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Nitrous oxide (N2O) is an important anthropogenic greenhouse gas and agriculture represents its largest source. It is at the heart of debates over the efficacy of biofuels, the climate-forcing impact of population growth, and the extent to which mitigation of non-CO2 emissions can help avoid dangerous climate change. Here we examine some of the major debates surrounding estimation of agricultural N2O sources, and the challenges of projecting and mitigating emissions in coming decades. We find that current flux estimates -- using either top-down or bottom-up methods -- are reasonably consistent at the global scale, but that a dearth of direct measurements in some areas makes national and sub-national estimates highly uncertain. We also highlight key uncertainties in projected emissions and demonstrate the potential for dietary choice and supply-chain mitigation.
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The potential for climate change mitigation through reducing
emissions of non-CO2 greenhouse gases has received increas-
ing attention in recent years. e importance of these gases
in terms of net anthropogenic climate forcing, and the low or nega-
tive marginal abatement costs of many non-CO2 mitigation strat-
egies, mean that any eective global climate change policy in the
twenty-rst century must consider them1. Nitrous oxide (N2O) is
one of the most important of these non-CO2 greenhouse gases and
agriculture represents its largest anthropogenic source, but the esti-
mation, projection and mitigation of these emissions each poses
Here we synthesize the latest debates over the estimation of agri-
cultural N2O emissions. We nd that so-called top-down and bot-
tom-up estimation methods are reasonably consistent at the global
scale, but that an increased number of eld measurements of direct
and indirect N2O uxes is required to improve the reliability of sub-
national-scale emission estimates.
For the projection of agricultural N2O emissions in the next few
decades we highlight the challenge of incorporating robust simula-
tions of changing human population, diet and bioenergy demand.
We stress the need for improved understanding of interactions
between climatic change, changing nitrogen status of ecosystems
and agricultural N2O uxes.
Finally, we examine the challenge of reducing agricultural N2O
emissions and estimate the potential impacts of dietary change and
reducing food wastage. We nd that dietary change may serve as a
powerful determinant of agricultural N2O emissions — a simplistic
scenario of reducing per capita poultry-meat consumption in the
developed world between 2012 and 2020 results in a relative cut
in global N2O emissions associated with this single food source of
We also nd that avoidance of food loss and wastage may yield
substantial reductions in agricultural N2O emissions. Consumer-
phase food wastage of just ve food types in the UK, for exam-
ple, constitutes >2Gg N2O-N yr–1 of ‘avoidable’ N2O emissions.
At a global scale, loss and wastage of these same ve foodstus
Global agriculture and nitrous oxide emissions
Dave S. Reay1*, Eric A. Davidson2, Keith A. Smith1,3, Pete Smith4, Jerry M. Melillo5, Frank Dentener6
and Paul J. Crutzen7
Nitrous oxide (N2O) is an important anthropogenic greenhouse gas and agriculture represents its largest source. It is at
the heart of debates over the ecacy of biofuels, the climate-forcing impact of population growth, and the extent to which
mitigation of non-CO2 emissions can help avoid dangerous climate change. Here we examine some of the major debates
surrounding estimation of agricultural N2O sources, and the challenges of projecting and mitigating emissions in coming
decades. We find that current flux estimates — using either top-down or bottom-up methods — are reasonably consistent at
the global scale, but that a dearth of direct measurements in some areas makes national and sub-national estimates highly
uncertain. We also highlight key uncertainties in projected emissions and demonstrate the potential for dietary choice and
supply-chain mitigation.
is associated with production-phase N2O emissions in excess of
200GgN2O-Nyr–1 (~3% of the global agricultural N2O source).
Agriculture and nitrous oxide emissions
Of the approximately 16TgN2O-N yr–1 emitted globally in the
1990s, between 40 and 50% was a result of human activities, with
much of the growth in N2O concentrations since the pre-indus-
trial era being attributed to the expansion in agricultural land
area and increase in fertilizer use3. Currently, the main sources
of anthropogenic N2O emissions are agriculture, industry, bio-
mass burning and indirect emissions from reactive nitrogen4 (Nr)
leaching, runo and atmospheric deposition5. Of these, emissions
from agricultural soils dominate5, widespread use of nitrogenous
fertilizers and increasing manure inputs combine to drive emis-
sions growth. With an increasing human population, and the con-
sequent need for more food production, both agricultural land
area and N2O emissions are likely to continue to rise in coming
decades1,7–10 (Fig.1).
Alongside industrialization and rising emissions of NOx from
fossil fuel burning, the intensication of agriculture and associ-
ated NH3 emissions has led to a three- to ve-fold increase in Nr
emissions over the past century11. is growth in anthropogenic
Nr emission and deposition, together with deliberate enhancement
of biological nitrogen xation and the manufacture of Nr for fer-
tilizers and industrial uses, has approximately doubled the global
Nr supply relative to the pre-industrial average3. As such, agricul-
ture has caused a huge perturbation to the global nitrogen cycle
since the industrial revolution, and has signicantly increased net
N2O emissions.
The estimation challenge
Direct measurements of agricultural N2O emissions have been
made for many decades. e myriad methods employed and their
associated challenges have themselves generated long-running
debates12–15, but these are beyond the scope of this Review. Instead
our focus here is on the challenge of estimating agricultural N2O
1School of GeoSciences, University of Edinburgh, Edinburgh EH8 9XP, UK, 2The Woods Hole Research Center, 149 Woods Hole Road, Falmouth,
Massachusetts 02540-1644, USA, 3Woodlands One, Pomeroy Villas, Totnes, Devon TQ9 5BE, UK, 4Institute of Biological and Environmental Sciences,
School of Biological Sciences, University of Aberdeen, Cruickshank Building, St Machar Drive, Aberdeen AB24 3UU, UK, 5The Ecosystems Center, Marine
Biological Laboratory (MBL), 7MBL Street, Woods Hole, Massachusetts 02543, USA, 6European Commission, Joint Research Centre, Institute for
Environment and Sustainability, Climate Change Unit, via Enrico Fermi 1, I-21020 Ispra, TP 290, Italy, 7Max Planck Institute for Chemistry, Department of
Atmospheric Chemistry, PO Box3060, D-55020 Mainz, Germany. *e-mail:
© 2012 Macmillan Publishers Limited. All rights reserved
emissions for locations and land uses where direct measurements
do not exist, or where temporal and spatial scales exceed the cover-
age of direct measurements.
