Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories

I NDIR EC T N 2 O EMI SS ION S FROMAGR ICU LTUR E
A CK NO WL E D GEM EN T S
This paper was written by Cindy Nevison with the support of ICF Kaiser Incorporated. Cindy Nevison. would
like to thank Peter Groffman, Sybil Seitzinger, Carolien Kroeze, Martin Schmid, Jeff Smith, and all members of
the Wageningen expert subgroup on indirect N2O emissions for their helpful comments.

ABSTRACTAgricultural perturbations to the global nitrogen cycle, directly and indirectly, lead to enhanced biogenic
production of nitrous oxide (N2O). Direct pathways include microbial nitrification and denitrification of fertiliser
and manure nitrogen that remains in agricultural soils or animal waste management systems. Indirect pathways
involve nitrogen that is removed from agricultural soils and animal waste management systems via volatilisation,leaching, runoff, or harvest of crop biomass. Like their direct counterparts, the long-term fate of agricultural
nitrogen also eventually provides substrate for microbial nitrification and denitrification, with associated N2O
production. According to the Revised 1996 National Greenhouse Gas Inventories (IPCC Guidelines,) andMosier et al., 1998), indirect N2O emissions account for one third of the total global agricultural N2O source andapproximately two thirds of the uncertainty in the total source. Indirect emissions include small contributions
from human sewage and volatilised nitrogen, but are derived predominantly from nitrogen lost through leachingand surface runoff. Because of their importance in defining both the magnitude and the uncertainty of the
agricultural N2O source, leaching/runoff emissions deserve high priority in any consideration of “good practice”
in the IPCC methodology.
Three major areas of uncertainty in estimating leaching-related N2O emissions are identified in this report.
Firstly, the entire amount of fertiliser and manure, including that assumed to be volatilised and burned as fuel issubject to a default leaching fraction of 0.3. Secondly, under current practices, this default leaching fraction iscommonly used by all countries, despite large variations within individual watersheds and agricultural systems.
Finally, the N2O emission factor assigned to leached nitrogen is estimated from a 3-step derivation which tracks
the leached fraction through groundwater, rivers and estuaries, and broadly assumes some microbial N2O
production at each step on the basis of limited information. The groundwater step, which currently accounts for
60 percent of leaching-related N2O emissions, is particularly problematic. In re-evaluating leaching/runoffrelated N2O emissions, all of these areas of uncertainty should be addressed.
The volatilisation N2O source in theory is meant to represent the fraction of fertiliser and manure that volatilises
to NOx and NH3 soon after application/deposition and subsequently redeposited on nearby soil, providing
substrate for nitrification and denitrification. In practice, the current methodology formulation is fairly
insensitive to assumptions about the volatilised fraction of fertiliser and manure. This is true because the direct
and volatised N2O emission factors are essentially the same (0.0125 and 0.01, respectively). Thus a re-evaluationof the default volatilisation fractions probably is not a first priority in refining the methodology. One question
with respect to the volatilisation source might be, whether the distinction between 0.0125 and 0.01 is meaningful
and is meant to be so.
Unlike leached and volatilised nitrogen, which are intricately linked to the direct and animal emissions
methodologies, sewage nitrogen is estimated from independent activity data. The independence of the sewage
nitrogen calculation is both a strength and a weakness of the current methodology. While cross-checks based on
independent inputs are useful for validation purposes, one of the original goals of the methodology was to track
agricultural nitrogen from “cradle to grave” in an internally consistent manner. Future refinement of themethodology might involve consistently linking harvested crop biomass to the long-term fate of sewage
nitrogen, food waste, animal fodder and manure.
Quality assurance (QA) and quality control (QC) activities should encourage the collection of more countryspecific information to estimate the various fates of agricultural nitrogen and its associated N2O emission factors.
Because these data are sparse and likely to remain so in the near future, QA/QC efforts should also consider
independent methods for validating methodology estimates. Two independent methods include the approach of
Seitzinger and Kroeze (1998) for estimating nitrogen loading to rivers, and semi-empirical gas transfer
calculations, in which N2O flux from estuaries is estimated based on observed surface supersaturation of N2O
and modelled gas-transfer coefficients. When compared to the methodology estimates, the former would be
useful for validating the estimated amount of leached nitrogen and the latter would be useful for validating N2O

