technical report no. 35

national carbonaccounting system

tech

nica

l rep

ort n

o. 3

5 Emission Sources of NitrousOxide from AustralianAgricultural and Forest Landsand Mitigation Options

Ram Dalal, Weijin Wang, G. Philip Robertson,William J. Parton, C. Mike Myer and R. John Raison

The National Carbon Accounting System:• Supports Australia's position in the international development of policyand guidelines on sinks activity and greenhouse gas emissionsmitigation from land based systems.

• Reduces the scientific uncertainties that surround estimates of landbased greenhouse gas emissions and sequestration in the Australian context.

• Provides monitoring capabilities for existing land based emissions andsinks, and scenario development and modelling capabilities thatsupport greenhouse gas mitigation and the sinks development agendathrough to 2012 and beyond.

• Provides the scientific and technical basis for internationalnegotiations and promotes Australia's national interests in internationalfora.

http://www.greenhouse.gov.au/ncas

For additional copies of this report phone 1300 130 606

EMISSION SOURCES OF NITROUS OXIDE FROMAUSTRALIAN AGRICULTURAL AND FOREST

LANDS AND MITIGATION OPTIONS

Ram Dalal+°, Weijin Wang+°, G. Philip Robertson*, William J. Parton^, C. Mike Myer#, R. John Raison° ~

+ Queensland Department of Natural Resources and Mines° CRC for Greenhouse Accounting

* Michigan State University^ Colorado State University

# CSIRO Atmospheric Research

~ CSIRO Forestry and Forest Products

National Carbon Accounting System Technical Report No. 35

June 2003

Australian Greenhouse Officeii

Printed in Australia for the Australian Greenhouse Office© Australian Government 2003

This work is copyright. It may be reproduced in whole or part for study or trainingpurposes subject to the inclusion of an acknowledgement of the source and nocommercial usage or sale results. Reproduction for purposes other than those listedabove requires the written permission of the Communications Team, AustralianGreenhouse Office. Requests and enquiries concerning reproduction and rights shouldbe addressed to the Communications Team, Australian Greenhouse Office,GPO Box 621, CANBERRA ACT 2601.

For additional copies of this document please contact the Australian Greenhouse OfficePublications Hotline on 1300 130 606.

For further information please contact the National Carbon Accounting System athttp://www.greenhouse.gov.au/ncas/

Neither the Australian Government nor the Consultants responsible for undertakingthis project accepts liability for the accuracy of or inferences from the materialcontained in this publication, or for any action as a result of any person’s or group’sinterpretations, deductions, conclusions or actions in reliance on this material.

June 2003

Environment Australia Cataloguing-in-Publication

Emission Sources of Nitrous Oxide from Australian Agricultural and Forest Lands and Mitigation Options

p. cm.

(National Carbon Accounting System technical report; no. 35)

ISSN: 1442 6838

1. Plant biomass-Australia-Measurement. 2. Vegetation mapping-Australia. I. Dalal,Ram. II. Australian Greenhouse Office. III. Series.

577.3*0994-dc21333.9539*0994-dc21

National Carbon Accounting System Technical Report iii

MAGNITUDE OF NITROUS OXIDE EMISSIONSFROM AUSTRALIAN AGRICULTUREAlmost 80% of N2O in the National Greenhouse GasInventory is produced by the agricultural sector; ofthis, 73% is emitted from agricultural soils and 24%from prescribed burning of savannas.

Australian sources of nitrous oxide (N 2O)emissions expressed in carbon dioxide (CO 2)equivalents and percent share of each sector in 1999.

Source CO2 equivalent CO2 equivalentMt/yr Percent share

Agriculture 22.27 78.7

Land Use Change and Forestry 0.66 2.3

Stationary Combustion 0.97 3.4Transport and Fugitive

emissions from Fuel 3.76 13.4

Industrial Plastics and Solvents, etc 0.65 2.2

Total 28.31 100

EXECUTIVE SUMMARY

Increases in the concentrations of greenhouse gases,carbon dioxide (CO2), methane (CH4), nitrous oxide(N2O), and halocarbons in the atmosphere due tohuman activities are associated with global climatechange. Carbon dioxide concentration in theatmosphere has increased by 30% and N2Oconcentration has increased by 16% since 1750. The global mean surface temperature has increasedby about 0.6oC in the last century. It is predicted toincrease much faster this century if no action is takento mitigate the emission rate of greenhouse gases.

Although atmospheric concentration of N2O is much smaller (314 ppb in 1998) than carbon dioxide(365 ppm), its global warming potential (cumulativeradiative forcing) is 296 times that of the latter in a 100-years time horizon. As a CO2 equivalent (N2O emission x 296), it contributes about 6% of the global warming effect due to all greenhousegases.

Fert

ilise

r use

(kt N

)

PastureHorticultureOilseedCottonSugarcaneCereals

0

100

200

300

400

500

600

700

800

Estimates of N fertiliser use by crops and pastures in 2000 (Chudleigh and Simpson 2001).

Australian Greenhouse Officeiv

Nitrous oxide emissions from agricultural soils come from nitrogen fertilisers (32%), soil disturbance(38%) and animal waste (30%). Since 1990, there hasbeen a steady decline in pasture area, accompaniedby decline in cattle and sheep numbers but increasein intensive livestock production. Therefore, N2Oemissions from soil disturbance and intensivelivestock production have steadily increased. There has also been a fast increase in nitrogenfertiliser use for cereal production, accounting for70% of the total fertiliser use in 2000 compared withjust over 50% in 1990.

NITROUS OXIDE EMISSIONS FROM AGRICULTURAL SOILSNitrous oxide is primarily produced in soil by theactivities of micro-organisms during nitrification ofammonium into nitrate, and denitrification of nitrate(and nitrite) into nitrogen gas.

The lack of oxygen or limited oxygen supply in soilto the active micro-organisms is the primary cause of N2O production during denitrification. Whenoxygen supply is low due to slow oxygen diffusionthrough water-filled pores in saturated orwaterlogged soils or due to high oxygen demandcreated by abundant carbon food source, micro-organisms utilise nitrite and nitrate in place ofoxygen. Thus, nitrate and nitrite are denitrified tonitric oxide (NO), nitrous oxide, and nitrogen (N2) gases.

The proportion of N2O to N2 gas in thedenitrification process depends on:

• nitrate and nitrite supply (generally higherN2O/N2 ratio at higher NO2

- or NO3-

concentrations);

• oxygen supply or water-filled pore space(higher N2O/N2 ratio at <60-80% water-filledpore space, but at saturation or above, it isalmost exclusively N2 gas emissions);

• temperature (N2O production rate increasesbut the N2O/N2 ratio decreases withincreasing temperature);

• pH and salinity (even very acidic soils,especially pH <4.5, also produce N2O); and

• carbon substrate supply (moderate supply ofcarbon substrate increases N2O productionbut high carbon substrate may lead to N2

production due to anaerobic conditions).

Since these variables in agricultural systems change over space and time at different rates, N2O production from soil is sporadic both in timeand space. Therefore, it is a challenge to measureN2O emissions from a given location and then scaleup to regional and national scales.

Estimates of N2O emissions from variousagricultural systems vary widely. For example, inflooded rice in the Riverina Plains, N2O emissionsranged from 0.02% to 1.4% of fertiliser N applied,whereas in irrigated sugarcane crops, 15.4% offertiliser applied at 160 kg N/ha was lost over a 4-day period (12 t/ha CO2 equivalent). Nitrousoxide emissions from the fertilised dairy pasturesoils in Victoria range from 6 to 11 kg N2O-N/ha(2.9-5.3 t/ha CO2 equivalent) when fertiliser isapplied at rates from 0 to 200 kg N/ha.

In arable cereal cropping, estimates of N2Oemissions range from <0.01% to 9.9% of N fertiliserapplications. Nitrous oxide emissions from soilnitrite and nitrates resulting from residual fertiliserand legumes are almost unknown but probablyexceed that from fertilisers due to frequent wetting and drying cycles over a longer period. In ley-cropping system, significant N2O losses could occur, due to the accumulation of 70-150 kgnitrate-N/ha, from legume-based pastures.However, limited data exist to quantify N2O losses in ley cropping system in Australia.

Extensive grazed pastures and rangelands contributeannually about 0.2 kg N/ha as N2O (93 kg/ha peryear CO2 equivalent). Unfertilised forestry systemsmay emit less but the fertilised plantations may emitmore N2O than the extensive grazed pastures.Australian data is sparse for the forestry systems.

National Carbon Accounting System Technical Report v

Burning of biomass such as forest vegetation,savannah grass, and agricultural residues is animportant source of nitrous oxide emissions. In 1999,about 24% of the total annual emissions of nitrousoxide from the agricultural sector were the result of direct emissions from prescribed burning ofsavannas. While combustion is clearly a majorsource of nitrous oxide emissions, the effect of firesextends beyond the direct contribution of emissionsduring combustion. Fire also influences processes ofN2O production within the soil by heating it, causingnatural pyrolysis or thermal degradation to both thelabile and intractable soil materials.

Overall, there is a need to examine the emissionfactors used in estimating emissions, for example1.25% of fertiliser or animal excreted nitrogenappearing as N2O (IPCC 1996). The impacts of anappropriate emission factor are at least four-fold:improve N2O emissions estimates in the NationalGreenhouse Gas Inventory; identify the agriculturalsectors that inefficiently utilise or dispose of N products (fertilisers, soil mineralisation, animalwaste and other products); examine mitigationoptions to reduce N2O emissions; and evaluate codeof practice, and policy/legislation that encouragesmitigation of N2O emissions from agriculture.

MITIGATION OF NITROUS OXIDE EMISSIONSThe primary consideration for mitigating N2Oemissions from the agricultural sector is to match thesupply of mineral N (ammonium, nitrite and nitrate)and keep it to a minimum commensurate with itsspatial and temporal needs of crops/pastures/trees.

Management practices to minimise N2O emissionsfrom N fertilisers and legumes as well as improve N use by crop/pasture or reduce application ratesinclude:

1. Apply fertiliser N at optimum rates by takinginto account all N sources available to thecrop/pasture from soil, and other N sourcessuch as legume, manure or waste.

2. Apply fertiliser N at the rate and time to meetcrop/pasture needs, and when appropriatethrough split application.

3. Avoid fertiliser N application outside thecrop/pasture-growing season. Avoid fallowperiods if season or availability of irrigationpermits.

4. Provide fertiliser N application guide throughcrop/pasture monitoring, yield maps and soiltests.

5. Apply other nutrients if required so thatnutrients supply to crop/pasture is balancedand N utilisation is optimised.

6. Avoid surface application, incorporate orband place so that fertiliser N losses areminimised and plant utilisation maximised.

7. Monitor and adjust fertiliser applicationequipment to ensure the precision and theamount of fertiliser applied.

8. Improve spatial fertiliser application throughGlobal Positioning System/GeographicalInformation System, yield/growth monitors,remote sensing, plant logging, soil tests andprecision farming.

9. Fertilizer should be in a form (such asgranulated) that can be applied evenly,conveniently and cost-effectively. In irrigated agricultural systems, applicationin sprinkler/drip irrigation may be aneffective option.

10. Fertilizer may be formulated with ureaseand/or nitrification inhibitors or physicalcoatings to mimic fertiliser N release to crop/pasture growth needs.

11. Practice good crop/pasture management,disease control and soil management tooptimise crop/pasture growth.

Australian Greenhouse Officevi

12. Use non-legume cover crops to utilise theresidual mineral N following N-fertilisedmain crops or mineral N accumulationfollowing legume-leys.

For manure management, the most effective practiceis the early application and immediate incorporationof manure into soil to reduce the direct N2Oemissions and secondary emissions from depositionof ammonia volatilised from manure and urine.

Secondary considerations to reduce N2O emissionsinclude:

• Oxygen supply/soil water content (water-filled pore space, <40% increases nitrificationbut reduces N2O loss, >90% increases N2 loss);examples include arable cropping/pasture/forestry, and flooded rice. Improve oxygendiffusion in soil by eliminating the compactedlayer.

• Carbon-substrate supply (readily availablecarbon creates ‘hot spots’ of microbial growth,and hence increases in N2O emissions); restrictreadily available supply - examples areaddition or incorporation of biomass of highcarbon: nitrogen ratio such as non-legumesrather than legume biomass.

• Soil organic matter management tomanipulate carbon substrate andoxygen/water supply.

• Soil pH and salinity (salinity and high pH enhance the N2O emissions due to thepersistence of nitrite); soil amendments suchas application of gypsum or crop residues ofhigh carbon: nitrogen ratio reduces N2Oemissions.

• Eliminate limitations of other nutrients such as phosphorus, potassium or zinc.

Perennial crop/pasture/tree systems mostly provideoptimum environment to reduce N2O emissions byusing mineral N and water effectively to produce

biomass. Management options for other agriculturalsystems should mimic the above to reduce N2Oemissions from the agricultural soils.

Nitrous oxide emissions from legume-basedpastures may be in the order of 1-2 kg N/ha, andsimilar amounts are estimated when these pasturesare terminated for cropping. However, there islimited information on N2O emissions during thefallowing period following the pasture phase.Besides, ley pasture termination early in the seasongives limited management options to reduce N2Oemissions from these systems.

Field burning of agricultural residues and theprescribed burning of tropical savanna andtemperate grasslands contribute significantly tonational emissions of N2O. Direct emissions of N2O into the atmosphere from field burning ofagricultural residues are being reduced by the use ofalternative management practices such as stubbleretention and green cane harvesting. Minimisingemissions from prescribed burning practicesassociated with pasture management will requirepractical management and monitoring protocolsspecifically designed to provide opportunities forlocal landholders to develop the expertise requiredto implement more appropriate pasturemanagement to eliminate or reduce burningpractices.

Land clearing disturbs the soil and thus enhances Nmineralisation and N2O emissions at least in the firstfew years. Restriction on land clearing, therefore,will reduce N2O emissions although the exactreductions are not known.

Current models such as DNDC and DAYCENT canbe used to simulate N2O production from soil afterparameterisation with the local data, appropriatemodification and verification against the measuredN2O emissions under different managementpractices and integrated spatially and temporally.

National Carbon Accounting System Technical Report vii

POLICY CONSIDERATIONS AND RESEARCH OPPORTUNITIESNitrogen fertiliser use is likely to increase forcrop/pasture production, since soil N supply isdeclining as improved pasture areas and soil fertilitydecrease, along with greater demand for productquality and supply.

Education is critical for the efficient use of fertilisersin crop/pasture production to reduce fertiliser wasteas well as to reduce N2O emissions. FertilizerIndustry Federation of Australia (FIFA) should playa pivotal role in partnership with the relevantindustry bodies in preparing Codes of Practice forEfficient Fertiliser Use (a current FIFA initiative:Guidelines for Developing Nutrient ManagementCodes of Practice).

Although, both State and Federal legislation exists to ensure quality assurance on fertiliser quality, policy consideration should be given to discouragefertiliser applications out of season, and in excess ofcrop demands. This will also require the eliminationof price incentives by suppliers for out of cropseason applications.

Incentives may be offered to producers of machineryand equipment for precise applications of fertilisers,when (at or near sowing or in-crop) and where(prescribed area in a paddock) it is needed. There isa limited scope to encourage the use of slow-releasefertilisers to mimic plant needs due to higher costs ofthe amended fertilisers, which are rarely recoveredby increased yields. Recently, it has been claimedthat the application of 3,4-dimethylpyrazolephosphate with urea, reduced N2O emissions by 45%over a 3-year period in the field in Germany. There isa need to examine its effectiveness over a number ofseasons, crop/pastures, and soils under warmerAustralian conditions where other products havebeen ineffective.

There are a number of other areas of research such as N2O emissions estimates in ley cropping andintensive livestock systems (the emission factors, the activity data, coverage of measurements, spatial

integration, and information on specific on-farmpractices), as well as mitigation options for reducingN2O emissions from agriculture.

Emission factor uncertainties remain since it isdifficult to obtain definitive N2O flux values. Some of the reasons are: the techniques - highprecision required for measuring atmospheric N2Oconcentration and the limitations of chamber andmicrometeorogical methods, large spatial variability,the sporadic nature of N2O emissions, and seasonaland climate variability.

In addition to fertilisers, research is needed inevaluating various mitigation options:

• For cropping systems - (i) no-till systems, (ii) timing of plant residue incorporation, (iii) legume management practice, (iv) animalmanure management and field applications,(v) nitrogen source - legume versus fertilisernitrogen, (vi) crop combinations, (vii) crop/pasture mix and duration, (viii) salinity, soiltype, season and climate variability;

• For irrigated pastures - (i) optimumutilisation of pastures, thus ensuring plantbiomass sink for nitrogen, (ii) hay or silageproduction when plant biomass is producedin excess, (iii) an optimum mix of grasses andlegumes, (iv) animal waste management, (v) soil type, season and climate variability;

• For extensive grazing lands - (i) optimumgrazing management, cell or rotationalgrazing and feed quality, (ii) regulatinglivestock numbers, (iii) fire frequency, (iv) soil type, season and climate variability;and

• For forestry plantations - (i) soil disturbance,(ii) time of logging, (iii) legume versusfertiliser nitrogen, (iv) planting- species and techniques.

Australian Greenhouse Officeviii

In summary, a directed national research program is needed for a considerable duration, to coversampling season and climate, and combined withchamber, mass balance and micrometeorogicaltechniques using high precision analyticalinstruments, simulation modelling, covering a rangeof strategic activities in the agriculture sector.

Although it is not considered in this review, werecognise that since CO2 emissions and sinks as wellas CH4 emissions and sinks interact strongly withN2O emissions from soil, a comprehensive researchprogram is needed to account for these interactionsand to arrive at cost-effective and efficientgreenhouse gas mitigation management, policy and legislation options.

ACKNOWLEDGMENTS

We thank Marie Halliday, Helen Scheu and CeceliaMcDowall, the Natural Resources and Mines Library, and Christine McCallum, Indooroopilly, for obtaining the research papers and reports.Numerous colleagues freely shared their ideas andinformation with us, in particular, Doug McGuffog,Fertilizer Industry Federation of Australia; PhilMoody for access to National Land and WaterResources Audit Report; and Beverley Henry and John Carter for general discussion about theNational Greenhouse Gas Inventory and TomDenmead, Ray Leuning, and Steve Del Grosso for sharing their literature. We also thank GaryRichards, Chris Mitchell and Wayne Strong, whoprovided the feedback and numerous suggestions toimprove the contents and presentation of this report.

National Carbon Accounting System Technical Report ix

GLOSSARY OF TERMS

Aerobic

Molecular oxygen being available for microbialgrowth, respiration or decomposition.

Ammonia volatilisation

Mass transfer of nitrogen as ammonia gas from soil to the atmosphere.

Anaerobic

Absence of molecular oxygen for microbial growth,respiration or decomposition.

Carbon dioxide

CO2, the principal anthropogenic greenhouse gas,contributing 60% of the enhanced greenhouse effect.

Carbon dioxide equivalent

Radiative activity and atmospheric residence time of a greenhouse gas compared with carbon dioxide(global warming potential). Carbon dioxideequivalent for nitrous oxide: multiply molecular N as N2O by 1.57, and then multiply by 296 (global warming potential) to obtain carbon dioxideequivalent (1 kg N2O-N = 465 kg CO2-equivalent).

Denitrification

Reduction of nitrogen oxides (usually nitrite andnitrate) to nitrogen oxides (NOx) with a loweroxidation state of nitrogen or molecular nitrogen(N2) by microbial activity (denitrification) or by chemical reactions involving nitrite and reduction of nitrogen oxides by combustion(chemodenitrification). Nitrogen oxides are used by microorganisms as terminal electron acceptors in place of oxygen in anaerobic or low-oxygenrespiratory metabolism.

Electron acceptor

A compound which accepts electrons during bioticor abiotic chemical reactions and is thereby reduced.

Field capacity

The content of water, on mass or volume basis, thatremains in a soil 48-72 hours after full wetting whenfree drainage is negligible.

Global warming potential

Relative warming effect of a unit mass of the gascompared with the same mass of carbon dioxideover a specific period (see also carbon dioxideequivalent).

Greenhouse effect

The absorption of infrared heat waves radiated backfrom the earth surface by the air, principally bycarbon dioxide, methane and nitrous oxide, andwater vapour, thus trapping heat by the atmospheremuch as does the glass in a greenhouse.

Methane

CH4; contribute about 20% to global warming.

Nitrogen mineralisation

The conversion of an organic form of nitrogen to aninorganic form as a result of microbial activity.

Nitrate reduction (biological)

The biological process whereby nitrate is reduced bymicroorganisms to ammonium for cell synthesis(assimilatory nitrate reduction) or to nitrite bymicroorganisms using nitrate as the terminalelectron acceptor in anaerobic respiration(dissimilatory nitrate reduction) (also seedenitrification).

Nitrification

Biological oxidation of ammonium to nitrite andnitrate, or a biologically induced increase in theoxidation state of nitrogen.

Nitrogen fixation

Conversion of molecular nitrogen (N2) to ammoniaand subsequently to organic nitrogen.

NOx gases

Oxygen state of nitrogen (nitrogen oxides) ingaseous form; major NOx gases are nitrous oxide(N2O), nitric oxide (NO), and nitrogen dioxide(NO2).

Australian Greenhouse Officex

Nitrous oxide conversion

N2O; contributes 6% to global warming.1 g N2O-N/ha/day = 0.365 kg N2O-N/ha/year

= 0.574 kg N2O/ha/year= 170 kg CO2 equivalent/

ha/year.

