2010 Ifa Greenhouse Gas (1)

8/8/2019 2010 Ifa Greenhouse Gas (1)

1/67

Greenhouse gas budgetsof crop production currentand likely future trends

Helen C. Flynn and Pete Smith


2/67

Greenhouse gas budgets of crop production current and likely future trendsHelen C. Flynn and Pete Smith

First edition, IFA, Paris, France, January 2010Copyright 2010 IFA. All rights reserved

The publication can be downloaded from IFAs web site.

28, rue Marbeuf,75008 Paris, FranceTel: +33 1 53 93 05 00Fax: +33 1 53 93 05 45/ [email protected]

Layout: Claudine Aholou-Putz, IFAGraphics: Hlne Ginet, IFA

The designation employed and the presentation of material in thisinformation product do not imply the expression of any opinionwhatsoever on the part of the International Fertilizer Industry

Association. This includes matters pertaining to the legal status ofany country, territory, city or area or its authorities, or concerningthe delimitation of its frontiers or boundaries.


3/67

3Greenhouse gas budgets of crop production current and likely future trends

About the report and the authors 5

Acknowledgements 5

Symbols, units, acronyms and abbreviations 6

Executive summary 7

1. Introduction 9

2. Recent and current greenhouse gas budgets 10

2.1 Overview of global and regional agricultural emissions and sources 10

2.2 Recent trends (1990-present) 11

2.3 N2O emissions from agricultural soils 11

2.3.1 Soil N2O emissions from N fertilizer use 11

2.3.2 Soil N2O emissions per unit of agricultural output 13

2.3.3 Soil N2O emissions from crop residue incorporation and N-fixing crops 13

2.4 CH4

emissions from rice cultivation 14

2.5 CH4

budget of other croplands 14

2.6 Greenhouse gas emissions from land use change 16

2.7 Indirect emissions from crop production 162.7.1 Emissions from fertilizer production and distribution 162.7.2 Emissions associated with other agrochemicals 172.7.3 On-farm energy use emissions 18

3. Future baseline emissions 19

3.1 General trends in future agriculture 19

3.2 Overview of baseline predictions 19

3.3 Regional trends 20

3.4 Future fertilizer use and associated emissions 22

4. Mitigation potential 24

4.1 Mitigation options and mechanisms 24

4.2 Overview of cropland management mitigation practices 244.2.1 Agronomy 244.2.2 Nutrient management 254.2.3 Tillage/residue management 254.2.4 Water management 254.2.5 Rice management 264.2.6 Agro-forestry 26

4.2.7 Land cover (use) change 26

Contents


4/67

4 International Fertilizer Industry Association

4.3 Per-area mitigation potentials 27

4.4 Total global mitigation potentials 29

4.5 N2O mitigation potential of improved nutrient management 30

4.5.1 Overview of factors affecting N use efficiency 30

4.5.2 N2O Mitigation potential case studies 34

4.6 Carbon sequestration potential of improved nutrient management 37

4.7 Mitigation potential of tillage and residue management 384.7.1 Zero tillage 384.7.2 Reduced, conservation or minimum tillage 404.7.3 Residue management 41

4.8 Mitigation potential of agronomy measures 424.8.1 Catch crops and increased cover 424.8.2 Crop selection and rotation 42

4.9 Mitigation potential in rice production 434.9.1 Water management 434.9.2 Rice cultivar 444.9.3 Fertilization and other additions 444.9.4 Treatment of crop residues 44

4.10 Mitigation of indirect emissions 454.10.1 Emissions from fertilizer production 454.10.2 On-farm energy use 46

5. Conclusions 47

Appendix A Comparing methodologies for calculating N2O emissions 48

References 51


5/67


About the report and the authors

About the report

Tis report has been prepared on request o theInternational Fertilizer Industry Association (IFA),as a contribution to the international negotiationson climate change. It provides an up-to-date state othe scientifc knowledge on greenhouse gas balancesin relation to crop production and ertilizer use. Tisreport has been written or policy makers, scientists

and the ertilizer industry.

About the authors

Dr Helen Flynn has worked as a Post DoctoralFellow in the Institute o Biological & EnvironmentalSciences at the University o Aberdeen since 2003.During this time she has written many reviews anddiscussion papers or various organizations, including

governmental bodies. Her recent reviews or NaturalEngland, the Scottish Government, and the EU

project have all ocused on the impacts o agricultureon carbon storage and greenhouse gas emissions.

Proessor Pete Smith is the Royal Society-WolsonProessor o Soils & Global Change in the Institute oBiological & Environmental Sciences at the Universityo Aberdeen. He is an internationally recognizedexpert in the area o agriculture and climate change.He has been a Convening Lead Author, Lead Authorand Author or various Intergovernmental Panel on

Climate Change (IPCC) Reports, or which IPCCwas awarded the Nobel Peace Prize (jointly withAl Gore) in 2007. He was awarded a Royal Society-Wolson Research Merit Award in 2008, and waselected as Fellow o the Society o Biology in 2008,as Fellow o the Royal Society o Edinburgh in2009, and as a Rothamsted Research Fellow in 2010.Proessor Smith contributes to many national andinternational projects on carbon cycling, greenhousegases, bioenergy and agriculture. He leads a team thatdevelops models o greenhouse gas emissions, liecycle analysis, crop growth and carbon storage, and

is an Editor or Global Change Biology and GlobalChange Biology Bioenergy (and our other journals).

Acknowledgements

Te authors are grateul or unding or this reviewrom the International Fertilizer Industry Association(IFA). Tey also acknowledge the valuable inputsprovided by Cliord Snyder (IPNI), Frank Brentrup(Yara) and Patrick Heer (IFA), who reviewed thedra report.


6/67


Symbols, units, acronyms and abbreviations(as used in this report)

BAT Best available technologyBMP Best management practiceC CarbonCH

4Methane

CI Confdence intervalCO

2Carbon dioxide

CO2-eq Carbon dioxide equivalent

DCD DicyandiamideDNDC DeNitrifcation-DeCompositionECCP European Climate Change ProgrammeEF Emission actorEU European UnionFAO Food and Agriculture Organization o the United NationsGcal Gigacalorie (109 calories)Gg Gigagram (109 grams = 1 thousand metric tonnes)GHG Greenhouse gasGWP Global warming potentialha HectareIFA International Fertilizer Industry AssociationIPCC Intergovernmental Panel on Climate ChangeK Potassium

kg Kilogramkm KilometreLCA Lie cycle assessmentLUC Land use changesMha Million hectaresmV MillivoltN NitrogenN

2O Nitrous oxide

NH3

AmmoniaNH

4+ Ammonium

NUE Nitrogen use e ciencyP Phosphorus

Pg Petagram (1015 grams = 1 billion metric tonnes)SOC Soil organic carbont Metric tonneTg Teragram (1012 grams = 1 million metric tonnes)UNFCCC United Nations Framework Convention on Climate ChangeUSA United States o AmericaUS-EPA United States Environmental Protection Agencyyr year


7/67


Agriculture contributes around 10-12 % o totalglobal greenhouse gas (GHG) emissions but isthe main source o non-carbon dioxide (CO

2) GHGs,

emitting nearly 60 % o nitrous oxide (N2O) and

nearly 50 % o methane (CH4) (Smith et al., 2007a).

N2O is produced by microbial transormations

o nitrogen (N) in soils and animal waste andthereore oen associated with N ertilizer inputs inagricultural systems. CH

4is generated when organic

matter decomposes under anaerobic conditionsand is mainly associated with ruminant livestock,manure storage and rice production under oodedconditions. Tese emissions are currently estimatedas 3.3 Pg CO

2-eq yr-1 rom CH

4and 2.8 Pg CO

2-eq

yr-1 rom N2O emissions (Smith et al., 2007a). Large

exchanges o CO2

occur between the atmosphere andagricultural ecosystems but emissions are thought tobe roughly balanced by uptake, giving a net ux oonly around 0.04 Pg CO

2yr-1, less than 1 % o global

anthropogenic CO2

emissions (Smith et al., 2007a).However, land use change towards more cultivated

land may contribute a urther 5.9 2.9 Pg CO2-eqyr-1, representing 6-17 % o total global GHGemissions (Bellarby et al., 2008), and i indirectemissions rom agrochemical and uel usage are alsoincluded, an extra 0.4-1.6 Pg CO

2-eq yr-1 (0.8-3.2 %)

can be attributed to agriculture. In total, direct andindirect emissions rom agricultural activity andland use change to agricultural use could contributearound a third o all GHG emissions (Bellarby et al.,2008).

Globally, agricultural land use has increased by0.8 % between 1991 and 2002, and these changes aresplit with an increase o 2.1 % in developing countries

partially mitigated by a 1.5 % drop in the developedworld (Smith et al., 2007a). Tis trend is likely tocontinue with projected increases in world population,and shis in diet requiring more resources per unito ood produced, being concentrated in areas suchas South and East Asia. I agricultural production isgoing to signifcantly increase while also minimizingits impact on uture climate change, it is importantto understand both its current contribution to GHGbudgets and how agricultural management practicescan inuence them. Tis report explores these issuesand identifes key gaps in our knowledge and problems

which are setting back our understanding. Teseinclude the lack o work addressing GHG emissionson the basis o agricultural productivity rather than

cultivated area, and inconsistent methodologies ormeasuring things like soil carbon under dierenttillage regimes and or calculating N

2O emissions,

which make comparisons between systems di cult.Tere is also a distinct lack o research coveringtropical regions, a gap which needs to be urgentlyaddressed given the likely increases in production inthese regions. Tis is especially important becausethe current trend, or example in Latin America, is

towards increasing areas o cultivation rather thanintensiying production on existing agriculturalland (van Vuuren et al., 2008). Tis will have adisproportionately large impact on GHG budgets dueto the loss o stored soil organic carbon (SOC) whichoccurs when orests and grasslands are converted tocropland (Murtyet al., 2002; Guo and Giord, 2002;Carlton et al., 2009).