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emissions from estuaries. Gas-transfer calculations are probably best performed by an expert group rather thanby individual Parties.
The methodology is based on widely available fertiliser, livestock population, human population and protein
consumption activity data that are reported on a country-by-country basis to the United Nations Food andAgricultural Organization (FAO). The FAO data contain their own inherent uncertainties, and the inventory
agency should ensure the accuracy of these inputs as well as the compiled inventory. The greatest uncertainty,
however, in the indirect N2O emissions estimate more likely stems from the methodology's detailed, multi-step
assumptions about the fate of agricultural nitrogen and associated N2O emission factors. In the case of Parties
replacing default partitioning factors with country-specific information with respect to the fate of agricultural
nitrogen, care must be taken that internal consistency of the methodology is maintained. Because of the complex
logic of the methodology, the potential for omitting or double-counting some sources of N2O production issignificant.
Currently, insufficient information exists to evaluate the success of individual Parties in using the IPCC indirectemissions methodology. This is due, to a large extent, to the inadequacy of the reporting table in the IPCC
Guidelines. Direct and most indirect emissions from the agricultural sector are lumped into one line called“Agricultural Soils.” This label is a misnomer with respect to indirect emissions, since approximately 85 percent
is estimated to come from groundwater, rivers, and estuaries. Some additional indirect agricultural N2O
emissions are reported in different sectors, including energy, waste, and land-use change. The dispersal of theindirect source among various sectors again illustrates the need for care in maintaining the methodology’s
internal consistency and for communication between inventory preparers.

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1

INTRODUCTION

1.1

Nature, magnitude, and distribution of source

1.1.1

Overview of N 2 O emissions

Atmospheric N2O is increasing at a rate of 0.2-0.3 percent/yr. This suggests an anthropogenic N2O source about
50 percent as large as the natural microbial source from soils and oceans. Enhanced microbial N2O production
associated with agricultural perturbations to the nitrogen cycle accounts for an estimated 75 percent of thisanthropogenic source. Biomass burning, which is closely tied to agriculture, supplies another ~7 percent, anddirect industrial N2O production contributes the remainder (IPCC, 1997). Natural and agricultural N2O sources
are not always easy to separate. Both are microbial in nature, and agricultural N2O production to some extent has
supplanted natural N2O production (Mosier et al., 1998). The 1997 estimate based on the IPCC Phase II
methodology suggests that, out of a total agricultural source of 6.3 Tg N/yr, 0.9 Tg N/yr overlaps with/replaces
natural N2O production in soils and oceans.

1.1.2

Need for an indirect N 2 O emissions category

Estimates of the agricultural N2O source in the early 1990s were based on global extrapolations of N2O emission
factors measured in fertilized fields. Because these measurements captured mainly direct short-term N2Oemissions, the resulting global estimates were often relatively small, ranging from 0.01 to 2.2, with mean values
generally less than 1 Tg N/yr [Eichner, 1990; IPCC, 1990; Matthews, 1994]. These estimates suggested that
fertiliser might be a modest or even relatively small source of the observed atmospheric N2O increase.
Increasingly, however, researchers began noticing elevated concentrations of dissolved N2O in drainage ditches,groundwater, rivers and estuaries contaminated by agricultural and sewage nitrogen, leading many to suggestthat indirect N2O emissions associated with agriculture may be just as important as direct emissions (Dowdell etal., 1979; Ronen et al., 1988; Minami and Oshawa, 1990; Seitzinger and Kroeze, 1998). With this new
perspective, recent N2O inventories, which consider both short and long term fates of indirect agricultural
nitrogen, have concluded strongly that agriculture is the dominant contributor to the anthropogenic N2O source(IPCC, 1997).