Nitrous oxide sinks

The stratosphere is the known nitrous oxide sink.Nitrous oxide in the stratosphere reacts with photonsand produces free oxygen radicals, which react withozone to convert N2O into nitric oxide (NO) andnitrogen (N2). This process depletes ozone in thestratosphere.

Nitrous oxide sources

The primary known source is from soil, primarilyproduced by microbial activity (see denitrification).

ppb nitrous oxide

Parts per billion or 1000th of ppm; 314 ppb N2O = 0.358 mg N2O-N/m3.

Water-filled pore space (WFPS)

The fraction of total porosity (total volume notoccupied by solids) of soil that is filled with water.WFPS >100% in flooded soils.

National Carbon Accounting System Technical Report xi

TABLE OF CONTENTSPage No.

Executive Summary iii

Acknowledgements viii

Glossary of Terms ix

1. Introduction 1

1.1 Sources and Sinks of Nitrous Oxide 1

2. N2O Production in Soil 5

2.1 Processes Involved in N2O Production in Soil 5

2.2 Factors Controlling N2O Production in Soil 5

2.2.1 Moisture and Aeration 5

2.2.2 Temperature 6

2.2.3 Soluble and Readily Decomposable Carbon 7

2.2.4 Soil and Fertilizer Nitrogen 8

2.2.5 Soil pH and Salinity 9

2.2.6 Limitation of Nutrients Other Than Nitrogen 9

2.3 Methods and Their Limitations in Measuring N2O Emissions from Soil 10

2.3.1 Chamber Methods 10

2.3.2 Micrometeorological Methods 13

2.3.3 Methods for Measuring N2O Emissions During Fire 15

3. Modelling of Nitrous Oxide Emissions from Soil 16

4. N2O Emissions from Various Ecosystems 19

4.1 N2O Emissions from Agricultural Systems 19

4.1.1 Cropping Soils 19

4.1.2 Horticultural Soils 24

4.2 N2O Emissions from Grazing Systems 24

4.2.1 Intensive Grazing 24

4.2.2 Extensive Grazing (improved pastures vs rangelands) 25

4.3 N2O Emissions from Forestry Systems 26

4.4 N2O Emissions from Other Systems 28

5. Mitigating N2O Emissions from Various Ecosystems 28

5.1 Mitigating N2O Emissions from Agricultural Systems 28

5.2 Mitigating N2O Emissions from Grazing Systems 29

5.3 Mitigating N2O Emissions from Forestry Systems 30

6. Summary and Conclusions 31

6.1 Policy Considerations and Research Opportunities 33

7. References 35

Australian Greenhouse Officexii

LIST OF TABLESPage No.

Table 1. Estimates of global warming potentials (GWP) of carbon dioxide, methane and nitrous oxide. 1

Table 2. Australian sources of nitrous oxide in 1999. 2

Table 3. Nitrous oxide emissions from Australian agriculture in 1999. 3

Table 4. Nitrous oxide emissions from agricultural soils in 1999. 4

Table 5. Estimates of nitrogen use by different crops. 4

Table 6. Comparison between the estimated enhanced emissions due to soil disturbance by in situ 7 biomass burning and directly from smoke plume emissions.

Table 7. A comparative estimation of nitrous oxide emissions from grazed pastures at WaggaWagga, New South Wales using NGGIC (1996) and IPCC (1996) methodology, andmicrometeorological methods (flux-gradient, convective boundary layer and mass balance). 15

Table 8. Estimates of mineral N (mostly nitrate-N) produced during 3-8 months following thetermination of the pasture phase and calculated nitrous oxide emissions due todenitrification. 23

LIST OF FIGURESFigure 1. Trends in N2O-N emissions from Australia from 1990 to 1999: ( ■ ) all sources and

(♦♦ ) the agricultural lands (Australian Greenhouse Office 2001; Dalal et al. 2003). 2

Figure 2. Trends in nitrogen fertiliser use in the Australian agriculture (data from Chudleighand Simpson 2001; Dalal et al. 2003). 3

Figure 3. A generalised relationship between water-filled pore space (WFPS) of soils and the relativefluxes of N2O (▲) and N2 ( ■ ) from nitrification and denitrification. N2O fluxes dominatebetween 50% and 80% of WFPS and N2 dominates above 80% WFPS (From Dalal et al. 2003). 6

Figure 4. A diagrammatic representation of the effect of the concentration of nitrate-N in soil on therelative N2O (▲) and N2 ( ■ ), and total denitrification losses (● ) (redrawn from Mosieret al. 1983; Dalal et al. 2003). 8

Figure 5. Probability distribution for chamber-based N2O flux measurements for a conventionallymanaged cropping system 1991-1999 (Robertson et al. 2000). Distributions tend to besimilarly skewed in even low-flux systems. 10

Figure 6. N2O and CO2 fluxes from an automated chamber located in a conventionally managedcropping system. Note the order of magnitude difference in N2O flux over the course `of day 182-183 (Phillip Robertson, unpublished data). 11

Figure 7. CO2 emission (soil + plant respiration) and N2O emission from lucerne. Note the order ofmagnitude difference in N2O flux on 23 October following rainfall.(Source: Meyer et al. 2001). 12

Figure 8. Denitrification fluxes across 0.5 ha of a Michigan old field. Average rates vary from 18 to>90 µg m-2 d-1 in the light vs. dark areas, respectively. (From Robertson et al. (1988)). 13

Figure 9. Measured and simulated N2O fluxes from a legume pasture in south-east Australia. (DNDCmodel from Li et al. (1992b), and modified DNDC model by Wang et al. (1997) includingchanges in WFPS, temperature, organic C pools and plant N uptake. (Adapted fromWang et al. 1997; Dalal et al. 2003)). 17

Figure 10. The N2O, NOx and N2 submodel of DAYCENT (adapted from Del Grosso et al. 2001b;Dalal et al. 2003). 18

National Carbon Accounting System Technical Report xiii

LIST OF FIGURES continued

Page No.

Figure 11. DAYCENT simulated (red bar) and observed (blue bar) N2O emissions from variousfarming systems, including conventional till (ct) and no-till (nt), soil textures (coarse,medium and fine), N application (10 kg N/ha), intensively cropped rye, crop rotations(G1, multiple cropping with FYM application and G2, multiple cropping with cattleslurry application) and irrigated barley and maize (Source: Del Grosso et al. 2001b). 20

Figure 12. Relationship between nitrous oxide emissions and nitrogen fertiliser used inAustralian agriculture from 1990 to 1999 (from Dalal et al. 2003). 31

Figure 13. A schematic diagram of nitrogen uptake pattern for a cereal crop. 33

Australian Greenhouse Officexiv

National Carbon Accounting System Technical Report 1

1.1. SOURCES AND SINKS OF NITROUS OXIDE

Land and oceans are the principal natural sources ofN2O emissions, with soils contributing about 65%and oceans about 30% (IPCC, 2001). N2O is verystable in the atmosphere, with a lifetime of about 114 yrs (IPCC, 2001). Probably the only significantprocess that removes N2O is its reaction in thestratosphere with excited oxygen atoms formed by photolysis of ozone (Crutzen, 1981). Micro-organisms in soil can reduce N2O into N2 underanaerobic conditions (Freney et al., 1978; Ryden,1981). However, the significance of soil as a sink for N2O remains uncertain and probably very small(Freney et al. 1978).

The Australian National Greenhouse Gas Inventory(NGGI) includes CO2, CH4 and N2O gases. Annual emissions of N2O exceeded 60 kilo tonnes ofN (94 kt of N2O) in 1999 (Figure 1), and nearly 80%was contributed by the Australian agriculture(Australian Greenhouse Office 2001). Consideringthe Global Warming Potential (GWP) of N2O as 296 compared to CO2 (Table 1), the CO2-equivalentemissions from N2O in 1999 were 28.31 Mt CO2-e(Table 2), (22.27 Mt CO2-e from the agriculturalsector), which were about 6% of the total CO2-eemissions from Australia. The rate of N2O emissionsincreased by 21% from 1990 to 1999; however, amuch steeper increase was recorded in the last 3 years than in the 1990-1996 period (Figure 1)(Australian Greenhouse Office 2001). Thus, the rateof increase for N2O is already more than 2.5 timesthat of allowable increases of 8% for all emissionsunder the Kyoto Protocol. This is a cause for concernand therefore requires concerted efforts in reducingN2O emissions from Australian agriculture.

1. INTRODUCTION

Over the 20th century, the global mean surfacetemperature has increased by about 0.6 ± 0.2oC(IPCC, 2001). This warming effect has primarilyresulted from the increase in the concentrations ofgreenhouse gases (CO2, CH4, N2O, and halocarbons)in the atmosphere due to human activities. Forexample, the atmospheric concentration of CO2 hasincreased from 280 ppm in 1750 to 365 ppm in 1998;and N2O has increased from 270 ppb to 314 ppbduring this period (IPCC, 2001). These gases absorblight in the infrared region, therefore trap thermalradiation emitted from the earth’s surface. It ispredicted that the global mean temperature is likely to increase by 1.4oC to 5.8oC during the next century, if no action is taken to mitigate theemission rate of the greenhouse gases (IPCC, 2001).

The global warming potential of N2O is 296 timesthat of CO2 over a 100-year time horizon (Table 1); and in spite of its lower rate of concentration rise(0.8 ppb/year from 1990 to 1999) than that of CO2

(1.5 ppm/year), N2O contributes approximately 6% of the warming effect caused by the increase ofthe various greenhouse gases.

Table 1. Estimates of global warming potentials (GWP) of carbon dioxide, methane and nitrous oxide.

Gas GWPA

CO2 1

CH4 23

N2O 296A IPCC (2001).

Australian Greenhouse Office2

Table 2. Australian sources of nitrous oxide in 1999.

SourceA N2O CO2 equivalentkt N/yr Mt/yr

Agriculture 47.92 22.27 (78.7%)B

Land Use Change and Forestry 1.43 0.66 (2.3%)

Stationary Combustion 2.09 0.97 (3.4%)

Transport and Fugitive emissions from Fuel 8.09 3.76 (13.4%)

Industrial Plastics and Solvents, etc 1.39 0.65 (2.2%)

Total 60.92 28.31 (100%)A Australian Greenhouse Office (2001; Dalal et al. 2003). B Percentage of the total N2O emissions from different

Australian sectors.

Of the total emissions of N2O as CO2-e of 28.31 Mt in1999 (Table 2), almost 22.3 Mt CO2-e was emittedfrom agricultural lands (16.17 Mt CO2-e) and firerelated activities (5.48 Mt CO2-e prescribedwoodland burning and 0.6 Mt CO2-e from treeclearing) (Table 3) (Australian Greenhouse Office

2001). Soil and land-based activities, therefore,account for the main sources of N2O (about 80%) inAustralia. However, large uncertainties exist in theseestimates (Table 3). Uncertainties in estimates ofdirect emissions of N2O from agricultural soils arecaused by uncertainties related to both the emissionfactors and activity data, lack of coverage ofmeasurements, spatial and seasonal aggregation,and lack of information on specific on-farm practicesas well as emissions not representative of allconditions.

The main sources of N2O relating to soil and land-based activities include: N fertiliser use, soil disturbance and legume-based ley pastures,livestock excretory products (urine, faeces andmanure) (Table 4), and grasslands and savannaburning (Table 3).

Year1988 1990 1992 1994 19981996 2000

All sources

y=0.1547x2 – 616.06x + 613525R2 = 0.97

30

35

40

45

50

55

60

65

Nitr

ous

oxid

e em

issi

ons

(kt N

)

Agricultural lands

Figure 1. Trends in N 2O-N emissions from Australia from 1990 to 1999: ( ■ ) all sources and ( ♦♦ ) theagricultural lands (Australian Greenhouse Office 2001; Dalal et al. 2003).


Table 3. Nitrous oxide emissions from Australian agriculture in 1999.

SourceA N2O kt N/yr CO2 equivalent Mt/yr Uncertainty95% confidence limit (%)

Agricultural Soils 34.78 16.17 (72.6%)B -56 to +120

Prescribed Burning of Savannas 11.80 5.48 (24.6%) -68 to +129

Crop Residue Burning 0.17 0.08 (0.3%) -39 to + 50

Manure Management 1.17 0.54 (2.5%) -7.6 to 22.8

Total 47.92 22.27 (100.0%)A Australian Greenhouse Office 2001; Dalal et al. 2003.B Percentage of the total N2O emissions from different Australian activities.

Nitrogen fertiliser use for agricultural productionhas increased sharply in recent years (Figure 2).Nitrogen fertiliser use for cereal crops increased by314% from 1987 to 1996 and it further increased by11% from 1996 to 2000 (Table 5). Although muchsmaller in amount, N fertiliser use for oilseed cropssuch as canola increased by 390% from 1996 to 2000. Since 1996, cereal/oilseed crops accounted for more than 70% of the total N fertiliser use.

For comparison, just over 50% of the total Nfertilisers was used in the agricultural sector tenyears earlier (1987). On the other hand, percentagesof the N fertiliser applications to improved pastureand horticultural crops were about 12% each in 1987,but reduced to only 6-7% each by 1996-2000. Overall,almost 90% increase in N2O emissions from 1990 to1999 was due to an increase in the rate of N fertiliserapplication (Australian Greenhouse Office 2001).

y = 6.6705x2 – 26552x + 3E+07R2 = 0.99

200

400

800

1,000

600

1,200

Nitr

ogen

fert

ilise

r use

(kt N

)

Year1990 1992 1994 19981996 2000

Figure 2. Trends in nitrogen fertiliser use in the Australian agriculture (data from Chudleigh and Simpson2001; Dalal et al. 2003).


Table 4. Nitrous oxide emissions from agriculturalsoils in 1999.

SourceA N2O CO2 equivalentkt N/yr Mt/yr

Fertilizer Use 11.14 5.18 (32.1%)B

Crop/Pasture Soil Disturbance 13.38 6.22 (38.4%)

Animal Faeces and Urine 10.26 4.77 (29.5%)

Total 34.78 16.17 (100.0%)A Australian Greenhouse Office (2001; Dalal et al. 2003). B Percentage of the total N2O emissions from different

Australian activities.

There are numerous reasons given for the increase in N fertiliser use for cereals/oilseed crops in recent years (Table 5). Some of these reasons are: (i) decrease in pasture area by 6 million ha in the last 10 years, hence lower legume N2-fixed supply of N to the following crops; (ii) increased premiumprice paid for higher wheat grain protein content;(iii) introduction of disease-break crops such ascanola, which itself demands higher N supply; and(iv) combined impact of technological changes oncrop yields and N demand (Angus 2001).

Table 5. Estimates of nitrogen use by different crops.

Crop Fertilizer N use (kt N)

1987A 1996B 2000C

Cereals 195 613 701

Sugarcane 58 100 96

Cotton 27 48 56

Oilseed/Pulses 4 14 55

Horticulture 43 50 71

Pasture 44 59 76

Total 371 884 1,055A Bellingham (1989). B Reuter (2001). C Chudleigh and Simpson (2001).

(Dalal et al. 2003).

Nitrous oxide emissions from soil disturbance(cultivation, agricultural activities, ley/cropping)showed a slight decline of 2.1% from 1990 to 1999due to decrease in ley/cropping area, shifting tocontinuous cropping.

Animal faeces and urine account for an increase of90% in the N2O emissions from 1990 to 1999 due toincreasing intensification of the livestock industries.However, there was a reduction in the fielddeposition of animal waste due to the reduction in sheep and cattle populations (AustralianGreenhouse Office 2001).

The burning of biomass such as forest vegetation,savanna grasslands, and agricultural residues is an important source of nitrous oxide emissions.Prescribed burning of grasslands and savannasprimarily in northern Australia aims at reducing the risk of uncontrolled fires during the dry winter-spring seasons in grazing lands. It is also supposedto rejuvenate pastures by recycling of P and K,which are generally low in the region’s soilsalthough pastures get further depleted of N after every fire.

It was estimated in 1999 that 24% of the total annualemissions of nitrous oxide from the agriculturalsector were the result of direct emissions fromprescribed burning of savannas (AustralianGreenhouse Office 2001). While combustion isclearly a major source of nitrous oxide emissions, the effect of fires extends beyond the directcontribution of emissions during combustion. Fires also cause substantial changes to the topsoilresulting in significant and persistent changes in the soil-to-atmosphere fluxes of nitrous oxide(Meyer et al. 1997), due to changes in soil Nmineralisation (Raison 1979). Emissions of N2Odirectly from savanna and grassland fires in 1999were estimated to be 11.8 kt, while the estimatedenhanced emissions due to soil disturbance by in situ biomass burning were in the range of 0.6-12.1 kt (NGGIC 1999). The estimates of N2Oemissions from 1990 to 1999 showed an increase of38% from savanna fires although there is a largeuncertainty in the estimates of total area affected byfires (Australian Greenhouse Office 2001). Suchestimates highlight the significant contribution madeby emissions due to soil N disturbance by in situ

biomass burning.


2. N2O PRODUCTION IN SOIL

2.1. PROCESSES INVOLVED IN N2O PRODUCTION IN SOIL

Nitrous oxide is produced in soil by at least threemicrobial-mediated mechanisms: (i) duringammonium oxidation to nitrite (nitrification) (ii) dissimilatory nitrate reduction (denitrification)and (iii) assimilatory nitrate reduction. Microbial assimilatory nitrate reduction is of minor importance in soils (<6% of total nitrate reduction) because it is inhibited by very lowconcentrations of ammonium or soluble organicnitrogen present in soil. Dissimilatory nitratereduction (denitrification) is probably the main source of N2O in soil (Tiedje 1994), although N2Oproduction by nitrification may sometimes be equally important (Granli and Bøckman 1994). The generalised Equation 1 below shows the first two mechanisms of nitrous oxide production in soil(Dalal et al. 2003).

The fourth mechanism implicated in N2O productionis the abiotic nitrite and nitrate reduction (involvingorganic matter and reductants such as ferrous iron)(Magalhaes and Chalk 1989) although its processmechanism is unclear and its overall contribution isuncertain (Venterea and Rolston 2000). It is favouredunder acidic conditions and may occur under bothaerobic and anaerobic conditions (Chalk and Smith1983).

2.2 FACTORS CONTROLLING N2O PRODUCTION IN SOIL

2.2.1 Moisture and Aeration

Nitrification increases with increasing water contentup to 50 to 60% of water-filled pore space (WFPS)(Figure 3), provided it is not limited by other factorssuch as NH4

+ supply (Linn and Doran, 1984). Therate of N2O production from nitrification is normallylow below 40% WFPS, but increases rapidly withincreasing water content up to 55−65 %WFPS(Goodroad and Keeney, 1984). When soil moistureexceeds 60−70% WFPS (depending on other factorse.g. temperature and decomposable C), increase in water content hinders aeration (limits oxygendiffusion) and promotes denitrification (Figure 3).Thus, the rate of N2O emission increases withincreasing moisture, from air-dry to field capacity(Freney et al. 1979).

Many field studies showed that irrigation or rainfallresults in high N2O emissions, especially when N fertiliser is applied with irrigation or soon beforethe irrigation event (Mosier and Hutchinson, 1981;Freney et al., 1985; Hansen et al., 1993). Providedother factors remain constant, the water content formaximal N2O emissions is usually such that bothaerobic and anaerobic sites are abundant. Thus soilwater contents within the range of 55 to 85% WFPSgenerally gives maximum N2O emissions fromdenitrification and/or nitrification (Granli andBøckman, 1994). Higher water content favoursdenitrification towards N2 formation. Thus, theN2O/N2 ratio decreases as the soil water contentexceeds 75% WFPS (Davidson 1992; Weier et al.,1993). If the soil remains at waterlogged conditionfor a prolonged period, denitrification and thus N2O production may cease because of lack of O2 and NO3

- production from nitrification.

SOM

NH4+ Fertiliser Nitrate Fertiliser

NH4+ NH2OH NH2ONO NO2 NO3

-

(Medium O2, low H2O): NO N2 (Low O2, high H2O)N2O N2O

Equation 1

(1)


Therefore, alternate wet and dry cycles stimulate N mineralisation from organic matter, promote NO3

-

accumulation during the dry period, and increasesN2O production during the wet period as long as itdoes not get waterlogged.

2.2.2 Temperature

Like other biological processes, nitrification anddenitrification rates increase with increasingtemperature within a certain range. The optimumsoil temperature for nitrification is generallybetween 25oC and 35oC (Haynes, 1986; Granli andBøckman, 1994). Higher temperature favours ahigher ratio of N2O/NO3

- from nitrification(Goodroad and Keeney, 1984).

Denitrification has been detected at temperatures <0oC, but usually becomes significant at >5oC(Granli and Bøckman, 1994). The reported optimumtemperature for denitrification varies greatly,ranging from 30 to 65oC (Bremner and Shaw, 1958;Malhi et al., 1990; Aulakh et al., 1992; Tiedje, 1994).

As the soil temperature increases, N2O emissionsalso increase, at least up to 37oC (Freney et al.

1979; Castaldi 2000). The ratio of N2O/N2 due todenitrification declines with increasing temperaturesabove 37oC (Keeney et al., 1979). The principalmechanism for gaseous N production at higher temperatures (>50oC) is probablychemodenitrification of NO2

- that can be rapidlyproduced by thermophilic nitrate respirers (Keeney et al., 1979), resulting in primarily N2 gas emissions from soil.