I agriculture continues to develop according toexisting trends and no action is taken to mitigateGHG emissions rom the sector, they are expectedto reach around 8.2 Pg CO

2-eq yr-1 by 2030 (Smith

et al., 2007a; Verg et al., 2007). However, there issignifcant potential to mitigate these emissionsusing existing agricultural technology. Estimateso this potential vary, especially when economicconsiderations are included in the calculations, butaround 1.5-4.3 Pg CO

2-eq yr-1 seems reasonable, with

the greatest potential laying in cropland managementpractices (Smith et al., 2007a). O these practices,improving nutrient management is particularlycrucial, especially given the need to increaseagricultural productivity while cultivating as littlenew land as possible. Key to this is improving cropN use e ciency (NUE) through the use o ertilizer

best management practices (BMPs); using the rightsource, at the right rate, at the right time, and atthe right place (Roberts, 2007). Implementationo ertilizer BMPs has been shown to both reduceN applications and associated N

2O emissions and

increase yields. For example, in China, the worldslargest consumer o mineral N ertilizers, BMPs havebeen shown to reduce N inputs by 20-40 %, increaseyields by 2-12 %, increase N recovery rates by 10-15 %and reduce N losses by 10-50 %, in comparison withtraditional arming practices (Zhang et al., 2007).Even in developed countries with existing trends o

improving NUE, there is still the potential or urthermitigation (ECCP, 2001; Halvorson et al., 2009; US-EPA, 2009).

Executive summary


8/67


Better integration o organic resources such asanimal waste and crop residues into crop nutritionprograms can assist in improving soil ertility whilealso helping to mitigate indirect emissions romertilizer production. Tese indirect emissionscurrently contribute around 420 g CO

2-eq yr-1 (IFA,

2009a) and there is considerable scope to mitigatethese, and any uture increases, using existingmethods such as carbon capture and N

2O abatement

technologies. Tis could save around 200 g CO2-eq

yr-1 (IFA, 2009a). Other GHG mitigation strategiesinclude the use o no-till or reduced tillage regimes.Tere is debate regarding the mitigation potentialo tillage measures. Tis is because assessing the netimpact on GHG emissions requires comparing theimpacts on both SOC, which is oen biased by feldmeasurements taken only in the top 30 cm o the soil

profle (Baker et al, 2007), and N2O emissions, whichare highly variable over time. Te balance o evidencedoes, however, point to a net beneft or suitablesoil types, although more research may still aid our

understanding in this area. Reducing tillage also givesindirect savings in terms o reducing on-arm uel useand associated emissions.

Agronomy measures are perhaps the most di cultmitigation practices to assess at present. Using catchcrops, legumes and particular types o crop rotationscould potentially reduce GHG emissions per hectareo cropland but can also impact on yields, potentiallyrequiring additional land to be cultivated at greatcost in terms o SOC losses. For example, the globalwarming potential (GWP) o an intensive continuousmaize crop may be 2-3 times higher, on a per hectarebasis, than that o a conventionally-tilled maize-wheat-soybean rotation, but produce only 63 % o thenet GHG emissions when compared on the basis oCO

2-eq per Gcal o ood yield (Robertson et al., 2000;

Adviento-Borbe et al., 2007; Snyder et al., 2009).

Tereore, more work is needed to compare net GHGemissions rom dierent cropping systems over thelong term and on a per unit o production basis.


9/67


Agriculture contributes around 10-12 % o totalglobal greenhouse gas (GHG) emissions but isthe main source o non-carbon dioxide (CO

2) GHGs,

emitting nearly 60 % o nitrous oxide (N2O) and

nearly 50 % o methane (CH4) (Smith et al., 2007a).

CO2

is mostly released when microbes decomposeplant or soil organic matter under aerobic conditions,or when organic matter is burnt, but uptake byvegetation means that the net ux accounts or less

than 1 % o global anthropogenic CO2 emissions(Smith et al., 2007a). N

2O is produced by microbial

transormations o nitrogen (N) in soils and animalwaste, under both aerobic and anaerobic conditions,and emissions are oen highest when available Nexceeds plant requirements, especially under wetconditions (Oenema et al., 2005; Smith and Conen,2004). CH

4is generated when organic matter decays

under anaerobic conditions, the main examplesbeing ermentation digestion by ruminant livestock,microbial decomposition o stored manure, and riceproduction under ooded conditions (Mosier et al.,

1998b). Emissions rom land use changes and uel andenergy use are all accounted or separately within theIntergovernmental Panel on Climate Change (IPCC)methodology, but i changes to cultivated land andindirect emissions associated with agriculture, suchas uel use or arm vehicles and or agrochemicaland ertilizer production, are also included, thenagriculture could contribute around a third o totalglobal GHG emissions, mainly due to deorestationor agriculture (Bellarbyet al., 2008).

Te world population has doubled over the past40 years and is predicted to reach 9 billion by 2040(US Census Bureau, 2008), putting increasing

demands on agricultural production. As a result,the US-EPA (2006a) estimates that GHG emissionsrom agriculture will increase by around 10-15 % perdecade over the next 30 years. However, emissions aredecreasing in some regions, such as Europe, and activemanagement o agricultural systems has the potentialto mitigate signifcant levels o GHG emissions,helping to limit the impact on uture climate.

Tis review ocuses on the GHG budgets o cropproduction, in terms o N

2O, CH

4and CO

2, and the

impact o ertilizer use on them. It does not considerammonia or other N oxides, and only briey touches

on the contribution o livestock production and

manure recycling to overall agricultural emissionsand their mitigation potential, except whenconsidering manure that is applied to cropland soils.Indirect emissions are also considered when theyrelate directly to agricultural production, or exampleon arm energy use and emissions associated with theproduction o ertilizers and other agrochemicals.

Te main body o the report is split into threesections. Te frst reviews the present level o

agricultural GHG emissions, ocusing particularly onN

2O emissions rom soils and the ertilizer applied to

them, at a range o scales, and includes a discussion onthe variability o feld measurements and uncertaintiesinherent in dierent calculation methodologies. TeCH

4balance o rice production and arable arming

is considered alongside issues surrounding the CO2

balance o changing land use. Indirect emissions romertilizer production and transport, agrochemicalproduction and on-arm uel use are also discussed.Te second section reviews estimates o utureagricultural GHG emission levels assuming a baseline

or business-as-usual scenario, at both global andregional level, and also estimates uture ertilizerrequirements. Te fnal section reviews optionsor mitigating these emissions, beginning with anoverview o mechanisms and potential managementstrategies, then reviewing their global technical andeconomical potential, and fnally provides an in-depth review o the mitigation potential o variousarable cropland management options, ocusing onimproved nutrient management, including casestudies o ertilizer use and e ciency in China andIndia, the two largest consumers o N ertilizer, andalso covering tillage and cropping systems. Mitigation

options are also reviewed with relation to rice cropsspecifcally, since ooded cropping systems are sodierent rom general arable conditions. In termso the mitigation o indirect emissions, the potentialor reducing emissions rom ertilizer production isdiscussed, and the impact o reduced tillage on on-arm energy use is also reviewed.

As this report covers multiple GHGs, all emissionlevels have been converted into CO

2equivalents

according to their global warming potentials (GWP),which are taken to be 296 or N

2O and 23 or CH

4

(IPCC, 2006), to allow easy comparison between

gases.

1. Introduction


10/67


2.1 Overview of global and regionalagricultural emissions and sources

According to the Agriculture chapter o the IPCCFourth Assessment Report (Smith et al., 2007a),approximately 40-50 % o the Earths surace ismanaged or agricultural purposes and contributes10-12 % o global greenhouse gas (GHG) emissions,around 5.1-6.1 Pg CO

2-eq yr-1 in 2005. Tis is made

up o 3.3 Pg CO2-eq yr-1 rom methane (CH4) and 2.8Pg CO

2-eq yr-1 rom nitrous oxide (N

2O) emissions.

Although there are large exchanges o carbon dioxide(CO

2) between the atmosphere and agricultural

ecosystems, emissions are thought to be roughlybalanced by uptake, giving a net ux o only around0.04 Pg CO

2yr-1, less than 1 % o global anthropogenic

CO2

emissions (electricity and uel use are notincluded in this sector) (Smith et al., 2007a). Landuse change is accounted or separately, but changeto cultivated land is thought to contribute a urther5.9 2.9 Pg CO

2-eq yr-1, 6-17 % o total global GHG

emissions (Bellarbyet al., 2008). I indirect emissionsrom agrochemical production and distribution andon-arm operations, including irrigation, are alsoincluded, an extra 0.4-1.6 Pg CO

2-eq yr-1 (0.8-3.2 %)

can be attributed to agriculture, meaning that, intotal, direct and indirect emissions rom agriculturalactivity and land use change to agricultural use couldcontribute as much as 32.2 % o all GHG emissions(Bellarbyet al., 2008).

Agriculture is the main source o global non-CO

2GHG emissions, contributing around 47 % o

anthropogenic CH4

emissions and 58 % o N2O,

although there is a large degree o uncertainty around

estimates or both agricultural contribution andtotal anthropogenic emissions. Te main sources,N

2O rom soils and CH

4rom enteric ermentation,

make up around 70 % o non-CO2

emissions romthe sector, with biomass burning, rice cultivation, andmanure management, accounting or the remainder(Smith et al., 2007a; see Figure 1).

Te relative magnitude o emissions and sourcesvary greatly between dierent regions o the world.In Europe, agriculture contributed only 11 % o totalGHG emissions in 1990, with CH

4emissions rom

agriculture contributing 41 % o total CH4

emissions,

and N2O rom the sector contributing 51 % o totalN

2O emissions (ECCP, 2001), whereas in nine Arican

countries, agriculture contributed over 80 % o totalGHG emissions in the mid 1990s (UNFCCC, 2005).