By more accurately quantifying the relationship between per-
turbations in Nr inputs and the associated increases in N2O emis-
sions, we may be able to improve estimates of current and future
agricultural N2O emissions around the world. However, deriving a
so-called N2O ‘emission factor’ (Box1) that is representative of this
relationship across the very wide range of management systems, cli-
mates and land uses that help comprise the global agricultural N2O
source is extremely challenging. Recent years have seen an intensi-
cation in the debate over how such N2O emission factors are derived
and applied9,16,17.
Crutzen etal.16 used a top-down approach to estimate the frac-
tion of newly created Nr that would have to be emitted as N2O to
balance the global N2O budget in 1860 and in the 1990s. For the
pre-industrial period, they estimated an N2O emission factor of 4.4–
5.1% for all newly created Nr (mostly natural, with a small anthro-
pogenic component). For the 1990s a similar N2O emission factor
of 3.8–5.1% seemed to explain the annual increase in atmospheric
N2O concentrations.
Using a combination of bottom-up and top-down methods,
Davidson9 then reported that an emission factor of ~4% of new Nr
underestimated atmospheric accumulation of N2O emissions in
the rst half of the twentieth century — a period when N2O con-
centrations were increasing faster than production of new Nr. is
increase in the atmospheric N2O burden occurred concurrently
with increased global manure production, and it was argued that
much of the Nr that supported crop and livestock expansion before
the Second World War may have been ‘mined’ from unfertilized,
newly tilled soils. e ‘mining’ of soil nitrogen in this context refers
to the depletion of soil organic nitrogen stocks accumulated in the
decades or centuries before land conversion to agriculture, and then
mobilized as a result of ploughing and overgrazing18.
Davidson9 showed that, when manure production and synthetic
fertilizer-nitrogen were partitioned as separate sources of N2O
emissions (with emission factors of 2% and 2.5% respectively), the
observed increase in N2O concentrations for the entire record of
atmospheric measurements from 1860to 2005 could be explained.
is nding highlights the need to consider the ‘cascade’ eect19 of
Nr, with manure production being one of several phases of recycling
of Nr. Recent calculations20 show that if the Crutzen etal.16 concept
of newly xed Nr is broadened to include NOx deposition and the
Nr mined from hitherto virgin land, then the application of a simple
4% emission factor does give a close t to the observed trend in
atmospheric concentration. us the Crutzen etal.16 explanation of
anthropogenic emissions remains plausible, based on the primary
N2O emissions from fertilizer, biological nitrogen xation, mining
of soil organic N and NOx sources being followed by emissions of
recycled Nr in manure production and management.
Top-down and bottom-up estimation. e Crutzen et al.16 esti-
mate raised the question of whether the bottom-up-derived N2O
emission factors used by the IPCC (for example Box1) and others
may, in aggregate, substantially underestimate emissions. However,
there is little evidence for any such systematic underestimation at
the global scale, with estimates made using the IPCC method17
being within the range generated using the Crutzen etal. method
(Table1). Del Grossoetal.17 noted that, as scale increases, agree-
ment between bottom-up and top-down estimates also increases.
Indeed, this convergence of estimates derived from dierent meth-
ods itself increases condence in the absolute values17.
At regional and sub-regional scales however, neither approach
can reliably estimate emissions in all circumstances. Freibauer21
1990 20002010202
Global emissions from agriculture (Tg N2O–N yr–1)
Agricultural soils
Manure management
Other agricultural sources
Human sewage
Figure 1 | Global N2O emissions from agriculture between 1990and
203010. Emissions from histosols, sewage sludge application, asymbiotic
fixation of soil nitrogen, and mineralization of soil organic matter are not
included in these estimates. ‘Other agricultural sources’ here includes
field burning of agricultural residues, prescribed burning of savannas and
open burning from forest clearing. See Supplementary Information for
Greenhouse-gas emission factors are widely used to estimate
emissions arising from a dened unit of a specic activity. Such
estimates are used both for international reporting to the United
Nations Framework Convention on Climate Change (UNFCCC)
and for myriad national and sub-national reporting purposes (for
example, European Union Emissions Trading Scheme; EU ETS).
As with the other ‘Kyoto protocol GHGs’, the Intergovernmental
Panel on Climate Change (IPCC) provides a methodology for
national and sub-national estimation of N2O emissions, based on
the sector from which the emissions arise. Emissions are esti-
mated using Tier 1, 2or 3 methodologies, where Tier 1 relies on
a universal emission factor combined with activity data, Tier 2
utilizes a country-specic emission factor, and Tier 3 involves
direct measurement or modelling approaches22.
For estimation of N2O emissions from the agricultural sector,
Tier 3 estimates are rarely available and default N2O emission
factors are oen employed. For example, the Tier 1 IPCC default
factor for direct N2O emissions arising from mineral nitrogen
fertilizer application to managed soils is 1% (ref. 22) (that is,
10 kg N2O-N is emitted for every tonne of nitrogen fertilizer
applied). To this would then be added an estimate of the indi-
rect N2O emissions from nitrogen leaching and runo, and from
atmospheric nitrogen deposition.
ese direct and indirect emission estimates do not cover
subsequent recycling of the added nitrogen and resulting N2O
emissions, instead these are covered by additional IPCC emis-
sion factors such as those for crop residues, manure and sewage
nitrogen22. As such, direct comparisons of ‘bottom-up’ emission
factors to those derived using global ‘top-down’ methods16 can-
not be made due to the diering ways in which the sources of
nitrogen inputs are considered17.
Box 1 | Greenhouse-gas emission factors.
© 2012 Macmillan Publishers Limited. All rights reserved
has shown good agreement between measured N2O emissions in
Europe and those derived from the bottom-up IPCC methodol-
ogy— but one might expect this given that the IPCC emission fac-
tors are themselves informed strongly by European measurements.
e top-down approach is currently limited by uncertainties
in the temporal and spatial attribution of observed changes in
atmospheric N2O concentrations, whereas bottom-up approaches
employing default emission factors may fail to properly represent
the heterogeneity among local conditions17,21. e use of national
and sub-national emission factors, or process-based models attuned
to local climate, soil characteristics and land-management practices
can help to reduce such uncertainty17. So too can on-going revisions
to default emission factors, based on new evidence and a wider
geographical spread22. An exemplar case of such revision is that of
the indirect component of agricultural N2O emissions (Syakila and
Kroeze6; Table1). ere, a recent update of the default emission fac-
tor for N2O production in aquatic systems, due to agricultural nitro-
gen leaching and runo, was made possible by an expansion in the
number of eld measurements6,22–24. e additional measurements
led to a reduction in this indirect N2O emission factor (called EF5-g)
from 0.025to 0.0075 kg N2O-N kg–1 N input, and the 50% over-
all reduction in estimated indirect emissions seen in Table1 (from
2.6to 1.3TgN2O-Nyr–1)6.
