b) removal of the gas source, e.g. by frequently and
completely removing manure from indoor storage pits;
(c) proper management of the bedding and manure heaps,
e.g. minimize compaction, frequent addition of straw/
litter, regular removal.
Option (a) requires additional equipment to extract heat
from the manure or to apply the additives. Sommer et al.
(2004) showed that cooling of pig slurry in-house reduced
CH4(and N2O) emissions with 21% relative to not cooling.
Furthermore, additives like lactic acid (Berg and Pazsiczki,
2003) and lime-stone can result in even further reductions
(up to 80%). Frequent and complete removal of the manure
from the pits (option (b); Osada et al., 1998) is effective, but
will only be feasible (and effective) in situations with
sufficient outdoor storage capacity and additional measures
to prevent CH4 emissions to occur outdoors. Anaerobic
digestion (biogas production), flaring/burning (chemical
oxidation; burning) or special biofilters (biological oxida-
tion; Melse, 2003) can be operated. Biogas production
(reviewed by Burton, 1997, and by Burton and Turner,
2003), combined with on-farm power/heat generation,
seems the most logical measure. Its feasibility will mainly
depend on the energy prize (use on own farm, delivering
electricity to the public net) and on possibilities (or
restrictions) to co-digest waste products to increase gas
production (see Nielsen and Hjort-Gregersen, 2005).
Proper management of bedding material (indoor;
Groenestein and Van Faassen, 1996) and manure heaps
(outdoor) will reduce GHG emissions, since substantial
amounts of CH4and N2O are produced under sub-optimal
conditions (Hu ¨ther et al., 1997).
3.2. Nitrous oxide
Options to reduce N2O emissions from specific sources
review of greenhouse gas emissions from agriculture in the
UK, Harrison et al. (2003) concluded that the most effective
potential specific options are: (1) choice of fertiliser form,
(2) nitrification inhibitors, (3) land drainage management,
(4) storage of solid manure, (5) N2O:N2 ratio, and (6)
housing systems and management.
3.2.1. Choice of fertiliser form
Fertiliser type is thought to influence N2O emissions,
with nitrate-based fertilisers resulting in greater emission
factors than ammonium-based fertilisers. For example, a
review conducted by Eichner (1990) suggested that the
average emission factor for ammonium nitrate was 0.44%
whilst that for urea was 0.11% of the N applied. In a more
recent experimental study, Dobbie and Smith (2003a)
compared N2O emissions from various fertiliser types with
and without various inhibitors (nitrification and urease).
Their results demonstrated that the use of urea on grassland
in spring reduced N2O emissions compared to the use of
ammonium nitrate (Dobbie and Smith, 2003a) in both years.
Application of a different fertiliser form, e.g. urea instead of
G.-J. Monteny et al./Agriculture, Ecosystems and Environment 112 (2006) 163–170166
ammonium nitrate, would have no extra cost and may even
be cheaper to purchase. Slow release fertilisers have been
formulated to help synchronise N release with plant growth.
Theoretically, it should be possible to provide sufficient
and maintain low soil mineral N concentrations throughout
be limited by the small soil mineral N pool. Indeed, Smith
et al. (1997) showed that N2O emissions were significantly
reduced following application of a coated slow release
ammonium nitrate based and coated slow release ammo-
nium sulphate based fertiliser compared to uncoated
3.2.2. Addition of a nitrification inhibitor
Nitrification inhibitors (NIs) can be added to urea or
ammonium compounds. In the study by Dobbie and Smith
(2003a) the use of a NI with urea fertilisers reduced N2O
emissions compared to urea alone. Nitrapyrin, dicyandia-
mide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP)
have well-demonstrated effectiveness for lowering N2O
emissions from fertiliser and animal slurries (Pain et al.,
1994). Dittert et al. (2001) demonstrated a win–win scenario
using DMPP additions to dairy slurry.