In 2005, N2O rom soils (mainly associated with

ertilizer and manure applications) was the mainsource o agricultural GHG emissions in seven outo ten world regions, while in the other three (LatinAmerica and the Caribbean, Eastern Europe and the

Caucasus and Central Asia, and OECD Pacifc), CH4rom enteric ermentation was the main source (US-EPA, 2006a), as these three regions had 36 % o worldcattle numbers and 24 % o world sheep in 2004 (FAO,2003). Emissions rom rice cultivation and biomassburning were heavily concentrated in developingcountries, with 97 % and 92 % o world totals,respectively. South and East Asia were responsibleor 82 % o CH

4emissions rom rice cultivation as it

is a dominant ood source in this region, while 74 %o total emissions rom biomass burning originatedin Sub-Saharan Arica, and Latin America and theCaribbean. Manure management was the only source

where resulting GHG emissions were higher indeveloped regions (52 %) than in developing regions(US-EPA, 2006a).

Te balance between the large uxes o CO2

emissions and uptake in agricultural land is uncertain.A study reported in the US Environmental ProtectionAgency Report (US-EPA, 2006b) showed that somecountries and regions have net emissions, whileothers have net removals o CO

2. However, except

or the countries o Eastern Europe, the Caucasusand Central Asia, which had an annual emission o26 g CO

2yr-1 in 2000, all other countries showed

very low estimated net uxes, whether emissionsor removals. For this reason, soil carbon uxes aremostly discussed in terms o mitigation potentialin this report (see section 4) as they are more

2. Recent and current greenhouse gas budgets

Figure 1. Global non-CO2 agricultural emissionsources in 2005 (Source: Smith et al., 2007a)

Manuremanagement

Rice production

BiomassburningCH4 from

enteric fermentation

N2O from soils

12%32%

38% 7%

11%


11/67


associated with land-use change (see section 2.6)than production rom land already under agriculturalmanagement, although indirect emissions associatedwith uel use and ertilizer production are covered insection 2.7. Emission levels and sources o N

2

O aredescribed, ocusing particularly on those associatedwith cropland management and ertilizer use, whileCH

4is mostly discussed in terms o rice production,

as animal production and manure management areoutside the scope o this report (see sections 2.3-2.5).

2.2 Recent trends (1990-present)

Globally, agricultural land use has increased by 0.8 %between 1991 and 2002, with an increase o 2.1 % indeveloping countries partially mitigated by a 1.5 %drop in the developed world, and now covers 5023

million hectares (Mha), 28 % o which is cropland(Smith et al., 2007a). In line with this increasein activity, CH

4and N

2O emissions rom global

agriculture have increased; Verg et al. (2007) reporta 6.5 % increase between 1990 and 2000, while the USEPA (2006a) report a 17 % increase between 1990 and2005 globally, with an annual average o 58 g CO

2-

eq yr-1, split roughly equally between the two gases,and with biomass burning (N

2O and CH

4), enteric

ermentation (CH4) and soil N

2O emissions together

explaining 88 % o this increase.On a regional basis, these changes represent a

substantial increase in agricultural emissions romthe developing world, and a decline in correspondingemissions rom Europe and other, generally developed,regions. According to the US-EPA, the changesbetween 1990 and 2005 are composed o a 32 % increasein non-CO

2emissions (equivalent to 73 g CO

2-eq

yr-1) rom the fve regions o Non-Annex I (developing)countries and a decrease o 12 % (equivalent to 15 gCO

2-eq yr-1) rom the other fve regions (with mostly

Annex I / developed countries) collectively (US-EPA,2006a), while data rom national GHG inventoriesshows that total agricultural GHG emissions romAnnex I countries declined by 21.3 % between 1990

and 2006 (UNFCCC, 2008). Tis decrease was mostlydue to political changes in the countries o Easternand Central Europe, the Caucasus and Central Asia,which led to agricultural de-intensifcation with lessinputs, and land abandonment (Smith et al., 2007a).Romanovskaya (2008) reports that total agriculturalemissions rom Russia in 2004 were only 45 % o the1990 levels. Verg et al. (2007), who split the worldinto the six World Meteorological OrganizationRegional Associations, report that, in Arica, non-CO

2agricultural production emissions (excluding

biomass burning) have increased by 19 % between

1990 and 2000; in Asia by 12 %; in South America by9 %; in North and Central America and the Caribbean

by 7 %; and in Southwest Pacifc by 6%, but havedecreased in Europe by 21 % over the same period.

2.3 N2O emissions from agricultural

soilsAs highlighted above, agriculture is the main sourceo anthropogenic N

2O emissions in the world,

contributing around 58 % (Smith et al., 2007a), andN

2O emissions rom world soils amounted to 2526 g

CO2-eq yr-1 in 2000 (Verget al., 2007). Tese emissions

are produced by the microbial transormation o Nin the soil, oen originating rom applied mineralertilizers and manure, and can be enhanced whenavailable N exceeds plant requirements, especiallyunder wet conditions (Oenema et al., 2005; Smith andConen, 2004). Quantiying these emissions in order

to accurately assess both their contribution to totalGHG emissions and the eectiveness o mitigationstrategies is, however, made di cult by the level ovariation, both spatially and over time (Mosier et al.,1998a). Direct N

2O emissions have been shown to

relate to N inputs and are thereore oen calculatedusing an emission actor (EF), which represents thepercentage o any N applied that is emitted in the ormo N

2O. Te deault EFs have large uncertainty limits,

and the IPCC recently reduced its deault EF rom1.25 % to 1 % as it considers a more recent review ofeld measurements around the world, which indicates

that the initial value was too high (IPCC, 2006), whileother researchers have argued that dierent EF valuesshould be used or dierent crops, climate or soilconditions. Te IPCC methodology allows country /region specifc EFs to be used where data is available.Tis issue, and the impact using dierent EFs ormodelling techniques can have on the quantifcationo emissions, are discussed urther in Appendix A atthe end o this report.

2.3.1 Soil N2O emissions from N fertilizer use

Te availability o N ertilizers has arguably playedthe greatest individual role in the dramatic increase in

agricultural productivity around the world since thebeginning o the 20th Century. It has been estimatedthat, in 2008, 48% o the global population is dependenton ood that would not be produced without Nertilizer inputs (Erisman et al., 2008). Fertilizer useis, however, very ine cient, with a high proportiono applied N being lost to the environment. In 2005,o approximately 100 g N used in global agriculture,only 17 g N was consumed by humans as crop, dairyor meat products (UNEP, 2007), and the global N usee ciency (as measured by recovery e ciency in thefrst year i.e. (ertilized crop N uptake - unertilized

crop N uptake)/N applied) o crops is generallyconsidered to be less than 50 % under most on-arm


12/67


conditions (ilman et al., 2002; Balasubramanian etal. 2004; Dobermann, 2007; IFA, 2007). Not all othis lost N contributes to global warming; around40 % may be denitrifed back to inert atmospheric N

2

(Gallowayet al., 2004). However, emission actors ashigh as 40 % (o applied N) have been reported orN

2O loss rom ertilizer applications (see able A1 in

Appendix A).Data available rom the International Fertilizer

Industry Association (IFADAA, 2009) indicatesthat world N ertilizer consumption was 93 g N yr-1in 2005. Figure 2 shows how this was split betweenregions, indicating that Asia used more than 60 %.Assuming an EF o 1 % as per the IPCC deaultmethodology (2006), this would give N

2O emissions

directly rom N ertilizer application o 433 g CO2-

eq yr-1 in 2005. In comparison, Verg et al. (2007)

estimate N2O emissions rom world N ertilizer usageat 444 g CO

2-eq in 2000 (17.6 % o total soil N

2O

emissions), using FAO (2004) ertilizer consumptiondata and the IPCC (2000) EF o 1.25 %. Tis indicatesthe degree o variability possible in estimates evenwhen the IPCC methodology is ollowed, highlightingthe di culty in quantiying both current emissionsand the eectiveness o measures to mitigate them.

On a regional basis, ertilizer use contributes tototal soil N

2O emissions and agricultural non-CO

2

emissions largely in line with its level o use. Verg etal. (2007) report that mineral N ertilizer applications

led to emissions o 14 g CO2-eq yr

-1

in Aricain 2000, representing just 4.1 % o total soil N2O

emissions and 2.2 % o total non-CO2

emissions romagricultural production (excluding biomass burning).Tis is because Arican crops are generally under-ertilized; small-scale Arican armers usually applyno ertilizer or rates well below the recommendedlevels or the maintenance o soil ertility (Batjes,2004). In comparison, in Asia, which includesboth China and India with their huge ertilizerconsumption levels (see section 4.5.2 below or casestudies o the impact o reducing this demand),ertilizer-induced emissions are calculated as 244 g

CO2-eq yr-1 in 2000, representing 22.7 % o total soilN

2O emissions and 9.1 % o total non-CO

2emissions

rom agricultural production (excluding biomassburning). South America shows a similar pattern toArica, with emissions o 18 g CO

2-eq yr-1 in 2000,

representing 5.2 % o soil N2O emissions and 2.4 %

o non-CO2

emissions rom agricultural production(excluding biomass burning). Te SouthwestPacifc also has ertilizer induced N

2O emissions

o only 19 g CO2-eq yr-1 or 2000 but, in this case,

they contribute 30.6 % o soil N2O emissions and

7.2 % o total non-CO2

emissions rom agricultural

production (excluding biomass burning). Europe andNorth and Central America have similar levels o Nertilizer-induced emissions, 73 and 76 g CO

2-eq yr-1

or 2000, respectively, but they make a much highercontribution to total soil N

2O emissions in Europe,

26.8 % vs. 17.9 % or North and Central America,despite having a airly similar contribution to totalnon-CO

2emissions o 11.7 % or Europe and 10.7 %

or North and Central America (Verg et al., 2007).Annex I countries (mainly developed countries

or transition economies such as the Former SovietUnion) report annual emissions rom ertilizerapplications to the UNFCCC. Values or reportedmineral N ertilizer-induced emissions range rom

just under 1 Gg CO2-eq yr

-1

or Liechtenstein to over56 g CO2-eq yr-1 or the USA, which, as the third

largest consumer o ertilizer N, emits almost asmuch directly ertilizer-induced N

2O as the whole

o the EU-27 (58 g CO2-eq yr-1). However, since

the USA has a much larger cropland area (411 Mhain 2007) than the EU-27 (190 Mha in 2007, basedon FAOSA, 2009), the average emission levelsare lower on a per hectare basis. For non-Annex Icountries such as China and India, emissions caninstead be estimated using ertilizer consumptiondata rom the IFA (IFADAA, 2009) and the IPCCdeault emission actor o 1 % (IPCC, 2006). With

estimated N2O emissions rom mineral N ertilizerso 148 g CO

2-eq or 2006 (roughly 0.3 % o global

total GHG emissions rom all sources), China alonecontributes more than the whole o Europe and theUSA put together (see section 4.5.2 or urther detailso Chinese and Indian ertilizer use, N use e ciencyand mitigation potential).