A central aim of future research into N2O emissions from agri-
cultural systems should therefore be to increase the global cover-
age of direct and indirect N2O ux measurements to encompass all
major agricultural land-use types and climates, land-use changes
and management practices. Such data could then provide robust
‘Tier 2’ emission factors for these systems and increase condence
in national and sub-national estimates. Addressing the current pau-
city of direct N2O measurements in much of the developing world
is of particular importance. Increased investment in monitoring has
the potential to improve the reliability of farm-scale emission esti-
mates, and so gain greater access to mitigation nancing through
the compliance and voluntary markets25,26.
The projection challenge
Projected N2O emissions associated with agriculture are sensitive
to drivers such as human population, per capita caloric intake, and
consumption of livestock products. Alongside continuing growth
in global population27, per capita food consumption is projected
to increase in the next few decades28, with demand for meat and
dairy products being especially strong28–30 (Fig. 2). ese projec-
tions represent changes in global average per capita intake, much
of the expected increase being driven by greater per capita cereal,
meat and dairy consumption in developing-world nations29. As a
result of the necessary expansion in crop and livestock production
to meet this demand, a substantial increase in N2O emissions from
agricultural soils is projected through to 203010,31.
Overall, N2O emissions associated with agriculture (including
human sewage) are projected to rise from around 6.4TgN2O-Nyr–1
in 2010 to 7.6TgN2O-Nyr–1 by 203010 (Fig.1), with much of this
growth resulting from increased nitrogen-fertilizer use in non-
OECD Asia, Latin America and Africa. Although these projections
provide a useful indicator of future emissions, uncertainties around
agricultural demand, interactions with climate change, and the
extent of mitigation eorts remain signicant.
Agricultural demand and bioenergy. As discussed previously,
future changes in human population and diet are a central deter-
minant of global food demand, and so of agricultural N2O emis-
sions. In addition to the challenge of developing robust scenarios
for food-related emissions, projections must also take account of
potential increases in demand for bioenergy.
Several recent studies have shown that an outcome of imposing
mitigation regimes that value only carbon from energy and indus-
trial sources is that they can create incentives to increase bioenergy
production and use32,33. Global production of wheat, coarse grains
and vegetable oils for biofuels use, for example, is projected to rise
from around 160 million tonnes in 2010 to over 200 million tonnes
by 202029. Expanded bioenergy programmes can, in turn, increase
terrestrial carbon emissions globally by increasing the conversion of
forests and unmanaged ecosystems to agricultural use — a perverse
result of curbing fossil-fuel-related emissions34. Increased produc-
tion of rst-generation energy crops (for liquid transport fuels —
bioethanol and biodiesel) may also increase N2O emissions, as large
areas of these crops are fertilized to maximize production. However,
many second-generation energy crops do not require large nitro-
gen-fertilizer additions, and their impact on N2O emissions is likely
to be much lower35. A central question therefore, is the degree to
which global biofuel crop production will transition to second-
generation energy crops, and the extent to which any expansion in
production will be conned to existing managed land.
A recent analysis of global biofuels programmes that employ
advanced cellulosic (second generation) technologies estimates
that, over the twenty-rst century, N2O emissions will be larger
than the carbon losses associated with land-use change and land
clearing36. Cumulative projected N2O emissions in the analysis by
Melillo etal.36 range between 510and 620TgN2O-N for the period
2000–2100, depending on how much of the new biofuels produc-
tion is conned to already managed land, and so minimizes new
forest clearing. Whereas cumulative N2O losses continually grow
over the twenty-rst century, net carbon ux inuenced by biofuels
production exhibits one of two distinct patterns: a substantial ux to
the atmosphere (a land source) if the increase in biofuels production
involves extensive forest clearing to establish biofuels crops (defor-
estation case); or a small ux to the land from the atmosphere (a
land sink) as carbon slowly accumulates in the soil fertilized in the
biofuels areas (intensication case). A global greenhouse-gas emis-
sions policy that both protects forests and encourages best practices
for nitrogen-fertilizer use37 may therefore dramatically reduce emis-
sions associated with biofuels production.
Feedbacks and interactions. Further increases in anthropogenic
Nr inputs to both managed and natural ecosystems are predicted38.
Agriculture accounts for about 75–85% of projected global NH3
emissions throughout 2000–2050 and it is likely that regions with
soils and ecosystems where Nr loads are already high are more prone
Table 1 | Recent estimates of agricultural N2O emissions (TgNyr–1) using dierent methodologies.
Source Del Grosso et al. (bottom-up)17,2 2 Del Grosso et al. (top-down)16, 17 Syakila & Kroeze 6Syakila & Kroeze 6
Direct 3.8 1.8 2.2
Animal production 0.4 }4.2–7.0 2.3 2.3
Indirect 1.6 1.3 2.6
Total 5.8*4.2–§
*Bottom-up, used IPCC 2006 methodology22. Top-down, used Crutzen et al.16. N2O emission factor of 3–5% for N inputs from symbiotic N fixation and synthetic fertiliser production. Bottom-up, used IPCC 2006
methodology22. §Bottom-up, used revised IPCC 1996 methodology5.
© 2012 Macmillan Publishers Limited. All rights reserved
to Nr deposition-induced N2O emissions39,40. Indeed, signicant
enhancements (50–60%) in the proportion of new Nr input emitted
as N2O have been reported for riparian forest soils exposed to a dec-
ade of NO3-rich runo41. Insucient eld data exist to condently
include a positive feedback response in regional or global-scale pro-
jections of indirect N2O emissions from agriculture, but it is possible
that an expansion in the area of nitrogen-saturated natural ecosys-
tems globally will serve to increase N2O emissions per unit of Nr
deposition in the future. As the microbial processes of nitrication
and denitrication are responsible for the bulk of agricultural N2O
emissions42–44, a greater understanding of the microbiological basis
of N2O uxes may also help to improve such feedback projections45.