Slurry injection is known to significantly decrease
ammonia emissions compared with surface spreading
(Misselbrook et al., 2002), but injection can result in
increased N2O emissions (Chadwick et al., 1999). Dittert
et al. (2001) found that the N2O emissions from slurry
treated with DMPP were 32% lower than from non-treated
slurry when injected into grassland, and the use of15N label
confirmed that this reduction was from slurry derived N2O.
Ammonia emissions were negligible.
is an approach that is being adopted in New Zealand in order
to reduce the N2O emissions from urine deposition (Di and
Cameron, 2003). The two main fertilizer manufacturers,
onal2005/specialist.htm (date of access: 13 July 2005))
and Ballance AgriNutrients (http://www.ballance.co.nz/
unewsapr07-05.html (date of access: 13 July 2005)) each
have their own NI product: Eco-N and N-care, respectively.
Eco-N is a finer product that is suspended in solution and
then irrigated onto pasture, while N-care is a solid product
that is mixed with urea fertilizer and then broadcast onto
effective on fertilizer but also on urinary N as it is sprayed
onto pasture. Costs of NIs may be offset by increased
efficiency. The degree of uptake of NI use may depend on
the public’s perception of introducing another chemical into
3.2.3. Land drainage
There is a well documented relationship between N2O
emissions and water filled pore space whereby water filled
pore space of more than 70% results in significant N2O
emissions (Maag, 1990; Dobbie and Smith, 2003b). There-
fore, improvement of soil physical conditions to reduce soil
wetness, especially in grassland systems, may significantly
reduce N2O emissions. For example, neglect of land
drainage in the UK since the cessation of subsidies means
that soil aeration status has been gradually deteriorating.
Improving drainage would be particularly beneficial on
grazed grassland. Soil compaction by traffic, tillage and
grazing livestock can increase the anaerobicity of the soil
and enhance conditions for denitrification. It is thought that
treading by cattle could increase emissions of N2O by a
factor of two (Oenema et al., 1997). Clark et al. (2001)
suggested that by avoiding compaction, the total national
N2O emission (for 1998) could be reduced by 3%.
3.2.4. Solid manure stores
Specific N2O mitigation options from solid manure heaps
solid manure heaps to reduce oxygen entering the heap and
maintaining anaerobic conditions has had mixed success in
reducing N2O emissions (Chadwick, unpublished). In
contrast, one would expect CH4emissions to be increased
following compaction of heaps, i.e. a case of swapping one
form of pollutant for another.
Nitrous oxide is one of the products of nitrification
(Bremner and Blackmer, 1978), whilst both nitrogen gas
(N2) and N2O are products of denitrification (Firestone and
Davidson, 1989). Increased knowledge of the factors
controlling the N2O:N2 ratio could be used to inform
management practices that may lead to a greater propor-
tional flux of N2(compared to N2O). Carbon quality is
known to influence the ratio of N2O:N2(Paul et al., 1993).
Hence, an improved understanding of the influence of
anaerobic digestion and storage of slurry on C quality at the
time of manure application may result in improved
management practices to reduce N2O emissions.
Amon et al. (2002) showed that the N2O emissions from
been stored for 6 months or had passed through an anaerobic
digester prior to spreading in comparison to fresh slurry. The
inference being that during storage and anaerobic digestion
readily available C (that could be used to fuel denitrification)
is incorporated into microbial biomass or lost as CO2or CH4,
hence there is less available C in the slurry to fuel
dentrification when the slurry is applied to land. Indeed
animal slurry, sinceCH4emitted duringstorage(asbiogas)is
used to produce heat and electricity, whilst N2O emissions
(see for example, Clemens et al., 2005).
3.2.6. Housing system and management
The choice of manure management and housing system
will influence greenhouse gas emissions, particularly N2O.
G.-J. Monteny et al./Agriculture, Ecosystems and Environment 112 (2006) 163–170167
Changes of practice, e.g. for reasons of animal welfare, may
increase straw use and hence the production of solid farm
yard manure (FYM). Animal housing and manure stores of
straw-based systems (deep litter) will result in greater N2O
emissions than the more anaerobic slurry-based systems
(Thorman et al., 2003; Groenestein and Van Faassen, 1996).