Manure application-induced N2O emissions are

accounted or separately rom those associated withmineral N ertilizer under the IPCC methodology.Country level emissions reported to the UNFCCC byAnnex I countries are generally lower than those or

mineral ertilizers due to a much smaller proportiono N being derived rom manures than mineralertilizers, ranging rom under 2 Gg CO

2-eq yr-1 up

Figure 2. Proportion of world N fertilizerconsumption for 2005 by region (Source: IFADATA,2009)

East asia

37

South

Asia

NorthAmerica

Western &Central Europe

Oceania, 1

Africa, 3

Eastern Europe &Central Asia, 3

West Asia, 3

Latin America &the Caribbean, 6

17

1311

93Mt N


13/67


to almost 12 g CO2-eq yr-1 or the USA, and are

di cult to estimate or countries which do not reportthem because manure applications are generally notrecorded at the international level, and must frst beestimated. Tis can be done by using animal numbersand estimates o the proportion o manure applied tocrops, and its N content, but multiplying estimatesmeans fnal estimates may have a very high degreeo uncertainty associated with them, especially asIPCC deault data on amounts o N excreted byanimals may be very dierent to locally measureddata or some countries (or example, China; Yue andErda, 2000). For China, manure applications havebeen estimated to contribute 25 % o direct soil N

2O

emissions, amounting to 40 g CO2-eq or 1990 (Yue

and Erda, 2000), although it has been suggested thatthe use o manure has since declined and mineral

ertilizers contributed around 74 % o direct soilN

2O emissions rom China by the mid 1990s (Zhu

and Chen, 2002), as opposed to the 54 % reportedby Yue and Erda (2000) or 1990. In India, manureapplications are reported to play a more signifcantrole in crop ertilization. Singh and Singh (2008) citedata indicating that it contributed 44 % o N inputsin 2000-01, amounting to 15.6 g N and producingN

2O emissions o 72.6 g CO

2-eq (assuming a 1 %

EF), although the authors do note this may be anoverestimate, especially as a substantial proportiono cattle excreta is used or other purposes. Bhatia et

al. (2004) argue that manure contributes only 3 % oIndian direct soil N2O emissions, amounting to just

1.31 g CO2-eq or 2000-01, which agrees with Garg

et al. (2006) in terms o percentage contribution,although Garg et al. (2006) estimate higher emissionsoverall, such that 3 % amounts to 2.79 g CO

2-eq or

2000.Despite being a signifcant source o soil N

2O

emissions, ertilizers do, as discussed above, make aconsiderable contribution towards eeding the worldsincreasing population (Erisman et al., 2007), andwhen used optimally, may help to reduce total GHGemissions per unit o production by maximizing plant

uptake or example, Lammel (2009) reports thatwheat and maize plants would fx around 40 % lessCO

2i not ertilized with N.

2.3.2 Soil N2O emissions per unit of

agricultural output

GHG emissions are generally reported on a per areabasis. However, agricultural productivity needs toincrease to eed 9 billion people by 2040-2050, i weare to avoid cropland spreading into previously non-agricultural land resulting in large GHG emissions.

Converting more land to crop production is likelyto increase GHG emissions more than intensiyingproduction on existing cropland (see section 4.2.7).

Tereore, lowering emissions per hectare wouldnot be benefcial i this necessitated land conversionto cropland, so comparisons between croppingmanagement strategies on a per unit o productionbasis is oen more useul. Assessment o emissions othis basis (e.g. Williams et al., 2006) is less requentin the literature, although oen done in lie cycleassessment (LCA) studies (e.g. Brentrup et al., 2004;Brentrup and Pallire, 2008). GHG emissions inuture should be assessed on a per-unit-product basisin addition to a per-unit-area basis.

2.3.3 Soil N2O emissions from crop residue

incorporation and N-fixing crops

Crop residues include non-harvested products andusually comprise the straw / haulms and the stubble

/ stover le on the feld aer the primary agriculturalproducts (e.g. grain, root crops) have been removed.According to IPCC guidelines, N

2O emissions rom

residues are calculated in the same way as N2O

emissions rom ertilizer inputs, by working out thelevel o N input rom the crop and then assuming adeault emission o 1 % o that input (IPCC, 2006).Input levels are determined by crop yield and Ncontent, which varies according to crop type, and theIPCC guidelines also include an equation and a tableo deault actors or estimating these. For Annex Icountries, crop residue incorporation is reported to

contribute between 0.13 Gg CO2-eq yr

-1

(Iceland)and 30.36 g CO2-eq. yr-1 (Russian Federation), with

a mean average o 2067 Gg CO2-eq yr-1 per country,

while N-fxing crops produce 0.21-1911 Gg CO2-eq

yr-1, with a mean average o 224 Gg CO2-eq yr-1 per

country, although this category o emissions is notreported separately or several countries, includingthe USA, Russia and Canada, which may be expectedto have some o the highest emissions.

Given the data required, these emissions are notstraightorward to estimate or other countries romreadily available international databases. For China,crop residues returned to the soil were estimated

by Yue and Erda (2000) to contribute 21 % o totaldirect soil N

2O emissions, amounting to 33 g CO

2-

eq or 1990, suggesting it is probably also one o thelargest N

2O emitters rom crop residue incorporation.

However, a lower estimate o 7.85 g CO2-eq (with a

range o 1.57-14.13 g CO2-eq) is given or the same

year by Xing and Yan (1999), and this study also givesa similar estimate o 8.14 (1.63-14.65) g CO

2-eq

or N2O emissions rom N-fxing crops or 1990. In

India, N-fxing crops added 4.1 g N to agriculturalsoils in 2000-01 (Singh and Singh, 2008), suggestingN

2O emissions o 18.6 g CO

2-eq (assuming a 1 %

EF), nearly an order o magnitude higher than romany o the Annex I countries that reported thiscategory o emissions separately. As or crop residues


14/67


are concerned, these are oen used or animal eed,and only around one third are recycled (Singh andSingh, 2008). Combined with the act that burningo crop residues is common practice in many areaso India (Sharma et al., 2008), incorporation may notbe a signifcant source o N

2O emissions. Bhatia et al.

(2004) argue that only 5 % o straw is incorporatedand estimate crop residues contribute 11 % o directsoil N

2O emissions, amounting to 4.09 g CO

2-eq or

1994-95.As with N

2O emissions rom ertilizer applications,

however, there is considerable variation in estimatedEF values, with numerous studies showing eitherlower or higher emissions than calculated by theIPCC deault values under dierent conditions. Forexample, Velthoet al. (2002) reported that the totalN

2O emission rom various types o residues ranged

rom 0.13 to 14.6 % o the N added with residues, andVinther et al. (2004) calculated that between 1.5 and14.1 % o total plant residue N was emitted as N

2O

during a fve month period ollowing incorporation.Other researchers have argued that assumptions needto be based on longer term measuring campaigns,rather than on emissions measured only during thecrop growing season. Ciampitti et al. (2008) reportedthat 28 % o total N

2O emissions rom soybean crops

occurred aer harvest.

2.4 CH4

emissions from rice cultivation

Rice paddies emit CH4

when they are ooded dueto the anaerobic decomposition o organic matterin the soil producing the gas, which then escapes tothe atmosphere mainly through diusive transportthrough the rice plants (Nouchi et al., 1990), or isoxidized beore reaching the surace. Te level oCH

4emission rom any given rice paddy is related

to actors that control the activity o the methane-producing (methanogens) and methane-oxidizingbacteria (methanotrophs) such as temperature, pH,soil redox potential and substrate availability, andalso soil type, rice variety, water management and

ertilization with organic carbon and N (see reviewsby Le Mer and Roger, 2001, and Conrad, 2002).Te interactions between CH

4emission levels and

these last three actors are discussed urther in themitigation section (4.9).

Globally, rice production is estimated to havecontributed 44 % o agricultural CH

4emissions

in 2000, and 16 % o total non-CO2

agriculturalemissions on a CO

2-equivalent basis (Verg et

al., 2007). In 2005, 97 % o emissions rom ricecultivation were rom developing countries, andSouth and East Asia was responsible or 82 % o this,

as it is a dominant ood source in this region (US-EPA, 2006a). Tis agrees with Verg et al. (2007), whoestimated that Asia as a whole contributed 82 % o

CH4

emissions rom rice in 2000, using a global EF o2.77 x 10-5 g CH

4km-2 yr-1 (calculated according to

Mosier et al., 1998b) to calculate total emissions romthe sector rom the total area under rice cultivationrom the FAO (2004) database. Tis global emissionactor corresponds to an average or the worlds ricepaddies, based on individual countrys EFs per squarekilometre, weighted or the countrys contributionto the total rice paddy areas. A range o estimatedCH

4emission levels rom rice growing countries,

mostly in Asia, and world totals, are given in able 1.Estimates o emissions rom Asian countries made byYan et al. (2003), were calculated using specifc EFsbased on reported emission levels or that country orclimatically similar regions (only those estimated toemit more than 400 Gg CH

4yr-1 are shown in able 1).