1.1.3

N 2 O production processes

N2O production occurs primarily via microbial nitrification and denitrification. Nitrification is the aerobic
oxidation of ammonium to nitrate, a process, which commonly accompanies the release (mineralization) of
ammonium from organic matter during decomposition and contributes to the internal recycling of nutrient
nitrogen. Denitrification is the anaerobic reduction of nitrate to molecular dinitrogen gas, a process, which
accounts for the major loss of fixed nitrogen from soils and oceans. Nitrous oxide is an obligate intermediate indenitrification, and often comprises 5 percent or more of the denitrification end product in soils. N2O is also
produced during nitrification, although by a less well understood mechanism. In normal oxygenatedenvironments, N2O generally accounts for <1 percent of the nitrification end product in soils. The fractional N2O
yield has been extensively studied in soil environments. It depends on a large number of variables includingorganic carbon availability, O2 partial pressure, soil moisture content, pH, and temperature (Bouwman et al.,1993). Because of these multiple variables, the average soil N2O yield is still highly uncertain, especially fromdenitrification.
Most indirect agricultural N2O production likely occurs in aquatic environments such as groundwater, rivers andestuaries, where much of the nitrogen lost from agricultural land through leaching, runoff, crop harvest andhuman consumption ultimately ends up. Measurements of fractional N2O yields are sparse in aquatic
environments, although the yields appear to be governed by many of the same variables described for soils. In
rivers and estuaries, N2O may be produced by nitrifiers and denitrifiers both in bottom sediments and in thewater column. Commonly, a uniform yield of 0.5 percent for both nitrification and denitrification has been
assumed for such environments (Mosier et al., 1998; Seitzinger and Kroeze, 1998).

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1.2

The current state of inventory methodologies

The IPCC Guidelines describe a comprehensive method, using widely available input data, which attempts toaccount for all N2O emissions, both direct and indirect, associated with agriculture. The IPCC Guidelines
encourage country-specific measurement programmes, particularly for tropical and developing countries, but
provide default emission factors. Given the many detailed steps of the methodology, most Parties appear to beusing the default values. The multi-step detail, however, is important for understanding the logic behind themethodology and as a starting point for revision and improvement.
The IPCC Guidelines divide the agricultural N2O source into 3 categories: direct emissions from agriculturalland, emissions from animal waste management systems, and indirect emissions associated with N that isvolatilised, leached, removed in biomass, or otherwise exported from agricultural land. Each of these 3
categories is estimated to contribute one third each to the total estimated agricultural source. Indirect emissions,however, account for a disproportionate share (approximately two thirds) of the uncertainty in the total source(Table 1), in which uncertainty is quantified mainly according to the range in the estimated N2O emission factors(see discussion below of EF4 and EF5). Thus, defining good practice for estimating indirect N2O emissions will
go a long way toward narrowing the uncertainty in the total agricultural N2O emissions inventory.

TABLE 1
GLOBAL N2O EMISSIONS CALCULATED WITH THE IPCC GUIDELINES (TG N Y-1)
Direct soil emissions• subtotal

2.1 (0.4-3.8)

Animal production• subtotal

2.1 (0.6-3.1)

Indirect emissions• atmospheric deposition

0.3 (0.06-0.6)• nitrogen leaching and runoff

1.6 (0.13-7.7)• human sewage

0.2 (0.04-2.6)• subtotal

2.1 (0.23-11.9)

Total

6.3 (1.2-17.9)*values in parentheses indicate estimate range which is derived from the emission factor ranges.

The indirect emissions category consists in theory of 5 different sources:(i) Volatilisation and subsequent atmospheric deposition of NH3 and NOx (N2O (G))(ii) Nitrogen leaching and runoff (N2O (L))(iii) Human consumption of crops followed by municipal sewage treatment (N2O(S))(iv) Formation of N2O in the atmosphere from NH3(v) Food processing.
In practice, sources D and E are not included in the methodology due to lack of information. Total indirectemissions are calculated as,
EQUATION 1
N2O INDIRECT= N2O(G) + N2O(L) + N2O(S)Of the 3 contributing sources, N2O(L) accounts for over 75 percent of estimated indirect emissions, as shown in
Table 1. In the methodology, N2O(G) and N2O(L) are closely linked to and dependent on assumptions about thefate of fertiliser and manure, while N2O(S) is calculated from independent activity data.

