AGRICULTURE

slurry was emitted as N2O from deep-litter systems for fattening pigs during a 4-monthmeasuring period. Large N2O losses may also occur during aerobic treatment of pig
slurry. Burton et al. (1993) found that approximately 0.05 kg N/kg nitrogen in slurry waslost as N2O during a four-day treatment period.
Losses of N2O from large lagoons with pig slurry in south-eastern United States were
negligible (Harper, personal communication). Concentration profiles of N2O above thelagoon suggest that absorption of N2O from the atmosphere by the pig slurry in the
lagoon may occur.
Losses of N2O from muck heaps were measured by Sibbesen and Lind (1993). They
arrived at a tentative estimate of 8 10-3 kg/kg nitrogen in the dung heap/yr. Recent
results indicate that losses were much larger during warm periods, as in the summer of
1995, than during colder conditions (Lind, personal communication, 1995).
In a study on total N2O emission from The Netherlands, Kroeze (1994) included N2Oemissions from stables. She distinguished four classes, kg N2O-N/kg nitrogen in thewaste: class 1 (<0.002) for anaerobic storage of waste; Class 2 (0.002-0.0125) for none of
the types of storage in the Netherlands; Class 3 (0.0125-0.025) for biological treatment ofcalf veal manure and Class 4 (>0.025) for deep-litter stables, nitric-acid-treated slurry.
Jarvis and Pain (1994) and Bakken et al. (1994) made inventories of N2O emissions fromlivestock holdings, but did not include N2O emissions from animals and animal waste
storage. Other studies (Bouwman et al., in press; Mosier et al., 1995b; Flessa et al.,submitted) assign an emission factor to nitrogen from animal slurry. No explicit
distinction was made between N2O emission from wastes during storage and treatment,
and N2O emission from wastes after deposition or spreading onto the land.
In conclusion, there is very limited information available on N2O emissions from animals
and from animal waste during storage and treatment. Moreover, there is a wide range inestimated losses, when expressed in N2O N/kg nitrogen in the waste. Losses fromanimal waste during storage range from <10-4 kg N for slurries to >0.15 kg N/kg nitrogenin the pig waste in deep-litter stables. Although N2O production may be affected bywaste spreading and waste processing, available data are too scarce to base a new
method on.
C)

N2O from animal grazing

A brief summary of estimates of N2O emissions derived from dung and urine deposits ofgrazing animals is compiled in Appendix A, Table A-1. The N2O emission is expressed as
gN/kg of the nitrogen in urine and/or dung. Two types of studies may be distinguished.
The first type focuses on emissions from a well-defined urine and/or dung patch. A
control treatment is generally included, to facilitate the calculation of urine and dung
derived emissions. The grazed grassland is the focus in the second type of studies.
Grazing derived emissions can be obtained properly when a non-grazing treatment isincluded. For the purpose of this compilation we consider that grazing derived emissions
are similar to 'dung and urine derived' emissions. This may not be completely true,
because grazing animals have also other effects than deposition of dung and urine, forexample, compaction of the soil by trampling, increased turnover of nitrogen fromstubble and roots, etc.
The duration of the studies ranged from 1 week up to 2 years. Though the bulk of the
N2O will be lost shortly after deposition in the field, significant amounts may still be
released from the urine and dung even after a couple of weeks after deposition. Hence,
short-term studies may underestimate the total N2O losses from animal excrements (Van
Cleemput et al., 1994; Velthof et al., submitted a;b).

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Grazing derived emissions range from 0.002 to 0.098 kg N2O–N/kg of nitrogen excreted(Koops et al., 1995; Muller et al., 1995a;b). The lower estimates are from well-drained
unfertilised grassland soils in New Zealand. Carran et al. (1995) examined five plots,
ranging from well drained high-fertile plots to poorly drained low-fertility plots. They did
not provide grazing derived emissions, probably because they did not include non-grazing
treatments. However, they provided data on annual dry matter yields. Assuming a meangrazing efficiency in their grazing trials of 80 per cent, for both bulls and sheep, a nitrogencontent in the clover/grass mixture of 30 g/kg dry weight, and a low background emission(20 per cent of the grazing trials), the grazing derived N2O emissions are likely in therange of 0.002-0.01 kg N2O–N/kg nitrogen excreted, which is rather low.
Large grazing derived emissions, induced by livestock nitrogen excretion, were obtainedon drained peat soils in the Netherlands. These intensively managed grassland on peatsoils have also a large background emission and a large fertiliser derived emission (Velthof
and Oenema, 1995).
Nearly all data pertain to temperate areas, with intensively managed grassland. The
nitrogen contents of dung and especially urine are higher from this intensively managed
grassland than from less intensively managed (sub)tropical grasslands. The fraction ofeasily hydrolysable nitrogen, i.e., urea and uric acid, is much smaller in dung and urine
from animals fed with a low nitrogen content ration than from animals fed with a highnitrogen content ration. This difference will probably result in a different emissions
factor. Unfortunately, data are lacking to sustain this hypothesis.
Differences in climate, i.e., rainfall and temperature patterns, may also have a significant
effect. Moist and warm environments facilitate the ammonification of organically boundnitrogen in urine and dung, and subsequently, nitrification and denitrification. As a result,the effect of a relatively low ratio of easily hydrolysable nitrogen versus total nitrogen inurine and dung in low-intensity managed tropical pastures may be compensated for by theeffects of temperature and moisture, to some extent. However, this is speculative sincelittle data exist to substantiate this proposition.
Nitrogen losses as N2O are probably lower in arid and semiarid regions and in colder
climates such as Sweden. Mosier and Parton (1985) found that during the course of ayear per kg of urea–N from simulated urine patches, only 0.006 kg N2O–N was emitted
as N2O. They did find in later studies that N2O emissions remained detectably higher 10
years after the urea had been applied to the semi-arid shortgrass prairie (Mosier et al.,1991).
An overall reasonable average emission factor for animal waste excreted in pastures is0.02 kg N2O–N/kg of nitrogen excreted. This emission factor is likely applicable for all
regions of the world and for all types of animals.