2.5 CH4 budget of other croplands

In aerobic soils used or crop production, CH4

production is very limited and oxidation o CH4

dominates the local ux, meaning arable soils arenet sinks or CH

4. CH

4oxidation is limited by the

availability o CH4, along with other biotic and abiotic

actors. As aerobic soils do not produce signifcantlevels o CH

4, the size o the sink is limited (as shown

in able 2) and estimated to amount to just 64.4 gCO

2-eq yr-1 globally or all cultivated soils (Mosier et

al., 1998b). Compared to undisturbed soils, cropland

soils are a weaker CH4 sink (Willison et al., 1995),with cultivated land consuming an average o only46 kg CO

2-eq ha-1 yr-1, in comparison with temperate

orests, which are thought to consume around 253 kgCO

2-eq ha-1 yr-1 (Mosier et al., 1998b). Boeckx and

Van Cleemput (2001) suggest an oxidation capacityo 34.5 kg CO

2-eq ha-1 yr-1 or European arable land,

giving a sink strength o 6.3 g CO2-eq or the EU-15,

based on land use data rom 1993.CH

4oxidation in arable soils may also be limited

because it is inhibited by agricultural managementpractices such as N ertilizer and pesticideapplications. Te inhibiting action o N additions is

well documented (see or example, Htsch et al., 1993;Htsch, 1996; Kravchenko et al., 2002; Seghers et al.,2003). It works in the short term because ammonium(NH

4+) intereres with the methanotrophic enzyme

system (Boechx and Van Cleemput, 1996; lustos etal., 1998) and, in the longer term, by changing themake-up o the microbial community. Seghers et al.(2003) also reported that N applications in the ormo mineral ertilizers had a much more negative eectthan organic manure or compost applications. Variousherbicides, such as atrazine, and also the insecticidemethomyl, have also been shown to inhibit CH

4

oxidation (opp et al., 1993; Ariet al., 1996; Boeckxet al., 1998; Priem and Ekelund, 2001).


15/67


Data or tropical systems, aside rom ricecultivation, is rather more scarce. For example, CH

4

dynamics associated with agroorestry systems arepoorly understood, despite complex mixtures o treesand agricultural crops (such as coee and cacao)being widely practised in Latin America, SoutheastAsia and equatorial Arica, and being considered

one o the most sustainable agricultural systems inthe tropics (Albrecht and Kandji, 2003). A reviewby Mutuo et al. (2005) argues that o the ew studiesthat have been carried out into CH

4uxes in humid

tropical regions, most have ocussed on short-termcropping systems or natural orests. Like temperatesystems, these studies have shown that upland orests

Table 1. Estimated CH4 emissions from rice cultivation (partially adapted from Mosier et al., 1998b; and Yan et al.,2003)

Country or region CH4

emission(Tg CO2-eq yr

-1)Reference

Bangladesh 17.6 ALGAS reporta

35.6 Yan et al., 2003

China 299-391 Wang et al., 1994

260 Lin et al. , 1994

222-291 ALGAS reporta

176 Yan et al., 2003

India 55.2-138 Parashar et al., 1994

135 Yan et al., 2003

94.07 27.37 Gupta et al., 2009

Japan 0.46-23.92 Yagi et al., 1994

8.95 National report to UNFCCCb

9.57 Yan et al., 2003

Myanmar 30.5 ALGAS reporta

30 Yan et al., 2003

Pakistan 12.1 ALGAS reporta

9.9 Yan et al., 2003

Thailand 11.5-202.4 Yagi et al., 1994


40.5 ALGAS reporta

40.2 Yan et al., 2003

Philippines 6.9-16.1 Neue et al., 1994


13 ALGAS reporta

12.2 Yan et al., 2003

USA 5.9-7.6 US-EPA, 2009

Vietnam 29.2 ALGAS reporta

28.7 Yan et al., 2003

Asia 577 Yan et al., 2003

World 1380 Watson et al., 1992

584-1242 Sass, 1994

729 Neue, 1997

aAs cited by Yan et al. (2003); ALGAS: Asia Least-cost Greenhouse gas Abatement Strategy reports, downloaded from the web-site of the Asian Development Bank (ADB); http://ntweb03.asiandevbank.org/oes0019p.nsf/pages/sitemap

bAs cited by Yan et al. (2003); country communications downloaded from UNFCCC website; http://www.unfccc.de/resource/natcom/nctable.html


16/67


are net sinks and that this sink strength is reduced byconversion to agriculture (Keller et al., 1990; Kellerand Reiners, 1994; Steudler et al., 1996; Verchot et al.,2000). Data rom the Peruvian Amazon and lowlandhumid tropics in Sumatra, Indonesia, reproduced inthe Mutuo et al. (2005) review, indicate that the CH

4

sink strength or orests is around 96 kg CO2-eq ha-1

yr

-1

, while agroorestry systems can consume between39 and 93 kg CO2-eq ha-1 yr-1 as CH

4, and cropping

systems can vary rom CH4

sinks o 56 kg CO2-eq

ha-1 yr-1 or low input systems to net sources o CH4

emissions o 49 kg CO2-eq ha-1 yr-1 or high input

systems, with cassava as an example crop giving a sinkstrength o 48 kg CO

2-eq ha-1 yr-1 (suruta et al., 2000;

Palm et al., 2002; scaled up rom data in g C m-2 h-1,assuming a constant rate).

2.6 Greenhouse gas emissions fromland use change

As discussed in section 2.1, the conversion ouncultivated to cultivated land is thought to contribute5.9 2.9 Pg CO

2-eq yr-1 globally, representing 6-17 %

o total GHG emissions (Bellarby et al., 2008). Tisfgure indicates both the signifcant contribution andthe degree o uncertainty surrounding this issue.

Since 1960, agricultural area has increased rom just under 4.5 to just over 4.9 billion ha in 2007(FAOSA, 2009). During the last 20 years, therehas been an overall increase in agricultural area rom4.86 billion ha in 1990, but showing year to yeaructuations, with the greatest area o 4.98 billion ha

recorded in 2001.Te close to tripling o global ood production

since 1960 has largely been met through increased

ood production per unit area. For example, Bruinsma(2003) suggests that 78% o the increase in cropproduction between 1961 and 1999 was attributableto yield increases, and 22% to expansion o harvestedarea, showing that whilst global agricultural areahas increased only slightly, the agricultural land ismanaged more e ciently. Land use has thereore

changed, despite smaller changes in land cover.While yield increases have outpaced increases inharvested area in most regions, the proportions vary. For example, 80% o total output growth wasderived rom yield increases in South Asia, comparedto only 34% in sub-Saharan Arica. In industrialcountries, where the amount o cultivated landhas been stable or declining, increased output wasderived predominantly through the developmentand adoption o agricultural knowledge, science andtechnology, which has served to increase yields andcropping intensity (van Vuuren et al., 2008). Terole o land use change and adoption o agricultural

knowledge, science and technology has, thereore, varied greatly between regions. In some regions,particularly in Latin America, the abundance o landhas slowed the introduction o new technologies (vanVuuren et al., 2008).

2.7 Indirect emissions from cropproduction

2.7.1 Emissions from fertilizer productionand distribution

Bellarbyet al. (2008) estimate that the production oertilizers emits between 284 and 575 g CO

2-eq yr-1,

representing 0.6-1.2 % o total global GHG emissions

Table 2. CH4

oxidation levels for aerobic agricultural soils (adapted from Boeckx and Van Cleemput, 2001)

Site description Oxidation level, mean and/or range(kg CO2-eq ha

-1 yr-1)aReference

Arable, Scotland 59 (1-153) Dobbie et al., 1996

Arable, Denmark 17 (6-24) Dobbie et al., 1996

Arable, Poland 17 Dobbie et al., 1996

Winter wheat and maize 7-10 Bronson and Mosier, 1993

Arable, England 0-11 Goulding et al., 1996

Arable 3-17 Mosier and Schimel, 1991

Arable, UK 25-109 Dobbie and Smith, 1994

Arable, UK 15 Willison et al., 1995

Wheat, UK 69 Dobbie and Smith, 1996

Set-aside, UK 13-50 Dobbie and Smith, 1996

Abandoned farmland 24 Ambus and Christensen, 1995

aConverted from mg CH4

m-2 d-1, assuming the same daily rate year round.


17/67


rom all sources. Tis is mainly due to the energy

required, although nitrate production also generatesN

2O emissions. In total, ertilizer production uses an

estimated 1.2 % o global energy demand annually, owhich 94 % is used or all N ertilizer production and87 % or ammonia production (IFA, 2009a). However,the actual energy consumed during production canvary widely as very modern ertilizer plants have thepotential to e ciently use the heat produced duringthe reaction process and, thereore, may even benet energy producers. Te most e cient ammoniaproduction plants use natural gas as a eedstock andconsume around 32 GJ per t ammonia, corresponding

to 1.8 t CO2 per t ammonia. Te use o other eedstocks(naphtha, uel oil, coal) requires a somewhat higherenergy consumption o around 45 GJ per t ammonia,resulting in 4.1 t CO

2emissions per t ammonia (IFA,

2009a). Phosphorus and potassium based ertilizersrequire around a tenth o energy needed or N basedertilizers (Lal, 2004b) with corresponding lower CO

2

emissions (IFA, 2009a).N

2O emissions rom the production o nitric acid

(which is used or the production o ammoniumnitrate based ertilizers) are in the range o 6-8 kgN

2O per t acid (1.8-2.4 t CO

2-eq per t acid) or an

average medium-pressure plant that has not installed

N2O abatement technology (IFA, 2009a) (see section4.10.1 or details o the mitigation potential o thistechnology). Holba (2009) reports that the productiono ammonium nitrate ertilizer emits just under 4 tCO

2-eq per t N using the best available technology in

European production plants, while urea productionemits around 3 t CO

2-eq per t N. Due to its high GWP,

N2O is thought to contribute 74 g CO

2-eq yr-1 (26%)

o the total global GHG emissions rom ertilizerproduction, which were estimated as 283 g CO

2-eq

yr-1 by Kongshaug (1998). able 3 shows an update othe estimate o ertilizer-associated emissions made

by Bellarbyet al. (2008), using emission levels romLal (2004b), which include transport and storage

as well as production, and the latest data on global

ertilizer production levels rom the IFA.Using updated energy requirements and correcting

or proportions o dierent ertilizer products, thelatest estimate by the IFA is 420 g CO

2-eq or 2007;

382.8 g CO2-eq or production (not including

ammonia etc. which is used or industrial purposesrather than ertilizers) plus 37.2 g CO

2-eq or

transport and distribution (IFA, 2009a). Tis meansthat globally, emissions rom ertilizer production,distribution, and storage account or around 0.8 % ototal global GHG emissions. Te potential to mitigatethese emissions by urther implementation o best

practice technology is discussed in section 4.10.1.