Direct combustion remains the major source of trace gas emissions from biomass burning. Nitrogenspecies emissions from biomass burning aredependent upon the nitrogen content of the fuel and fire intensity and duration of flamingcombustion vs. smouldering combustion (Lobert et al. 1990). Molecular nitrogen is the mostsignificant species emitted, with the largestcontribution coming from flaming combustion(Kuhlbusch et al. 1991). Lobert et al. (1990) found that

0

0.2

0.6

0.8

0.4

1.0

N2ON2

Water filled pore space, WFPS (%)0 20 40 8060 100

Rela

tive

N2O

or N

2 e

mis

sion

Figure 3. A generalised relationship between water-filled pore space (WFPS) of soils and the relative fluxesof N2O (▲) and N2 (■ ) from nitrification and denitrification. N 2O fluxes dominate between 50% and 80% ofWFPS and N2 dominates above 80% WFPS (From Dalal et al. 2003).


up to half of the biomass nitrogen can be convertedto molecular nitrogen, N2, through the process ofpyrodenitrification. It is also during the hot flamingphase that N2O is emitted (Lobert et al. 1990;Kuhlbusch et al. 1991), which comprises less than 1 percent of total N lost during fire.

Fire also influences processes of N2O productionwithin the soil by heating it; causing naturalpyrolysis or thermal degradation to both the labileand intractable soil N material (Meyer et al. 1997).This in turn promotes the rate of mineralisation,effectively increasing the mineral nitrogenconcentrations in the soil. Increased soil ammoniumpools will then promote nitrification rates, leading to substantial increases in nitrate within the soil(Raison 1979) and increasing the likelihood offurther nitrogen flow through denitrification (Meyer et al. 1997).

Changes to the fluxes of nitrous oxide between soiland the atmosphere appear to be proportional to fire intensity (Meyer et al. 1997). Studies show thatmedium to high intensity fires such as savannah andgrassland fires may cause significant and persistentincreases in nitrous oxide, while low temperatureprescribed fires or the field burning of wheatresidues do not appear to cause any significantchange (Table 6). Uncertainty remains as to theeffects of rainfall on nitrous oxide fluxes betweensoil and the atmosphere. Some studies haveindicated that substantial increases in N2O emissionsoccurred only after the soil was subjected tosimulated rainfall events. Other studies, however,

demonstrate that enhancement of N2O emissions canbe independent of rainfall events (Meyer et al. 1997).It appears that this variability in emission rates isrelated to the extent of the disturbance to soilorganic N and its subsequent mineralisationfollowing fire (Meyer et al. 1997).

2.2.3 Soluble and Readily Decomposable Carbon

Organic materials such as plant litter, root exudates,manures, or native soil organic matter are thesources of carbon and energy for heterotrophicdenitrifying organisms. Oxygen consumption insoils with high decomposable C contents is normallylarge, which may result in anaerobic micrositesbecause of insufficient replenishment of air bydiffusion. The occurrence of the anaerobic micrositesis interactively dependent on the availability oforganic C, moisture, soil texture and structure as well as temperature. As discussed above,simultaneous presence of anaerobic and aerobic sitescreates a situation favourable for N2O production.

Many studies have demonstrated that soildenitrification capacity increases with increasingorganic C content, especially water-soluble C content(Burford and Bremner, 1975; Drury et al., 1991; Iqbal, 1992). Others have found that incorporation of plant materials enhances the rate of denitrification(Dorland and Beauchamp, 1991; Aulakh et al., 1991).Soil disturbance such as drying-wetting and freezing-thawing can liberate more available C, and thus cangreatly increase the rate of denitrification (Fotch andVerstraete, 1977). Although the ratio of N2O/N2 from

Table 6. Comparison between the estimated enhanced emissions due to soil disturbance by in situbiomass burning and directly from smoke plume emissions.

Fire Category Enhanced Soil Emissions (Gg) Smoke plume Emissions (Gg)N2O NOx N2O NOx

Savanna and Temperate Grassland 0.6-12.1 164 15.4 896

Wheat 0 0 0.1 4.7

Coarse Grain 0 0 0.04 2.2

Sugar Cane 0.005-0.1 1.3 0.1 5.6

Prescribed burning 0 ? 0.23 9.5

(Source: Meyer et al. 1997)


denitrification decreases with increasing available Csupply (Weier et al., 1993), the total amount of N2Oproduced from denitrification may be enhanced bythe addition of organic materials.

The relationship of organic C availability tonitrification is less straightforward. Addition oforganic materials with high C/N ratios promotesmicrobial immobilisation of NH4

+ and hencecompetes for this substrate against nitrification. If the organic materials have low C/N ratios,however, the rates of nitrification and hence N2Oproduction are increased by supplying more NH4

+ from mineralisation. Decomposable organicmaterials increase the respiration rate of micro-organisms and may induce O2-limitation, whichenhances N2O production from nitrification.

In general, addition of degradable organic materialsincreases N2O production in soils containing NO3

- or applied with fertiliser NO3- (Murakami

et al., 1987). High amount of N2O can also be

produced if materials containing degradable organicN (e.g. animal and green manures) is applied(Bremner and Blackmer, 1981; Goodroad et al., 1984).

2.2.4 Soil and Fertiliser Nitrogen

Generally, the rate of denitrification increases withincreasing NO3

- content in soil under conditionssuitable for denitrification (e.g. high moisture).When other factors such as temperature andavailable organic C are limiting, however, changes inNO3

- content can have little effect on denitrificationrate. Under most circumstances, the presence ofNO3

- inhibits the rate of N2O reduction to N2

(Blackmer and Bremner, 1978), which results inhigher N2O/N2 ratio at similar moisture and oxygencontent. The mechanisms for this inhibitory effectmay be: (i) NO3

- is reduced to NO2- that inhibits

N2O reduction (Firestone et al., 1980); and (ii) NO3- is

preferred over N2O as an electron acceptor duringdenitrification (Cho and Sakdinan, 1978) (Figure 4).However, flushes of N2O production are observed

0

0.2

0.6

0.8

0.4

1.0

Nitrate-N (mg/kg soil)0 10 20 40 5030 60

Den

trifi

catio

n N

loss

Total denitrification lossesN2 N2O

Figure 4. A diagrammatic representation of the effect of the concentration of nitrate-N in soil on the relativeN2O (▲) and N2 (■ ), and total denitrification losses ( ● ) (redrawn from Mosier et al. 1983; Dalal et al. 2003).


usually immediately after NO3- addition. In a few

hours or days, N2O production decreases, and N2

production increases, even when relatively highconcentrations of NO3

- are still present (Rolston et al., 1978). This phenomenon was explained as theresult of a lag period between the activation of NO3

- reductase and N2O reductase enzymes (Letey et al., 1980).

Under normal field conditions, nitrification is limited by the formation of NH4

+ frommineralisation. In fields applied with fertiliserscontaining NH4

+, significant N2O emissions havebeen observed (Bremner and Blackmer, 1981;Hutchinson and Brams, 1992). Wang and Rees (1996)found that NH4

+- or urea-N added to soils producedmore N2O than did NO3

- under aerobic conditions.A significant positive relationship between NH4

+

content in soils and N2O production was observed(Wang and Rees, 1996), confirming that nitrificationis a significant source of N2O under aerobicconditions.

The rate of N2O emission after fertiliser applicationis interactively influenced by the amount and type offertiliser N, soil properties and the environmentalconditions (Granli and Bøckman 1994). For example,use of NO3

- fertilisers in waterlogged fields or insoils rich in organic C, or NH4

+ fertiliser applied tomoist and partially aerated soils, generally results inlarge N2O emissions.

2.2.5 Soil pH and Salinity

Soil pH is a secondary controller of denitrification by mainly affecting the nitrification process.Nitrification is sensitive to extremes in soil pH. The optimal pH for nitrification is approximately 7 to 8 (Fotch and Verstraete, 1977; Haynes, 1986).Laboratory incubations of soils added with NH4

+

under aerobic conditions showed that N2Oproduction could increase by many times withincreasing pH up to about 8 (Bremner and Blackmer,1981; Minami and Fukushi, 1983; Wang and Rees,1996). At higher pH (pH >8.2), nitrite accumulates

in soil, and this is then reduced to N2O sincecompetitive biological oxidation of nitrite byNitrobacter is prohibited (Chalk and Smith 1983).

The maximum rate of denitrification occurs at a pH range of about 7 to 8 (Bremner and Shaw, 1958;Bryan, 1981). Although NO3

- reduction was detectedat a pH as low as 3.5 (Fotch and Verstraete, 1977),denitrification declines if soil acidity shifts towardslower pH. Because the reduction of N2O is inhibitedmore than the reduction of NO3

- by acidicconditions, N2O production is enhanced or evenbecomes dominant at pH <5.5 to 6.0 (Burford andBremner, 1975; Weier and Gilliam, 1986). As the pHincreases, denitrification products tend more, orcompletely, towards N2 production (Fotch andVerstraete, 1977).

High salinity inhibits both nitrification anddenitrification (Inubushi et al., 1999). N2O reductaseis susceptible to salt, which may result in N2Oaccumulation from denitrification under salineconditions (Menyailo et al., 1997). Therefore, N2Oproduction from nitrification could be promoted byincreased salt concentration (Low et al., 1997). Theeffects of soil salinity on nitrification, denitrificationand N2O production have been less studied than theeffects of other regulating factors. More research isrequired on this topic.

2.2.6 Limitation of Nutrients Other Than Nitrogen

Limitations of other essential nutrients for plantgrowth limit the ability of plants to utiliseammonium and nitrate N and reduces the overallplant sink for mineral N absorption. Hall andMatson (1999) observed that N2O emissions from 15 kg N/ha applications were much higher from aphosphorus-limited forest soil than the soil high inplant available phosphorus in a tropical forest. Since many Australian soils are low in plantavailable phosphorus, this has implications,especially for large areas of extensive grazing landsand rangelands, and forest soils. No Australian data exist to confirm these observations.


2.3 METHODS AND THEIR LIMITATIONS IN MEASURING N2O EMISSIONS FROM SOIL

N2O exchange between soil and the atmosphere is not difficult to measure but high spatial andtemporal variability at local scales makesextrapolation even to small landscape units veryproblematic. High spatial and temporal variabilityalso hinders efforts to identify biological sources and controls of fluxes. The nitrous oxide gas can bemeasured by infrared analysers (Denmead 1979),and gas chromatography using electron capturedetectors (Kammann et al. 2001), tunable diode-laser,infrared detectors, and molecular sieves (0.5 nm)(Van Cleemput et al. 1992).

There are two main strategies for measuring N2Oflux in situ: chambers placed on the soil surface forshort periods of time and micrometeorologicalapproaches. Each has strengths and weaknesses.

2.3.1 Chamber Methods

Chamber methods represent the most accessibletechniques for measuring N2O fluxes (Mosier 1989,Hutchinson and Livingston 1993, Holland et al.

1999). They have been instrumental for documentingdifferences in fluxes among different ecosystems andmanagement regimes, but tend not to capture spatialand temporal variability very well.

In their simplest configuration, chambers are simplyopen-bottom cylinders or boxes placed on the soilsurface for a period of time, usually 1-2 hours,during which gases emitted from the soil accumulatewithin the enclosed headspace. The headspace isthen sampled periodically, and the linear portion ofthe accumulation curve is assumed to be the gas fluxrate. Generally chambers are fitted with a rubberseptum through which gases are withdrawn foranalysis, and most chamber designs include a smallvent to buffer against abrupt changes in barometricpressure over the installation period (see Holland

N2O (g/ha/d)0 50 100 150 200

-4

-3

-2

2

3

-1

1

0

4

Expe

cted

val

ue

Figure 5. Probability distribution for chamber-based N 2O flux measurements for a conventionally managed cropping system 1991-1999 (Robertson et al. 2000). Distributions tend to be similarly skewed in even low-flux systems.


et al. 1999) and reduce microclimate within thechamber. More sophisticated designs employ collarsthat are placed permanently in the soil; the fluxchamber is then placed on the collar prior tosampling rather than inserted into the soil in order to avoid periodic soil disturbance.

Although static flux chambers are inexpensive andeasy to use, they generally cover only a small soilsurface area and are deployed briefly because theiruse is labour-intensive and because they can affectthe soil microclimate and thus gas flux if left in placefor too long. Yet the consequences of missing animportant flux event can be great. The temporaldistribution of N2O fluxes tends to be log-normallyskewed in most ecosystems (Fig. 5). Annual fluxestimates are almost always based on many near-zero values averaged with a few number of values 1 – 3 orders of magnitude higher. In one recent study(Wagner-Riddle et al. 1996a), as much as 40% of theannual emissions of N2O from one system occurredas a single event.

Automated chambers (e.g. Brumme and Beese 1992,Wang et al. 1997, Ambus and Robertson 1998, Weitzet al. 1999, Galle et al. 2002) provide near-continuousmeasurements of gas fluxes without the labourexpense of high-frequency field campaigns. Theyhave been extremely useful for documenting short-term changes in fluxes from specific environments(Fig. 6 and 7), and should be especially useful forparameterising quantitative models of N2O flux.However, automated chambers are expensive tomaintain and similar to static chambers, perhapsmore importantly, measure fluxes from relativelysmall areas, typically <0.25 m2. This can be asignificant limitation for whole-ecosystem estimatesof N2O flux because the short-range spatialvariability of fluxes tends to be high (Fig. 8).Automated chambers also tend to be inoperable inheavy snow, and fluxes of trace gases such as N2Othrough snow cover may be a significant part ofannual budgets in some environments (Wagner-Riddle 1996b).

Day of year182 183 184 185

0

5

20

25

10

15

30

µg C

or n

g N

cm

–2 h

r–1

CO2 flux N2O flux

Figure 6. N 2O and CO2 fluxes from an automated chamber located in a conventionally managed croppingsystem. Note the order of magnitude difference in N 2O flux over the course of day 182-183 (PhillipRobertson, unpublished data).


Day of October 199510 20 2515 30

0

5

10

15

20

N2O

flux

(ng

N m

–2 s

–1)

CO2 f

lux

(g C

m–2

s–1

)

Day of October 10 20 2515 30

0

50

100

150

N2O

CO2

Figure 7. CO 2 emission (soil + plant respiration) and N 2O emission from lucerne. Note the order ofmagnitude difference in N 2O flux on 23 October following rainfall. (Source: Meyer et al. 2001).


Because of the effort required to measure fluxes frommore than a few chambers at a time, there are veryfew estimates of the within-site spatial variability of N2O fluxes. We know that CO2 fluxes can bevariable even in monoculture crops such as wheatsystems (Aiken et al. 1991). And studies of the spatialvariability of denitrification, the most importantsource of N2O in many ecosystems, suggest equallyhigh variability for N2O flux. For example, Folorunsoand Rolston (1984) found coefficients of variation>500% for denitrification fluxes across a fallowvegetable field in central California. Robertson et al.

(1988) found spatial variability log-normally skewedacross a mid-Michigan old cultivated field. As fortemporal variability, noted above, they found theaverage whole-site flux dominated by a relatively fewautocorrelated locations at which fluxes were onaverage 5-fold greater than fluxes elsewhere in thefield (Figure 8). Overcoming this variability with very large chambers (e.g. Christensen et al. 1996) isusually impractical and leads to a different set ofcompromising assumptions such as uniformity of

air mixing and longer equilibration periods that may affect microclimate within chamber.

Capturing temporal and spatial variability for N2Ogas fluxes is thus very important to accuratelyquantify ecosystem-wide fluxes. It is less importantfor documenting differences among ecosystems atthis point, although once most of the within-sitevariability in ecosystems is captured, the cross-sitecomparisons with better precision can be made, and more subtle patterns may emerge. But at least for now, one of the major problems facingbiogeochemists attempting to assemble landscape to global N2O and other trace gases budgets remainsthe same problem as in the 1980’s (Robertson et al.

1989), that is, how to accurately quantify the fluxfrom a single ecosystem.

2.3.2 Micrometeorological Methods

Researchers studying ecosystem fluxes other thanN2O such as CO2, NH3, and CH4 have turned tomicrometeorology to integrate system-wide fluxes

Figure 8. Denitrification fluxes across 0.5 ha of a Michigan old field. Average rates vary from 18 to >90 µg m -2 d-1 in the light vs. dark areas, respectively. (From Robertson et al. (1988)).

Distance East (m)

Dist

ance

Nor

th (m

)


(e.g. Denmead 1983, Freney et al. 1983, Wofsy et al.

1993, Ham and Knapp 1998). Micrometeorologicalapproaches are based on measurements of movingair masses over ecosystems, and have the advantageover chambers of spatial and temporal integration.Fluxes are typically measured for areas as large as 2-3 km2 in forested systems and as large asseveral ha in grasslands, and fluxes are measuredcontinuously during daylight hours, not just whilechambers are in place. Fluxes also include canopyinteractions, which are important for some gasessuch as CO2 and NH3.

Sensors mounted on towers detect the movementand gas content of air above and within the plantcanopy; the rate and direction of flux (from theecosystem vs. into the ecosystem) can be determinedfrom information about concentrations, gradients,and turbulence (Fowler and Duyzer 1989; Lenschow1995). Determination of CO2 flux by eddy correlationis now routine due to the advent of fast-reacting 3-D anemometers and continuous infrared gasabsorption (IRGA) detectors.

Until recently, micrometeorological approaches havenot been available for N2O fluxes. This is because gas sensor technology has not until recently beensufficiently sensitive to detect the small changes inconcentration required to establish a flux gradient(typically 2 ppbv for N2O) against a relatively highatmospheric background (ca. 320 ppbv N2O).Recently, however, substantial advances in instrumentdesigns have provided the opportunity to deploymicrometeorological systems capable of detectingN2O fluxes at much lower rates than were previouslyavailable. These systems, based either on tunablediode laser (TDL) or Fourier-transform infraredspectroscopy (FTIR) detectors (Kolb et al. 1995), arenot yet as sensitive as chamber-based approachesusing traditional gas chromatography detectionsystems. But for ecosystems in which annual fluxesare derived mainly from high short-interval fluxevents that are difficult to predict in advance, theseapproaches show promise for quantifying annual fluxmeasurements for entire landscape units.

Micrometeorological systems for N2O have beendeployed at only a handful of sites worldwide.However, where they have been deployed they haveshown general agreement with short-term chambermeasurements (Christensen et al. 1996, Mosier et al.

1996; Leuning et al. 1999; Denmead et al. 2000) andsufficient sensitivity to detect fluxes in the systemsexamined (Wagner-Riddle et al. 1996a, 1997). Veryrecent advances in FTIR (Griffith and Galle 2000)suggest special promise for detecting modest fluxesof a suite of gases on a continuous basis at sites withavailable infrastructure (e.g. access to power andliquid nitrogen).

Leuning et al. (1997) and Denmead et al. (2000), for example, measured micrometeorological N2Oemissions from grazed pastures at Wagga Wagga,and found general agreement with fluxes calculatedusing NGGIC (1996) and IPCC (1996) methodologies(Table 7). Amongst the micrometeorologicalapproaches used, the mass-balance approachappears to be most precise since N2O concentrationsare larger and thus more easily measured due tohigher stocking densities than in the normal fieldsituation. On the other hand, application of flux-gradient approach is difficult due to low N2Oconcentrations over a large region. Although bothtemporal and spatial variability in N2O emissionestimates by micrometeorological approaches arehigh, these estimates are considerably larger thanthose estimated from NGGIC algorithms (N2Oemission factors of 0.4% for urine and 1.25% fordung) but closer to those estimated from IPCC(1996) algorithms, which employ N2O emissionfactor of 2% for both urine and dung N (Denmead et al. 2000).


Table 7. A comparative estimation of nitrous oxideemissions from grazed pastures at Wagga Wagga,New South Wales using NGGIC (1996) and IPCC(1996) methodology, and micrometeorologicalmethods (flux-gradient, convective boundary layerand mass balance).

Methodology N2O-N emissionA

(kg N/ha.year)

NGGIC (1996) 1.0

IPCC (1996) 1.8

Micrometeorological:

Flux-gradient 2.2 ± 1.2

Convective boundary layer 1.8 ± 1.4

Mass balance: ε = 0.115 6.4

Mass Balance: ε = 0.039B 2.7A Calculated from Denmead et al. (2000).B Excludes N2O emissions following rainfall.

(from Dalal et al. 2003).

The major limitations of N2O emissionmeasurements by micrometeorological methodsinclude a high deployment cost and technicallimitations associated with weather conditions. The deployment cost is related to the technicalexpertise required and instrumentation, costs forwhich are several orders of magnitude higher thanthose for chambers. Nitrous oxide measurementcampaigns using micrometeorological approachesthus tend to focus on a single ecosystem type, andcontinuous measurements for more than a fewweeks at a time are rare. Weather limitations arerelated to boundary layer conditions and airturbulence; in general, fluxes are not measurable at night or during periods of rainfall.

For the foreseeable future it is likely that acombination approach will work best, one that uses chambers to measure low fluxes and to makecomparisons among different habitats and landmanagement strategies, and that usesmicrometeorological approaches to spatiallyintegrate fluxes. Both automated chambers andmicrometeorological approaches can provideimportant information about temporal fluxes,especially across environmental events that triggerhigh fluxes.

2.3.3 Methods for Measuring N 2O Emissions During Fire

Emissions of nitrogen containing compounds fromthe burning of biomass can be measured using avariety of techniques. Such techniques include realtime in situ measurements of N2O made over largeprescribed fires, the collection of grab-bottlesamples, and analysis of small laboratory biomasstest fires.