METHODOLOGY FOR ESTIMATING N2O FROMANIMAL PRODUCTIONAs already discussed there are three potential sources of N2O emissions related toanimal production. These are (a) animals themselves, (b) animal wastes during storage
and treatment, (c) dung and urine deposited by free-range grazing animals. N2Oemissions emitted directly from animals are not reported here. Emissions from manure
applied to agricultural soils from stables (e.g., daily spreading) and from grazing animals(pasture range and paddock) are considered to be emissions from agricultural soils. N2Oemissions from other animal waste management systems (AWMS) are not directly

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attributable to soils and are reported under Manure Management (Section 4.2).
Emissions from manure used as fuel should be reported in the Energy Chapter.
Nonetheless, all sources of N2O from animal production and agricultural soils aredescribed here as part of the N-cycle. Caution must be applied in reporting N2Oemissions under the appropriate source categories defined above.
EQUATION 2
N2OANIMALS = N2O(AWMS)=∑[ N(T) x Nex(T) x AWMS(T) x EF3(AWMS)]
where:N2OANIMALSN2O(AWMS)===

N2O emissions from animal production in a country (kg N/yr)
N2O emissions from Animal Waste Management Systems in
the country (kg N/yr);[N(T=1) x Nex(T=1) x AWMS(T=1) x EF3(AWMS)]+ ...
+ [N(T=TMAX) x Nex(T=TMAX) x AWMS(T=TMAX) x EF3(AWMS)] ;

N(T)

=

number of animals of type T in the country;

Nex(T)=

N excretion of animals of type T in the country (kg N/animal/yr); (see Table 4-20);

AWMS(T)=

fraction of NEX(T) that is managed in one of the different
distinguished animal waste management systems for animals oftype T in the country; (see Table 4-21);

EF3(AWMS)=

N2O emission factor for an AWMS (kg N2O-N/kg of Nex inAWMS); (see Table 4-22);

T=

type of animal category;Nitrogen excretion
General statistics about animal numbers are provided by FAO and detailed information isavailable for many countries. Default values are provided in Table 4-20, which wascompiled on the basis of data provided by Ecetoc (1994), and references therein, Vetter
et al. (1989), Steffens and Vetter (1990). There are still uncertainties in the values listed
in Table 4-20. Estimates for cattle and swine may be too high. Hence, these estimates(default values) need further attention. The excretion data are in reasonable agreementwith Bouwman (in press), although some of the excretion factors as given by Bouwman(in press) are lower than the factors in Table 4-20. Once available, countries may chose
to use nitrogen excretion data from the Ammonia Expert Panel of the UN-ECE task
force on emission inventories. For some countries it may be desirable to distinguishother animal types than indicated in Table 4-20. If such country values are available theyshould be used.

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TABLE 4-20
TENTATIVE DEFAULT VALUES FOR NITROGEN EXCRETION PER HEAD OF ANIMAL PER REGION(KG/ANIMAL/YR)A
RegionType of Animal
NondairycattleDairycattlePoultry

Sheep

Swine

Other
animals

North America

70

100

0.6

16

20

25

Western Europe

70

100

0.6

20

20

25

Eastern Europe

50

70

0.6

16

20

25

Oceania

60

80

0.6

20

16

25

Latin America

40

70

0.6

12

16

40

Africa

40

60

0.6

12

16

40

Near East &Mediterranean

50

70

0.6

12

16

40

Asia & Far East

40

60

0.6

12

16

40

a Source: Ecetoc (1994), Vetter et al. (1988), Steffens and Vetter (1990).

Animals as direct source of N2O
Current available information suggests that some N2O may be released directly fromanimals. However, the rate of release is probably low. A value less than 0.1 g N2O–N/kg
nitrogen excreted would result in a global N2O emission of less than 0.1 Tg, whichsuggests that animals are a minor source. This source is therefore not included in themethodology.
Animal Waste Management Systems
The types of Animal Waste Management System (AWMS) distinguished by Safley et al.
(1992) and their compilations for a large number of countries are proposed for thismethodology. Descriptions of these management systems can be found Table 4-8.
Tables 4-21 and 4-6 can be used to estimate nitrogen excretion per AWMS. The AWMS
is an important regulating factor in N2O emission from animal wastes during storage andtreatment. The data provided per country in Safley et al. (1992) could be used for
estimating N2O emissions from animal wastes. Significant differences in emission factors
are expected between some of the AWMS.
There are several AWMS considered here:• Anaerobic lagoons;• Liquid systems;• Daily spread;• Solid storage and drylot;• Pasture range and paddock;

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AGRICULTURE• Used for fuel;• Other systems.
N2O emissions from all AWMS are reported under Manure Management (Section 4.2),
with three exceptions:• stable manure that is applied to agricultural soils ( e.g., daily spread);• dung and urine deposited by grazing animals on fields (pasture range and paddock);• manure used for fuel.
The first of these sources is captured in the methodology for estimating direct emissions
from agricultural soils (Section 4.5.2). The second source is reported under direct soil
emissions of N2O from animal production (Section 4.5.3). The third source, manure used
as fuel, is reported in the Energy Chapter.
The class "used for fuel" is not included here as a source of N2O, because this possible
source of N2O is considered an energy-related emission. Nevertheless, countries should
estimate the amount of manure nitrogen that is used as fuel, because that amount is notapplied to soils. A problem exists for the class 'Used for fuel', as it includes 'anaerobic
digesters'. Moreover, it is the dung that is used for fuel and not the urine. These two
factors may lead to a possible overestimation of the amount of N2O emitted from wastes
in the class 'Used for fuel', if not properly corrected. While significant N2O losses may
occur during burning, no N2O losses are expected from anaerobic digesters. Anaerobic
digesters are used especially in Asia. Data of Erda Lin (personal communication, 1995)
suggest, however, that only 0.5 per cent of the total amount of animal wastes in China
are used in anaerobic digesters.