2.7.2 Emissions associated with otheragrochemicals

Te production o crop protection products isestimated to account or 3-140 g CO

2-eq yr-1 by

Bellarbyet al. (2008), based on per km2 emissions o220-9220 kg CO

2-eq, calculated using emissions per

kg rom Lal (2004c) and an application rate o 0.5-2 kg ha-1 based on Clemens et al. (1995), multipliedby a total cropland area o 15.41 million km2 (in2003; FAOSA, 2007). A recent study into herbicide

application, energy e ciency and CO2 emissionsrom cereal cropping, reported that the applicationo herbicides increases CO

2emissions by 4.4 %,

because o the energy required or the productionand application o the herbicides, as well as the greateramount o energy required or harvesting caused byhigher yields, but that overall, herbicide applicationincreased energy e ciency, with emissions per unit ograin equivalent produced reduced by 36.4 % (Deikeet al., 2008). Similarly, Berryet al. (2008) report thatungicide application to UK wheat crops producesCO

2emissions o 0.06 g CO

2-eq yr-1, but that

emissions per unit o grain produced are reduced,such that an extra 0.93 g CO

2-eq would be produced

Table 3. Total annual GHG emissions from the production, distribution and storage of mineral fertilizers, usingBellarby et al. (2008) methodology.

Fertilizer type Total emissions(kg CO2-eq kg

-1 of fertilizer

nutrient produced)a

World production in 2007(Tg of nutrient)b

Total global GHG emission(Tg CO2-eq yr

-1)

N 3.3 - 6.6 104.9 346.17 - 692.34

P 0.36 - 1.1 54.4 19.58 - 59.84

K 0.36 - 0.73 33.4 12.02 - 24.38

Total 192.7 377.77 - 776.56

aTaken from Lal (2004b)bIFA, 2009a. N products used for industrial purposes are not included


18/67


19/67


Baseline predictions are based on business-as-usual scenarios that assume current trends inagricultural production (see below) will continue,such that the world will continue to develop muchas it does today, and that no new policies will beintroduced, either in response to these developmentsor to reduce GHG emissions. Tey are used, thereore,to help assess the possible impact o individual policy

changes or mitigation options on uture emissionlevels.

3.1 General trends in future agriculture

Te IPCC Working Group III (contribution to theIPCC Fourth Assessment Report, Smith et al., 2007a)considered the main trends in the agricultural sectorwith implications or uture GHG emissions to be:

Land use and productivityLand productivity will continue to increase, albeit at a

declining rate, as urther technological progress givesdeclining returns, and greater use is made o marginalland with lower productivity. Tis increases the risko soil erosion and degradation, with highly uncertainconsequences or CO

2emissions (Lal, 2004a; Van

Oost et al., 2004).

Tillage practicesConservation tillage and zero-tillage are increasinglybeing adopted (accounting or 3.5 % o arable land by1999, according to the FAO (2001)), reducing energyusage rom reduced on-arm uel use, despite higherembedded energy in the increased herbicide use, and

oen increasing carbon storage in soils. However,assessing the eect o this on the GHG balance isdi cult, especially as they are oen combined withperiodic tillage.

Additional inputsIrrigation and ertilizer use increases will berequired to support increasing productivity, in turnincreasing energy demands (or moving water andmanuacturing ertilizer; Schlesinger, 1999). Tismay lead to increased GHG emissions on a per-areabasis (Mosier, 2001), although this depends on the

e ciency o water and ertilizer use, and lower GHGemissions per-unit-product.

LivestockGrowing demand or meat is likely to induce changesin land use, particularly increases in grassland, andalso increased demand or animal eeds (e.g. cereals),with associated increases in CO

2emissions. Larger

herds o bee cattle will increase emissions o CH4

and N2O, although this may be partially mitigated

by the use o intensive systems (with lower emissions

per unit product), which are expected to increase ata aster rate than grazing-based systems. Increases inmanure production will also increase GHG emissions.

Transport and energyChanges in policies such as subsidies, and regionalpatterns o production and demand are causingan increase in international trade o agriculturalproducts. Tis is expected to increase CO

2emissions,

due to greater use o energy or transportation.However, there is also an emerging trend or greateruse o agricultural products (e.g. bioplastics, biouels

and biomass or energy) as substitutes orossil uel-based products, which has the potential to reduceGHG emissions in the uture.

3.2 Overview of baseline predictions

When the IPCC Fourth Assessment Report (Smithet al., 2007a) was prepared, no baseline agriculturalnon-CO

2GHG emission estimates or the year 2030

had been published. Instead, the report includes anestimate based on the US-EPA (2006a) prediction thataggregate emissions will increase by ~13 % during thedecades 2000-2010 and 2010-2020. Assuming similar

rates o increase (10-15 %) or 2020-2030, agriculturalemissions might be expected to rise to 80008400 gCO

2-eq yr-1, with a mean o 8300 g CO

2-eq by 2030.

Verg et al. (2007) are in broad agreement with this,predicting that non-CO

2emissions rom agricultural

production (excluding those rom biomass burning)will reach 8189 g CO

2-eq by 2030. Tese increases

will be driven by increases in production to supportpopulation growth in areas such as South and EastAsia, Latin America and Arica, and increaseda uence leading to changes in dietary preerencesand increased commercialization o production, with

associated increases in ertilizer usage and animalrearing (Smith et al., 2007a). Rosegrant et al. (2001)

3. Future baseline emissions


20/67


project that an additional 500 Mha will be convertedto agriculture during 1997-2020, mostly in LatinAmerica and Sub-Saharan Arica, and that there willbe a 57 % increase in global meat demand over thesame period, mostly in South and Southeast Asia, andSub-Saharan Arica.

Using a baseline scenario taken rom a studypublished by the Netherlands EnvironmentalAssessment Agency (MNP, 2006), which projectsthe world developing over the next decades very much as it does today, without anticipatingdeliberate interventions or responses to the projecteddevelopments, and with no implementation opolicies or emission reduction, Verburg et al. (2008)report modelled GHG emissions up to 2050. Teypredict that CO

2emissions rom land use (agriculture

including land-use change) will show a net increase

o approximately 18 g yr-1 between 2000 and 2015,with the strongest increases in Asia, Arica and theAmericas, while a decrease in emissions is ound inChina. Between 2015 and 2030, there will be a globalnet decrease in CO

2emissions o approximately 30

g yr-1, with largest declines in Latin America, Asia,and the OECD Pacifc, and increased emissions inEurope, Russia, Arica and North America. By 2030,the modelling study estimates that CH

4emissions

rom ruminants and manure will reach around 3200g CO

2-eq yr-1, and N

2O emissions (soil including

ertilizer, and manure emissions) will reach around

1300 g CO2-eq yr

-1

, with both gases showing thestrongest increases in Arica.Focusing on emissions related to crop production,

N2O rom agricultural soils, the largest contributor to

agricultural GHG emissions, is predicted to increaseby 47 % (compared to 1990 levels) to 2937 g CO

2-

eq by 2020 by the US-EPA (2006a), while the FAOestimates a 35-60 % increase in total agricultural N

2O

emissions (including those rom manure) by 2030(FAO, 2003). CH

4emissions rom rice cultivation are

predicted to increase rom 601 g CO2-eq in 1990 to

776 g CO2-eq by 2020 (US-EPA, 2006a), assuming a

sustained increase in irrigated production.Te FAO,

however, orecasts that the global area under ricecultivation will grow by just 4.5 % to 2030 (FAO, 2003)and, thereore, emissions may increase little rom thissource, especially i rice is grown under continuouslyooded conditions, or i new lower CH

4emitting rice

cultivars are developed and adopted (Wang et al.,1997). Future CO

2emission levels rom agriculture

are uncertain, but most likely to decrease or remain atlow levels, or example due to increased adoption oconservation tillage practices (FAO, 2001). However,i emissions rom land use change are included, CO

2

emissions may increase; Verburg et al. (2008) suggest

a strong increase o CO2 emissions up to 2020, causedby land clearing o natural vegetation or agricultural

land use in Arica, Latin America, Southeast Asiaincluding Indonesia, and South Asia including India.