Real time in situ measurements of N2O made overlarge prescribed fires involves collecting air samplesabove the fire, which are then subjected to a gaschromatogram with Ni detection (Cofer et al. 1991).Alternatively, air can be collected in stainless steelgrab-bottles and analysed 4-8 hours after collection.The bulk of evidence suggests that concentrations ofN2O in grab bottles will be stable for several hoursafter collection (Cofer et al. 1991).

Small laboratory biomass test fires require smallscale burning apparatus built to simulate open fires.An inherent limitation in measuring N2O emissionsusing these test fires is that only direct combustionemissions of N2O are measured. Combustion itself,however, is not the only source of N2O; significantand persistent increases in N2O also result from soildisturbance by in situ biomass burning. Thus, N2Omeasured through laboratory biomass test fires andnot over the soil during field collections do notconstitute the total sum of combustion and soilprocesses (Cofer et al. 1991). Laboratory biomass test fires also vary from field collections in that fieldcollections typically involve sampling aged smokeplumes, thereby allowing combustion products moreopportunity to undergo heterogeneous N2Oproducing reactions on aerosols (Cofer et al. 1991).


3. MODELLING OF NITROUS OXIDEEMISSIONS FROM SOIL

Since N2O emissions from agroecosystems aresporadic, and temporally (diurnal, season) andspatially variable, modelling of these systems isessential to provide estimates of N2O emissions overa number of seasons and areas for the NationalGreenhouse Gas Inventory.

Ecosystem models are necessary to simulate N2Oemissions from soil. These models must include theamount of N in soil and biomass, as well as the N fluxes (organic N, ammonium N, nitrate N),which contribute to the N2O emissions from soil andbiota. Also, the ecosystem models are used to extendthe results of spot measurement and short timeexperiments to the regional and global estimates of N2O emissions. As a first approximation, simple empirical models are used to estimate N2O emissions from total nitrogen additions. For example, IPCC (1996) recommends a value of1.25% of fertiliser N and animal manure N toestimate the total amount of N2O emissions fromthese sources, whereas Taylor (1992) suggested netprimary production as a basis of estimating N2Oemissions.

On the other hand, highly complex models, whichexplicitly simulate the biological, physical, andchemical processes governing N flows and fluxes inan ecosystem are desirable for scenario simulationsin terms of mitigation options but they require largedata sets and measurements for parameterisation.

A large number of models have been developed tosimulate N2O fluxes from natural and managedecosystems (Li et al.1992a, Riley and Matson 2000,Parton et al. 2001, Potter et al. 1996, Grant and Pattey1999). The simpler models were developed tosimulate nitrogen gas fluxes (NOx, N2O, and N2) atregional and global scales (Parton et al. 1988, Potteret al. 1996), by assuming that gaseous N loss isproportional to N mineralization, with theproportion of N loss for each gas (N2, N2O, andNOx) being a function of the soil water filled pore

space (Fig. 3). The more process oriented nitrogengas flux models (Li et al. 1992b, Grant and Pattey1999, Parton et al. 2001) were developed to simulatethe impact of crop management practices andfertiliser N inputs on N gas fluxes. These process-oriented models all simulate gas fluxes of N2, N2Oand NOx from nitrification and denitrification andinclude detailed descriptions of the impact of soiltemperature, NO3

-, NH4+, water and texture on N

gas fluxes. The models use different approaches tosimulate nitrification and denitrification. However,the theoretical bases of the models are similar andare based on extensive field and laboratory data(Firestone and Davidson 1989, Davidson andSchimel 1995, Groffman 1991). Some of the modelssimulate the dynamics of the microbes that areresponsible for soil nitrification and denitrificationsuch as a process-based model, DNDC(Denitrification and Decomposition) (Li et al. 1992a),while other models simulate nitrification anddenitrification as a function of frequently measuredand modelled variables such as soil water,temperature, NO3

-, NH4+, and soil respiration

(Del Grasso et al. 2001a). Some of the highlymechanistic models simulate microbial growth rates,and solute and gas transport through the soil profileand aggregates (Smith 1980, Grant and Pattey 1999).

A formal comparison of models that simulate N2Ogas fluxes was done by Frolking et al. (1998) andincluded the forerunner of the DAYCENT, DNDC,CASA and NITRO models. The model results werecompared with observed daily N2O gas fluxes fromfour different agroecosystem sites, which rangedfrom fertilised grasslands in Scotland to croppingsystems in Germany and included sites withdifferent soil textures. The comparison demonstratedthat models simulated the major differences in N2Ogas fluxes for the various sites fairly well. However,there were major differences in simulated N2 andNOx gas fluxes (not measured at the sites used in themodel comparison) among the models. The authorssuggested that new model comparison effortsinclude sites where fluxes of N, NOx and N2O are measured at the same time.


DNDC and the DAYCENT (Li et al. 1992a, 1992b, DelGrasso et al. 2001a, 2001b, Parton et al. 2001) havebeen used extensively to simulate the impact ofmanagement practice on N gas fluxes. The DAYCENTmodel has been used to simulate the effect of thedominant management practice on net greenhousegas fluxes (CO2, N2O and CH4) for dryland andirrigated regions in the US Great Plains and the CornBelt regions (Del Grasso et al. 2001a, 2001b). Themodel results suggest that adopting no-tillagepractices for the Corn Belt region and reducing thefrequency of fallow in the dryland regions of the USGreat Plains will substantially reduce greenhouseemissions for these regions. DNDC has been used tosimulate N2O gas fluxes for current agriculturalpractices in US (Li et al. 1992b) and is capable ofsimulating the impact of new management practicesthat have the potential to reduce agriculturalgreenhouse gas fluxes.

Wang et al. (1997) simulated fluxes of CO2 and N2Oby DNDC in a legume pasture system in south-eastAustralia in 1993. They had to modify DNDC bypartitioning the total soil organic C into plantresidue, microbial biomass, and humus using theconstant proportions of 0.4:0.4:0.2 at the start ofsimulations. Further, within DNDC, they had tomodify the fraction of water-filled pore space abovewhich denitrification takes place from 0.4 to 0.6.Another modification was to use the soil surfacetemperature instead of the air temperature since the former could be higher by as much as 20oC insummer. After these modifications, they obtained areasonable agreement between measured andsimulated N2O emissions from a legume pasture (Fig. 9). This emphasizes the verification andvalidation of imported models withparameterisation of the Australian conditions.

0

2

4

10

14

6

12

16

8

18

DNDC (Li et al. 1992) DNDC (Wang et al. 1997)Measured

Trip 1 Trip 2 Trip 3

Nitr

ous

oxid

e (g

N/h

a.da

y)

Figure 9. Measured and simulated N 2O fluxes from a legume pasture in south-east Australia. (DNDC modelfrom Li et al. (1992b), and modified DNDC model by Wang et al. (1997) including changes in WFPS,temperature, organic C pools and plant N uptake. (Adapted from Wang et al. 1997; Dalal et al. 2003)).


Conceptually, DAYCENT model is based on theassumption that the total gas emissions from soil areproportional to nitrogen cycling through the systemand soil gas diffusivity determines the relativeamounts of the respective N gas species emittedfrom soil. The DAYCENT model includes submodelsfor soil organic matter decomposition, land surfaceparameters, plant productivity, and trace gas fluxes. The submodel for N2O and N2 fluxes fromdenitrification assumes that N gas flux fromdenitrification is controlled by the most limitingfactor among soil nitrate concentration, carbonsubstrate supply, and oxygen supply (Fig. 11).

The DAYCENT simulated reasonably well theobserved N2O emissions from various farmingsystems, including conventional till and no-till, soiltextures (coarse, medium and fine), N application(10 kg N/ha), intensively cropped rye (Scotland),crop rotations (Germany) and irrigated barley andmaize in Colorado (Fig. 11).

Although DAYCENT simulates seasonal pattern of N2O fluxes from grasslands reasonably well, itsimulates these fluxes very poorly on a daily basis,and hence the significance of diurnal fluctuations inN2O emissions due to changes in soil water andtemperature. Also, soil mineral nitrogen appears tobe consistently underestimated (Parton et al. 1998).Further improvements in simulation modelling isrequired, taking into account the soil texturedifferences, clay mineralogy, and integration of the ‘hot spots’ over time and field scale.

Figure 10. The N 2O, NOx and N2 submodel of DAYCENT (adapted from Del Grosso et al. 2001b; Dalal et al. 2003).

N2ON gasnitNH4+SOM N

Biom N

NOx

NO3-NO3-Fert

N2

NH4-Fert

N gasden

D/DORainfall

Soil H2O, Temp, C, pH, Texture D/DO

D/DO

∞

Denitrification

Hyd

∞ ∞Min

Soil H2O, Temp, C, pH, Texture

NO3-: C∞

Nitrification


4. N2O EMISSIONS FROM VARIOUS ECOSYSTEMS

4.1 N2O EMISSIONS FROM AGRICULTURAL SYSTEMS

4.1.1 Cropping Soils

Flooded rice cultivation. Rice is primarily grown inthe Riverina area of New South Wales and Ord Riverirrigation area in Western Australia. By worldstandards, Australian rice yields are high (>10t/ha)and therefore, the crop demands high rates ofnitrogen fertiliser application to meet its N needs.Since the soil is usually waterlogged, N gaseouslosses are expected to be mainly as N2 gas (Figure 3).Often, the limited supply of soluble and readilyavailable C, low nitrate concentration, andcompeting crop demand for N limits the totalgaseous N losses from flooded rice systems(Rennenberg et al. 1992).

For example, application of ammonium sulfate at 80 kg N/ha to flooded rice resulted in only 0.1% asN2O loss (Freney et al. 1981). It is estimated that N2O emission from the flooded rice can be as low as0.02% from 80 kg N/ha of urea application (Mosieret al. 1989), provided soils are flooded for a numberof days before N fertiliser is applied. This loss couldbe an underestimate due to the N2O dissolved andretained in water and not measured (Heincke andKaupenjohann 1999). Thus, total N2O losses could be higher than measured from short-periodobservations. Also, when soil experiences wetting-drying cycles such as in dry-seeded rice, a commonpractice in the Riverina region, it could be a sourceof N2O if mineral N (ammonium and/or nitrate) isalso present in soil. For example, over an 18-dayperiod after flooding, from 0.8% to 1.4% of nitratenitrogen present initially in soil was lost as N2O(Denmead et al. 1979a).

Secondary emissions of N2O could occur from thedeposition of NH3 volatilised from flooded ricefields after the application of ammoniacal fertiliserssince ammonia has a short lifetime in theatmosphere. In flooded rice, NH3 volatilisation losses

can account for from 20% to >80% of the totalfertiliser N losses (Mosier et al. 1989).

Sugarcane cropping. Main areas of sugarcanecultivation are coastal Queensland and northernNew South Wales, and the Ord River irrigation areain Western Australia, thus encompassing tropical tosubtropical environments.

About 10% of the N fertiliser is used for sugarcaneproduction (Table 5). The rates of fertiliserapplication vary from 100 kg N/ha to 300 kg N/ha.It is estimated that sugarcane soils emit more than 10 kt of N2O-N per year (Weier 1998). Improved crop management practices such as sugarcane trashretention and no-till have improved the productivityof sugarcane soils. However, it may not havereduced the total N2O emissions from the sugarcanelands. For example, nitrate applied to a sugarcanesoil at the rate of 160 kg N/ha lost 0.13% and 15.4%of N as N2O from the cultivated and no-till soil,respectively, over a 4-day period after the fertiliserapplication and irrigation. Although N2 is the majorproduct of denitrification loss of fertiliser N fromfine-textured soils, N2O becomes a major gaseous N loss when soil nitrate concentrations are high(Weier et al. 1996) (Fig 4).

Split application of the N fertiliser may reduce therapid N2O losses. Split application of urea andammonium sulfate to sugarcane soil at 80% WFPSand 100% WFPS results in lower N2O emissionsinitially compared with full application of ureaalthough total N2O emissions over a given seasonare not significantly different (Weier 1999).

Application of sugarcane trash (10t/ha) to soilfertilised with KNO3 or urea at the rate of 160 kgN/ha, and followed by 50 mm of irrigation,increased N2O emissions, and CO2 respiration,especially from KNO3; the mean values were 13.3 kgN2O-N/ha.day for the trash-retained compared with 11.3 kg N2O-N/ha.day without trash retention(Weier 2000).

Nitrous oxide emissions from N added to sugarcanesoils of different texture differed. For example, more


rye NO3 G1 G2 barley H2Orye-urea corn H2O0

10

20

40

50

N2O

gN

ha–1

d–1

)N

2O g

N h

a–1 d

–1)

30

wwff-ct wwff-nt gras, CO medium medium-Ncoarse-Ncoarsegrass, NE fine0

0.5

1.0

1.5

Observed Simulated

Figure 11. DAYCENT simulated (red bar) and observed (blue bar) N 2O emissions from various farmingsystems, including conventional till (ct) and no-till (nt), soil textures (coarse, medium and fine), N application (10 kg N/ha), intensively cropped rye, crop rotations (G1, multiple cropping with FYMapplication and G2, multiple cropping with cattle slurry application) and irrigated barley and maize (Source: Del Grosso et al. 2001b).


gaseous N was lost from a fine-textured soil thanfrom a coarse-textured soil; almost 3.2-19.6% of the applied N was lost from a fine-textured soil ascompared to <1% from a coarse-textured soil, with45% to 78% appearing as N2O gas. The N loss wasclosely related to the soil nitrate concentration andthe soil water content (Weier et al. 1996).

Field burning of sugar cane. The burning of sugarcane crops immediately before harvest continues tocontribute to agricultural and national emissions ofN2O. This contribution is decreasing, however, withthe rapid introduction of green cane mechanicalharvesting in which sugar cane crops are only burnt once every three or four years at the end of the sowing/ratoon cycle (Commonwealth ofAustralia 2000). This change in harvesting practice isevident in N2O emission estimates. The NationalGreenhouse Gas Inventory 2000 reported thatalthough N2O emissions from field burning ofagricultural residues increased by 37.2% from 1990to 2000, a 26.8% decline in emissions from sugarcane burning occurred due to changes in harvestingpractice (Australian Greenhouse Office 2002). Low tomedium intensity fires associated with the fieldburning of sugar cane can also produce enhancedemissions of N2O due to soil disturbance by in situ

biomass burning (Meyer et al. 1997). In 1990 theseenhanced N2O emissions were estimated to bebetween 0.005 and 0.1 kt (Meyer et al. 1997).

Cotton cultivation. Although cotton is grown indrier areas than sugarcane, large areas of cotton cropare flood-irrigated, thus increasing the frequency ofanaerobic conditions. Nitrogen fertiliser applicationsare also higher in irrigated cotton than rain-fedcotton, often in excess of 100 kg N/ha. Also, cotton is grown in warmer conditions than sugarcane. It is, therefore, expected that N2O emissions will besubstantial from irrigated cotton areas (Granli andBøckman 1994) although no detailed studies areavailable for Australia.

Grain cropping. Cereal and oilseed crops are grownon about 22 million ha, and another 23 million hacarry improved pastures, which are brought under

cultivation every 3-4 years. In south-eastern andWestern Australia, improved pastures with asignificant legume component, historically providedlarge part of N supply to cereals, while in northernNew South Wales and Queensland, soil N was theprimary source of crop N. Reduced area underimproved pastures and depleting N supply from the Australian soils, have resulted in increasing useof N fertilisers for cereal/oilseed cropping sincegrain legumes only occupy 2 million ha compared to6 million ha reduction in improved pastures (Angus2001). The combined N2O emissions from croppingand ley farming soils are in the order of 24.5 kt N/yr(11.9 Mt CO2-e) in 1999, and probably increasingevery year. Available N resulting from N fertiliserapplication or from the mineralisation of soil N andlegume N essentially behaves similarly, providedsoil water and aeration, temperature, soluble andreadily available C, pH, salinity and soil texture arealso similar.

Loss of N as N2O from fertiliser as well as soilmineral N varies considerably. Application of urea to ten soils resulted in N loss as N2O, ranging fromnone to 9.9% of the fertiliser application. Nitrousoxide losses were significantly correlated with nitriteconcentration, soil pH and organic carbon content(Magalhaes et al. 1987; Magalhaes and Chalk 1987).About 5.8% N as N2O was emitted from ureaapplied at 600 mg N/kg soil to an acid loamy sand(Magalhaes and Chalk 1987).

Provided nitrates are present in soil, crop growthgenerally increases N2O emissions by increasing the oxygen demand due to the presence ofdecomposable organic matter and root exudates.Restricted pore space in many cropping soils furtherretards oxygen diffusion as the water content in thesoil increases, resulting in substantial N2O emissions(Stefanson 1973; Burford and Stefanson 1973). Oncethe soil is waterlogged, N2 is the main source ofdenitrification losses. Also, as nitrate concentrationin soil is depleted due to the crop uptake, N2Oemissions also decrease.


Crop residue retention (stubble retention) andminimum till are increasingly practised in theAustralian cereal belt. This practice changes the soilnitrate levels, soluble and readily available organicmatter, soil water content and aeration, andfrequently soil surface temperature, thus potentiallyaffecting the N2O emissions significantly differentfrom that of conventional cultivation. For example,addition of wheat straw at the rate of 10.5 t/ha to aVertisol doubled the rate of loss of denitrification ofapplied urea. The N2O emissions were about 0.5% inVertisol and 3.0% in Alfisol of applied N when strawwas added, and remained higher than conventionaltill treatment although total denitrification rateswere similar in both soils (Avalakki et al. 1995). In Western Australia, texture-contrast soils(Chromosols) experience temporary waterlogging in winter and have the potential to denitrify andemit N2O (Bronson and Fillery 1998).

Soil temperature effects on N2O emissions arenoticed when seasonal effects on N2O emissionsfrom cropping soils are studied. Decreasingtemperature from 30oC to 5oC slowed the rate ofN2O emissions from a Vertisol and an Alfisol; but the N2O/N2 ratio increased (Avalakki et al. 1995).However, in subtropical environments, thetemperature effects appear to be less marked. For example, almost 75% of N2O emissions occurredin equal amounts in spring and summer under blackgram (Vigna mungo) in subtropical Queensland.About 88% of the variation in N2O emissions arefound to be associated with monthly rainfall and nitrate concentration (Weier et al. 1991). The microbial population of N2O producers appearsto be controlled by the soil water content under ablack gram (Vigna mungo) crop (Weier et al.1993b).

Emissions of N2O from the nitrification and thedenitrification processes may occur at differenttimes. When 120 kg N/ha as urea was applied inirrigation water to sunflower growing on acalcareous Vertisol, about 2 kg N/ha was emitted as N2O during the first 23 days after fertiliserapplication; about half in the first 11 days and the

other half after the second irrigation, when most ofthe fertiliser was present as nitrate. Thus almostequal amount of N as N2O was lost fromammonium initially and then from nitrate after thesecond irrigation (Freney et al. 1985). Furthermore,there may be regional differences in N2O emissionpatterns since in Western and Southern Australiamajor rainfall events occur in winter while there issummer-dominant rainfall in northern Australia.

Field burning of wheat and coarse grain stubble.

The field burning of agricultural residues, notably forwheat crops, continues to be a small but significantcontributor to agricultural and national emissions ofN2O. In 1998 it was estimated that 25% of the stubblefrom wheat crop was burnt annually (NGGIC 1999).Burning of agricultural residues in Australia is,however, becoming less common with the increasingadoption of stubble retention as a form of landmanagement (Commonwealth of Australia 2000).Despite this reduction in field burning, CO2-eemissions of CH4 and N2O from the burning ofagricultural residues, estimated to be 0.4 Mt in 2000, represent a 37.2% increase since 1990(Australian Greenhouse Office 2002). A 36% increasein the area of land sown for crops since 1990 mayhave contributed to the increase in emissions overthe period 1990 to 2000 (Australian GreenhouseOffice 2002). The fire intensity classification is low forfield burning of wheat residues and coarse grains,indicating that no enhanced emissions of N2O due tosoil disturbance by in situ biomass burning is likely(Meyer et al. 1997).

Ley cropping. Pastures in rotation with crops havebeen successfully used for soil fertility restoration and animal grazing in temperate and Mediterraneanareas of southern and south-western Australia.They are also increasingly being used in north-easternAustralia as the native soil fertility declines undercontinuous cereal cropping (Weston et al. 2000).Legume-based ley pastures have made significantcontribution to soil fertility and the crops following these pastures, and gained N benefits from the mineralisation of legume N after termination of the pasture phase.


Under the pasture phase, N2O emissions fromgrazed pastures near Wagga Wagga, NSW wereestimated to vary from 0.35 ± 0.03 kg N/ha.year(Galbally et al. 1994; Wang et al. 1997) to 2.2 ±1.2 kg N/ha.year (Denmead et al. 2000). Since mostnon-dairy pastures in Australia are not N fertilised,the N2O emissions estimates are within the range ofthose from unfertilised soils (1-2 kg N/ha.year) in the northern hemisphere (Bouwman 1994).However, information is lacking on legume-basedpastures in subtropical and tropical Australia, withsummer-dominant rainfall.

The termination of ley pasture containing legumesfor the cropping phase mineralises a substantialamount of organic N into mineral N (Table 8), andalso produces soluble organic C from litter and rootdecomposition. In Table 8, a conservative estimate of N2O emissions from denitrification following thetermination of the pasture phase indicates aboutsimilar or higher losses to that during the pasturephase (Galbally et al. 1994). However, Smith et al.