Likewise, the impacts of future climate change on soil nitrogen
cycling and net N2O emissions from agriculture are potentially
signicant46, yet remain dicult to quantify at a global scale. A
recent examination of modelled N2O emissions from Australian
pasture-based dairy systems under future climate change scenar-
ios indicated an increase in emissions of up to 40% (ref. 47). Here,
warmer soil temperatures coupled with wet, but unsaturated, soils
during cooler months resulted in an increased opportunity for
N2O production. Enhanced N2O emissions from upland agricul-
tural soils under increased atmospheric CO2 concentrations have
also been reported48. Conversely, modelling of N2O emissions from
a humid pasture in Ireland under future climate change indicated
that a signicant increase in above-ground biomass and associ-
ated nitrogen demand would serve to avoid signicant increases
in N2O emissions49. Although direct studies of agricultural N2O
uxes under simulated future climates do suggest increased emis-
sions in response to warming50 or increased CO248, examination of
the combined eects of warming, summer drought and increased
CO2 indicate that temperature change may be of most importance
in temperate, extensively managed grasslands51. Overall, it is likely
that changes in food demand, land management and nitrogen-use
eciency will be much more important determinants of global N2O
emissions than climate change in the twenty-rst century. However,
signicant indirect eects of climate change on agricultural N2O
uxes, such as reduced crop productivity52, altered nitrogen leach-
ing rates53, and enhanced ammonia volatilization54,55 require further
investigation and quantication.
The mitigation challenge
Agriculture accounted for approximately 60% (~6 Tg N2O-N)
of total global anthropogenic emissions of N2O in 2005, largely
through emissions from agricultural soils aer application of
nitrogen fertilizer, meaning that the agricultural sector oers the
greatest potential for N2O mitigation31.
Nitrogen-use eciency. On average, of every 100 units of nitrogen
used in global agriculture, only 17 are consumed by humans as crop,
dairy or meat products56. Global nitrogen-use eciency of crops, as
measured by recovery eciency in the rst year (that is, fertilized
crop nitrogen uptake — unfertilized crop N uptake/N applied),
is generally considered to be less than 50% under most on-farm
In the agricultural mitigation (Working Group III) chapter of
the IPCC's fourth assessment report31, the global mitigation poten-
tial for N2O reduction in agriculture was quantied using outputs
from the DAYCENT model61. Projections in demand for food
were considered to require an overall increase in fertilizer nitrogen
requirements, and large improvements in nitrogen-use eciency
by 2030 (for agronomic rather than climate change mitigation rea-
sons) were assumed in the baseline, leading to a limited potential
for mitigation31,62. However, given signicant over-fertilization in
some regions such as China and India63,64, the mitigation potential
may be larger than reported by the IPCC in 200765. Potential mitiga-
tion options for N2O reduction rely on improving nitrogen-use e-
ciency, which could be increased by up to 50%66,67 by practices such
as changing the source of N, using fertilizers stabilized with urease
or nitrication inhibitors or slow- or controlled-release fertilizers,
reducing rates of nitrogen application in over-fertilized regions, and
optimizing nitrogen fertilizer placement and timing65,68–70. In some
under-fertilized regions (such as Africa71,72) more fertilizer nitro-
gen may be needed to increase yields. Although the N2O emissions
would be expected to increase, the N2O emissions per unit of agri-
cultural product may be signicantly decreased.
Given the increased demand for fertilizer nitrogen to feed
>9 billion people by 2050 (for example, from ~100Tg to 135TgN
by 203067) and the potentially very large expansion in biofuel pro-
duction discussed earlier, N2O emissions from agriculture are likely
to rise in absolute terms. e risk is that large increases in anthro-
pogenic N2O emissions from the agricultural sector will partly oset
eorts to reduce CO2 emissions from the energy supply sector and
Normalized change (year 2006 = 100)
Per capita consumption cereals
Per capita consumption meat
Per capita consumption dairy
Global population
2006 2008 2010 2012 2014 2016 2018 2020
Figure 2 | Normalized change (base year 2006) in projected global
population27 and global average per capita consumption of cereals, meat
and dairy products between 2006and 202029.
Per capita poultry meat consumption (kg yr–1)
2006 2008201020122014201620182020
Estimated global emissions arising from poultry
meat consumption (Gg N2O–N yr–1)
Per capita, developed world
‘Convergence’ with Japan
Per capita, Japan
Per capita, developing world
emissions scenario
emissions scenario
Figure 3 | Average per capita poultry-meat consumption between
2006and 2020. The developed world (black bars), Japan-only (green
bars), the developing world (yellow bars), and a ‘convergence’ scenario
whereby average per capita consumption in the rest of the developed
world converges with that in Japan between 2012and 2020 (red bars).
Lines show estimated global N2O emissions arising from poultry-meat
consumption using the OECD-FAO29 consumption scenario (black
circles) and the ‘convergence’ scenario (red circles). See Supplementary
Information for further details.
© 2012 Macmillan Publishers Limited. All rights reserved
others — undermining global eorts to avoid 2°C of post-industrial
warming. A key mitigation challenge, therefore, is to reduce N2O
emissions per unit of fertilizer nitrogen applied, and per unit of
agricultural product73.
Dietary choice. In addition to measures that directly reduce supply
side emissions, there exists signicant potential for mitigation via
the demand side through addressing human dietary choice70,74. Just
as a shi towards a greater per capita caloric intake and increased
proportion of animal products in diets is expected to enhance agri-
cultural N2O emissions, policies that achieve a reduction in animal
product consumption30,74,75 or successfully address excessive caloric
intake76 can reduce them. For example, Popp etal.30 estimate a 24%
reduction in global soil N2O emissions by 2055 under a ‘decreased
meat’ scenario, where per capita caloric intake increases as a func-
tion of GDP, but the share of livestock products in this intake is
reduced by 25% every ten years between 2005 and 2055.
Such mitigation potential of dietary change for future agricul-
tural N2O emissions can be further exemplied by using OECD-
FAO projections29 for per capita meat intake through to 2020
(Fig.2). For example, by combining average per capita poultry-meat
intake in the developed and developing world with projected popu-
lation change27, and by then applying an estimate of production-
phase N2O emissions for poultry meat77, global emissions are seen
to increase from 548GgN2O-Nyr–1 in 2012 to 657GgN2O-Nyr–1 by
2020 (Fig.3). Part of this increase is driven by further rises in aver-
age per capita poultry-meat consumption in the developed world
(from 25.6kg per capita per yr in 2012 to 28 kg per capita peryr
in 2020). However, if per capita intake in the rest of the developed
world over this period were instead to converge with the relatively
low levels estimated for Japan (the ‘convergence’ scenario), global
poultry-meat-related N2O emissions would actually decrease to
533GgN2O-Nyr–1 (Fig. 3). Relative to the estimate derived from
OECD-FAO per capita consumption projections, this ‘convergence’
scenario would constitute a 50% decrease in developed world poul-
try-meat N2O emissions and a 19% decrease in global emissions.