So, a management change from straw- to slurry-based
systems may result in lower N2O emissions.
Some dairy and beef farmers are extending the grazing
season to reduce feed costs and labour. This will in general
not affect CH4emissions, butit may increase the risk of N2O
emissions and nitrate leaching. Minimising the grazing
period is likely to reduce N2O emissions, since the more
uniform return of excreta via slurry spreading results in
lower emissions than from urine deposited by grazing
animals (Oenema et al., this issue).
4. Interactions with other policies
There are important interactions between mitigation
measures for gaseous emissions and nitrate leaching (risk of
pollution swapping), so mitigation practices need to be
evaluated at the system level (i.e. holistically). Brink et al.
(2001) indicated that NH3abatement will result in a 15%
lower emission of N2O, mainly due to adaptations in animal
houses and low emission manure application techniques.
Also reversed interactions are observed. A move from straw
based cattle housing systems to slurry-based systems to
reduce N2O emissions would result in increased ammonia
emissions (Chambers et al., 2002). The mitigation strategies
for N2O may have effects on other policy issues: e.g.
substituting urea for ammonium nitrate would increase NH3
emissions (Misselbrook et al., 2000). Improving land
drainage may increase NO3?leaching, both of which would
also result in increased indirect N2O emissions. Policies
relating to nitrate vulnerable zones (NVZs) will result in
more organic manures being spread during the growing
season, so the interaction between manure and fertiliser
nitrate on N2O emissions may be important. Slurry applied
at the same time as fertiliser nitrate increases N2O emission,
Laughlin, 2001, 2002). Microbial degradation of organic C
in slurries should be allowed to occur for a few days in the
soil before applying nitrate-containing fertiliser.
Mitigation strategies for NH3in animal husbandry were
found to have no effect on CH4emissions (Brink et al.,
2001). This is mainly because the N- and C-cycles in
agriculture are only integrated to some extent and
consequently pathways for mitigation differ. Methane
emission reduction options have to be based upon animal
nutrition (enteric fermentation) and manure management
inside or outside the animal houses. Because of the potential
of CH4for energy production, the on-farm production and
climate change problem from both reduced emissions of
CH4 and CO2 (from fossil fuels). Moreover, anaerobic
digestion results in a manure product with an increased
amount of NH3, that is readily available for plant uptake,
available C, with may reduce N2O emissions after land
spreading. Furthermore, the odour (smell) is reduced due to
degradation of VFA in manure, which results in a reduced
Agriculture in general, and livestock production in
particular, contribute to global warming through emissions
of the non-CO2GHGes CH4and N2O. Most CH4is emitted
from ruminants (animal + manure), whereas, N2O is mainly
emitted from fertilized land.
Methane mitigation options from ruminants focus on
increasing production per animal, modifying diet, decreas-
ing numbers of methanogens and methanogen activity and
by reducing livestock numbers. Manure related CH4can be
reduced by minimizing uncontrolled storage (indoors).
Controlled storage offers possibilities for utilization of CH4
Nitrous oxide mitigation options include better N use
(from fertilisers and manures), land drainage, use of
nitrificationinhibitors.Mitigation ofN2Ofrom solidmanure
heaps could be achieved through the use of high C additives
and compaction. Anaerobic digestion of slurries can be used
to (a) directly reduce CH4 emissions through biogas
generation (heat and energy production) and (b) indirectly
reduce N2O emissions when slurries are applied to land by
decreasing the readily available C content.
It is essential that GHG mitigation options take other
policies into account, e.g. the requirement to reduce NO3?
leaching and NH3volatilisation. It should be noted that, a
reduction in the amount of fertiliser N used through more
efficient use, e.g. by timing applications and rates to crop
requirements, as well as an integrated approach to the use of
animal manures with fertilisers to supply N for crop growth
should reduce the risk of excess mineral N remaining in the
manure management would play an important role in
reducing not only N2O emissions but also other losses of N,
e.g. as ammonia and nitrate.
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