(1988) measured N2O emission rate of 30 kg/ha.yearfrom a field sown to irrigated sunflower cropfollowing 8 years of lucerne pasture. Furthermore,waterlogging of these soils after organic N mineralisation has a very high potential for

denitrification (12-89%), including N2O emission,especially in summer dominant rainfall regions (Pu et al. 1999).

No account was taken of the N2O emissions duringnitrification in Table 8. Wang et al. (1997) estimatedthat 55-73% of the total soil N2O emission occursduring aerobic nitrification. Thus N2O emissionsduring nitrification of residue N from legume-basedpasture will double the estimated N2O emissions,that is, from 0.6 kg N/ha to 1.4 kg N/ha, after thetermination of the pasture phase.

Increasing use of lucerne is being made for N2

fixation and lowering the water table in the croppingregions, where salinity may become a problem.Lucerne is very effective in fixing a substantialamount of atmospheric N2, often exceeding 100 kgN/ha/year (Peoples and Baldock 2001, Table 8).However, after termination of a lucerne phase,nitrate builds up rather rapidly, especially in thesubtropical environment (Hossain et al. 1996). Whenthe soil experiences wetting and drying cyclesduring the summer months, the nitrate may be lostdue to denitrification, including N2O emission. A somewhat similar situation may occur in southernand Western Australia in late summer and earlyautumn. It has the implications for the termination

Table 8. Estimates of mineral N (mostly nitrate-N) produced during 3-8 months following the termination ofthe pasture phase and calculated nitrous oxide emissions due to denitrification.

Previous pasture Location Soil type Soil depth Mineral N Calculated emissionA

(m) (kg /ha) N2O CO2-e(kg N/ha) (kg/ha)

Legume + grassB Warra, QLD Vertisol 0-1.2 147 0.7 340

LucerneB Warra, QLD Vertisol 0-1.2 123 0.5 230

MedicB Warra, QLD Vertisol 0-1.2 96 0.3 135

PastureC Junee, NSW Kandosols 0-1.5 148 0.7 340

PastureD SA Chromosols 0-0.6 79 0.4 185

Sub clover-basedE Moora, WA Deep sand 0-1.4 106 0.5 250A Percent denitrification measured for winter grown legume, 12%; perennial legume, 16%; and legume + grass pasture, 20% (Pu et al. 1999), and 2.5% of the total denitrification loss is assumed to be N2O emission (Avalakki et al. 1995).B Hossain et al. (1996).C Angus et al. (1998). D Xu et al. (1996).E Anderson et al. (1998).

(from Dalal et al. 2003)


time for a legume phase, especially in subtropicaland tropical regions, and management of legumeresidues in other environments. Unfortunately, data are lacking to confirm these statements.

Similarly, the extent of N2O emissions during andfollowing a pulse crop in the Australian cereal belt is unknown.

4.1.2 Horticultural Soils

Nitrogen application rates on horticultural soils aregenerally high, often exceeding 200 kg N/ha/yearfor banana plantations (Reuter 2001). Although thedenitrification rates may be low since waterloggingis avoided, the N2O emissions are likely to be highdue to high fertiliser rates. Also, many horticulturalsoils, especially in eastern Australia, are acidic, andtherefore, N2O may be the dominant denitrificationproduct (Ryden and Lund 1980). On bananaplantations, loss rates for N2O are estimated to range from 1.3% to 2.9% of applied N (Bouwman1998). In vegetable crops, N2O emissions rangedfrom <2% to >10% of fertiliser N applied (Ryden andLund 1980), thus they are much higher than the grain cropping systems.

4.2 N2O EMISSIONS FROM GRAZING SYSTEMS

4.2.1 Intensive Grazing

Dairying. Historically, most of the N supply fordairy pastures was derived from pasture legumes. With increasing competition in the dairy industry, N fertiliser is being increasingly used to enhanceproductivity. Since optimum production is achievedbetween 450 and 600 kg N/ha/year (Eckard 1998),pasture legumes, which fix about 20-200 kgN/ha/year (Peoples and Baldock 2001), do notsupply enough N for optimum production, hence N fertiliser application is needed.

Over 60% of farms in south-eastern Australia nowapply up to 200 kg N/ha/year (Eckard 1998), while in New South Wales and Queensland about100-150 kg N/ha/year are applied to subtropicalpastures and up to 300 kg N/ha/year on temperate

pastures (Cowan et al. 1995). Besides, another 30-50 kg N/ha/year is supplied as feedsupplements.

Nitrous oxide emissions from dairy pasture soils inVictoria vary from 6 to 11 kg N/ha (2.8- 5.1 t/ha of CO2- e) from 0 and 200 kg N/ha N applications,respectively (Eckard et al. 2001). At two intensivelygrazed pastures in New Zealand, N2O emissionlosses varied from 0.5 kg N/ha/year on a lowfertility site to 3 kg N/ha/year on a high fertilitysite. These losses were associated with soil watercontent, nitrate and ammonium concentration andtemperature. It is suggested that grazing animalshave a significant impact on emission through hoof damage on wet soils (Carran et al. 1995),especially in a warmer environment. Peak losses of N may occur in early spring and autumn in theMediterranean environment, and lower N losses insummer due to low soil water contents. However, in the subtropical and tropical environments, largeN losses are also likely to occur in summer.

Higher N losses are expected from flood-irrigatedpastures but no Australian data are available on N2O emissions over an extended period. Prasertsaket al. (2001) estimated that 40% of applied urea at therate of 115 kg N/ha was lost from an ungrazed dairypasture in tropical Queensland; about half was lost as ammonia volatilisation and the other halfpresumed to be denitrified although the proportionof N2O emissions to total denitrification losses arenot known. Addition of water to a grass sward as small as 5 mm of irrigation increased nitrousoxide emission rates markedly. Nitrous oxide wasproduced near the soil surface, and accompanied by the net increase in soil nitrate (Denmead et al.

1979b). With the soil moist to less than field capacity(~60% WFPS), average daily emissions ranged from 6 to 25 g N/ha/day (Denmead et al. 1979b).The population of N2O producers appears to be controlled by the soil water content (Weier et al.1993). In the USA, almost 37% of fertiliser N(about 240 kg N/ha) was lost from irrigatedpastures (Barton et al. 1999). Studies on N2O


emissions from irrigated pastures are required toestimate N2O losses, both in the temperate andsubtropical regions.

Another source of N2O emissions from the dairyindustry is the application of dairy waste topastures, including manure and effluents. Bothcomponents are high in soluble C and hence have a potential to produce N2O when applied to soilalthough overall impact on total N2O emissions fromagriculture is small (Australian Greenhouse Office2001).

4.2.2 Extensive Grazing (Improved Pastures vs Rangelands)

Large areas of rangelands are used for extensivegrazing although in many areas exotic pastures have been introduced since tree clearing to enhancepasture productivity. The N2O emissions are likely to be low in most rangelands; the values reportedrange from 0 to 1.1 kg N/ha/year, with a medianvalue of 0.2 kg N/ha/year (Galbally et al. 1992;Leuning et al. 1999). Although the rates of N2Oemissions from rangeland soils may be low,considering the extent of the total rangeland area(>400 million ha), it is important to measure N2Oemissions in the field over an extended period, sincesmall amounts of rainfalls may trigger significantnitrification activity and hence N2O productionfollowing a prolonged dry period. For tropicalsavannas the rates could be much higher, but limited data are available.

Introduction of exotic species may result in increasedpasture productivity and thus increase soluble Ceven in deeper layers. For example, in a green panic(Panicum maximum) pasture, significant amounts ofN2O emissions were measured at 50-55 cm depth in the field (Weier et al. 1991; Weier et al. 1993b).

Soil temperatures in rangelands vary considerablynot only between seasons but also diurnally. TheN2O emissions show a diurnal cycle, varying withthe temperature of the surface soil. Peak nitrousoxide emission rates occur in the afternoon andminimum near sunrise. Seasonal variation shows

the largest emissions of N2O in spring (Denmead et al. 1979b). Almost 75% of N2O emissions occur in spring (55%) and summer (20%). These areassociated with CO2 concentrations due to microbialrespiration (Weier et al. 1991), and hence intenseoxygen demand, resulting in partial anaerobiosis.

Prescribed burning of savanna and temperate

grasslands. The burning of tropical savanna andtemperate grasslands continues to contributesignificantly to agricultural and national emissionsof N2O. In Australia, savanna and temperategrassland ecosystems are burnt eitheranthropogenically or as a result of wildfire. Theprescribed burning of tropical savannas occurs for avariety of reasons including pasture management,fuel reduction and traditional Aboriginal fires(Galbally and Meyer 2003). In 1999 it was estimatedthat 24% of the total annual emissions of nitrousoxide from the agricultural sector were the result ofdirect emissions from prescribed burning ofsavannas, carried out primarily in NorthernAustralia (Australian Greenhouse Office 2001).

Direct combustion remains as the major source ofN2O emissions from savanna and grassland fires.However, the relationship between soil nitrogencycling and fire intensity indicates that medium tohigh intensity fires, such as savanna and grasslandfires, may also cause significant and persistentincreases in N2O due to soil disturbance by in situbiomass burning (Meyer et al. 1997). Emissions ofN2O directly from savanna and grassland firesin1999 were estimated to be 11.8 kt, while theestimated enhanced emissions due to soildisturbance by in situ biomass burning were in the range of 0.6-12.1kt (Australian GreenhouseOffice 2001). Such estimates highlight the significantcontribution made by emissions due to soildisturbance by in situ biomass burning.

The nitrous oxide emissions from the urine patchescould be significant in both improved pastures andrangelands (Bronson et al. 1999). Usually, animalfaeces are voided in large areas, thus avoidinganaerobic N mineralisation from animal waste.


The IPCC (1996) default value for 1.25% of total Nvoided needs to be examined after strategic fieldmeasurements.

4.3 N2O EMISSIONS FROM FORESTRY SYSTEMS

Whilst a broad picture of N2O emission patterns and controls is emerging in forests in the northernhemisphere (e.g. Brumme et al. 1999), very few directmeasures have been made in Australia. There aretwo main sources of N2O emissions from forests –fire (both prescribed burning and wildfire) and soilmineral – N transformations, specifically nitrificationand de-nitrification (e.g. Robertson et al. 1987).

For tropical forests the median rate of N2O emissionsis reported to be 1.7 kg N/ha/year (Bouwman 1998).Although Kiese et al. (2002) also recorded similarrates (<1.8 kg N2O-N/ha/year) in the dry season in three tropical rainforest sites in northeastQueensland, in the wet season, N2O emission rateswere 4 to 10 times higher than in the dry season.Assuming on average 3 months of wet season, theannual rate of N2O emission is estimated to varyfrom 3.2 to 6.7 kg N/ha/year from the northeastQueensland rainforests.

Nitrous oxide emissions from mangrove forests andmangrove sediments could be substantial becausemangrove forests are characterised by high Nturnover rates and high C production, as well asreceiving nutrients from runoff from inlandagricultural areas (Corredor et al. 1999). However,there have been no measurements of emissions from Australian mangrove forests.

In Australian forests, the following managementpractices may have important consequences foremissions of N2O to the atmosphere:

• Fire management, which determines directlyemissions due to prescribed burning (low-intensity fuel reduction burns, and higherintensity slash burns) and indirectly the extentand intensity wildfire and thus emissions due to wildfire.

• Harvesting (often associated with slashburning) which can increase rates of soilnitrification.

• Afforestation of grazed pastures which affects the nature of the soil N cycle.

• N fertiliser (or effluent) application toplantation forests.

A brief discussion of each of these follows.

Most Australian native forests are N limited, andthere is typically a tight link between ammoniumproduction and uptake in the soil (Connell et al.1995; Attiwill and Adams, 1996). As a consequence,rates of nutrification are typically very low. Low andslowly growing nitrifying populations in such forest soils appears to be the main cause of slownitrification (e.g. Vitousek et al. 1982; Khanna et al.1991), and the addition of inoculum can be sufficientto induce nitrification without changing any othersoil characteristics (Bauhus et al. 1993).

Soil heating during high intensity fire results in animmediate increase in soil NH4-N concentration (e.g. Raison 1979; Walker et al. 1986;) and subsequentincreased mineralization of fire-modified soilorganic matter (Raison et al. 1990). Both of theseprocesses provide a greater pool of soil NH4-N afterfire, and hence opportunity for initiation or increasein nitrification (e.g. Tiedemann et al. 1978; Raison1979; Ellis et al. 1982; Weston and Attiwill 1996). In the field, nitrification was induced (it did notoccur in unburnt soil) under ashbeds followingintensive harvest and slash burning of coastalVictorian eucalypt forest growing on low fertilitysoils (Raison et al. 1991). However, significantnitrification rates did not occur until ~ 9-18 monthsafter fire, by which time recolonising vegetationexists to take up much of the nitrate, thus reducingthe risks of denitrification. On higher fertility soilsunder mountain ash (E. regnans) forest, nitrificationis greatly increased following stand-replacingwildfire as well as after clearfelling andslashburning (Adams and Attiwill 1986; Weston and Attiwill 1996). Under these situations


nitrification rates and nitrate accumulation are muchgreater, and more prolonged (up to 1 year) as is thepotential for N2O losses.

Low-intensity prescribed burning is widely applied as a management tool for fuel reduction inAustralian native forests. Too frequent application ofsuch fire can result in depletion of soil N stocks andlowered rates of soil N mineralization (see Raison et

al. 1993 for discussion of evidence and mechanisms).Application of low-intensity prescribed fire howeverprobably has little effect on N2O emissions from theforest soils, which typically have rather low rates ofmineralization and negligible or very low rates ofnitrification. Meyer et al. (1997) concluded that low-intensity prescribed burns applied to forests used foreither wood production or for conservation, may notchange the flux of N2O between the soil and theatmosphere. However, this conclusion is based on a very limited set of observations.

Fires do result in direct emission of N2O as aconsequence of combustion processes (Galbally et al.1992; Prather et al. 2001). The total direct combustionemissions of N2O from fires (prescribed burns andwildfire) in Australia in 1997 was estimated to be 291 kt CO2-e (NGGI, 1999).

The effects of intense wildfire on nitrification rates inforests which are not killed, but which re-sprout viaepicormic growth has been little studied. Such forestresponse is the most widespread in the Australianlandscape (stand replacing fires are confined to ash-type forests such as E. regnans). Khanna and Raison(1986) found that high intensity (crown defoliating)fire in E. pauciflora forest did not stimulatenitrification even under ashbeds. Generally theuptake of NH4

-1 by the recovering vegetation wouldbe expected to limit the potential for prolongednitrification and thus N2O loss.

Grazed pastures are often significant sources of N2Oemissions (e.g. Yamulki et al. 2001) resulting fromhigh N inputs to the soil from legumes, fertiliser and animal excreta, and consequent rapid rates of nitrification which create potential for N2Oformation and loss. Following afforestation, rates

of N input and soil N mineralization decline. Forexample, O’Connell et al. (2003) have found thatinputs of C – rich litter result in a rapid decline insoil N mineralization rates within a few years afterE. globulus plantations are established on improvedpastures in the SW of WA.

Afforestation will also reduce CH4 emissions bygrazing animals, and also creates a potential forforest soil to become an enhanced sink (byoxidization) for CH4. (e.g. MacDonald et al. 1997).

Thus, there is the potential for afforestation ofgrazed pastures, which is currently occurring atrates of 60-100,000 ha per annum in Australia, tohave a major beneficial effect on non-CO2 GHGemissions. It is thus important to quantify the effectsof such land-use change on total (carbon storageplus change in non-CO2 emissions) GHG balance,and to enhance our understanding of the processesaffecting such change.

N fertilisers are used to establish plantations, andsometimes are applied to stimulate growth at mid-rotation. Annual denitrification rates for plantationforest soils vary, depending on stand age, sitepreparation, fertilisation, and wastewaterapplication. Denitrification rates are likely to behigher after clear felling and N fertilisation thanunder natural forest but are probably lower than forgrazed rangelands. The rates of denitrification mayrange from 0.3 kg N/ha/year to 13 kg N/ha/yearunder N fertilisation (Barton et al. 1999). However,the exact measurements of N2O emissions orN2O/N2 ratio are rare under Australian forests and plantation soils.

In a study of denitrification losses following theapplication of treated sewage effluent to youngplantations, Smith and Bond (1999) concluded thatlosses were very small on a freely draining soil.However, measurements of N2O emissions were not made.

Pu et al. (2001) measured significant emission of N2O following harvest of hoop pine plantations insouth-east Queensland. Losses were greatest under


windrows of decaying slash, and the authorssuggested that significant rates of denitrificationmay last for 2 years after harvest. It is well knownthat final harvest increases soil N mineralization,including nitrification, in plantation forests (e.g. Smethurst and Nambiar 1990) and that sites are vulnerable to N losses during the inter-rotationperiod. However, little is known of N2O emissionrates during this period, and further studies areneeded to quantify this.

4.4 N2O EMISSIONS FROM OTHER SYSTEMS

Termite mounds emit significant amounts of nitrousoxide during spring and summer (Khalil et al. 1990;French et al. 1997). Exact contribution of termitemounds to N2O emissions is not known since it iscalculated from the estimates of CH4 production as a ratio of CH4/N2O of 20:1 on a mass basis(Galbally et al. 1992).

5. MITIGATING N2O EMISSIONS IN VARIOUS ECOSYSTEMS

5.1 MITIGATING N2O EMISSIONS FROMAGRICULTURAL SYSTEMS

Flooded rice cropping. In waterlogged or floodedsoils, where aeration is restricted, less N2O isemitted into the atmosphere because more N2O is converted into N2 through the denitrificationprocess. Since mineral N content governs the Nsupply both to crops and the denitrifiers, increasingthe efficiency of mineral N use to crops should result in lower amount of mineral N available fordenitrification. Addition of nitrapyrin to soil afteranhydrous ammonia application of 60-80 kg N/hasignificantly reduced fertiliser-induced loss ofnitrous oxide only in a calcareous soil, whichaccumulated nitrite in the fertiliser band (Magalhaeset al. 1984). Wax-coated calcium carbide reducessignificantly the rate of N2O emission whilenitrapyrin is much less effective in a flooded ricesystem (Keerthisinghe et al. 1993). Denitrificationand N2O losses of urea from flooded rice systemsare further reduced when urea is deep placed ascompared to surface broadcast application(Keerthisinghe et al. 1993).

The strategies that increase the efficiency of Nfertiliser use will reduce N2O emissions (Aulakh et al. 1992; Mosier et al. 1996). These strategiesinclude: fertiliser form (reduce anhydrous ammoniause), rate and method of application, matching Nsupply with demand, supplying fertiliser in theirrigation water, applying fertiliser to the plantrather than the soil, and the use of slow-releasefertilisers, and urease and nitrification inhibitors(Freney 1997a).

Although these approaches enhance nitrogen useefficiency, they do not necessarily reduce N2Oemissions significantly. However, newly developedurease and nitrification inhibitors and coated-ureahave the capacity to prevent loss of N, including the loss as N2O, as well as increase crop yields.


Arable cropping. The above principles apply to allagricultural systems. In arable systems, soil structure(soil texture), nitrate, soluble and readily available C,and water content appear to be major factors thataffect the N2O:N2 balance between N2O diffusioninto the atmosphere and its further reduction to N2 gas (Weier 1998).

Nitrate concentration in the soil can be kept at lowlevels by applying N fertiliser to crop when cropneeds it and in the amount the crop can readily utiliseit through regular soil analysis for mineral N and cropmonitoring for N, split applications, and applying indrip irrigation. Further reductions in N2O emissionsmay be achieved by the use of cover crops during thefallow period to remove residual nitrate from the soilprofile (Weier et al. 1998). However, these practiceswill increase costs of crop production.

Similar to that in flooded-rice soils, urease andnitrification inhibitors such as wax-coated calciumcarbide (Keerthisinghe et al. 1993), etridiazole,dicyandiamide and 3,4-dimethylpyrazole phosphate(Weiske et al. 2001) have been found to reduce nitrateconcentration in arable soils from the application ofammoniacal fertilisers, and thus reducing N2Oemissions. For example, Weiske et al. (2001) foundthat dicyandiamide and 3,4-dimethylpyrazolephosphate reduced N2O emissions from the fertilisedplots over a 3-year period by 29% and 45%,respectively. However, the cost-effectiveness of thelatter two nitrification inhibitors needs to be furtherinvestigated, both in terms of economics of use and N use efficiency and also N2O emissionreduction benefits.

The claimed benefits of 3,4-dimethylpyrazolephosphate in reducing CO2 fluxes and increasingCH4 oxidation (Weiske et al. 2001), if confirmed infurther field experiments, could provide furtherimpetus for the use of nitrification inhibitors.Similarly, the usefulness of urease inhibitors such as Agrotain (n-butyl-thiophosphoric triamide) also need to be tested (McGuffog 2001) since it mayhave an added benefit of reducing N2O emissions inthe nitrite formation process as well.

Australian broadacre agriculture, which produceswool, sheepmeat, beef, cereals and other broadacrecrops, also produces significant emissions ofgreenhouse gases (Phipps and Hall 1994). Themarginal cost of reducing greenhouse gases from Australian agriculture by 20% is estimated to be$20/t of CO2 equivalent, or $4/t for nitrous oxidemitigation alone (Phipps and Hall 1994).

Increasing nitrogen use efficiency should reducegaseous losses of N, including that of nitrous oxide.