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2

METHODOLOGICAL ISSUES

2.1

Selection of the estimation method

The IPCC Guidelines outline a method for estimating indirect N2O emissions from agricultural based on widely
available fertiliser, crop production, human population, and livestock population and management data reported
to the FAO. The guidelines involve factors which partition agricultural nitrogen into different various fates, suchas leaching, removal from the field in crop biomass, and volatilisation, and which assign N2O emission factors toeach fate. Hereafter, these are referred to as partitioning factors and emission factors, respectively. Among 34
countries reporting greenhouse gas emissions from agricultural soils before August, 1998, 12 used the simpler
1995 IPCC Methodology, 7 used the IPCC Guidelines described below with default factors, 7 used countryspecific factors, 2 used a mix of methods, and 6 provided no information about which method they used (Table
1, UNFCCC 1998/7). Note that the United Nations Framework Convention on Climate Change (UNFCCC)
report did not partition agricultural soils by greenhouse gas (although presumably N2O is the dominantcomponent), nor did it partition N2O into direct and indirect emissions. Hence the usefulness of these statistics interms of assessing the indirect N2O methodology is unclear.

2.2

Science and logic behind factors and equations

2.2.1

Volatilisation and subsequent atmospheric deposition of
NH 3 and NO x

N2O(G) accounts for manure and fertiliser nitrogen that volatilises as NOx or NH3 soon after application to soil,
but subsequently redeposits on soil, providing nitrogen substrate for nitrifiers and denitrifiers. Model andmeasurement studies indeed suggest that most volatilised agricultural nitrogen simply redeposits on nearby soil.

EQUATION 2
N2O(G) = (NFERT ● FRACGASF + NEX ● FRACGASM) ● EF4
Where:FRACGASF: partitioning factor for the fraction of synthetic fertiliser N applied to soils that volatilises
as NH3 and NOx (Default = 0.1)
FRACGASM: partitioning factor for the fraction of livestock N excretion that volatilises as NH3 andNOx. (Default = 0.2)
NFERT:

synthetic fertiliser use in country from Food and Agriculture Organisation (FAO) data
(kg N/yr)NEX:amount of N excreted by livestock (kg N/yr). Calculated from FAO livestock populations
and N excretion/animal data (Mosier et al., 1998)

EF4:

emission factor for atmospheric deposition

Default partitioning factors assume 10 percent (FRACGASF) of synthetic fertiliser nitrogen and 20 percent(FRACGASM) of manure nitrogen are volatilised. The higher value assumed for manure reflects the greater
likelihood of NH3 volatilisation from urea. The volatilised fractions are then assumed to redeposit and areassigned an emission factor EF4 of 0.01, on the basis of a limited number of studies of N deposition on soils(Bowden et al., 1991; Brumme and Beese, 1992) (see Table 2). (Note, these were generally forest soils receiving
nitrogen deposition generated by energy use and industrial activities.) The default value of EF4 is very similar toEF1 =0.0125, the direct emission factor from agricultural land. EF1 was derived from a linear regression
analysis of a much more extensive body of available N2O measurements from fertilized fields (Bouwman, 1996).

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Interestingly, if no volatilisation of fertiliser and manure nitrogen were assumed, this nitrogen would be subject
to the very similar direct emission factor EF1 rather than EF4. The uncertainty in total agricultural N2O
emissions therefore appears fairly insensitive to FRACGASF and FRACGASM, barring revisions in anddivergence of the values of EF1 and EF4. Total emissions would, in fact, be completely insensitive, if EF1 were
simply rounded off to 1 rather than set at 1.25. (Question: Is 3-significant-figure precision justified for aparameter that has a ± 80 percent uncertainty). One area for future improvement might involve evaluating
whether the distinction between EF1 and EF4 is meaningful and intended or an artefact of the increased
precision of EF1. Perhaps EF4 should simply be set equal to EF1, assuming a large fraction of volatilised
agricultural nitrogen redeposits on nearby agricultural land rather than forest soil. A second area for future
improvement might involve accounting for microbial N2O emissions associated with other sources ofatmospheric NOx and NH3 deposition, such as fossil fuel combustion. Such emissions should be assigned to thecountry which originates rather than receives the volatile nitrogen, as is currently done for agricultural NOx andNH3.