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Western Europe

North America

Region00000Poultry (E)

Sheep

Swine

Other animals (F)0

Other animals (F)Dairy Cattle

0

Swine

8

0

Sheep

Non-dairy Cattle (D)00Other animals (F)Poultry (E)

25

Swine

0

0

Sheep

Dairy Cattle

5

Poultry (E)010Dairy Cattle

Non-dairy Cattle (D)0Anaerobic
LagoonNon-dairy Cattle (D)Type of Animal

0

0

0

0

1

0

0

0

0

0

24

0

0

0

0

0

37

0

Daily
SpreadReference Manual

0

29

0

28

18

39

0

77

0

13

46

55

0

50

0

4

23

1

LiquidSystem

0

0

0

0

67

52

0

23

2

1

21

2

0

18

2

0

23

14

Solid Storage
and Drylot

92

27

73

1

13

0

96

0

87

2

8

33

92

0

88

1

0

84

Pasture Rangeand Paddock

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Used Fuel% of Manure Production per Animal Waste Management Systems

8

45

27

71

0

1

4

0

11

84

1

9

8

6

10

90

7

1

Other
System

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TABLE 4-21
DEFAULT VALUES FOR PERCENTAGE OF MANURE N PRODUCED IN DIFFERENT ANIMAL WASTE MANAGEMENT SYSTEMS IN DIFFERENT WORLD REGIONS(FROM SAFLEY ET AL., 1992)

Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories:44.102Africa00
001Poultry (E)

Sheep

Swine

Other animals (F)0

Other animals (F)Dairy Cattle

0

Swine

0

0

Sheep

Non-dairy Cattle (D)0Poultry (E)0Other animals (F)

0

55

Swine

Dairy Cattle

0

Sheep

0

0

Poultry (E)Non-dairy Cattle (D)0Dairy Cattle

Latin America0Non-dairy Cattle (D)Oceania

Anaerobic
LagoonType of Animal

Region

0

0

0

0

12

1

0

2

0

0

62

0

0

0

0

0

0

0

Daily
Spread

0

93

1

0

0

3

0

51

0

0

1

0

0

17

0

0

0

0

Solid Storage
and Drylot

99

0

99

81

83

96

99

0

100

42

36

99

100

0

100

3

100

100

Pasture Rangeand Paddock

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Used
Fuel

1

0

1

19

5

0

1

40

0

49

0

1

0

28

0

98

0

0

Other System

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0

7

0

0

0

0

0

8

0

9

1

0

0

0

0

0

0

0

LiquidSystem% of Manure Production per Animal Waste Management Systems

TABLE 4-21 (CONTINUED)DEFAULT VALUES FOR PERCENTAGE OF MANURE N PRODUCED IN DIFFERENT ANIMA WASTE MANAGEMENT SYSTEMS IN DIFFERENT WORLD REGIONS(FROM SAFLEY ET AL., 1992)

AGRICULTURE

Reference Manual

0

0
1
0

Sheep

Swine

(D) Includes buffalo(E) Includes chickens, turkeys and ducks(F) Includes goats, horses, mules, donkeys and camels

Other animals (F)

38

1

0

1

0

0

21

16

0

0

0

0

3

2

Daily
SpreadReference Manual

0

2

4

0

0

Poultry (E)0Other animals (F)

32

6

0

Swine

0

Dairy Cattle

0

Sheep

1

0

0

Poultry (E)00LiquidSystem

0

53

0

0

0

14

0

68

0

0

3

0

Solid
Storage andDrylot

95

0

83

44

24

29

100

0

100

71

77

77

PastureRange and
Paddock

0

7

0

1

46

40

0

0

0

0

18

18

Used Fuel% of Manure Production per Animal Waste Management Systems

Non-dairy Cattle (D)0Dairy Cattle

Asia and Far East0

Non-dairy Cattle (D)Near East andMediterranean

Anaerobic
LagoonType of Animal

Region

5

0

17

52

0

0

0

0

0

28

0

2

Other
SystemTABLE 4-21 (CONTINUED)DEFAULT VALUES FOR PERCENTAGE OF MANURE N PRODUCED IN DIFFERENT ANIMA WASTE MANAGEMENT SYSTEMS IN DIFFERENT WORLDREGIONS (FROM SAFLEY ET AL., 1992)

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Tentative (default) emission factors (EF3) for the different AWMS are shown in Table 422. These factors were derived on the basis of a very limited amount of information.
Uniform factors for all over the world are proposed. This may be incorrect, as
temperature and moisture may have positive effects on the size of the processes and,hence, on losses. However, as animal production systems are found in warmer regions,and low-intensity systems have less easily hydrolysable nitrogen in the excretions
discussed above, a uniform factor for all regions would seem appropriate.
TABLE 4-22
TENTATIVE DEFAULT VALUES FOR N2O EMISSION FACTORS FROM ANIMAL WASTE PER ANIMALWASTE MANAGEMENT SYSTEM,KG N2O–N/KG NITROGEN EXCRETED
Animal Waste Management Systema

Emission Factor EF3

Anaerobic lagoonsb

0.001 (<0.002)

Liquid systemsb

0.001 (<0.001)

Daily spreadc

0.0 (no range)

Solid storage and drylotc

0.02 (0.005-0.03)

Pasture range and paddock (grazing)d0.02 (0.005-0.03)

Used as fuele

Not included in this Chapter

Other systemsb

0.005

a The fraction of manure nitrogen produced in different Animal Waste Management Systems for cattle, swine andbuffalo can be estimated as proposed in Table 4-21, or as given by Safley et al. (1992).
b To be reported under “Manure Management”.
c To be reported under “Agricultural Soils” (Workbook, Section 4-6) under direct soil emissions from agricultural
fields after spreading. (Emissions are assumed not to occur before spreading).
d To be reported under “Agricultural Soils” (Workbook, Section 4-6) under direct soil emissions from animal
production.
e To be reported in the Energy Chapter.