Similar potential reductions are seen when per capita pig and
sheep meat consumption are examined. Using the methodology
outlined above (see Supplementary Information for details), global
N2O emissions in 2020 arising from pig meat consumption fall from
615GgN2Oyr–1 (using OECD-FAO projections) to 546GgN2Oyr–1
under the ‘convergence’ scenario; sheep meat emissions are reduced
from 123to 107GgN2O-Nyr–1.
Clearly, such estimates provide only an indication of how
mitigation of agricultural N2O emissions may be achieved through
dietary change. e N2O emission factor for meat production is
likely to vary considerably between locations, and over time. Also,
any apparent reduction in emissions observed with the decrease in
per capita poultry, pig or sheep meat consumption in developed-
world diets must be set against any resultant increases in consump-
tion of other foodstus.
An additional challenge in projecting and mitigating food-
related N2O emissions, therefore, is that of obtaining robust esti-
mates of N2O emission intensities for dierent foodstus in dierent
geographical locations. An emerging area of food-related N2O emis-
sions that requires just such investigation is that of the aquaculture
industry — an industry that has grown at an annual rate of 8.7%
since 197078, but for which the amount of N2O produced globally
remains poorly quantied79. Williams and Crutzen79 estimate cur-
rent emissions from this source at around 0.12TgN2O–Nyr−1, and
suggest that this may rise to more than 0.6TgN2O-Nyr–1 within
20years if the aquaculture industry continues to grow at its current
rate. For these estimates they employ an N2O emission factor of 5%
for sh farm waste and 2% for human wastewater, while acknowl-
edging the dearth of direct measurements and the urgent need for
quantication of N2O emissions from global carp and shrimp farm-
ing in particular.
Food loss and waste. Alongside interventions aimed at reducing
average dietary N2O emissions intensity, reductions in food loss and
waste — especially for N2O-intensive foodstus — may also help
address agricultural N2O emissions through the demand side. A
simplistic comparison of global average food loss and wastage rates
(~30%)80 with agricultural N2O emissions (Table 1) would sug-
gest potential N2O emissions reductions through complete avoid-
ance of food loss and wastage in excess of 1Tg N2O-N yr–1. e
realistic potential for such mitigation will inevitably vary depend-
ing on food type, production and location, but a useful example is
that of milk wastage in the UK. Of the 13 million tonnes of raw
milk produced for domestic consumption in the UK in 200929 some
360 thousand tonnes (~3%) was wasted in the consumer phase81.
Of this, more than 99% was designated as ‘avoidable wastage’81 and
constituted avoidable emissions of 0.25Gg N2O-N yr–1 (assuming
7.1kgN2O-Nper10,000litres77). Almost half of this milk wastage
was a result of too much being served, with the rest being discarded
as too old81. Although milk is a relatively N2O-intensive product
and constitutes a large proportion of avoidable food waste80, a wider
‘Food loss and waste’ emissions (Gg N
O–N yr
Global food per year (Kt)
Food production
Food ‘loss and waste’
‘Food loss and waste’ emissions
Figure 5 | Mass of global production (left axis) for five food types
in 200929, estimated ‘loss and wastage’ along supply chain80, and
estimated N2O emissions77 (right axis) associated with the production
of ‘lost and wasted’ food (grey bars). See Supplementary Information for
UK food per year (tonnes)
Avoidable emissions (Gg N
O–N yr
Milk Poultry
Food wasted
Avoidable food waste
Avoidable emissions
Figure 4 | Estimated mass of consumer-phase food waste (left axis),
‘avoidable’ food waste, and ‘avoidable’ production-phase N2O emissions
(right axis) for five food types in the UK in 200977,81. Production-phase
N2O emissions (grey bars) for avoidable food waste were estimated by
multiplying the production-phase emission factor77 for each of the five food
types by the mass of each food type wasted in the consumer phase. See
Supplementary Information for further details.
© 2012 Macmillan Publishers Limited. All rights reserved
examination of avoidable consumer food wastage in the UK under-
lines the potential for demand-side mitigation (Fig.4).
For wastage of the ve foodstus examined (milk, poultry meat,
pig meat, sheep meat and potatoes), emission reductions in the UK
totalling more than 2 Gg N2O-N yr–1 seem achievable. As such,
interventions aimed at altering consumer behaviour — such as
towards smaller purchasing, serving and consumption volumes —
have the potential to signicantly reduce agricultural N2O emissions
in the UK.
At the global scale, N2O emissions associated with the produc-
tion of food that is lost or wasted can be approximated using an
average supply-chain loss rate80 in combination with global pro-
duction data29 and the production emission factors used above77
(Fig.5). Food ‘loss and wastage’ is here dened as the mass of a food
directed for human consumption that is lost or wasted in the sup-
ply chain. Food ‘losses’ refer to a decrease in the edible food mass
at the production, post-harvest and processing phases. Food ‘wast-
age’ refers to a decrease in the edible food mass in the retail and
consumer phase.
For the ve food types examined, loss and wastage-associated
emissions total more than 200GgN2O-Nyr–1 along the supply chain
(~3% of global N2O emissions from agriculture for these ve food
types alone). Again, the proportion that is realistically avoidable will
vary greatly depending on food type, location and stage in the sup-
ply chain, but very substantial emissions reductions seem possible
by addressing distribution and consumer-phase wastage80,82.
In this Review we have examined agricultures current and potential
future role in global N2O emissions. We nd that recent estimates of
agricultural N2O emissions using top-down and bottom-up meth-
odologies are in reasonable agreement at the global scale, with con-
sideration of N2O emissions arising from recycled nitrogen (such
as manure nitrogen) being important in the convergence of these
estimates. An on-going challenge in estimating national and sub-
national uxes is the limited geographical spread of measurements,
whereas for projecting future uxes robust modelling of human
population and diet is vital. Direct measurements of N2O emissions
from fast-expanding food-production sectors, such as aquaculture,
are also urgently required if global projections of food-related emis-
sions are to be improved.
For mitigation, improving nitrogen-use eciency in agricul-
tural production remains a key strategy by which increased food
demand in the future can be met without a commensurate increase
in N2O emissions. However, we suggest that very signicant emis-
sions reductions may also be achieved by better addressing dietary
choice and food wastage. Relatively high per capita meat intake
and consumer-phase food wastage in the developed world indi-
cates such interventions may be especially eective in some of the
Future studies should explore the drivers of national-scale die-
tary change and food wastage in more depth. Such work may then
help identify interventions that would reduce average dietary N2O
emissions intensity and highlight points in the supply chain where
the most eective waste reductions can be made.