Mitigating N2O emissions arising from field burningof sugar cane, wheat stubble, and coarse grainstubble involve the use of alternative managementpractices, such as the adoption of stubble retention,which reduces direct N2O emissions into theatmosphere by minimising the field burning ofagricultural residues (CSIRO, 2000). The practice ofcrop residue retention is increasing in both theAustralian cereal belt and in the sugar cane industry,with the adoption of techniques such as green caneharvesting and trash blanketing.

5.2 MITIGATING N2O EMISSIONS FROM GRAZING SYSTEMS

Dairying. Since N fertiliser use is likely to increaseon dairy pastures, the N fertiliser managementpractices must ensure that pastures use N efficiently.Therefore, generally similar strategies are requiredfor fertiliser management to that required forcropping, mentioned above, with a major significantdifference. Unlike crops, most established pastureshave active extensive root systems throughout thegrowing season. By monitoring pastures and soilmineral N, it is possible to arrive at the pasture Nrequirement in a given season in commensuratewith the pasture growth. Then N fertiliserapplication must be made just enough to meet the pasture N requirement. Thus, mineral N in soil under pasture can be kept low, which may resultin low N2 and N2O losses from irrigated pastures(Eckard et al. 2001). However, nitrogen fertiliserapplications to dryland pastures with episodic andunreliable rainfall provide a challenge for efficient N management.


Waterlogged pastures can be better managed if floodirrigation is avoided and sprinkler irrigation isintroduced for irrigation as well as N fertiliserapplication. This also avoids the hoof damage to soilstructure and thus maintains oxygen diffusion intosoil. However, the effect of sprinkler irrigation onN2O emissions from fertiliser application as well as soil mineral N is unknown. Barton et al. (1999)reported that improved drainage in forest soilsreduced N losses from 40 kg N/ha/yr to <1 kgN/ha/yr. However, this may increase NO3 losses in drainage waters.

Efficient management of legumes in pasture mayresult in lower N fertiliser needs. However, withincreasing rates of N fertiliser applications, legumeN contribution is likely to decrease. Although theaccompanying grass in the pasture theoreticallyshould better use legume N, once the legumeorganic N is mineralised, the fate of mineral N islikely to be similar to that from fertiliser.

Extensive grazing. Generally, N2O emissions fromrangelands are about 0.2 kg N/ha/year. A number of options have been suggested to reduce the N2Oemissions from these areas. Williams (1994)suggested that increasing the efficiency of animalproductivity per unit of N consumed might be themost economical way to reduce N2O emissions fromrangelands. These management options are likely toenhance the resource management of rangelands as well. On the other hand, Howden et al. (1996)suggested that reducing sheep stock number andspring lamb production appear to be two options for reducing nitrous oxide emissions from theAustralian grazing lands, although this approach is likely to reduce farm income by about 15% byreducing the stock number by 18% (Howden et al.

1996). However, these options could form an overallstrategy for sustainable grazing systems.

Minimising emissions from those prescribed burningpractices associated with pasture management willrequire practical management and monitoringprotocols specifically designed to provide

opportunities for local landholders to develop the expertise required to implement moreappropriate pasture management and burningpractices (Australian Greenhouse Office 2001).It should not be assumed, however, that stoppinganthropogenic fires would lead to a reduction ingreenhouse gas emissions, as these would bereplaced by natural wildfires. Fire will continue toplay a major role in many rangeland ecosystemssince specific flora and fauna are fire dependent andremoving fires will result in a loss of biodiversity.

5.3 MITIGATING N2O EMISSIONS FROM FORESTRY SYSTEMS

Nitrogen management for plantations andagroforestry systems follows similar principles tothat of good N fertiliser management practicesdiscussed above. That is, the rate of N fertiliserapplication and soil mineral N should meet the tree plantation N need and that mineral N in soil is kept low.

Land preparation for plantation and agroforestryshould involve minimum soil disturbance orrestricted to a limited area to reduce organic Nmineralisation. Understorey legumes could beutilised to provide N to trees and plantations,especially in the early years.

Prescribed fires in forestry management appears torelease negligible or low amounts of N2O (Meyer et

al. 1997) due to low flame intensity (Kuhlbusch et al.

1991), and probably it is an appropriate practice fornot only controlling wild fires but also reducing N2O emissions from forestry systems.


6. SUMMARY AND CONCLUSIONS

Within the NGGI, there is a close relationshipbetween the amount of nitrogen fertiliser used andthe estimated N2O emissions by NGGIC (1999) (Fig. 12). The IPCC (1996) default emissions factor is1.25 kg of N2O-N emitted for 100 kg of fertiliser N,while in Figure 12, it appears to be 1.6 kg of N2O-N per 100 kg of fertiliser N use, assuming N2O emissions from other sources has remainedconstant over the last 10 years.

Most N2O emissions measurements are of very shortduration and over a limited area, and therefore donot measure the total N2O emissions from eitherfertiliser or soils accurately. When N2O emissionshave been measured for over a year, about 2% ofnitrogen fertiliser applied appears as N2O intemperate environments (Cates et al. 1987; Mosier et al. 1996). No long-term N2O emissionmeasurements exist for the subtropical and tropicalregions. Bouwman (1998) believes that the N2Oemission rates in these regions are likely to be higher

Nitrogen fertiliser use (kt)400 500 600 700 900800 1,000

y = 0.016x + 31.82R2 = 0.95

30

35

40

45

50

Nitr

ous

oxid

e em

issi

ons

(kt N

)

Figure 12. Relationship between nitrous oxide emissions and nitrogen fertiliser used in Australianagriculture from 1990 to 1999 (from Dalal et al. 2003).

than the temperate regions. There is a need tomeasure these emissions for the Australiansubtropical and tropical ecosystems.

Nitrous oxide emissions from legume-basedpastures may be in the order of 1-2 kg N/ha, andsimilar amounts are estimated when these pasturesare terminated for cropping. However, there islimited information on N2O emissions during thefallowing period following the pasture phase.Similarly, a few measurements are available toestimate the N2O emissions from frequent fires insavannas. Since these areas are large, even modestN2O emissions per unit area would have a largeimpact on National Greenhouse Gas Inventory.Besides reducing the fire frequency of savannas, andley pasture termination early in the season, limitedmanagement options are available to reduce N2Oemissions from these systems.

Management practices to improve nitrogen useefficiency and minimise N2O emissions fromnitrogen fertilisers include the following (Freney1997b; Laegreid et al. 1999; McGuffog 2001):


1. Apply fertiliser N at optimum rates by takinginto account all N sources available to thecrop/pasture from soil (ammonium andnitrate N in the soil at the time of cropsowing, and in-crop N mineralisation), andother N sources such as manure or waste.

2. Apply fertiliser N at the rate and time to meetcrop/pasture needs (Fig. 13), and whenappropriate through split application.

3. Avoid fertiliser N application outside the crop/pasture growing season, and especially prior toa clean fallow period. Avoid fallow periods ifseason or availability of irrigation permits.

4. Provide fertiliser N application guide throughcrop/pasture monitoring and soil tests, andadjust fertiliser application rates and timingaccordingly.

5. Apply other nutrients if required so thatnutrients supply to crop/pasture is balancedand N utilisation is optimised.

6. Avoid surface application so that fertiliser Nlosses are minimised and plant utilisationmaximised. Incorporate fertiliser N with soil;apply band placement or point placementclose to the plant roots.

7. Monitor and adjust fertiliser applicationequipment to ensure the precision and amount of fertiliser applied, and control over appropriate spatial distribution (GlobalPositioning System/Geographical InformationSystem) according to the information fromyield monitors, crop/pasture monitors(including remote sensing), and soil tests.

8. Fertilizers should be in a form (such asgranulated) that can be applied evenly,conveniently and cost-effectively. In irrigatedagricultural systems, application insprinkler/drip irrigation may be an effective option.

9. Fertilizer may be formulated with ureaseand/or nitrification inhibitors or physicalcoatings to synchronise fertiliser N release tothat of crop/pasture growth needs so that atany given time minimum amount of mineralN (ammonium and nitrate) is present in soil.

10. Practice good crop/pasture management,disease control and good soil management to optimise crop/pasture growth and henceefficient fertiliser N utilisation. Avoid/orreduce cultivation early in the fallow periodand retain plant residues to minimisemineralisation and nitrate accumulationduring the fallow period.

11. Use cover crops to utilise the residual mineralN following N-fertilised main crops or mineralN accumulation following legume-leys.

For manure management, the most effective practiceis the early application and immediate incorporationof manure into soil to reduce the direct nitrous oxideemissions and secondary emissions from depositionof ammonia volatilised from manure and urine.

Secondary considerations to reduce nitrous oxideemissions include:

• Oxygen supply/soil water content (water-filled pore space <40% increases nitrificationbut reduces nitrous oxide loss, >90% increasesdenitrification as a nitrogen gas loss);examples include arable cropping/ pasture/forestry, and flooded rice. Improve oxygendiffusion in soil by eliminating the compactedlayer.

• Carbon substrate supply (readily availablecarbon) creates ‘hot spots’ of microbialgrowth, and hence nitrous oxide emissions;examples are addition or incorporation ofbiomass of high carbon: nitrogen ratio such as non-legumes rather than legume biomass.

• Soil organic matter management tomanipulate carbon substrate andoxygen/water supply.


• Soil pH and salinity (salinity and alkaline pHenhance the nitrous oxide emissions due tothe persistence of nitrites); soil amendmentssuch as application of gypsum or cropresidues of high carbon: nitrogen ratio reduces nitrous oxide emissions.

Perennial crop/pasture/tree systems mostly provideoptimum environment to reduce nitrous oxideemissions by using mineral nitrogen and watereffectively to produce biomass. Management optionsfor other agricultural systems should mimic theabove to reduce nitrous oxide emissions from theagricultural soils.

Prescribed burning of savanna primarily carried out in northern Australia continues to contribute to nitrous oxide and other oxides of nitrogen (NO,NO2, etc) emissions. Even light rainfall followingburning increases nitrous oxide emissions. However,it is not known whether elimination of prescribedburning would reduce the annual amounts ofnitrous oxide emissions although the amounts of NO

and NO2 emissions will be reduced but increase thefrequency of wild fires.

Land clearing disturbs the soil and thus enhancesnitrogen mineralisation. For the first few years afterclearing nitrous oxide emissions may be an order of magnitude greater than undisturbed lands.Restriction of land clearing, therefore, will reducenitrous oxide emissions although the exactreductions are not known.

6.1 POLICY CONSIDERATIONS ANDRESEARCH OPPORTUNITIES

Nitrogen fertiliser use is likely to increase forcrop/pasture production, since soil N supply isdeclining as improved pasture areas decrease. Also crop/livestock production will intensify due to marketing pressure, and greater control overproduct quality and supply.

Education is critical in the efficient use of fertilisersfor crop/pasture production to reduce fertiliserwaste as well as reduce nitrous oxide emissions.Fertilizer Industry Federation of Australia (FIFA)

Sowing Anthesis Maturity Harvest-4

-3

-2

2

3

-1

1

0

4

Cum

ulat

ive

plan

t N u

ptak

e

Figure 13. A schematic diagram of nitrogen uptake pattern for a cereal crop.


should play a pivotal role in partnership with therelevant industry bodies in preparing Codes ofPractice for Efficient Fertiliser Use (a current FIFAinitiative - Cracking the Nutrient Code: Guidelinesfor Developing Nutrient Management Codes ofPractice).

Although, both State and Federal legislations existfor fertiliser quality assurance, consideration shouldbe given to discourage fertiliser applications out ofseason, and in excess of crop demands. This will also require the elimination of price incentives bysuppliers for out of crop season applications.

Incentives may be offered to producers formachinery and equipment for precise applications of fertilisers, when (at or near sowing or in-crop)and where (prescribed area in a paddock) it isneeded. There is a limited scope to encourage theuse of slow-release fertilisers to mimic plant needsdue to higher costs of the amended fertilisers, whichare rarely recovered by increased yields. Recently, it has been claimed that the application of 3,4-dimethylpyrazole phosphate with urea, reduced nitrous oxide emissions by 45% over a 3-year period in the field in Germany. We need toexamine its effectiveness under Australianconditions.

There are a number of other areas of research onnitrous oxide emissions, both for improving National Greenhouse Gas Inventory (reducing theuncertainties in the emission factors, the activitydata, lack of coverage of measurements, spatialaggregation, and lack of information on specific on-farm practices), as well as mitigation options forreducing nitrous oxide emissions from agriculture.

Emission factor uncertainties remain since it isdifficult to obtain definitive nitrous oxide fluxvalues. Some of the reasons are: the techniques - high precision required for measuring atmosphericnitrous oxide concentration and the limitations ofchamber and micrometeorogical methods, largespatial variability, the sporadic nature of nitrousoxide emissions, and seasonal and climatevariability. Simulation modelling should

complement these measurements over seasons and locations.

In addition to fertilisers, research is needed toevaluate various mitigation options for croppingsystems - (i) No-till systems, (ii) Timing of plantresidue incorporation, (iii) Legume managementpractice, (iv) Animal manure management and fieldapplications, (v) Nitrogen source- legume versusfertiliser nitrogen, (vi) Crop combinations, (vii)Crop/pasture mix and duration, (viii) Salinity and sodicity effects, and (ix) Soil type, season and climate variability;

For irrigated pastures – (i) Optimum utilisation of pastures, thus ensuring plant biomass sink fornitrogen, (ii) Hay or silage production when plantbiomass is produced in excess, (iii) An optimum mix of grasses and legumes, (iii) Animal wastemanagement, (iv) Soil type, season and climatevariability;

For extensive grazing lands – (i) Optimum grazingmanagement, cell or rotational grazing and feedquality, (ii) Regulating livestock numbers, (iii) Firefrequency, (iv) Soil type, season and climatevariability; and

For forestry plantations – (i) Soil disturbance, (ii) Time of logging, (iii) Legume versus fertilisernitrogen, (iii) Planting- species and techniques, (iv) Salinity and sodicity.

In summary, a dedicated national research program is needed over a reasonable length of time combining chamber, mass balance andmicrometeorogical techniques using high precisionanalytical instruments, and covering a range ofstrategic activities in the agriculture sector,mentioned above.

We recognise that carbon dioxide emissions andsinks as well as methane emissions and sinksinteract strongly with nitrous oxide emissions fromsoil, a comprehensive research program is needed to account for these interactions to arrive at cost-effective and efficient greenhouse gas mitigationmanagement, policy and legislation options.


The Kyoto Protocol, Articles 3.3 and 3.4, provides anopportunity to reduce nitrous oxide emissions fromagricultural lands. Admittedly, designing policy toreduce N2O emissions from agriculture is not asimple one (Hinchy et al. 1998) since N forms anintegral component of any sustainable agriculturalsystems. If appropriate price signals were to bepassed to producers about abatement options, policymeasures have to be applied at the farm level.However, monitoring and enforcement costs per unitof emission abatement are likely to be high (Hinchyet al. 1998).

Policy and regulatory arrangements need to be putin place to support greenhouse mitigation optionsfor nitrous oxide. These may include:

(i) Mechanisms for measuring, monitoring and verifying nitrous oxide emissions and the compliance with the contractualarrangements;

(ii) Mechanism to integrate nitrous oxideemissions and abatement options with othergreenhouse gases abatement programs such as carbon sinks, and natural resourcemanagement;

(iii) Devise framework for allocating mandatorycarbon sinks to offset nitrous oxides as a trade off;

(iv) Encourage the national and internationalmarketing for trading in the offsetting ofnitrous oxide emissions;

(v) Encourage research and development on theimpact of abatement options, and tradingarrangements on the environment,profitability and sustainability of theagricultural industries; and economic andsocial welfare of the rural communities andAustralian community.

7. REFERENCES

Adams, M.A. and Attiwill, P.M. (1986). Nutrient

cycling and nitrogen mineralization in eucalypt forests

of southeastern Australia. II. Indices of nitrogen

mineralization. Plant and Soil 92: 341-362.

Aiken, R. M., Jawson, M.D., Grahammer, K. andPolymenopoulos, A.D. (1991). Positional, spatially

correlated, and random components of variability in

carbon dioxide efflux. Journal of EnvironmentalQuality 20: 301-308.

Ambus, P. and Robertson, G.P. (1998). Automated

near-continuous measurement of carbon dioxide and

nitrous oxide fluxes with a photo acoustic infra-red

spectrometer and flow-through soil cover boxes. SoilScience Society of America Journal 62: 394-400.

Anderson, G.C., Fillery, I.R.P., Dolling, P.J. andAsseng, S. (1998). Nitrogen and water flows under

pasture-wheat and lupin-wheat rotations in deep sands in

Western Australia. 1. Nitrogen fixation in legumes, net N

mineralisation, and utilisation of soil-derived nitrogen.

Australian Journal of Agricultural Research 49: 345-361.

Angus, J.F. (2001). Nitrogen supply and demand in

Australian agriculture. Australian Journal ofExperimental Agriculture 41: 277-288.

Angus, J.F., van Herwaarden, A.F., Fischer, R.A.,Howe, G.N. and Heenan, D.P. (1998). The source of

mineral N for cereals in south-eastern Australia.Australian journal of Agricultural research 49: 511-522.

Attiwill, P.M. and Adams, M.A. (1996). Nutrition ofeucalypts. CSIRO Publishing, Melbourne, pp 440.

Aulakh, M.S., Doran, J.W. and Mosier, A.R. (1992).Soil denitrification: significance, measurement and effects

on management. Advances in Soil Science 18: 2-57.

Aulakh, M.S., Doran, J.W., Walters, D.J., Mosier, A.R.and Francis, D.D. (1991). Crop residue type and

placement effects on denitrification and mineralisation.

Soil Science Society of America Journal 55: 1020-1025.


Australian Greenhouse Office (2001). National

Greenhouse Gas Inventory 1999 with Methodology

Supplements. Australian Greenhouse Office,Commonwealth of Australia, Canberra.

Australian Greenhouse Office (2002). National

Greenhouse Gas Inventory 2000 with Methodology

Supplements. Australian Greenhouse Office,Commonwealth of Australia, Canberra.

Avalakki, U.K., Strong, W.M. and Saffigna, P.G.(1995). Measurements of gaseous emissions from

denitrification of applied nitrogen-15. II. Effects of

temperature and added straw. Australian Journal of Soil Research 33: 89-99.

Barton, L., McLay, C.D.A., Schipper, L.A. and Smith,C.T. (1999). Annual denitrification rates in agricultural

and forest soils: A review. Australian Journal ofAgricultural Research 37: 1073-1093.

Bauhus, J., Khanna, P.K. and Raison, R.J. (1993). The effect of fire on carbon and nitrogen mineralization

and nitrification in an Australian forest soil. AustralianJournal of Soil Research 31: 621-39.

Bellingham, P. (1989). Nitrogen production and use in

Australia. Pp. 1-12. Proceedings of InternationalFertilizer Association Production and InternationalTrade Meeting, Paris.

Blackmer, A.M. and Bremner, J.M. (1978). Inhibitory

effect of nitrate on reduction of nitrous oxide to molecular

nitrogen by soil microorganisms. Soil Biology andBiochemistry 10: 187-191.

Bouwman, A.F. (1994). Direct emission of nitrous oxide

from agricultural soils. RIVM Report No. 773004004.RIVM, Bilthoven, The Netherlands.

Bouwman, A.F. (1998). Nitrogen oxides and tropical

agriculture. Nature 392: 866-867.

Bremner, J. M. and Blackmer, A. M. (1981). Terrestrial

nitrification as a source of atmospheric nitrous oxide. In:Denitrification, nitrification and atmospheric N2O.(Ed. C.C. Delwiche) pp.151-170. John Wiley & SonsLtd., Chichester, UK.

Bremner, J.M. and Shaw, K. (1958). Denitrification in

soil. II. Factors affecting denitrification. Journal ofAgricultural Science 51: 40-52.

Bronson, K.F. and Fillery, I.R.P. (1998). Fate of

nitrogen-15 labelled urea applied to wheat on a

waterlogged texture-contrast soil. Nutrient Cycling in Agroecosystems 51: 175-183.

Bronson, K.F.; Sparling, G.P. and Fillery, I.R.P. (1999).Short-term N dynamics following application of 15N-labelled urine to a sandy soil in summer.

Soil Biology and Biochemistry 31:1049-1057.

Brumme, R. and Beese, F. (1992). Effects of liming and

nitrogen fertilisation on emissions of CO2 and N2O from

a temperate forest. Journal of Geophysical Research 97:851-858.

Brumme, R., Borken, W. and Finke, S. (1999).Hierarchical control on nitrous oxide emission in forest

ecosystems. Global Biogeochemical Cycles 13: 1137-1148.

Bryan, B.A. (1981). Physiology and biochemistry of

denitrification. In: Denitrification, nitrification andatmospheric N2O. (Ed. C.C. Delwiche) pp. 67-84.John Wiley & Sons, Ltd., New York, USA.

Burford, J.R. and Bremner, J.M. (1975). Relationships

between the denitrification capacities of soils and total,

water-soluble and readily decomposable soil organic

matter. Soil Biology and Biochemistry 7: 389-394.

Burford, J.R., and Stefanson, R.C. (1973).Measurement of gaseous losses of nitrogen from soils.

Soil Biology and Biochemistry 5:133-141.

Carran, R.A., Theobald, P.W. and Evans, J.P. (1995).Emission of nitrous oxide from some grazed pasture soils

in New Zealand. Australian Journal of Soil Research33: 341-352.