4.5.4

Indirect N2O Emissions
Used in Agriculture.

from

Nitrogen

OVERVIEW OF SOURCES
The pathways for synthetic fertiliser and manure input that give rise to indirect emissions
are considered to be:
A. Volatilisation and subsequent atmospheric deposition of NH3 and NOx (originatingfrom the application of fertilisers);
B. Nitrogen leaching and runoff;
C. Human consumption of crops followed by municipal sewage treatment;
D. Formation of N2O in the atmosphere from NH3;
E. Food processing.
Of these pathways, methodologies for estimating N2O emissions from A-C are proposed.
Nitrous oxide emissions from human waste are described below. However, these N2O
emissions are allocated to the Waste Chapter (see Section 6.4, Reference Manual andWorkbook). At present, information is insufficient to estimate emissions from D and E.

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In order to estimate the associated N2O fluxes, the following data are needed:•

Synthetic nitrogen fertiliser consumption (NFERT). This is available by country from
FAO yearbooks and is probably the most reliable piece of input data.

•

Livestock nitrogen excretion (Nex) can be estimated reasonably well from FAO
livestock populations and measured kg N/animal/yr excretion factors as given in
Table 4-20.

•

Crop production (Crop) is available from FAO production yearbooks in kg dry
biomass/yr.

•

Sewage nitrogen production can be estimated from FAO per capita protein
consumption data (PROTEIN) and human population counts (Nr PEOPLE). Protein
consumption may vary by a factor of 2 between countries, e.g., Americans andIndians consume 110 and 55 g protein/person/day, respectively.

Emissions of NH3 and NOx (kg N/yr) are estimated from fertiliser use and livestock
nitrogen excretion.
These N2O–N emissions are to be calculated from a country's NOx and NH3 emissions
and nitrogen transported in leaching and runoff, so that all N2O formed as a result ofNOx and NH3 emissions and leaching and runoff in country Z are assigned to country Z,
even if the actual N2O formation takes place in another country. This implies that NOx
and NH3 and nitrogen from leaching and runoff imported into a country is not included in
the calculations.
A.
Atmospheric deposition of NOx and NH3
Atmospheric deposition of nitrogen compounds such as nitrogen oxides (NOx) andammonium (from NH3) fertilise soils and surface waters and as such enhance biogenic
N2O formation. However, it is recognised that other sources of atmospheric inputs of N
compounds to agricultural soils are important. These sources include fuel combustion,for example. Atmospheric deposition of these sources is not accounted here because
only those N emissions originating from the application of fertilisers are presently
considered. Indeed, Brumme and Beese (1992) showed that after two decades ofatmospheric deposition of acidifying compounds (ammonium and sulphuric acids), N2O
emissions from German forest soils were enhanced by up to a factor of 5. Reported
rates of N2O emissions are between 0.002 and 0.016 kg N2O–N/kg of the amount of
nitrogen deposited onto soils (Bowden et al., 1991; Brumme and Beese, 1992; Kasimir,
personal communication). This is within the range of emission factors suggested in
Section 4.5.2 for synthetic fertilisers. We therefore propose to calculate N2O-N
emissions as 0.01 kg N2O-N /kg of NOx-N and NH3-N emitted annually within a country(EF4, Table 4-23).
TABLE 4-23
DEFAULT EMISSION FACTORS FOR INDIRECT EMISSIONS
EF4 (N deposition)=

0.01 (0.002-0.02) kg N2O-N/kg NH3-N and NOX–N emitted

EF5 (leaching/runoff)=

0.025 (0.002-0.12) kg N2O-N/kg N leaching/runoff

EF6 (sewage)=

0.01 (0.002-0.02) kg N2O-N/kg sewage-N produced

Agricultural ammonia emissions can be derived from NH3 volatilisation studies. Animal
manure (dung + urine) is one of the most important sources of NH3. According to Van
der Hoek (1994), up to 50 per cent of the mineral nitrogen in animal manure (i.e., about

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25 per cent of total N) may be lost shortly as NH3 after application to soil. He also
shows that this percentage depends considerably on the application technique used.
Schimel et al. (1986) assumed that, as a minimum estimate, 20 per cent of manure
nitrogen applied to soils is volatilised as NH3 soon after application. The amount of NH3
volatilised may be lower in acid and near neutral pH soils. According to Bouwman (inpreparation), about 25 per cent of livestock nitrogen excretion is emitted as NH3 worldwide. For synthetic fertilisers Van der Hoek (1994) uses a much lower percentage of
only 2 per cent of the nitrogen used in the Netherlands that is lost as NH3. Bouwman (inpreparation), however, estimated that almost 10 per cent of synthetic fertiliser-N isemitted as ammonia world-wide. Although climate and fertiliser type (e.g., urea orammonium sulphate) may influence ammonia volatilisation, we use default values for NH3
and NOx volatilisation: 0.1 kg nitrogen/kg synthetic fertiliser nitrogen applied to soils and0.2 kg nitrogen/kg of nitrogen excreted by livestock are proposed (FracGASF and FracGASM,
Table 4-19).
B.
Leaching and Runoff
A considerable amount of fertiliser nitrogen is lost from agricultural soils through leaching
and runoff. The leached/runoff nitrogen enters groundwater, riparian areas and wetlands,
rivers and eventually the coastal ocean. In many world areas, it is one of the mostimportant inputs of nitrogen to those systems. A WHO/UNEP report (1989) showedthat over 10 per cent of European rivers had a nitrate content ranging from 9 to 25 mg
nitrate-N/L. Other sources include sewage, industries and atmospheric deposition.
Fertiliser nitrogen in ground water and surface waters enhances biogenic production of
N2O as the nitrogen undergoes nitrification and denitrification.
The fraction of the fertiliser and manure nitrogen lost to leaching and surface runoff(FracLEACH) may range from range 0.1-0.8 (Seitzinger and Kroeze, in preparation). A
value of 0.3 is proposed as default here (Table 4-24). For this purpose total nitrogenexcretion is used (Nex) in order to include manure produced during grazing:
EQUATION 3
NLEACH = [NFERT + NEX] x FracLEACH
The sum of the emission of N2O due to NLEACH in: 1) groundwater and surface drainage(EF5-g), 2) rivers (EF5-r), and 3) coastal marine areas (EF5-e) is calculated to obtain the
N2O emission factor (EF5) for NLEACH. Although not specified, the total amount of
nitrogen eventually denitrified remains the same but some is denitrified in riparian area
and wetlands before the nitrogen reaches the ocean.
In future assessment
methodologies, a separate emission factor should be used in the workbook for each ofthese three environments.
TABLE 4-24
DEFAULT VALUES OF PARAMETERS FOR INDIRECT EMISSIONS
FracNPR