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Author contributions
D.S.R. conceived the Review, conducted the analyses of diet and food waste impacts, and
prepared the manuscript. All authors contributed in the writing and editing of
the manuscript.
Additional information
e authors declare no competing nancial interests. Supplementary information
accompanies this paper on Reprints and
permissions information is available online at
Correspondence should be addressed to D.S.R.
© 2012 Macmillan Publishers Limited. All rights reserved
... In addition, the collection of experimental models studied on climate change shows that if the rate of increase in greenhouse gas concentrations increases in this way, the average temperature of the earth will increase dangerously in the near future (IPCC, 2007). In addition to industrial and management activities, the agricultural sector also produces greenhouse gases (Reay et al., 2012;Talebmorad, et al., 2021). Due to the fact that many soils has been cultivated for more than 100 years, intensive agriculture and tillage have reduced soil carbon by 30 to 50%, which causes it to be released into the atmosphere and global warming, and as a result the agricultural sector itself is affected by climate change (Salinger, 2005). ...
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Greenhouse gas emissions and their effects on global warming are one of the serious challenges of developed and developing countries. Investigating the amount of greenhouse gas emissions of different countries makes it possible to determine the share of countries in the production of greenhouse gases. The purpose of this study is to use DAYCENT and DNDC models to estimate the emission rate of methane, nitrous oxide, and carbon dioxide greenhouse gases as well as to estimate the global warming potential in Khuzestan agricultural lands in Iran. For this purpose, the gas sampling was done in rice, wheat, and sugarcane fields using a static chamber, and then the concentration of methane, nitrous oxide, and carbon dioxide was determined by using gas chromatography. In the following, DAYCENT and DNDC models were used to estimate gas emissions and the global warming potential of these gases was estimated. Finally, TOPSIS method was used to prioritize gas emissions. In order to evaluate the modeling accuracy, the statistical indicators of maximum error, root mean square error, determination coefficient, model efficiency, and residual mass coefficient were used. According to the results, the highest measured gas flux was obtained for rice fields at Baghmalek and the lowest for sugarcane in Abadan. The results of DAYCENT model estimation showed that the highest emissions were obtained for methane gas and rice cultivation, and lowest gas emissions were obtained for sugarcane cultivation. The results of DNDC model estimation also showed that the highest flux was determined for nitrous oxide gas in rice cultivation. The results of the estimation of global warming potential also showed that it was the highest in sugarcane cultivation (Shushtar station) and the DAYCENT model, and the lowest was also in wheat cultivation and the DNDC model. The statistical results of the estimation of DAYCENT and DNDC models showed that the DAYCENT model in sugarcane cultivation (Shushtar station) was the most accurate in estimating carbon dioxide gas, and the lowest accuracy was related to the DNDC model and sugarcane cultivation (Shushtar station) in estimating nitrous oxide gas. According to the results of agricultural activities in Khuzestan province, they have made a major contribution to the production of greenhouse gases, which, or the lack of attention to this issue, will have an effect on the future climate of this region.
... The distribution of a great amount of nitrogen to soil when the plants are not able to use it, makes no sense economically and poses many environmental threats [55]. Conversely, the use of foliar fertilization as an efficient supplement to the usual crop management practices, can help Mediterranean farmers to achieve environment-friendly crop production without renouncing the socioeconomic benefits [30,31]. ...
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... Nonetheless, many challenges are still addressed and need to be overcome, such as emissions, water footprint and phosphorus. The potential for climate change mitigation through reducing emissions of non-CO 2 greenhouse gases in agriculture has been discussed for many years [81]; however, for the agriculture sector to perform reduced greenhouse gases emission, climate-smart activities and improved food security are impetus for a more sustainable agricultural future [82]. ...
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The global agribusiness context faces at the same time challenges of feeding a growing global population that is used to safe and nutritious food, opportunities based on innovation, high technology and efficiency in the agri-food production systems from field to table. Given the context, this article aims to present the main key aspects of the circular economy to agro-industrial cooperatives. These contributions were named key aspects, such as circular and symbiotic practices, competitive advantages, innovation, cooperation and barriers and opportunities. The field presents a problem that few literature in fact discusses circular economy approaches in the context of agro-industrial cooperatives. As a methodological procedure, a literature review was carried out in three databases to obtain relevant documents and thus analyse and discuss some characteristics based on circular economy practices applied in agro-industrial cooperatives. As a result, a diagnosis of the current scenario that agro sector organizations are facing in terms of the main rural activities and sustainable practices that relate to the circular economy; measures taken to generate competitive advantage; innovation behaviour; and how linear and circular business models are being applied in the agroindustry. A framework is presented to show potential routes strategies for closing the cycle in an agro-industrial cooperative. The opportunities are based on the implementation of high technology in the field, the use of bioenergy and the development of new circular business models throughout the agro-value chain. The study has contributions to rural properties and managers of cooperatives in terms of waste reduction, innovation generation and increases in activities and processes based on circular economy.
... Much experimental data are now available for the development of country-specific EFs and several countries use Tier 2 or Tier 3 approaches in their inventories. However, most countries still report their direct N 2 O emissions using Tier 1 EFs, especially in the developing world (Reay et al., 2012;Mancia et al., 2022), where insufficient data are available for a higher tier approach. Given the importance of developing nations in the share of the global food production and the potential to increase yields to meet future food demand (Alexandratos and Bruinsma, 2012;Takahashi et al., 2020), development of Tier 2 EFs and approaches to estimate N 2 O emission and mitigation practices for these regions must be seen as a priority. ...
According to the available guidelines, good practices for calculating nitrous oxide (N 2 O) emission factors (EFs) for livestock excreta and manure application include that sampling duration should be of at least one year after the nitrogen (N) application or deposition. However, the available experimental data suggest that in many cases most emissions are concentrated in the first months following N application. Therefore resources could be better deployed by measuring more intensively during a shorter period. This study aimed to assess the contribution of the N 2 O flux in the period directly after N application to the annual net emission. We used a database of 100 year-long plot experiments from different excreted-N sources (dung, urine, farmyard manure and slurry) used to derive EFs for the UK and Ireland. We explored different shorter potential measurement periods that could be used as proxies for cumulative annual emissions. The analysis showed that the majority of emissions occur in the first months after application, especially in experiments that i) had urine as the N source, ii) had spring N application, iii) were conducted on fine-textured soils, or iv) showed high annual emissions magnitude. Experiments that showed a smaller percentage of emissions in the first months also had a low magnitude of annual net emissions (below 370 gN 2 ON ha − 1 year − 1), so the impact of measuring during a shorter period would not greatly influence the calculated EF. Accurate EF estimations were obtained by measuring for at least 60 days for urine (underestimation: 7.1%), 120 days for dung and slurry (4.7 and 5.1%) and 180 days for FYM (1.4%). At least in temperate climates, these results are promising in terms of being able to estimate annual N 2 O fluxes accurately by collecting data for less than 12 months, with significant resource-saving when conducting experiments towards developing country-specific EFs.