Castaldi, S. (2000). Responses of nitrous oxide,

dinitrogen and carbon dioxide production and oxygen

consumption to temperature in forest and agricultural

light-textured soils determined by model experiment.Biology and Fertility of Soils 32: 67-72.


Cates, R.L., Jr. and Keeney, D.R. (1987). Nitrous oxide

production throughout the year from fertilised and

manured maize fields. Journal of EnvironmentalQuality 16: 443-447.

Chalk, P.M. and Smith, C.J. (1983).Chemodenitrification. In: Gaseous loss of nitrogenfrom plant-soil systems. (Eds. J. R. Freney, and J. R.Simpson) pp. 65-89. Martinus Nijhoff/Dr W JunkPublishers, The Hague.

Cho, C.M. and Sakdinan, L. (1978). Mass spectrometric

investigation on denitrification. Canadian Journal ofSoil Science 58: 443-457.

Christensen, S., Ambus, P., Arah, J.R.M., Clayton, H., Galle, B., Griffith, D.W.T., Hargreaves, K.G.,Klemedtsson, L., Lind, A.M., Maag, M., Scott, A.,Skiba, U., Smith, K.A., Welling, M. and Wienhold,F.G. (1996). Nitrous oxide emission from an agricultural

field: comparison between measurements by flux chamber

and micrometeorological techniques. AtmosphericEnvironment 30: 4183-4190.

Chudleigh, P.D. and Simpson, S.L. (2001). The contribution of fertilisers to agricultural production

in Australia. Pp. 20-40. ‘Fertilizers in Focus’.Conference, Fertilizer Industry Federation ofAustralia Inc. 28-29 May 2001.

Cofer, W.R., Levine, J.S., Winstead, E.L. and Stocks,B.J (1991). New Estimates of nitrous oxide emissions from

biomass burning. Nature 349:689-691.

Commonwealth of Australia (2000). Greenhouse sinks

and the Kyoto protocol. An issues paper. Pp. 1-108.Australian Greenhouse Office, Canberra, Australia.

Connell, M.J., Raison, R.J. and Khanna, P.K. (1995).Nitrogen mineralization in relation to site history and soil

properties in a range of Australian forest soils. Biologyand Fertility of Soils 20: 213-220.

Corredor, J.E., Morell, J.M. and Bauza, J. (1999).Atmospheric nitrous oxide fluxes from mangrove

sediments. Marine Pollution Bulletin 38: 473-478.

Cowan, R.T., Lowe, K.F., Ehrlich, W., Upton, P.C. and Bowdler, T.M. (1995). Nitrogen-fertilised grass

in a subtropical dairy system. 1. Effect of level of

nitrogen fertiliser on pasture yield and soil chemical

characteristics. Australian Journal of ExperimentalAgriculture 35: 125-135.

Crutzen, P.J. (1981). Atmospheric chemical processes

of the oxides of nitrogen, including nitrous oxide.

In: Denitrification, nitrification and atmosphericN2O. (Ed. C.C. Delwiche) pp. 17-44. John Wiley &Sons, Ltd., New York, USA.

CSIRO Atmospheric Research (2002). Biomass

burning and trace gas emissions, Available online at www.dar.csiro.au/sourcesink/biomass.

Dalal, R.C., Wang, W., Robertson, G.P. and Parton,W.J. (2003). Nitrous oxide emission from Australian

agricultural lands and mitigation options: A review.Australian Journal of Soil Research 41: 165-195.

Davidson, E.A. (1992). Sources of nitric oxide and

nitrous oxide following wetting of dry soil. Soil ScienceSociety of America Journal 56: 95-102.

Davidson, E.A. and Schimel, J.P. (1995). Microbial

processes of production and consumption of nitric oxide,

nitrous oxide and methane. In: Biogenic trace gases:Measuring Emissions from Soil and Water. (Eds. P.A.Matson, and R.C. Harriss) pp. 327-357. Blackwell,Malden, Mass.

Del Grosso, S.J., Ojima, D.S., Parton, W.J., Mosier,A.R., Peterson, G.A., and Schimel, D.S. (2001a).Simulated effects of dryland cropping intensification on

soil organic matter and greenhouse gas exchanges using

DAYCENT ecosystem model. Environmental Pollution116: S75-S83.

Del Grosso, S.J., Parton, W.J., Mosier, A.R., Hartman,M.D., Keough, C.A., Peterson, G.A., Ojima, D.S. andSchimel, D.S. (2001b). Simulated effects of land use, soil

texture, and precipitation on N gas emissions using

DAYCENT. In: Nitrogen in the Environment:Sources, Problems, and Management. (Eds. R.F.Follett and J.L. Hatfield) pp. 413-430. ElsevierScience, B.V.


Denmead, O.T. (1979). Chamber systems for measuring

nitrous oxide emission from soils in the field. SoilScience Society of America Journal 43:89-95.

Denmead, O.T. (1983). Micrometeorological methods for

measuring gaseous losses of nitrogen in the field. In:Gaseous Loss of Nitrogen from Plant-Soil Systems.(Eds. J.R. Freney and J. R. Simpson) pp. 133-157.Martinus Nijhoff Publishers, The Hague,Netherlands.

Denmead, O.T., Freney, J.R. and Simpson, J.R.(1979a). Nitrous oxide emission during denitrification in

a flooded field. Soil Science Society of America Journal43:716-718.

Denmead, O.T., Freney, J.R. and Simpson, J.R.(1979b). Studies of nitrous oxide emission from a grass

sward. Soil Science Society of America Journal 43: 726-728.

Denmead, O.T., Leuning, R., Jamie, I. and Griffith,D.W.T. (2000) Nitrous oxide emissions from grazed

pastures: measurements at different scales.

Chemosphere - Global Change Science 2: 301-312.

Dorland, S. and Beauchamp, E.G. (1991).Denitrification and ammonification at low soil

temperatures. Canadian Journal of Soil Science 71:293-303.

Drury, C.F., McKeeney, D.J. and Findlay, W.I. (1991).Relationships between denitrification, microbial biomass

and indigenous soil properties. Soil Biology andBiochemistry 23: 751-755.

Eckard, R.J. (1998). A critical review of research on the

nitrogen nutrition of dairy pastures in Victoria. Pp1-31.ILFR, The University of Melbourne and AgricultureVictoria, Ellibank, DNRE, Melbourne.

Eckard, R.J., Chapman, D.F., White, R.E., Smith, A.,Chen, D. and Durling, P.A. (2001). Nitrogen balances

in high rainfall, temperate dairy pastures of southeastern

Australia. Pp. 171-172. Proceedings of the XIXInternational Grasslands Congress, Sao Pedro,Brazil.

Ellis, R.C., Webb, D.P. and Davies S.K. (1982). The

effects of regeneration burning upon the nutrient status of

soil in two forest types in southern Tasmania. Plant andSoil 65: 171-186.

Firestone, M.K. and Davidson, E.A. (1989). Microbial

basis of NO and N2O production and consumption in

soils. In: Exchange of Trace Gases between TerrestrialEcosystems and the Atmosphere. (Eds. M.O.Andreae, and D.S. Schimel) pp. 7-21. John Wiley and Sons, New York.

Firestone, M.K., Firestone, R.B. and Tiedje, J.M.(1980). Nitrous oxide from soil denitrification: factors

controlling its biological production. Science 208: 749-751.

Focht, D.D. and Verstraete, W. (1977). Biochemical

ecology of nitrification and denitrification. In: Advancesin microbial ecology. (Ed. M. Alexander) pp. 135-214.Plenum Press, New York, USA.

Folorunso, O.A. and Rolston, D.E. (1984). Spatial

variability of field-measured denitrification gas fluxes.

Soil Science Society of America Journal 48: 1214-1219.

Fowler, D. and Duyzer, J. H. (1989).Micrometeorological techniques for the measurement of

trace gas exchange. In: Exchange of Trace Gasesbetween Terrestrial Ecosystems and the Atmosphere.(Eds. M.O. Andreae, and D.S. Schimel) pp.189-208.John Wiley and Sons, New York.

French, J.R.J., Rasmussen, R.A., Ewart, D.M. andKhalil, M.A.K. (1997). The gaseous environment of

mound colonies of the subterranean termite Coptotermes

lacteus (Isoptera: Rhinotermitidae) before and after

feeding on mirex-treated decayed wood bait blocks.Bulletin of Entomological Research 87: 145-149.

Freney, J.R. (1997a). Emission of nitrous oxide from

soils used for agriculture. Nutrient Cycling inAgroecosystems 49:1-6.

Freney, J.R. (1997b). Strategies to reduce gaseous

emissions of nitrogen from irrigated agriculture.

Nutrient Cycling in Agroecosystems 48:155-160.


Freney, J.R., Denmead. O.T. and Simpson, J.R. (1978).Soil as a source or sink for atmospheric nitrous oxide.

Nature 273: 530-532.

Freney, J.R., Denmead. O.T. and Simpson, J.R. (1979).Nitrous oxide emission from soils at low moisture

contents. Soil Biology and Biochemistry 11:167-173.

Freney, J.R., Denmead, O.T., Watanabe. I. andCraswell, E.T. (1981). Ammonia and nitrous oxide losses

following applications of ammonium sulfate to flooded

rice. Australian Journal of Agricultural Research32:37-45.

Freney, J. R., Simpson, J. R. and Denmead, O. T.(1983). Volatilization of ammonia. In: Gaseous Loss ofNitrogen from Plant-Soil Systems. (Eds. J. R. Freneyand J. R. Simpson) pp. 1-32. Martinus Nijhoff/Dr. W.Junk Publishers, Boston.

Freney, J.R., Simpson, J.R., Denmead, O.T.,Muirhead, WA. and Leuning, R. (1985).Transformations and transfers of nitrogen after irrigating

a cracking clay soil with a urea solution. AustralianJournal of Agricultural Research 36:684-694.

Frolking, S.E., Mosier, A.R., Ojima, D.S., Li, C.,Parton, W.J., Potter, C.S., Priesack, E., Stenger, R.,Haberbosch, C., Dorsch, P., Flessa, H. and Smith,K.A. (1998). Comparison of N2O emissions from soils at

three temperate agricultural sites: simulations of year

round measurements by four models. Nutrient Cyclingin Agroecosystems 52: 77-105.

Galle, B., Weslien, P., Samuelsson, J., Klemedtsson,Å. K. and Klemedtsson, L. (2002). An automatic field

chamber system based on FTIR/GC analysis, applied in

measurements of N2O and CO2 emissions from an organic

soil. European Journal of Soil Science 53: 000(in press).

Galbally, I.E., Fraser, P.J., Meyer, C.P. and Griffith,D.W.T. (1992). Biosphere-atmosphere exchange of trace

gases over Australia. In: Australia’s renewableresources: sustainability and global change. (Eds.R.M.Gifford and M.M. Barson) pp. 117-149. Bureauof Rural Resources: AGPS Press; Canberra; Australia.

Galbally, I.E., and Meyer, C.P. (2003). Australian

National Greenhouse Gas Inventory: Development and

Current Status, Bureau of Rural Resources. CSIRODivision of Atmospheric Research, Aspendale,Victoria.

Galbally, I.E., Meyer, C.P., Wang, Y.P., Weeks, I.A.,Smith, C., Howden, S.M., Elsworth, C.M., Petraitis,B., Johnson, E., McLachlan, G. and Huang, G. (1994).The role of legume pasture in Greenhouse gas emissions

from Australia. 32pp. RIRDC Project CSD 47A, Final Report, Canberra, Australia.

Goodroad, L.L. and Keeney, D.R. (1984). Nitrous

oxide production in aerobic soils under varying pH,

temperature and water content. Soil Biology andBiochemistry 16: 39-43.

Goodroad, L.L., Keeney, D.R. and Peterson, L.A.(1984). Nitrous oxide emissions from agricultural soils in

Wisconsin. Journal of Environmental Quality 13: 557-561.

Granli, T. and Bøckman, O.C. (1994). Nitrous oxide

from agriculture. Norwegian Journal of AgriculturalSciences Supplement 12: 7-128.

Grant, R.F. and Pattey, E. (1999). Mathematical

modelling of nitrous oxide emissions from an agricultural

field during spring thaw. Global BiogeochemicalCycles 13: 679-694.

Griffith, D.W.T. and Galle, B. (2000). Flux

measurements of NH3, N2O and CO2 using dual beam

FTIR spectroscopy and the flux-gradient technique.

Atmospheric Environment 34: 1087-1098.

Groffman, P.M. (1991). Ecology of nitrification and

denitrification in soil evaluated at scales relevant to

atmospheric chemistry. In: Methane, Nitrogen Oxidesand Halomethane. (Eds. J.E. Rogers andW.B.Whitman) pp. 201-217. American Society of Microbiology, Washington, D.C.

Hall, S.J. and Matson, P.A. (1999). Nitrogen oxide

emissions after nitrogen additions in tropical forests.Nature 400: 152-155.


Ham, J. M. and Knapp, A.K. (1998). Fluxes of CO2,

water vapour, and energy from a prairie ecosystem during

the seasonal transition from carbon sink to carbon source.

Agricultural and forest Meteorology 89: 1-14.

Hansen, S., Mæhlum, J.E. and Bakken, L.R. (1993).N2O and CH4 fluxes in soil influenced by fertilisation

and tractor traffic. Soil Biology and Biochemistry 25:621-630.

Haynes, R.J. (1986). Nitrification. In: Mineral nitrogen in the plant-soil system. (Ed. R.J. Haynes)pp.127-165. Academic Press, New York.

Heincke, M. and Kaupenjohann, M. (1999). Effects of

soil solution on the dynamics of N2O emissions: A review.Nutrient Cycling in Agroecosystems 55: 133-157.

Hinchy, M., Fisher, B.S. and Graham, B. (1998).Emissions trading in Australia: developing a framework.

62 pp. ABARE Research Report. No. 98-1, Canberra.

Holland, E.A., Robertson, G.P., Greenberg, J.,Groffman, P., Boone, R. and Gosz. J. (1999). Soil CO2,

N2O, and CH4 Exchange. In: Standard Soil Methodsfor Long-Term Ecological Research. (Eds. G.P.Robertson, C. S. Bledsoe, D.C. Coleman, and P. Sollins) pp.185-201. Oxford University Press, New York.

Hossain, S.A., Dalal, R.C., Waring, S.A., Strong,W.M. and Weston, E.J. (1996). Comparison of legume-

based cropping systems at Warra, Queensland. I. Soil

nitrogen and organic carbon accretion and potentially

mineralisable nitrogen. Australian Journal of SoilResearch 34: 273-87.

Howden, S.M., White, D.H. and Bowman, P.J. (1996).Managing sheep grazing systems in southern Australia

to minimise greenhouse gas emissions: Adaptation of an

existing simulation model. Ecological Modelling86:201-206.

Hutchinson, G.L. and Brams, E.A. (1992). Nitric oxide

versus nitrous oxide emissions from an ammonium

ion-amended Bermuda grass pasture. Journal ofGeophysical Research 97: 9889-9896.

Hutchinson, G. L., and Livingston, G. P. (1993). Use of chamber systems to measure trace gas fluxes. In:Agricultural Ecosystem Effects on Trace Gases andGlobal Climate Change. (Eds. L.A. Harper, A.R.Mosier, J.M. Duxbury and D.E. Rolston) pp. 206.American Society of Agronomy, Madison,Wisconsin.

Inubushi, K., Barahona, M.A. and Yamakawa, K.(1999). Effects of salts and moisture content on N2O

emission and nitrogen dynamics in yellow soil and

Andosol in model experiments. Biology and Fertility of Soils 29: 401-407.

IPCC (1996). Ecophysiological, ecological, and soil

processes in terrestrial ecosystems: A primer on general

concepts and relationships. In: Climate change, 1995:impacts, adaptations, and mitigation of climatechange: scientific-technical analyses: contribution ofworking group II to the second assessment report ofthe Intergovernmental Panel on Climate Change.(Eds. R.T. Watson, M.C. Zinyowera and R.H. Moss)pp. 57-74.Cambridge University Press, Cambridge,UK.

IPCC (2001). Technical summary. In: Climate change2001: The scientific basis. Contribution of WorkingGroup I of the Intergovernmental Panel on ClimateChange. (Eds. J. T. Houghton, Y. Ding, D. J. Griggs,M. Noguer, P. J. van der Linden, X. Dai, K. Maskell,C. A. Johnson). Cambridge University Press,Cambridge.

Iqbal, M. (1992). Potential rates of denitrification in

2 field soils in southern England. Journal ofAgricultural Science 118: 223-227.

Kammann, C., Groundage, L. and Jager, H.J. (2001).A new sampling technique to monitor concentrations of

CH4, N2O and CO2 in air at well-defined depths in soils

with varied water potential. European Journal of SoilScience 52: 297-303.

Keeney, D.R., Fillery, I.R. and Marx, G.P. (1979). Effect of temperature on the gaseous nitrogen products of

denitrification in a silt loam soil. Soil Science Society ofAmerica Journal 43: 1124-1128.


Keerthisinghe, D.G., Lin, X.J. and Luo, Q.X. (1993).Effect of encapsulated calcium carbide and urea

application methods on denitrification and N loss from

flooded rice. Fertilizer Research 45: 31-36.

Khalil, M.A.K., Rasmussen, R.A., French, J.R. andHolt, J.A. (1990). The influence of termites on

atmospheric trace gases: CH4, CO2, CHCl3, N2O, CO,

H2 and light hydrocarbons. Journal of GeophysicalResearch 95: 3619-3634.

Khanna, P.K. and Raison, R.J. (1986). Effects of fire

intensity on solution chemistry of surface soil under a

Eucalyptus pauciflora forest. Australian Journal of SoilResearch 24: 423-434.

Khanna, P.K., Raison, R.J. and Bauhus, J. (1991).Constraints to nitrification in soils under Eucalyptus

native forests. Pp. 202-203. Proceedings. ThirdAustralian Forest Soils and Nutrition Conference,Melbourne.

Kiese, R. and Butterbach, B.K. (2002). N2O and CO2

emissions from three different tropical forest sites in the

wet tropics of Queensland, Australia. Soil Biology andBiochemistry 34: 975-987.

Kolb, C.E., Wormhoudt, J.C. and Zahniser, M.S.(1995). Recent advances in spectroscopic instrumentation

for measuring stable gases in the natural environment.

In: Biogenic Trace Gases: Measuring Emissions fromSoil and Water. (Eds. P. A. Matson and R. C. Harriss)pp. 259-290. Blackwell Science, Ltd., Oxford.

Kuhlbusch, T.A., Lobert, J.M., Crutzen, P.J., andWarneck, P. ( 1991). Molecular nitrogen emissions from

denitrification during biomass burning. Nature 351: 135-137.

Laegreid, M., Bockman, O.C. and Kaarstad, O.(1999). Agriculture, Fertilizers, and the Environment.

Pp. 1-294. CABI Publishing: Wellingford, U.K.

Lenschow, D. H. (1995). Micrometeorological techniques

for measuring biosphere-atmosphere trace gas exchange.

In: Biogenic Trace Gases: Measuring Emissions fromSoil and Water. (Eds. P. A. Matson and R. C. Harriss)pp.126-163. Blackwell Science, Ltd., Oxford.

Letey, J., Valoras, N., Hadas, A. and Focht, D.D.(1980). Effect of air-filled porosity, nitrate concentration,

and time on the ratio of N2O/N2 evolution during

denitrification. Journal of Environmental Quality 9:227-231.

Leuning, R., Denmead, O.T., Griffith, D.W.T., Harper,L.A., Freney, J.R., Jamie, J.M. and Turati, F. (1999).Verifying current estimates of non-CO2 greenhouse gas

emissions from animals, landfills and pastures with direct

measurements. Comptes Rendus de l’Academied’Agriculture de France 85: 102-135.

Leuning, R., Denmead, O.T., Griffith, D.W.T., Jamie,J.M., Isaacs, I., Hacker, J., Meyer, C.P., Galbally, I.E.,Cleugh, H.A., Raupach, M.R. and Essler, M.B. (1997).Assessing biogenic sources and sinks of greenhouse gases

at three interlinking scales. Consultancy Report 97-56,Australian Department of the Environment, Sportsand Territories, Canberra.

Li, C.S., Frolking, S. and Frolking, T.A. (1992a). A model of nitrous oxide evolution driven by rainfall

events: I. Model structure and sensitivity. Journal ofGeophysical Research 97, 9759-9776.

Li, C.S., Frolking, S. and Frolking, T.A. (1992b). A model of nitrous oxide evolution driven by rainfall

events: II. Model applications. Journal of GeophysicalResearch 97, 9777-9783.

Linn, D.M. and Doran, J.W. (1984). Effect of water-

filled pore space on carbon dioxide and nitrous oxide

production in tilled and nontilled soils. Soil ScienceSociety of America Journal 48: 1267-1272.

Lobert, J.M., Scharffe, D.H., Hao, W.M., and Crutzen,P.J. (1990). Importance of biomass burning in the

atmospheric budgets of nitrogen-containing gases.Nature 346:552-554.

Low, A.P., Stark, J.M. and Dudley, L.M. (1997). Effects

of soil osmotic potential on nitrification, ammonification,

N-assimilation, and nitrous oxide production. SoilScience 162: 16-27.


MacDonald, J.A., Skiba, U., Sheppard, L.J., Ball, B.,Roberts, J.D., Smith, K.A. and Fowler, D. (1997). The effect of nitrogen deposition and seasonal variability

on methane oxidation and nitrous oxide emission rates in

an upland spruce plantation and Moorland.