0.16 kg N/kg of protein

FracLEACH

0.3 (0.1-0.8) kg N/kg of fertiliser or manure N

Groundwater and surface drainage
Supersaturated concentrations of nitrous oxide in groundwater and in surface waterdraining agricultural lands may occur due to leaching of N2O from the soil towards
drainage and groundwater, or production during nitrification and/or denitrification offertiliser nitrogen in the groundwater or drainage ditches. Many factors can affect theamount of N2O in these waters including the amount of nitrogen leaching into the

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groundwater, different land use practices, soil types and climate. Fertiliser nitrogen in
groundwater or drainage water is primarily in the form of NO3-N. A review of theliterature indicates that while the range of N2O concentrations reported is large, there issome relationship between the concentration of N2O-N and NO3-N in groundwater andagricultural drainage water.
The ratio of N2O-N to NO3-N concentration in
groundwater and agricultural drainage water at over 25 locations in urban, agriculturaland woodland areas in Japan, Israel and the United States ranged from 0.0001 to 0.06
(Dowdell et al., 1979; Minami and Fukuski, 1984; Ronen et al., 1988; Minami and Oshawa,
1990; Ueda et al., 1991; Ueda et al., 1993). The ratio of N2O-N to NO3-N in agriculturaldrainage ditches and groundwater under agricultural fields ranged from approximately
0.0003 to 0.06. The ratios of N2O-N to NO3-N in agricultural drainage ditches weregenerally lower (0.003 or less) than ratios in agricultural groundwater. Rapid loss of N 2O
to the atmosphere may account for the generally lower ratios in drainage ditch water.
The ratio of N2O-N to NO3-N in agricultural groundwater was generally between 0.003
and 0.06, with values between 0.007 and 0.02 common. Assuming that all N LEACH is in theform of NO3, we recommend a default emission factor of 0.015 (EF5-g) for N2O fromNLEACH in groundwater and drainage ditches, with a range of 0.003 to 0.06. The amountof N2O emitted from groundwater (by upward diffusion or following entry ofgroundwater into surface water through rivers, irrigation, and drinking water) andagricultural drainage water is then estimated as:
EQUATION 4
N2O emissions from groundwater and agricultural drainage water=
NLEACH x EF5-g
where EF5–g = 0.015 kg N2O-N/kg NLEACH, assuming that all N2O produced in aparticular year is emitted during that year.
RiversOnce NLEACH from groundwater and surface water enters rivers, additional N2O is
produced associated with nitrification and denitrification of NLEACH (Seitzinger andKroeze, in preparation). It is assumed that minimal denitrification occurs in groundwaterand therefore that all NLEACH enters rivers.
Nitrification: N2O can be produced during nitrification of NLEACH in rivers. While much of
the NLEACH may enter rivers as nitrate, algae and aquatic plants can assimilate the nitrate
into organic matter, which is released as ammonia, following decomposition of thatorganic matter. Ammonia in rivers is rapidly nitrified (Lipschultz et al., 1986). The
NLEACH entering rivers nitrifies on average 0.5-3 times during river transport. We
assume for our default methodology that all NLEACH entering rivers is nitrified once during
river transport. The N2O yield (moles N2O-N/mol of NO3-N) during nitrification is
generally between 0.002 and 0.003 at atmospheric oxygen levels (0.2 atm partialpressure); Goreau et al., 1980), although enhanced yields of N2O are found at reduced
O2 concentrations (Goreau et al., 1980). While reduced oxygen levels occur in somerivers, especially those with high nutrient inputs, we suggest an N 2O yield of 0.003 fornitrification.
Denitrification: During river transport a considerable amount of nitrogen is lost via
denitrification in riverine sediments. A wide range of denitrification rates has beenmeasured in rivers or streams; rates are generally lowest in unpolluted streams (Duff etal., 1984) with highest rates in polluted rivers/streams (Robinson et al., 1979; Cooper andRevised 1996 IPCC Guidelines for National Greenhouse Gas Inventories:

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Cooke, 1984; Seitzinger, 1988, 1990; Christensen and Soerensen, 1988; Christensen etal., 1989). Estimates of the magnitude of N-removal via denitrification range from 1 to 75
per cent of the external nitrogen inputs based on mass balance models and/or frommeasurements of denitrification (Seitzinger, 1990). Factors likely to affect the fraction of
nitrogen removed by denitrification include length and depth of the river, flow rate, water
residence time, oxygen content, organic content of sediments, and season. In a numberof rivers denitrification removed 50 per cent of the nitrogen inputs, even over shortsections (Kaushik and Robinson, 1976; Hill, 1979, 1981, 1983; van Kessel, 1977; Swankand Caskey, 1982). For the assessment we assume that denitrification removes 50 per
cent of NLEACH inputs to rivers. N2O associated with denitrification (Jorgensen et al.,1984) is released from river sediments. The ratio of N2O:N2 emitted from river
sediments is generally within the range 0.001-0.005, although in heavily polluted sediments
yields up to 6 per cent have been observed (Seitzinger, 1988). A constant ratio of 0.005
for N2O-N emission to denitrification (N2–N production) in rivers is suggested.
In summary, the emission factor for NLEACH in rivers due to nitrification anddenitrification [EF5-r] is thus equal to 0.005 x NLEACH [for nitrification] plus 0.005 x(NLEACH/2) [for denitrification], or 0.0075 x NLEACH. Therefore, N2O-N produced fromNLEACH during river transport = NLEACH x (EF5-r), where EF5-r = 0.0075.
Estuaries
Rivers are the major conduit for nitrogen transport to the coastal ocean (via estuaries).
As discussed above, half of NLEACH is assumed to be removed by denitrification in rivers in
the form of N2 and N2O. The remaining 50 per cent of NLEACH is discharged by rivers toestuaries. Nitrogen inputs to estuaries can undergo nitrification and denitrification, withassociated N2O production.
Nitrification: Pelagic nitrification rates in estuaries generally range from 0-22 umol/l/d(Berounsky and Nixon, 1993). Estuarine nitrification rates are affected by a number offactors such as ammonia concentrations, temperature (Berounsky and Nixon, 1985 and1993), oxygen (Helder and DeVries, 1983), suspended particulate matter (Helder and
DeVries, 1983; Owens, 1986), and light (Horrigan and Springer, 1990). However, no
predictive factor has been developed to estimate pelagic nitrification rates across a rangeof estuaries. In Narragansett Bay (USA), approximately half of the river inputs ofinorganic nitrogen to the Bay were nitrified in the bay (Berounsky and Nixon, 1993;
Seitzinger and Kroeze, in preparation). For the assessment methodology, we assume that
half of the rivers inputs of NLEACH are nitrified again in estuaries, and that the ratio of
N2O-N to NO3–N produced is 0.005, as discussed above for rivers.
Denitrification: Some of the most extensive studies of denitrification are in estuaries(Kemp et al., 1990; Jenkins and Kemp, 1984; Jensen et al., 1984 and 1988; Smith et al.,1985). A relatively good relationship has been found between denitrification andinorganic nitrogen inputs to estuaries from rivers. The amount of nitrogen removed bydenitrification is equivalent to a relatively constant percentage (50 per cent) of inorganic
nitrogen inputs to a variety of estuaries (Seitzinger, 1988). Those estuaries vary in a
number of characteristics including nitrogen loading rates (25 to 516 x 10-6 mol N m-2/h),
extent of inter-tidal area (<1 per cent to 50 per cent), and latitude (subtropical to subarctic). For the assessment methodology, 50 per cent of the NLEACH that is carried toestuaries by rivers is denitrified, and the ratio of N2O-N to denitrification (N2-N) emitted
is 0.005, as discussed above for rivers. NLEACH that enters estuaries but is not denitrified,is either buried in the sediments as organic nitrogen or exported to the continental shelfregion where additional N2O can be produced. Nitrous oxide production associatedwith this fraction of NLEACH is not accounted for in this methodology.

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In summary, the Phase II methodology assumes the following: 1) half of the NLEACH istransported to estuaries by rivers, 2) half of the NLEACH in estuaries is nitrified again in
the estuary with a ratio of N2O-N to NO3-N of 0.005, and 3) half of the NLEACH inestuaries is denitrified in the estuary with a N2O-N to denitrification (N2-N) ratio of
0.005. Therefore, N2O-N produced from NLEACH in estuaries = NLEACH x (EF5-e) where
EF5-e = 0.0025.
The combined emission factor [EF5] for N2O due to NLEACH in: 1) groundwater andsurface drainage (EF5-g = 0.015 kg N2O-N/kg NLEACH), 2) rivers (EF5-r = 0.0075 kg
N2O-N/kg NLEACH), and 3) coastal marine areas (EF5-e = 0.0025 kg N2O-N/kg NLEACH) is
0.025 (EF5). Therefore:
EQUATION 5
NLEACH = [NFERT + Nex] x FracLEACH and N2O(L) = NLEACH x EF5
where the default values are FracLEACH = 0.3 kg N/kg N input to soils and EF5 = 0.025 kg
N2O-N/kg NLEACH (see Tables 4-23 and 4-24).
C.
Human consumption followed by municipal sewage treatment
Nitrous oxide emissions from human waste are described below. However, these N2O
emissions are allocated to the Waste Chapter (see Section 6.4, Reference Manual andWorkbook).
Consumption of foodstuffs by humans results in the production of sewage. Sewage canbe disposed of directly on land (night-soil or spray irrigation) or discharged into a water
source (e.g., rivers and estuaries). Before disposal on land or into water, it also can beprocessed in septic systems or wastewater treatment facilities. During all of these stages,
nitrous oxide can be produced during nitrification and denitrification of sewage nitrogen.
Sewage nitrogen (NSEWAGE) production can be estimated from FAO per capita protein
consumption data (Protein) and human population counts (NrPEOPLE), assuming that
nitrogen constitutes about 16 per cent by weight of protein (FracNPR, Table 4-23).
EQUATION 6NSEWAGE = Protein x FracNPR x NrPEOPLE
Nitrous oxide emissions resulting from sewage nitrogen are estimated following: landdisposal or wastewater treatment of sewage, and input of sewage nitrogen to rivers andestuaries.
Disposal or wastewater treatment of sewage
No studies were found quantifying nitrous oxide emissions from land disposal of sewage,
although supersaturated concentrations of N2O in groundwater under cultivated land
irrigated with sewage effluent have been reported (Ronen et al., 1988). A few studies
have documented N2O emission associated with wastewater treatment operations (e.g.,
Hemond and Duran, 1989; Hanaki et al., 1992; Hong et al., 1993; Debruyn et al., 1994;
Czepiel et al., 1995).