Nitrogen (N) application strongly affects both the total spikelets and grain weight in rice (Oryza sativa L.), thereby affecting grain yield. Grain weight is closely related to the grain-filling process after the heading stage, and can be regarded as a combination of grain size and grain density (GD). However, there is a lack of information about the response of GD in rice to N. Here, we examined in a lager panicle hybrid indica rice at two field experimental sites the responses of grain traits (including GD), grain yield, and yield components to various N treatments and their relationships with each other. In this study, the grains with six GD ranges were fractionated into the light grain (1.00 g ml⁻¹ ≤ GD < 1.15 g ml⁻¹) and heavy grain or high-density grain (GD ≥ 1.15 g ml⁻¹). High N application increased the total spikelets m⁻², but did not result in high grain yield due to reduced grain weight (seed-setting rate and 1000-grain weight). Reduction of the 1000-grain weight under high N was related to the decrease in grain volume and high-density grain content (the ratio of the weights of high-density grains to the total grains weight). As N application increased from 0 to 225 kg ha⁻¹, on average, the high-density grain content decreased by 31.93 %, from 78.21 % to 53.24 %. Grain plumpness and GD were the main factors affecting grain weight. GD was more important to the grain weight when grain size was smaller, and plumpness degree and GD were both crucial for grain weight when grain volume was larger. Compared with light grains, heavy grains had higher amylose content and lower crude protein content. These results indicated that the constraint and compensation relationship between spikelet number and grain weight in rice was also reflected in the equilibrium between grain size and GD. Although high N input in rice production increased the total spikelets m⁻², high N input decreased the grain volume, especially the high-density grain content.
Changing redox conditions in paddy fields due to more frequent events govern the soil biogeochemical processes that further affect the generation and emission of N2O from soil. However, studies on the effect of rice cropping on soil N2O emission under rice-growing seasons and relevant mechanisms are scarce. A double rice cropping-fallow (RF) field in central China, with rice cropping (RF-CC) and non-rice cropping (RF-NC) cultivation, were selected to investigate that effect of rice planting on soil N2O emissions and key functional genes related to N2O-production and consumption, such as the ammonia-monooxygenase gene derived from ammonia-oxidizing archaea (AOA-amoA) and ammonia-oxidizing bacteria (AOB-amoA) and nitrous oxide reductase gene (nosZ). The results of the static opaque chamber-gas chromatography technique showed that seasonal cumulative N2O emissions from RF-NC treatment during the first and second rice growing season were 1.02 ± 0.17 and 2.95 ± 0.12 kg N ha⁻¹, respectively, and were comparable to those from RF-CC treatment (0.82 ± 0.09 and 2.97 ± 0.18 kg N ha⁻¹, respectively), indicating rice cropping had no crucial effect on soil N2O emissions. No significant difference was found in the abundance of the aforementioned genes between two treatments. For both RF-CC and RF-NC treatments, N2O fluxes were positively correlated with the soil available nitrogen, such as dissolved inorganic N (DIN) and microbial biomass N (MBN), suggesting that soil available N was a key factor controlling N2O emissions. Increased transcripts of the AOA-amoA gene may facilitate N2O production and were confirmed by the positive linear relations between N2O fluxes and the abundance of AOA-amoA gene for both treatments. The structural equation model (SEM) indicated that both soil available N and AOA-amoA gene contributed more than 70% to their effects on N2O emission for both treatments. These results implied that soil N2O emissions during therice-growing period could be regulated by the interaction of soil parameters and related functional genes, rather than the effect of rice cropping under a RF system.
Reducing greenhouse gas emissions and loss of soil fertility, while ensuring stable yield, is crucial to achieving “Carbon Peak” and “Carbon Neutrality” in grain production but is different to achieve. In this study, we aimed to understand the effects of conservation tillage on the yield, GHG emissions, soil carbon and nitrogen sequestration, and net ecosystem economic benefit (NEEB) to promote the transformation of tillage methods in the Loess Plateau, China, based the continuous application (>11 yr) of conservation tillage. Four-year observations showed that zero tillage and chisel plough tillage obviously reduced N2O and CO2 emissions but greatly increased CH4 uptake relative to plow tillage. Furthermore, the coupling relationship between CO2 and N2O fluxes was weakly antagonistic during the winter wheat growing season, whereas there was a strong synergistic coupling between these fluxes during the summer maize growing season. An antagonistic coupling relationship appeared between CH4 and N2O fluxes, whereas CO2 and CH4 fluxes appeared to be randomly related. Importantly, when carbon (C) emission reached 17.5 Mg C ha⁻¹yr⁻¹, and nitrogen (N) emission reached 7.8 kg N ha⁻¹yr⁻¹, the soil changed from a C sink to C source; when C emission reached 17.3 Mg C ha⁻¹yr⁻¹, and N emission reached 6.8 kg N ha⁻¹yr⁻¹, the soil changed from a N sink to N source. Considering yield gains, agricultural activity costs, and global warming potential costs together, chisel plough tillage significantly increased NEEB by 19.87%. Together, the advantages of long-term chisel plough tillage can reduce greenhouse gases emissions and increase NEEB while achieving soil carbon and nitrogen sequestration. Therefore, chisel plough tillage practice has both economic and environmental benefits.
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Increasing contributions of nitrous oxide (N 2 O) from agriculture to the atmosphere is a concern. We quantified N 2 O emissions from barley fields after repeated injections of liquid manure in Central Alberta, Canada. Manure alone was injected in the fall or spring, and we also evaluated two nitrification inhibitors (NIs: nitrapyrin and DMPP) admixed with the manure. Flux measurements were done with surface chambers from soil thawing to freezing. Soil moisture, ammonium and nitrate were repeatedly measured. Across all manure treatments, annual N 2 O emissions ranged broadly from 1.3 up to 15.8 kg N 2 O–N ha − 1 , and likewise, the direct emission factor (EF d ) varied widely from 0.23 up to 2.91%. When comparing the manure injections without NIs, spring-manure had higher annual N 2 O EF d than fall-manure. The effectiveness of NIs on reducing emissions manifested only in moist soils. The spring thaw after the last manure injections was very wet, and this generated high N 2 O emissions from soils that had received repeated manure injections in the previous years. We interpreted this result as an increased differential residual effect in soils amended with spring-manure in the previous growing season. This outcome supports the need to account for emissions in succeeding springs when estimating N 2 O EF d of manure injections. Neglecting this residual spring-thaw N 2 O emission would lead to a substantial underestimation of year-round EF d . Across all treatment combinations, increased spring-thaw N 2 O emissions were associated with increases in both moisture and postharvest nitrate in these heavily-manured soils.