3.3 Regional trends

Te IPCC Fourth Assessment (Smith et al., 2007a)considers that the highest projected growth inemissions is or the Middle East and North Arica,and Sub-Saharan Arica, with a combined 95%increase in the period 1990 to 2020 (US-EPA, 2006a).Sub-Saharan Arica is the one region o the worldwhere per-capita ood production is currently eitherin decline, or roughly constant at a level that is notadequate (Scholes and Biggs, 2004), in part due tolow and declining soil ertility (Sanchez, 2002) andinadequate ertilizer inputs. Te slowly rising wealtho urban populations is likely to increase demand

or livestock products, resulting in intensifcationo agriculture and expansion into areas which arecurrently largely unexploited, particularly in Southernand Central Arica (including Angola, Zambia, DRC,Mozambique and anzania), and a consequentincrease in GHG emissions. However, Verg et al.(2007) consider that, in Arica, the AIDS epidemicmay impact on this projected growth as, according toFAO estimates, AIDS has killed some seven milliono Aricas agricultural workers and could result in16 million more deaths by 2020, removing nearlya quarter o Arican agricultural workers rom the

labour pool within 20 years (CGIAR, 2001). On theother hand, since current agricultural practices inArica are extremely labour-intensive, a shrinkingworkorce means that there is a need or increasedproductivity per worker (as well as per hectare) unlessworkers can be lured back to agriculture throughimproved rural livelihoods. Verburg et al. (2008)estimate that Arican CH

4emissions rom ruminants

and manure will increase by approximately 10 gCO

2-eq yr-1 in 2000-2015, and by approximately 12

g CO2-eq yr-1 in 20152030, while N

2O emissions

rom soils and manure rom the region will increaseby approximately 3 g CO

2-eq yr-1 in 2000-2015, and

by approximately 4 g CO2-eq yr-1 in 2015-2030.In East Asia, a large increase in GHG emissions

rom animal sources is projected. Between 1961 and2004, total production o meat in Asian developingcountries increased more than 12 times and milkproduction by more than our times (FAOSA, 2006).Since the per-capita consumption o meat and milkis still much lower in these countries in comparisonwith developed countries, these trends are expectedto continue or a relatively long time, and accordingly,US-EPA (2006a) orecast increases o 153% and 86%in emissions rom enteric ermentation and manure

management, respectively, rom 1990 to 2020. InSouth Asia, emission increases are mostly due to


21/67


expanding use o N ertilizers and manure to meetdemands or ood, resulting rom rapid populationgrowth. Verburg et al. (2008) estimate that CH

4

emissions (rom ruminants and manure) rom SouthAsia will increase by ~8 g CO

2

-eq yr-1 in 2000-2015and ~4 g CO

2-eq yr-1 in 2015-2030, while those rom

Southeast Asia will increase by ~2 g CO2-eq yr-1 in

2000-2015, and ~1 g CO2-eq yr-1 in 2015-2030, and

those rom China will increase by ~4 g CO2-eq yr-1

in 2000-2015, and by ~2 g CO2-eq yr-1 in 2015-2030.

Emissions o N2O rom soils and manure, meanwhile,

are orecast to increase by a total o ~4 g CO2-eq yr-1

in 2000-2015 or South and Southeast Asia combined,and by ~1 g CO

2-eq yr-1 or China over the same

period, while in 2015-2030, China shows a declineo ~1 g CO

2-eq yr-1, with South and Southeast Asia

together still increasing by a total o ~2 g CO2-eq yr-1

(Verburg et al., 2008).In Latin America and the Caribbean, agricultural

products are the main source o exports. Signifcantchanges in land use and management have occurred,especially orest conversion to cropland andgrassland, resulting in increased GHG emissionsrom soils (CO

2and N

2O). Between 1961 and 2004,

the cattle population increased linearly rom 176 to379 million heads, partly oset by a decrease in thesheep numbers rom 125 to 80 million heads. All otherlivestock categories have increased in the order o 30to 600 % since 1961, and cropland areas, including

rice and soybean, and the use o N ertilizers have alsoshown dramatic increases (FAOSA, 2006). Anothermajor trend in the region is the increased adoption ono-till agriculture, particularly in Brazil, Argentina,Paraguay and Uruguay. Tis is practised on ~30 Mhaevery year in the region, although it is not known howmuch o this is under permanent no-till management(Smith et al., 2007a). Verburg et al. (2008) estimatethat agricultural CH

4emissions rom Latin America

(including Brazil) will increase by ~8 g CO2-eq yr-1

in 2000-2015 and by ~6 g CO2-eq yr-1 in 2015-2030,

while agricultural N2O emissions rom the same

region will increase by ~1.5 g CO2-eq yr-1 in 2000-

2015 and by ~0.5 g CO2-eq yr-1 in 2015-2030.In the countries o Central and Eastern Europe

and Central Asia, agricultural production is currentlyabout 60-80% o that in 1990, but is expected togrow by 15-40 % above 2001 levels by 2010, asthese countries increase in wealth. Arable land areais orecast to increase by 10-14 % or the whole oRussia due to agricultural expansion. Te widespreadmove to more intensive management could result ina 2 to 2.5-old rise in grain and odder yields, witha consequent reduction in arable land, but possibleincrease N ertilizer use. Decreases in ertilizer N

use since 1990 have led to a signifcant reductionin N

2O emissions but, under avourable economic

conditions, applications are expected to rise again,although they are unlikely to reach pre-1990 levels inthe near uture (Smith et al., 2007a). US-EPA (2006a)projects a 32% increase in N

2O emissions rom soils

in these two regions between 2005 and 2020, which isequivalent to an average increase rate o 3.5 g CO

2-

eq yr-1. In comparison, Verburg et al. (2008) estimatethat agricultural N

2O emissions rom Eastern Europe,

Central Asia, Russia and the Caucasus will increase by~2 g CO

2-eq yr-1 in 2000-2015, and by ~1 g CO

2-

eq yr-1 in 2015-2030. Emissions o CH4

or the regionare predicted to increase by ~1 g CO

2-eq yr-1 in

2000-2015, and by ~0.5 g CO2-eq yr-1 in 2015-2030

(Verburg et al., 2008).Te only developed regions showing a consistent

increase in GHG emissions in the agricultural sectorare North America and developed countries o the

Pacifc, with increases o 18 % and 21 %, respectively,between 1990 and 2020. In both cases, this trendis largely driven by CH

4and N

2O emissions rom

manure management and soils. In Oceania, Nertilizer use, although still very low in internationalterms, has increased sharply with a fve old increasesince 1990 in New Zealand and a 2.5 old increase inAustralia over the same period (Smith et al., 2007a).Te practice o burning sugar cane residues inAustralia may contribute to this as it reduces nutrientreturns to the soil (Verg et al., 2007). In contrast,North American N ertilizer use levels have remained

stable or around 25 years and here the main driveror increasing emissions is management o manurerom cattle, poultry and swine production, andmanure application to soils. Te US-EPA estimatesthat CH

4and N

2O emissions associated with manure

management have increased by almost 40 % (addedtogether, on a CO

2-eq basis) between 1990 and

2007 (US-EPA, 2009). In both regions, conservationpolicies have reduced CO

2emissions rom land

conversion; land clearing in Australia has declined by60 % since 1990 with vegetation management policiesrestricting urther clearing, while, in North America,some marginal croplands have been returned to

woodland or grassland (Smith et al., 2007a). Verburget al. (2008) provide more conservative estimateswhich do not include increases rom 1990 to 2000.Tey estimate that CH

4emissions rom North

America will increase by ~2 g CO2-eq yr-1 in 2000-

2015 and by


22/67


associated with the adoption o a number o climate-specifc and other environmental policies in theEuropean Union (EU), as well as economic constraintson agriculture. For example, successive reorms o theCommon Agricultural Policy (CAP) since 1992 havecontributed to GHG reduction, and the 2003 EU CAPreorm is expected to continue this trend, mainlythrough reduction o animal numbers (Binfeld et al.,2006). Verburg et al. (2008) predict a decline in CH

4

emissions, but these are outweighed by an increase inN

2O emissions. However, the baseline scenario in this

study does not include the implementation o any new

agricultural or environmental policies, and CentralEurope is included in the same category as WesternEurope so the region is not directly comparable either.

able 5 shows the projected non-CO2

agriculturalemission levels (excluding biomass burning) or thesix World Meteorological Organization RegionalAssociations or 2015 and 2030, calculated by Verget al. (2007) based on projectedood requirements, givenpopulation evolution accordingto the World Resource Institute(2004) and FAO (2004). Telatest inventory rom the US-

EPA suggests that the increasesin emissions or this regionmay have been over-estimated,as non-CO

2emissions rom US

agriculture have only increasedby 7.5 % on a CO

2-eq basis

between 1990 and 2007 (US-EPA, 2009).

3.4 Future fertilizer use and associatedemissions

Erisman et al. (2008) used the IPCC Special Reporton Emission Scenarios (SRES) (Nakicenovic et al.,2000) to predict uture ertilizer demand dependingon economic, demographic and technologicaldevelopments, specifcally population growth, Nuse e ciency, biouel production, increased meatconsumption and other dietary changes. Tey estimateN ertilizer demand will be between approximately100 and 140 g N by 2030. In comparison, the FAO

(2000) predict baseline ertilizer consumption by2030 o around 135 g N and also give an estimateo 95 g N based on a scenario o improved nutrientuse e ciency, and ilman et al. (2001) orecastusage o 135 g N by 2020, increasing to 236 gby 2050, suggesting a level o around 170 g N by2030 i a linear increase is assumed. Work done by

Table 5. Projected non-CO2

emissions (Tg CO2-eq yr-1) from agricultural production (excluding biomass burning) for

2015 and 2030 by region (adapted from Verg et al., 2007).

2015 2030

Region emissions change 2015-2000 emissions change 2030-2000

Africa 796 27 % 1422 127 %

Asia 3203 20 % 3788 42 %

S. America 966 28 % 1207 59 %

N. and Central America 789 11 % 877 23 %

SW Pacific 296 12 % 329 25 %

Europe 594 -5 % 566 -10 %

World total 6644 17 % 8189 45 %

Figure 3. World mineral N fertilizer consumption since 1961 (IFADATA, 2009),with forecast trend lines assuming mean increase rate from 1996-2006 (red

line) or 2001-2006 (green line).

Tg N

0

20

40

60

80

100

120140

160

180

2020201020001990198019701961 2030


23/67


the International Energy Agency (IEA) suggests abaseline consumption o 121 g N yr-1 by 2020 and129 g N yr-1 by 2030 but suggests that policy changespromoting the use o biouels could increase thisto 128 g N yr-1 by 2020 and 149 g N yr-1 by 2030(Gielen, 2006). Figure 3 illustrates the increase inworld N ertilizer consumption rom 1961 to 2006according to the IFA, indicating that the decline in Napplications rom the late 1980s due to the collapseo the Former Soviet Union only lasted until 1994,and more recently levels have increased steadily.Assuming the mean increase rate o either 1996-2006 (red line on Figure 3) or 2001-2006 (green line),which illustrates the sudden increase in demandpartly caused by interest in biouels, gives a business-as-usual baseline consumption o 118-137 g N yr-1by 2020, and 132-166 g N yr-1 by 2030.