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Three studies have directly measured N2O emissions from operating wastewater
treatment facilities (Hemond and Duran, 1989; Czepiel et al., 1995; Velthof and Oenema,1993). All studies reported low rates of N2O emission. For example, nitrous oxide
emissions from a secondary treatment wastewater facility in New Hampshire (USA) wereapproximately 0.0006 kg N2O-N/kg sewage N, assuming 3.2 kg sewage nitrogen are
produced/person/yr (Czepiel et al., 1995). Velthof and Oenema (1993) found N2O lossesof 0.022 kg/day per day in a vented closed waste water treatment facility that had a daily
input of 900 kg N, suggesting that N2O losses were 0.00005 kg/kg nitrogen entering thesystem.
Additional N2O released to the atmosphere following discharge ofsupersaturated effluent to the environment is also low (0.0007 kg N2O-N/kg sewage N)(Hemond and Duran, 1989). Laboratory studies simulating wastewater treatments
processes demonstrate that conditions in the treatment facility can affect the amount ofN2O produced, including the ratio of nitrate to oxidisable carbon and nitrogen loading
rate (Nogita et al., 1981; Hanaki et al., 1992). It is difficult to relate these laboratory
results to emissions from sewage treatment facilities. For example, in the laboratory
study of Nogita et al. (1981), 100 times more N2O-N was formed per unit of sewage
nitrogen than in the field study of Czepiel et al. (1995).
For the Phase II methodology N2O associated with sewage treatment and land disposal is
assumed to be negligible. This is based on the low emission rates of N2O reported for
operating wastewater treatment facilities (Hemond and Duran, 1989; Czepiel et al., 1995;
Velthof et al., submitted a;b), and the lack of information on N2O production from landdisposal of human sewage. This assumption should be reviewed in the future, as new data
become available.
Rivers and estuaries
N2O is produced in rivers and estuaries following nitrification and denitrification of
sewage nitrogen inputs (Seitzinger and Kroeze, in preparation). The sewage nitrogen canbe discharged directly to aquatic environments (e.g., rivers, estuaries) or enter aquatic
environments following leaching from terrestrially disposed sewage. Here it is assumed
that minimal removal of sewage nitrogen occurs during land disposal or sewage
treatment, and that all sewage nitrogen enters rivers and/or estuaries. This latterassumption should be reviewed in the future, as more data become available.
Nitrous oxide emissions in rivers and estuaries due to nitrification and denitrification of
sewage nitrogen are estimated using the same assumptions used for fertiliser nitrogenleached to rivers and estuaries (see B). These assumptions result in emission coefficientsof EF6–r = 0.0075 kg N2O–N/kg NSEWAGE (rivers) and EF6–e = 0.0025 kg N2O–N/kg
NSEWAGE (estuaries). The sum of N2O emissions in rivers (0.0075 x NSEWAGE) andestuaries (0.0025 x NSEWAGE) associated with nitrification and denitrification of NSEWAGE is
calculated as:
EQUATION 7
N2O(S) = NSEWAGE x EF6
where:
EF6

4 . 110=

0.1 kg N2O–N/kg NSEWAGE (Table 4-23)

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D.
Formation of N2O in the atmosphere from NH3
Dentener and Crutzen (1994) proposed that oxidation of NH3 and subsequent reactionof the intermediate NH2 radical with NO2 could lead to a production of 0.9 (+0.9+–0.4)
Tg N2O (0.6 Tg N/yr).
The most important reactions for N2O production are given by:
NH3 + OH
NH2 + NO2
NH2 + O3→→→

NH2 + H2O
R1
N2O + H2O
R2
NH2O + O2 (and other products) R3

The homogeneous reaction of NH3 with OH radical (R1) is rather slow, and is only ofimportance in regions with high OH and low sulphate aerosol concentrations. More than95 per cent of the global amount of NH3 oxidised by OH occurs between 30o N and 30o
S. The chemistry of the amine radical NH2 is not known, reactions R2 and R3 having
uncertainties of a factor of 2 (DeMore et al.,1994). In addition, emissions andconcentrations of NH3 and NO2 in tropical regions are poorly quantified.
Dentener and Crutzen (1994) parameterized natural NH3 emissions from vegetation
using a highly uncertain NH3 canopy compensation point (the atmospheric concentration
above which plants assimilate and below which they emit NH3). Without considering thiscompensation point, N2O production was reduced by 55 per cent. Other sources of
NH3 in the tropics include animal waste decomposition (both from wild and domestic
animals), fertiliser application and biomass burning emissions. Considering the relative
strengths of these sources, about half of the atmospheric N2O production may be
associated with agricultural nitrogen, amounting to about 0.4 Tg N2O/yr. Due to the highuncertainty of this estimate (ca. 100 per cent), we have not included this potentially
important source in our agricultural N2O emissions inventory. More measurements on
the co-occurrence of high NH3, NO2 and OH concentrations in the tropics are needed
to provide more insight in the photochemical production of N2O. Furthermore
laboratory experiments on the reaction rates, especially of reactions R2 and R3, would be
extremely valuable.
E.
Food processing operations
Some food processing operations are sources of N2O. A fraction of the edible crop
harvest is not consumed by people and enters the waste stream, for instance when it islandfilled, composted, burned or fed to animals. At this point, there are no data tocalculate the magnitude of this N2O source and therefore, there is no methodology at
the present time (For future purposes, this source would be reported under Industrial
Processes).

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METHODOLOGY FOR ESTIMATING INDIRECT N2O
Based on the above, we propose the following methodology for calculating a country's
indirect N2O emissions (kg N/yr):
EQUATION 8
N2Oindirect = N2O(G) + N2O(L) + N2O(S)where:
N2O(G)=

N2O produced from atmospheric deposition of NOx and NH3(kg N/yr);

N2O(L)=

N2O produced from nitrogen leaching and runoff (kg N/yr);

N2O(S)=

N2O produced from human sewage (kg N/yr) to be reported in
the Waste Chapter.

A.