Sustainable ammonia synthesis at mild conditions that relies on renewable energy sources and feedstocks is globally sought to replace the current Haber-Bosch process. Electricity-driven plasma catalysis is receiving increasing attention...
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Inputs of carbon to soil may be used to stimulate microbial growth and immobilize excess nitrogen from sources such as livestock urine. However, the growth responses of microbial taxa to carbon inputs under conditions of excess soil nitrogen remain poorly understood. Using DNA metabarcoding and a field-based soil lysimeter experiment, we characterised the temporal responses (up to 112 days) of bacterial and fungal communities to a simulated bovine urine event plus inputs of labile carbon (sucrose) at two concentrations. Fungal communities were impacted more strongly than bacterial communities by carbon inputs under simulated urine patch conditions and had more variable responses among taxa. The richness of Chytridiomycota and Glomeromycota were most negatively affected, and Tremellomycetes most positively affected, by carbon inputs. A minority of fungal ASVs had greatly increased abundances in response to carbon, while fungal trophic composition became highly dominated by saprotrophs by the experiment end. Bacterial taxa showed consistent trends of declining (to about 14 days) and recovering (to 112 days) richness in response to urine and carbon inputs, but carbon-related evenness and abundance trends varied between taxa. Actinobacteria, Bacteroidetes, Betaproteobacteria, and Gammaproteobacteria each increased in abundance in response to carbon, whereas Acidobacteria, candidate division WPS-1, Planctomycetes, Deltaproteobacteria, and Verrucomicrobia each decreased in abundance. These results show that labile carbon inputs to limit nitrogenous leaching support the resilience of prokaryote communities to bovine urine events but may have long-term impacts on fungal community composition and function, with potential consequences for soil food webs, carbon sequestration, and agricultural productivity.
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Most prior studies have found that substituting biofuels for gasoline will reduce greenhouse gases because biofuels sequester carbon through the growth of the feedstock. These analyses have failed to count the carbon emissions that occur as farmers worldwide respond to higher prices and convert forest and grassland to new cropland to replace the grain (or cropland) diverted to biofuels. By using a worldwide agricultural model to estimate emissions from land-use change, we found that corn-based ethanol, instead of producing a 20% savings, nearly doubles greenhouse emissions over 30 years and increases greenhouse gases for 167 years. Biofuels from switchgrass, if grown on U.S. corn lands, increase emissions by 50%. This result raises concerns about large biofuel mandates and highlights the value of using waste products.
Jerome believed that the task of the commentator was to convey what others have said, not to advance his own interpretations. However, an examination of his commentaries on the Prophets shows that their contents are arranged so as to construct a powerful, but tacit, position of authority for their compiler. By juxtaposing Jewish and Greek Christian interpretations as he does, Jerome places himself in the position of arbiter over both exegetical traditions. But because he does not explicitly assert his own authority, he can maintain a stance of humility appropriate for a monk. Here, Jerome may have been a more authentic representative of the tradition of Origen than was his rival, for all that he was willing to abjure Origen's theology.
Developing countries, particularly those in sub-Saharan Africa (SSA), remain marginalized in global carbon markets despite significant mitigation opportunities in agriculture and forestry. The economic potential for mitigation through agriculture in the African region is estimated at 17 per cent of the total global mitigation potential for the sector. Similarly, Africa's forestry potential is 23 per cent of the global total for the sector. To unleash the huge potential for mitigation in SSA, carbon markets should be expanded to include projects related to agriculture, forestry and other land uses (AFOLU). Given the important synergies between agricultural mitigation and adaptation, and the difficulties in reaching out to smallholder farmers and herders, as well as the increasing poverty and hunger in the region, this article suggests that not only should carbon markets be expanded to include more AFOLU project types, but carbon markets should also increase benefits directed at smallholder farmers. Domestic policies in SSA should also be reformed to increase the profitability of environmentally sustainable practices that generate income for small producers and create investment flows for rural communities. This review paper provides an overview of global carbon markets, focusing on opportunities for carbon trading in agriculture in SSA. Major constraints to the participation of SSA in global carbon markets are discussed, and options for integrating the region into global carbon markets are proposed.
Emissions of nitrous oxide (N2O), a potent greenhouse gas, tend to be underestimated by standard methods of quantification provided by the Intergovernmental Panel on Climate Change (IPCC) [IPCC, 2006], recent research suggests. Better quantification of agricultural N2O emissions improves greenhouse gas inventories, allows for better evaluation of the environmental impacts of different cropping systems, and increases the understanding of the nitrogen (N) cycle in general. Proper quantification of N2O emissions is particularly important in the context of calculating net greenhouse gas emissions from biofuel cropping systems because these emissions offset the greenhouse gas benefits of displacing fossil fuel and can even lead to biofuel systems being a net greenhouse gas source [Crutzen et al., 2008]. The global warming potential of N2O is approximately 300 times that of carbon dioxide, and N2O emissions represent approximately 6% of the global anthropogenic greenhouse gas source [IPCC, 2007]. N2O also contributes to stratospheric ozone destruction. N2O is produced in soils through the microbial processes of nitrification and denitrification. Soil water content, temperature, texture, and carbon availability influence N2O emissions, but the strongest correlate is usually N inputs to the system, especially at large scales [Stehfest and Bouwman, 2006]. In addition to direct emissions, N inputs to agricultural soils also contribute to N2O emissions indirectly [IPCC, 2006] when nitrate that has leached or run off from soil is converted to N2O via aquatic denitrification and when volatilized non-N2O N-oxides and ammonia are redeposited on soils and converted to N2O.
Highlights ► Climate change will strengthen the importance of indirect rather than direct N2O emissions from agricultural use of reactive N. ► Denitrification and N2O emissions from agriculture are mediated by a multitude of climate-change-sensitive controls. ► Extreme events may increase indirect rather than direct N2O emissions. ► Warmer temperature may either decrease or increase direct N2O emissions and increase indirect N2O losses. ► Via the plant–soil link, elevated atmospheric CO2 concentrations may increase direct but decrease indirect N2O emission. ► The overall net response of N2O losses to climate change remains mostly uncertain.