TABLE 2SUMMARY OF DEFAULT EMISSION FACTORS RELEVANT TO INDIRECT N2O EMISSIONS
FactorDescription

kg N2O-N/kg N input

Derivation

EF1

direct emissions

0.0125

Linear regression of large number ofmeasurements from agricultural soils (Bouwman,
1996)(0.0025-0.0225)
EF4

volatilisation/deposition
emissions0.01 (0.002-0.02)

estimated from small number of measurementsfrom forests (Mosier et al., 1998)

EF5

leaching/runoff emissions

0.025 (0.002-0.12)

estimated from 3-step derivation tracking leachednitrogen through groundwater, rivers, and estuaries(Mosier et al., 1998)

EF6

sewage emissions

0.01 (0.002-0.12)

Same as EF5, but assuming no groundwater phase

2.2.2

Nitrogen leaching and runoff

N2O(L) represents N2O production by nitrification and denitrification of agricultural nitrogen that is lost from thefield through leaching and runoff into groundwater, drainage ditches, rivers, and finally estuaries.

EQUATION 3
NLEACH = (NFERT + NEX) ● FRACLEACH
N2O(L) = NLEACH ● EF5
Where:FRACLEACH: partitioning factor for the fraction of fertiliser and manure N applied to soils that is lost
through leaching and runoff. Default = 0.3 (0.1-0.8)
EF5:

emission factor for leaching/runoff
EF5-g (groundwater = 0.015)+EF5-r (rivers = 0.0075)+EF5-e (estuaries= 0.0025)

Note that all fertiliser and animal waste (i.e., NFERT + NEX), even that assumed to be volatilised or burned, ismultiplied by FRACLEACH.
N2O (L) is by far the major component of N2OINDIRECT and is one of the major sources of uncertainty in theentire agricultural N2O emissions estimate (Table 1). Hence, narrowing the uncertainty in the agricultural N2O
source requires careful re-evaluation of the assumptions used to derive N2O(L) and consideration of independent
methods that might be used to validate the N2O(L) estimate. The uncertainties in N2O(L) are threefold. They
involve uncertainties in the nitrogen inputs, NFERT+NEX, in the partitioning factor FRACLEACH, and in the
N2O emission factor EF5. The entire nitrogen input from fertiliser and manure is multiplied by FRACLEACH.
In contrast, in the direct emissions calculation, NFERT and NEX are scaled down by various partitioning factors

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before multiplication by EF1. The true amount of nitrogen subject to leaching is uncertain, since the value of
FRACLEACH derived for agriculture may not be appropriate for all fates of N. For example, a large fraction of
the nitrogen content of animal waste burned as biofuel may be pyrodenitrified to atmospheric N2 (Crutzen and
Andreae, 1990).