Atmospheric deposition of NOx and NH3

Methodology:
EQUATION 9
N2O(G) = (NFERT x FracGASF + NEX x FracGASM) x EF4
where :
EF4=

emission factor for atmospheric deposition (kg N2O-N/kg NH3-N
and NOx–N emitted) (see Table 4-23);

FracGASF=

fraction of synthetic fertiliser nitrogen applied to soils thatvolatilises as NH3 and NOx (kg NH3-N and NOx–N/kg of N input)
(see
Table
4-19);

FracGASM=

fraction of livestock nitrogen excretion that volatilises as NH3 andNOx (kg NH3-N and NOx–N/kg of N excreted) (see Table 4-19).

NFERT

=

Nex

=

fertiliser nitrogen use in country (kg N/yr). Recommended source:
FAO data;
livestock nitrogen excretion in country (kg N/yr)(see Table 4-20).

Input:

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B.

Leaching and runoff

Methodology:
NLEACH=(NFERT + Nex) x FracLEACH

N2O(L)=NLEACH x EF5

FracLEACH=

fraction of nitrogen input to soils that is lost through leaching andrunoff (kg N/kg of nitrogen applied) (see Table 4-24);

EF5=

emission factor for leaching/runoff (kg N2O-N/kg N leaching/runoff)(see Table 4-23);

NLEACH=N leaching in country (kg N/yr).

NFERT

=

see A.

Nex=

see A.

where :

Input:C.

Sewage treatment (see Waste Chapter, Section 6.4)

Methodology:
EQUATION 10
NSEWAGE = PROTEIN x NrPEOPLE x FracNPR
N2O(S) = NSEWAGE x EF6
where:
EF6=

emission factor for sewage treatment (kg N2O-N/kg sewage-N
produced) (see Table 4-23);

FracNPR=fraction of nitrogen in protein (kg N/kg of protein) (see Table 424);

PROTEIN=annual per capita protein consumption in country(kg protein/person/yr). Recommended source: FAO;

NrPEOPLE=

number of people in country. Recommended source: FAO.

Input:

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Future WorkThe revised methodology for N2O described above is a generalised approach which
treats all agricultural systems as being the same under all climates, in all soils, in all crops
and in all management systems. This clearly provides uncertainties in inventory
calculations. However, the ranges of conversion factors provided should cover the
potential N2O emissions from each country, whatever climate, soils and set of crops isinvolved. To make significant improvement in inventory methodologies for N2O, the next
step is to utilise process-based models to produce country inventories. These would
include models of direct emissions from agricultural soils, appropriate animal management
models for N2O from animal production, simulation models which represent nitrogentransformations in aquatic systems, including riparian areas, wetlands, rivers estuaries,
continental shelves and the deep ocean.
Since soil carbon and nitrogen cycles are tightly integrated, both carbon and nitrogenshould be considered together so that various aspects of the carbon and nitrogen cycle
and CO2 and N2O production can be more accurately defined. For example, the amountof nitrogen leached from agricultural fields represents a very large component of the
global N2O production according to this revised methodology. The accuracy of thenitrogen leaching fraction prediction is closely tied to carbon turnover in the soil as it
controls nitrogen mineralisation and immobilisation. The turnover and retention of
nitrogen in all soils is intimately linked with the carbon cycle. Conversely, carbon
retention in soils is directly tied to mineral nitrogen availability.
There are additional issues that include: (1) development of methodologies that represent
the effect of cropping system, soil, and climate on CO2 and N2O budgets; (2) including
soil methane oxidation in national budgets (without the soil sink component, atmosphericmethane concentrations would be increasing about two times faster than the increase
rate observed in the 1980's); (3) including the impact of NOx emissions from agriculturalsoils on local and regional atmospheric oxidants and ozone concentration; (4) determining
the impact of carbon and nitrogen losses and retention on system sustainability; (5)considering mitigation methodologies to decrease CO2 and N2O emissions fromagriculture and to improve the soil sink capacity for CH4; and (6) investigating errors that
may arise as a result of aggregating field scale data to the national level.

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Appendix A
Estimates of Nitrous Oxide Emissions from Dung andUrine Deposits of Grazing Animal.
This appendix presents a brief summary of estimates of nitrous oxide emissions derived
from dung and urine deposits of grazing animals.

TABLE A-1
EMISSION OF N2O FROM ANIMAL DUNG AND URINE DEPOSITED IN GRASSLAND :THE AMOUNT OF N2O EMITTED IS EXPRESSED IN % OF THE AMOUNT OF N EXCRETED BY THE GRAZING ANIMAL.
Country

Soil Type

Treatment

PeriodN2 O
Emission

Reference

United Kingdom

clay loam

urine

4wks

1-5

Monaghan and Barraclough (1993)

New Zealandsilt loam

urine

6 wks

<0.5

Sherlock and Goh (1983)

Germany

loess

urine

11 wks

3.8

Flessa et al. (submitted)

Germany

loess

dung

11 wks0.5

Flessa et al. (submitted)

The Netherlands

clay

urine

4 wks

0.5

Velthof and Oenema (1994)

The Netherlands

peat

urine

3 wks

38

Koops et al. (unpublished)

The Netherlands

sand

urine

2 wks

8-16

De Klein and Logtestijn (1994)

United Kingdom

clay loam

grazing

1 wk

18

Velthof et al. (submitted a;b)

The Netherlands

sandgrazing

32 wks1.0

Velthof and Oenema (1995)

The Netherlands

clay

grazing

32 wks2.1

Velthof and Oenema (1995)

The Netherlands

peatgrazing

32 wks1.5Velthof and Oenema 1995)

The Netherlands

peatgrazing

32 wks7.7Velthof and Oenema (1995)-

urine/dung

1 yr

0.4-1.3

The Netherlands

sandgrazing

2 yrs

1.5

Velthof et al. (submitted a;b)

The Netherlands

clay

grazing

2 yrs

3.3

Velthof et al. (submitted a;b)

The Netherlands

peatgrazing

2 yr

2.3Velthof et al. (submitted a;b)

The Netherlands

peatgrazing

2 yrs

9.8

Velthof et al. (submitted a;b)silt loam

grazing

1 yr

0.2-1.0

Carran et al. (1995)

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Germany

New Zealand

Poggemann et al. (1995)

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