Atmospheric Environment 31: 3693-3706.

Magalhaes, A.M.T. and Chalk, P.M. (1987). Nitrogen

transformations during hydrolysis and nitrification of

urea. 2. Effect of fertiliser concentration and nitrification

inhibitors. Fertilizer Research 11: 173-184.

Magalhaes, A.M.T. and Chalk, P.M. (1989). Interaction

of methyl nitrite with the inorganic fractions of soils.

Journal of Soil Science 40: 349-358.

Magalhaes, A.M.T., Chalk, P.M. and Strong, W.M.(1984). Effect of nitrapyrin on nitrous oxide emission

from fallow soils fertilised with anhydrous ammonia.

Fertilizer Research 5: 411-421.

Magalhaes, A.M.T., Nelson, D.W. and Chalk, P.M.(1987). Nitrogen transformations during hydrolysis and

nitrification of urea. 1. Effect of soil properties and

fertiliser placement. Fertilizer Research 11: 161-172.

Malhi, S.S., McGill, W.B. and Nyborg, M. (1990).Nitrate losses in soils: effect of temperature, moisture and

substrate concentrations. Soil Biology andBiochemistry 22: 733-737.

McGuffog, D. (2001). The Australian fertiliser sector.‘Fertilizers in Focus’. Conference, Fertilizer IndustryFederation of Australia Inc. 28-29 May 2001.

Menyailo, O.V., Stepanov, A.L. and Umarov, M.M.,(1997). The transformation of nitrous oxide by

denitrifying bacteria in Solonchaks. Pochvovedenie1997, 213-215.

Meyer, C. P., Galbally, I. E., Wang, Y. P., Weeks, I. A.,Jamie, I. and Griffith, D.W. T. (2001). Two automaticchamber techniques for measuring soil-atmosphereexchanges of trace gases and results of their use in theOASIS field experiment. Pp.1-33. CSIRO AtmosphericResearch Technical Paper No. 51. CSIROAtmospheric Research, Aspendale, Victoria.

Meyer, C.P, Galbally, I.E., Wang, Y.P., Weeks, I.A.,Tolhurst, K.G., and Tomkins, I.B. (1997). TheEnhanced Emissions of Greenhouse Gases from Soilfollowing Prescribed Burning in a Southern EucalyptusForest. CSIRO Division of Atmospheric Research,Aspendale, Victoria.

Minami, K. and Fukushi, S. (1983). Effects of phosphateand calcium carbonate application on emission of nitrousoxide from soils under aerobic conditions. Soil Scienceand Plant Nutrition 29: 517-524.

Mosier, A. R. (1989). Chamber and isotope techniques.In: Exchange of Trace Gases Between TerrestrialEcosystems and the Atmosphere. (Eds. M.O.Andreae and D.S. Schimel) pp.175-187. John Wileyand Sons, New York, NY.

Mosier, A.R., Chapman, S.L. and Freney, J.R. (1989).Determination of dinitrogen emission and retention infloodwater and porewater of a lowland rice field fertilisedwith 15N-urea. Fertilizer Research.19: 127-136.

Mosier, A.R., Duxbury, J.M., Freney, J.R.,Heinemeyer, O. and Minami, K. (1996). Nitrous oxide emissions from agricultural fields: Assessment,measurement and mitigation. Plant and Soil 181: 95-108.

Mosier, A.R. and Hutchinson, G.L. (1981). Nitrousoxide emissions from cropped fields. Journal ofEnvironmental Quality 10: 169-173.

Mosier, A. R., Parton, W. J. and Hutchinson, G. L.(1983). Modelling nitrous oxide evolution from croppedand native soils. Environmental BiogeochemistryEcology Bulletin 35: 229-241.

Murakami, T., Owa, N. and Kumazawa, K. (1987).The effects of soil conditions and nitrogen form on nitrousoxide evolution by denitrification. Soil Science andPlant Nutrition 33: 35-42.

NGGIC (1996). Australian Methodology for theEstimation of Greenhouse Gas Emissions and Sinks,Agriculture. Workbook for Non-Carbon Dioxide Gasesfrom the Biosphere, Workbook 5.1, Revision 1, 1996.pp.1-74. National Greenhouse Gas InventoryCommittee, Canberra.


NGGIC (1999). National Greenhouse Gas Inventory:Analysis of trends 1990 to 1997 and National Greenhouseresponse strategy Indicators 1990 to 1997. NationalGreenhouse Gas Inventory Committee, Canberra.

O’Connell, A.M., Grove, T.S., Mendham, D.S. andRance, S.J. (2003). Changes in soil N status and Nsupply rates in agricultural land afforested with eucalyptsin south-western Australia. Soil Biology andBiochemistry (in press).

Parton, W.J., Hartman, D.S. Ojima, D.S. and Schimel,D.S. (1998). DAYCENT: Its land surface submodel:description and testing. Global Planetary Change 19:35-48.

Parton, W.J., Holland, E.A., Del Grosso, S.J.,Hartman, M.D., Martin, R.E., Mosier, A.R., Ojima,D.S. and Schimel, D.S. (2001). Generalized model forNOx and N2O emissions from soils. Journal ofGeophysical Research 106:17,403-17,419.

Peoples, M.B. and Baldock, J.A. (2001). Nitrogendynamics of pastures: nitrogen fixation inputs, the impactof legumes on soil nitrogen fertility, and the contributionsof fixed nitrogen to Australian farming systems.Australian Journal of Experimental Agriculture 41:327-346.

Phipps, S. and Hall, N. (1994). Reducing greenhouse

gas emissions from Australian agriculture: A regional

analysis. ABARE-Research-Report No. 94.5, 44pp.Australian Bureau of Agricultural and ResourceEconomics; Canberra; Australia.

Potter, C.S., Matson, P.A., Vitousek, P.M. andDavidson, E.A. (1996). Process modelling of controls

on nitrogen trace gas emissions from soils worldwide.Journal of Geophysical Research 101: 1361-1377.

Prasertsak, P., Freney, J.R., Denmead, O.T., Saffigna,P.G. and Prove, B.G. (2001). Significance of gaseous

nitrogen loss from a tropical dairy pasture fertilised with

urea. Australian Journal of Experimental Agriculture41: 625-632.

Prather, M., Ehalt, D., Dentener, F., Derwent, R.,Dlugokencky, E., Holland, E., Isaken, I., Katima, J.,Kirchhoff, V., Matson, P., Midgley, P. and Wang, M.(2001). Atmospheric chemistry and greenhouse gases. In Climate Change 2001. The Scientific Basis (Eds.J.T. Houghton and others). Pp. 239-287. IPCC,Cambridge Univ. Press, Cambridge.

Pu, G., Saffigna, P.G. and Strong, W.M. (1999).Potential for denitrification in cereal soils of northern

Australia after legume or grass-legume pastures.

Soil Biology and Biochemistry 31: 667-675.

Pu, G.X., Saffigna, P.G. and Xu, Z.H. (2001).Denitrification, leaching and immobilization of 15N –

labelled nitrate in winter under windrowed harvesting

residues in hoop pine plantations of 1-3 years old in

subtropical Australia. Forest Ecology andManagement 152: 183-194.

Raison, R.J. (1979). Modification of the soil environment

by vegetation fires, with particular reference to nitrogen

transformations: A review. Plant and Soil 51: 73-108.

Raison, R.J., Jacobsen, K.L., Connell, M.J., Khanna,P.K., Bauhus, J., Falkiner, R.A.. Smith, S.J.,Plotrowski, P. and Keith, H. (1991). Nutrient cycling

and tree nutrition. In: Collaborative SilvicultureSystems Research in East Gippsland between CSIROand the Victorian Department of Conservation andEnvironment. Pp. 1-96. Report by CSIRO Division ofForestry, Canberra, Australia.

Raison, R.J., Keith, H. and Khanna, P.K. (1990).Effects of fire on nutrient-supplying capacity of forest

soils. In: Impact of intensive harvesting of forest siteproductivity, (Eds. W.J. Dyck and C.A. Mees). FireResearch Institute Bulletin No. 159, New Zealand.

Raison, R.J., Heith, H., Khanna, P.K. and O’Connell(1993). Effects of repeated fires on nitrogen and

phosphorus budgets and cycling processes in forest

ecosystems. In: Fire in Mediterranean Ecosystems.(Eds. L. Trabaud and R. Prodon). Pp. 347-363. Report No. 5. Ecosystem Research Report Series,Commission of the European Communities,Brussels.


Rennenberg, H., Wassmann, R., Papen, H. and Seiler,W. (1992). Trace gas exchange in rice cultivation.

Ecological Bulletin 42: 164-173.

Reuter, D. (2001). Nutrient balance in regional farming

systems. Pp. 57-63. ‘Fertilizers in Focus’. Conference,Fertilizer Industry Federation of Australia Inc. 28-29May 2001.

Riley, W.J. and Matson, P.A. (2000). NLOSS:

a mechanistic model of denitrified N2O and N2 evolution

from soil. Soil Science 165: 237-249.

Robertson, G.P., Huston, M.A., Evans, F.C. andTiedje, J.M. (1988). Spatial variability in a successional

plant community: patterns of nitrogen availability.

Ecology 69: 1517-1524.

Robertson, G.P., Andreae, M.O., Bingemer, H.G.,Crutzen, P.J., Delmas, R.A., Duyzer, I. Fung, J.H.,Harriss, R.C., Kanakidou, M., Keller, M., Melillo,J.M., and Zavarzin, G.A. (1989). Trace gas exchange

and the physical and chemical climate: critical

interactions. In: Trace Gas Exchange BetweenTerrestrial Ecosystems and the Atmosphere. (Eds.M.O. Andreae and D.S. Schimel). John Wiley, Berlin.

Robertson, G.P., Paul, E.A. and Harwood, R.R.(2000). Greenhouse gases in intensive agriculture:

Contributions of individual gases to the radiative forcing

of the atmosphere. Science 289: 1922-1925.

Robertson, G.P., Vitosek, P.M., Matson, P.A. andTiedje, J.M. (1987). Denitrification in a clearcut loblolly

pine (Pinus taeda. L) plantation in the southeastern U.S.

Plant and Soil 97: 119-129.

Rolston, D.E., Hoffman, D.L. and Toy, D.W. (1978).Field measurement of denitrification. 1. Fluxes of nitrogen

and nitrous oxide. Soil Science Society of AmericaJournal 42: 863-869.

Ryden, J.C. (1981). Nitrous oxide exchange between a

grassland soil and the atmosphere. Nature 292: 235-237.

Ryden, J.C. and Lund, L.J. (1980). Nature and extent

of directly measured denitrification losses from some

irrigated vegetable crop production units. Soil ScienceSociety of America Journal 44: 505-511.

Smethurst, P.J. and Nambiar, E.K.S. (1990). Effects of

slash and litter management on fluxes of nitrogen and

tree growth in a young Pinus radiata plantation.Canadian Journal of Forestry Research 20: 1498-1507.

Smith, C.J., Freney, J.R., Chalk, P.M., Galbally, I.E.,McKenny, D.J., and Cai, G.X. (1988). Fate of urea

nitrogen applied in solution in furrows to sunflowers

growing on a red-brown earth: transformations, losses

and plant uptake. Australian Journal of AgriculturalResearch 39:793-806.

Smith, K.A. (1980). A model of the extent of anaerobic

zones in aggregated soils, and its potential application to

the estimation of denitrification. Journal of Soil Science31: 263-277.

Stefanson, R.C. (1973). Evolution patterns of nitrous

oxide and nitrogen in sealed soil-plant systems. SoilBiology and Biochemistry 5: 167-169.

Smith, C.J. and Bond, W.J. (1999). Losses of nitrogen

from effluent-irrigated plantation. Australian Journal ofSoil Research 37: 371-389.

Taylor, J.A. (1992). A global three-dimensional

Lagrangian tracer transport modelling study of the

sources and sinks of nitrous oxide. Mathematics andComputers in Simulation 33: 597-602.

Tiedemann, A.R., Helvey, J.D. and Anderson, T.D.(1978). Stream chemistry and watershed nutrient

economy following wildfire and fertilisation in eastern

Washington. Journal of Environmental Quality 7: 580-588.

Tiedje, J.M. (1994). Denitrifiers. In: Methods of SoilAnalysis, Part 2. Microbiological and BiochemicalProperties. (Eds. RW Weaver, JS Angel, and PSBottomley) pp. 245-267. Soil Science Society ofAmerica: Madison, Wisconsin.

Van Cleemput, O., Van Hoorde, J. and Vermoesen, A.(1992). Emission of N2O under different cropping

systems. In: Proceedings of Workshop: Nitrogencycling and leaching in cool and wet regions ofEurope. (Eds. E. Francois, K. Pithan and K. Bartiaux-Thill) pp. 20-21. CRA, Gembloux.


Venterea, R.T. and Rolston, D.E. (2000). Mechanisms

and kinetics of nitric and nitrous oxide production during

nitrification in agricultural soil. Global Change Biology6: 303-316.

Vitousek, P.M., Gosz, J.R., Grier, C.C., Melillo, J.M.and Reiners, W.A. (1982). A comparative analysis of

potential nitrification and nitrate mobility in forest

ecosystems. Ecological Monographs 52: 155-172.

Wagner-Riddle, C. and Thurtell, G.W. (1998). Nitrous

oxide emissions from agricultural fields during winter

and spring thaw as affected by management practices.

Nutrient Cycling in Agroecosystems 52: 151-163.

Wagner-Riddle, C., Thurtell, G.W., Kidd, G.K.,Beauchamp, E.G. and Sweetman, R. (1997). Estimates

of nitrous oxide emissions from agricultural fields over 28

months. Canadian Journal of Soil Science 77: 135-144.

Wagner-Riddle, C., Thurtell, G.W., Kidd, G.E.,Edwards, G.C. and Simpson, I.J. (1996a).Micrometeorological measurements of trace gas

fluxes from agricultural and natural ecosystems.

Infrared Physics and Techology 37: 51-58.

Wagner-Riddle, C., Thurtell, G.W., King, K.M., Kidd,G.E. and Beauchamp, E.G. (1996b). Nitrous oxide

and carbon dioxide fluxes from a bare soil using a

micrometeorological approach. Journal ofEnvironmental Quality 25: 898-907.

Walker, J., Raison, R.J. and Khanna, P.K. (1986). Fire. In: Australian Soils: The Human Impact (Eds. J.S. Russell and R.F. Isbell). Pp. 185-216.University of Queensland Press, Brisbane, Australia.

Wang, W.J. and Rees, R M. (1996). Nitrous oxide

production from different forms of fertiliser nitrogen. In:Progress in nitrogen cycling studies: Proceedings ofthe 8th nitrogen workshop held at the University ofGhent, September 1994. (Eds. O. Van Cleemput andG. Hofman) pp. 659-662. Kluwer AcademicPublishers, Dordrecht; The Netherlands.

Wang, Y.P., Meyer, C.P., Galbally, I.E. and Smith, C.J.(1997). Comparisons of field measurements of carbon

dioxide and nitrous oxide fluxes with model simulations

for a legume pasture in southeast Australia. J.Geophysical Research 102:28,013 – 28,024.

Weier, K.L. (1998). Sugarcane fields: sources or sinks

for greenhouse gas emissions? Australian Journal ofAgricultural Research 49:1-9.

Weir, K.L. (1999). N2O and CH4 emission and CH4

consumption in a sugarcane soil after variation in

nitrogen and water application. Soil Biology andBiochemistry 31: 1931-1941.

Weier, K.L. (2000). Trace gas emissions from a trash

blanketed sugarcane field in tropical Australia. In: Sugar2000 Symposium: Sugarcane: research towardsefficient and sustainable production. (Eds. J.R.Wilson, D.M. Hogarth, J.A. Campbell and A.L.Garside) pp. 271-272. CSIRO Division of TropicalCrops and Pastures; Brisbane; Australia.

Weier, K.L., Doran, J.W., Power, J.F. and Walters, D.T.(1993). Denitrification and the dinitrogen/nitrous oxide

ratio as affected by soil water, available carbon, and

nitrate. Soil Science Society of America Journal 57:66-72.

Weier, K.L. and Gilliam, J.W. (1986). Effect of acidity

on denitrification and nitrous oxide evolution from

Atlantic coastal-plain soils. Soil Science Society ofAmerica Journal 50: 1202-1205.

Weier, K.L., McEwan, C.W., Vallis, I., Catchpoole,V.R. and Myers, R.J.K. (1996). Potential for biological

denitrification of fertiliser nitrogen in sugarcane soils.Australian Journal of Agricultural Research 47:

67-79.

Weier, K.L., MacRae, I.C. and Myers, R.J.K. (1991).Seasonal variation in denitrification in a clay soil under a

cultivated crop and a permanent pasture. Soil Biologyand Biochemistry 23: 629-635.


Weier, K.L., MacRae, I.C. and Myers, R.J.K. (1993).Denitrification in a clay soil under pasture and annual

crop: losses from 15N-labelled nitrate in the subsoil in

the field using C2H2 inhibition. Soil Biology andBiochemistry 25:999-1004.

Weier, K.L., Rolston, D.E., Thorburn, P.J. andHogarth, D.M. (1998). The potential for N losses via

denitrification beneath a green cane trash blanket.

Proceedings of the 20th conference of the AustralianSociety of Sugar Cane Technologists 1998: 169-175.

Weston, C.J. and Attiwill P.M. (1996). Clearfelling and

burning effects on nitrogen mineralisation and leaching in

soils of old-age Eucalyptus regnans forests. ForestEcology and Management 89: 13-24.

Weston, E.J., Doughton, J.A., Dalal, R.C., Strong,W.M., Thomas, G.A., Lehane, K.J., Cooper, J.C., King,A.J. and Holmes, C.J. (2000). Managing long-term

fertility of cropping lands with ley pastures in southern

Queensland. Tropical Grasslands 34: 169-176.

Weiske, A., Benckiser, G., Herbert, T. and Ottow,J.C.G. (2001). Influence of the nitrification inhibitor

3,4-dimethylpyrazole phosphate (DMPP) in comparison

to dicyandiamide (DCD) on nitrous oxide emissions,

carbon dioxide fluxes and methane oxidation during three

years of repeated application in field experiments. Biology& Fertility of Soils 34: 109-117.

Weitz, A.M., Keller, M., Linder, E. and Crill, P.M.(1999). Spatial and temporal variability of nitrogen oxide

and methane fluxes from a fertilised tree plantation in

Costa Rica. Journal of Geophysical Research 104: 97-107.

Williams, N (1994). Greenhouse gas emissions from

Australian beef and sheepmeat industries; on farms, in

feedlots and in transport and meat processing facilities.Pp1-82. Australian Meat Research Corporation,Canberra.

Wofsy, S.C., Goulden, M.L. and Munger, J.W. (1993).Net exchange of CO2 in a midlatitude forest. Science 260:1314-1317.

Yamulki, S., Wolf, I., Bol, R., Grant, B., Brumme, R., Veldkemp, E. and Jarvis, S.C. (2001). Effects of

dung and urine amendments on the isotopic content of

N2O released from grasslands. Rapid CommunicationsMass Spectrometry 14: 1356-1360.

Xu, Z.H., Amato, M., Ladd, J.N. and Elliott, D.E.(1996). Soil nitrogen availability in the cereal zone of

south Australia. II. Buffer-extractable nitrogen,

mineralisable nitrogen, and mineral nitrogen in soil

profiles under different land uses. Australian Journal of Soil Research 34: 949-965.

Series 1 Publications Set the framework for development of the National Carbon Accounting System (NCAS) anddocument initial NCAS-related technical activities (see http://www.greenhouse.gov.au/ncas/ publications).

Series 2 Publications Provide targeted technical information aimed at improving carbon accounting for Australianland based systems (see http://www.greenhouse.gov.au/ncas/publications).

Series 3 PublicationsDetail protocols for biomass estimation and the development of integrated carbon accountingmodels for Australia (see http://www.greenhouse.gov.au/ncas /publications).Of particular note is Technical Report No.

28. The FullCAM Carbon Accounting Model: Development, Calibration and Implementationfor the National Carbon Accounting System.

Series 4 PublicationsProvide an integrated analysis of soil carbon estimation and modelling for the National CarbonAccounting System, incorporating data from paired site sampling in NSW, Qld and WA.A preliminary assessment of nitrous oxide emissions from Australian agriculture is also included(see http://www.greenhouse.gov.au/ncas/publications).

Series 5 Publications include:

39. Continuous Improvement of the National Carbon Accounting System Land CoverChange Mapping.

40. Modelling Change in Litter and Soil Carbon Following Afforestation or Reforestation -Calibration of the FullCAM ‘Beta’ Model.

41. Calibration of the FullCAM Model to Eucalyptus globulus and Pinus radiata andUncertainty Analysis.

42. Outcomes from the Workshop: Deriving Vegetation Canopy Cover Estimates.

43. The Impact of Tillage on Changes in Soil Carbon Density with Special Emphasis onAustralian Conditions.

44. Spatial Estimates of Biomass in ‘Mature’ Native Vegetation.

The National Carbon Accounting System provides a complete

accounting and forecasting capability for human-induced sources and

sinks of greenhouse gas emissions from Australian land based

systems. It will provide a basis for assessing Australia’s progress

towards meeting its international emissions commitments.

http://www.greenhouse.gov.au

technical report no. 35 Emission Sources of Nitrous Oxide from

Australian Agriculturaland Forest Lands and M

itigation Options

technical report no. 35

Documents

Transcript of technical report no. 35