2.2.2.1

FRACLEACH

In contrast to FRACGASF and FRACGASM, the total agricultural N2O emission estimate is highly sensitive tothe assumed fraction (FRACLEACH) of synthetic fertiliser and manure lost to leaching and runoff. Thissensitivity results from the fact that the emission factor EF5 =0.025 associated with leached nitrogen is twice aslarge as the direct emission factor EF1 =0.0125 from agricultural fields. Indeed, Monte Carlo simulations
confirm that FRACLEACH is one of the major uncertainties in the total N2O estimate (Mosier et al. 1998).
(Note, the sensitivity of the methodology to FRACLEACH may decrease if EF5 is lowered -see discussion
below).
In known cases in which country-specific values of FRACLEACH have been used, lower values of 0.15-0.2
have been substituted for the current default of 0.3, leading to lower total agricultural N2O emissions (M.
Schmid, Switzerland, private communication; R. Pipatti, Finland, private communication; K Rypdal, Norway,
private communication, E. Rasmussen, Denmark, private communication, S. Jarvis, U.K., private
communication, J. Smith, U.S.A., private communication; UNFCCC/SPSTA/1998/7 (for New Zealand)). Whilethese country-specific values may well be based on good science and extensive measurements, in only one case
(Switzerland) was sufficient documentation provided for this author, acting as an independent reviewer, toevaluate the appropriateness of the country-specific value (M. Schmid, private communication).
The Swiss value was based on a compilation of N leaching values (in kg N/ha/y) for various crops measured in
Switzerland by lysimeters located just below the main rooting zone (Prasuhn and Braun, 1994). For each crop, asomewhat subjective average leaching value was taken and multiplied by the area (in ha) covered by that crop to
calculate the total N leached. This sum was then divided by the total N input to agriculture from fertiliser,sludge, compost, and animal waste, yielding a value of 0.2 for FRACLEACH (although one could easily havechosen different averages to yield a FRACLEACH of 0.3). By way of validation, the averages of Prasuhn andBraun were used to estimate N loading in various Swiss rivers. These estimated N loadings generally comparedwell to observed N loadings, although the measured loadings were subject to large uncertainties. A further
uncertainty in the comparison was that the N leaching inputs were reduced by 15-25 percent to account for
reductions in N concentration that had been observed to occur between the root zone and groundwater fromgrassland and arable land through which cultivated fields drain. However, these reductions may not account for
further N removal that occurs in the riparian zone between groundwater and rivers (Groffman et al., 1999). The
Swiss example, which was by far the most thoroughly described FRACLEACH calculation available to thisauthor, suggests the need for caution and clear guidelines before accepting country-specific values of
FRACLEACH.
The current FRACLEACH default of 0.3 was based largely on the general knowledge of the expert group that
met in Geneva in 1995, and the range of 0.1-0.8 was justified on the basis of the global-scale modelling study of
N loading in rivers by Seitzinger and Kroeze, 1998. Otherwise, this default is not documented in Mosier et al.,1998. To critically examine the current default, I reviewed 6 specific case studies in which the inputs and outputsof agricultural N were explicitly measured at the watershed level over a number of years and a mass balance for
N was constructed (Keeney and DeLuca, 1993; Randall and Iragavarapu, 1995; Weed and Kamwar, 1996; Davidet al., 1997; Randall et al., 1997; Steinheimer et al., 1998). (All these studies took place in the Midwestern U.S.,
generally in maize and/or soybean fields underlain by drainage tiles, which have been shown to increase leaching
to rivers.) In these studies, the inorganic nitrogen loading in nearby rivers was typically equivalent about 20
percent of N inputs. Some variation was found between till and no-till systems and between crop types (deeprooted crops tended to reduce leaching loss), but by far the most significant factor determining interannual
variability in leaching loss was precipitation. Low leaching and accumulation of inorganic soil N tended to occur
during dry years, followed by large leaching losses in subsequent wet years. In one study, the fraction of N
inputs leached ranged from 3-70 percent, depending on interannual variability in rainfall (Weed and Kanwar,
1996).

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While the above discussion might suggest a value of 0.2 for FRACLEACH, a few cautionary notes are in order.
First, these mass balance studies were somewhat inconsistent in their definition of N inputs and outputs. Somestudies considered N2 fixation and mineralization of crop residue as explicit inputs, while others ignored N2
fixation and assumed that mineralization of last year’s crop residue was simply balanced by uptake of N into thecurrent crop stover. Moreover, lumping maize and soybean (an N2 fixer) together, results in a larger crop uptake
efficiency (>60 percent) for N inputs than the efficiency (<50 percent) that would be calculated if maize wereconsidered separately (NRC, 1993; David et al. 1997).
Secondly, several studies found that NO3- concentrations in rivers were not necessarily correlated over time withfertiliser and animal waste inputs to nearby fields. These studies concluded, rather, that cultivation and tillage ofsoil, with or without fertiliser input, may enhance the rate of soil organic N mineralization, leading to large
leaching losses (Keeney and DeLuca, 1993; David et al., 1997). Note that the IPCC currently does not consider
this enhanced-mineralization source of leached N. Third, while ~20 percent of N inputs tended to end up inrivers, often, an additional ~30-40 percent of N inputs was unaccounted for (Keeney and DeLuca, 1993; Randalland Iragavarapu, 1995; David et al., 1997; Steinheimer et al., 1998). A variety of fates were suggested for this“missing” N, including denitrification, volatilisation to NH3 or other reactive N gases (including through plantleaves), leaching into groundwater, and loss in the riparian zone. Note that these latter two fates would fall underthe IPCC definition of NLEACH, and would imply that FRACLEACH should be greater than 0.2. Finally, theabove studies do not consider organic N, which may constitute a significant fraction of total leached N(Seitzinger and Kroeze, 1998). Since FRACLEACH in theory encompasses total inorganic + organic N, studies
that consider only inorganic N may underestimate the true amount of N leaching.