Currently, the IFA orecasts that N ertilizerconsumption will reach 102 g N yr-1 in 2009/10

(Heer and Prudhomme, 2009) in light o currenteconomic problems, and 111.1 g N yr-1 by 2013/14,which suggests growth may be nearer the lowerestimate, at least or the next ew years. Even so, thislowest business-as-usual projection o mineral Nertilizer consumption o 118 g N yr-1 by 2020 mayproduce soil N

2O emissions o around 550 g CO

2-eq

yr-1 (assuming a 1 % EF), which is an increase o 24 %over 20 years using the estimate or 2000 made by Verget al(2007). Tis will also increase indirect emissionsassociated with ertilizer production, with theincrease being highly dependent on the proportion oproduction plants using the best available technology(BA). For example, new ammonia production plantsusing BA today produce less than 40 % o the GHGemissions o the average plant using coal, naphtha oroil as a eedstock (IFA, 2009a) (see sections 2.7.1 and

4.10.1).


24/67


4.1 Mitigation options and mechanisms

Agricultural GHG uxes are produced by complexand heterogeneous mechanisms, but the activemanagement o agricultural systems oers possibilitiesor mitigation, many using current technologies whichcould be implemented immediately. Tese mitigationpractices include cropland management, grazingland management, management o agricultural

organic soils, restoration o degraded lands, livestockmanagement, manure/biosolid management, andbioenergy production. Tis report will ocus onpractices related to cropland, and particularly tonutrient management.

Mitigation opportunities can be based onreducing emissions, enhancing removals or storage,or avoiding or displacing emissions (Smith et al.,2007b). Tis third category includes using biouelsinstead o ossil uels and avoiding bringing new areaso land under agricultural cultivation. Practices thatreduce emissions seek to better manage the ows o

carbon and N within the agricultural ecosystem. Forexample, practices that increase crop N use e ciencyoen reduce N

2O emissions (Bouwman, 2001).

Practices that enhance removals or storage act tosequester carbon or build carbon sinks, by increasingthe photosynthetic input o carbon and/or slowingthe return o stored carbon to CO

2via respiration,

fre or erosion. Agricultural ecosystems contain largecarbon reserves (IPCC, 2001a), mostly in the ormo soil organic matter. Historically, these systemshave lost more than 50 Pg C (Paustian et al., 1998;Lal, 1999, 2004a), but some o this can be recoveredthrough improved management. Vegetation can also

store signifcant amounts o carbon in agro-orestrysystems or other perennial plantings on agriculturallands (Albrecht and Kandji, 2003). Agricultural landshave been shown to remove CH

4rom the atmosphere

by oxidation processes, although orests remove more(ate et al., 2006), and this eect is small compared toother GHG uxes (Smith and Conen, 2004).

Many practices have been suggested to mitigateemissions, and they oen work by more than onemechanism, and aect more than one gas, sometimesin opposite ways. Tereore, it is important to considerthe net beneft, which depends on the combined

eects on all gases (Robertson and Grace, 2004; Schilset al., 2005; Koga et al., 2006). emporal patterns oemissions also need to be taken into consideration, as

these may vary between practices or or dierent gasesor a given practice; in some cases, emissions can bereduced indefnitely, while other reductions may betemporary (Marland et al., 2003a; Six et al., 2004).Finally, it must be considered whether practices aectradiative orcing through other mechanisms; orexample, aerosols or albedo (Marland et al., 2003b;Andreae et al., 2005).

4.2 Overview of cropland managementmitigation practices

Croplands have a high potential or mitigating netGHG emissions as theyare oen intensively managed.Practices that could be implemented all into theollowing partially overlapping categories:

4.2.1 AgronomyImproved agronomic practices increase yields andgenerate higher inputs o carbon residue and can,thereore, increase soil carbon storage (Follett, 2001).

Examples include using improved crop varieties,extending crop rotations, especially those withperennial crops that allocate more carbon belowground, and avoiding or reducing allow periods(West and Post, 2002; Lal, 2003, 2004a; Freibauer etal., 2004; Smith, 2004a, b). Adding more nutrients,when the soil is poor, can also promote soil carbongains (Alvarez, 2005), but the benefts may be osetby higher N

2O emissions rom soils and CO

2rom

ertilizer manuacture (Schlesinger, 1999; Prez-Ramrez et al., 2003; Robertson, 2004; Gregorich etal., 2005).

Emissions per hectare can also be reduced by using

cropping systems that are less reliant on ertilizers,pesticides and other inputs, thereby reducing GHGcosts rom their production as well (Paustian et al.,2004). Te use o rotations with legume crops is animportant example o this (West and Post, 2002;Izaurralde et al., 2001), as the biologically fxed Nreduces the need or external N inputs, although itcan still be a source o N

2O emissions (Rochette and

Janzen, 2005; Parkin and Kaspar, 2006; Ciampitti et al.,2008). Te GHG balance o legumes may not alwaysbe as straightorward as this suggests. Soybeans inrotation with maize have been shown to reduce soil

carbon storage in comparison with continuous maizeunder some management practices (Adviento-Borbeet al., 2007). It has been suggested that the greater

4. Mitigation potential


25/67


amount o N available to maize crops planted aersoybeans is not due to a net input o N rom theatmosphere, but instead the result o mineralizationo soybean residues and enhanced mineralization osoil organic matter because soybean residues have alower C:N ratio than maize residues (Salvagiotti etal., 2008). Reducing emissions per unit area may notreduce total GHG emissions rom crop production ithe measures reduce productivity and require extraland to be taken into agricultural production (Carltonet al., 2009).

Another group o agronomic practices are thosethat provide temporary vegetative cover betweensuccessive agricultural crops, or between rows o treeor vine crops, known as catch or cover crops. Teseadd carbon to soils (Arrouays et al., 2002; Barths etal., 2004; Freibauer et al., 2004; Ogle et al., 2005) and

may also reduce N2O emissions by extracting plant-available N unused by the preceding crop (Veltho andKuikman, 2000).Te mitigation potential o variousmeasures within this category is discussed urther insection 4.8 below.

4.2.2 Nutrient managementNitrogen applied in the orm o ertilizers, manures,biosolids and other N sources is not always usede ciently by crops (Gallowayet al., 2003; Cassman etal., 2003), and the surplus is particularly susceptible toemission o N

2O (McSwiney and Robertson, 2005).As

a result, improving N use e ciency (NUE) can reduceN2O emissions, both on- and o-site, by also reducing

leaching and volatile losses, and indirectly reduce GHGemissions rom N ertilizer manuacture (Schlesinger,1999). Practices that improve NUE include adjustingapplication rates based on precise estimation o cropneeds; using slow- or controlled-release ertilizersor nitrifcation inhibitors (which slow the microbialprocesses leading to N

2O ormation); improving

timing by applying N when it is least susceptible toloss, oen just prior to plant uptake; making N moreaccessible to crop roots by placing it more preciselyinto the soil; or avoiding N applications in excess o

immediate plant requirements (Robertson, 2004;Dalal et al., 2003; Paustian et al., 2004; Cole et al.,1997; Monteny et al., 2006). In many countries, theertilizer industry is advancing the principles osound nutrient management via an approach termed4R Nutrient Stewardship (IFA, 2009b), promotingertilizer best management practices. Measureswithin this category are discussed urther below andtheir mitigation potential is examined or several casestudies (see sections 4.5 and 4.6).

4.2.3 Tillage/residue management

Advances in weed control methods and armmachinery now allow many crops to be grown withminimal tillage (reduced tillage) or without tillage (no-

till), and these practices are increasingly being usedaround the world (e.g. Cerri et al., 2004).Because soildisturbance tends to stimulate carbon losses throughenhanced decomposition and erosion (Madari et al.,2005), reduced- or no-till agriculture oen results insoil carbon gain, but this is not always the case (Westand Post, 2002; Ogle et al., 2005; Gregorich et al.,2005; Alvarez 2005). Some researchers (e.g. Baker etal., 2007; Baker and Gri s, 2005) have argued thatsampling protocols have biased the results, and thatdierent tillage regimes aect the depth distributiono SOC, with conservation tillage leading the higherlevels near the surace and conventional tillage givinghigher C levels deeper in the soil profle (Carter, 2005;Dolan et al., 2006), suggesting that some studies mayreport a redistribution rather than an increase in soilC (Powlson and Jenkinson, 1981; Machado et al.,

2003). Nevertheless, when such studies are excludedrom analysis, most studies do show modest increasesin SOC under zero/reduced tillage (Ogle et al., 2005).

Adopting reduced- or no-till may also aect N2O

emissions but the net eects, which seem to dependon soil and climatic conditions, are inconsistentand not well quantifed globally (Cassman et al.,2003; Smith and Conen, 2004; Helgason et al.,2005; Li et al., 2005;). In some areas, reducedtillage promotes N

2O emissions, while elsewhere

it may reduce emissions or have no measurableinuence (Marland et al., 2001). No-tillage systems

can, however, reduce CO2 emissions rom energyuse (Marland et al., 2003b; Koga et al., 2006).Retaining crop residues also tends to increase soilC because they are the precursors or soil organicmatter, which is the main C store in soil. Avoidingthe burning o residues, e.g. mechanizing sugar caneharvesting and eliminating the need or pre-harvestburning (Cerri et al., 2004) also avoids emissions oaerosols and GHGs generated rom fre, althoughCO

2emissions rom uel use may increase. Te

eectiveness o these measures as mitigation practicesin terms o their impacts on both C storage and N

2O

emissions are examined urther below (see section

4.7).

4.2.4 Water managementAround 18% o global cropla

Documents

2010 Ifa Greenhouse Gas (1)