2.2.2.2

EF5

The derivation of EF5, the leached nitrogen N2O emission factor, involves a multi-step set of assumptions of
nitrification and denitrification in groundwater and rivers and subsequent (de)nitrification in estuaries. The logic
runs as follows: All of NLEACH enters groundwater or drainage ditches, where a fraction EF5-g =0.015 (0.0030.06) is lost to N2O within one year. EF5-g is based on a compilation of observed N2O/ NO3- ratios ingroundwater and drainage ditches (Mosier et al., 1998). All of NLEACH then continues into rivers, where all isnitrified once during river transport and half is denitrified, i.e., lost to the atmosphere, by denitrification in river
sediments. An N2O yield of 0.005 is assumed for both nitrification and denitrification, resulting in a river N2Oemission factor EF5-r of 0.0075. The surviving half of NLEACH ultimately flows into estuaries, where half isnitrified and half is denitrified. Again, (de)nitrification N2O yields are both assumed to be 0.005, resulting in an
estuary N2O emission factor EF5-e of 0.0025.
The assumption of 0.015kgN2O/kgN for EF5-g is based on literature search of 6 studies, in which the ratio of
N2O/ NO3- in groundwater was found to range typically from 0.007 to 0.02 (Mosier et al., 1998 and references
therein). The ratio in ditch water was found to be generally lower, i.e., 0.003 or less. This author’s own review of
4 out of 6 of the cited papers and one other paper (see Table 3) shows lower yields of .0002-.0044 (groundwater)and 0.0005-0.01 (drainage ditches) and no strong difference between groundwater and drainage ditches (Dowdell
et al., 1979; Ronen et al., 1988; Minami and Oshawa, 1990; Ueda and Ogura, 1991; Muehlherr and Hiscock,1997). On the basis of Table 3, a value of 0.001 (0.0002-0.01) seems more appropriate for EF5-g than 0.015.
The observed N2O/NO3- ratio in groundwater should be distinguished from that in the ocean. In ocean depth
profiles, N2O, NO3- and O2 utilization are highly correlated, suggesting N2O production associated with aerobic
mineralization and nitrification (Yohinari, 1976; Cohen and Gordon, 1979). In groundwater, however, N2O
generally is not well correlated to O2 utilization (Ueda and Ogura, 1991), implying that the observed N2O/ NO3ratio cannot be interpreted as the N2O yield of in situ nitrification, as has been done in ocean analyses. In fact,
Ronen et al. 1988 conclude that most NO3- in groundwater is not produced in situ. Despite this caveat, theobserved N2O/ NO3- ratio in groundwater currently may be the best available parameter for linking N2O toleached N.

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TABLE 3
SUMMARY OF DEFAULT EMISSION FACTORS RELEVANT TO INDIRECT N2O EMISSIONS
Referenc

Study Location

N2O/NO3-

ContaminantsComments

England0.01 (month after
fertilization)

Fertiliser

N2O shown as bars, NO3 ascurves on a very hard-to-readlog scale graph

Drainage Ditches
Dowdell et al. 1979

0.01-0.001 (othermonthsMinami and
Oshawa, 1990

Japan

0.0005-0.001

Fertiliser

Ronen et al., 1988

Israel

0.002-0.003

Fertiliser and
Sewage,extremelycontaminatedUeda and Ogura,
1991

Japan

0.0002-0.0044

SewageMuelherr andHiscock, 1997

EnglandGroundwater
ratio of 0.06 cited in Mosier
et al., 1998 is actually ratioof observed N2O:estimatedNO3 produced in situ
13 wells < 0.001
3 wells > 0.001
0.0005-0.0025

Fertiliser

I assumed NO3 is reported as
mg NO3/L, as written. If
actually mg N/L, then ratio is0.0001-0.0006

There may have been some confusion in the interpretation of Ronen et al. (1988), on the source of the highest
cited groundwater N2O/ NO3- ratio of 0.06. Ronen et al. estimated the rate of in situ mineralization/nitrification
based on organic C input to the aquifer, and then took the ratio of observed N2O to the estimated fraction of NO3produced in situ. The N2O/in situ NO3- ratio is considerably higher than the actual observed N2O/total NO3ratio, which was only 0.002-0.003, even in the very contaminated aquifers they studied.
The derivation of EF5 in the IPCC Phase II methodology was a courageous first attempt to estimate the potential
N2O production associated with leached agricultural nitrogen. Each step of the 3-step derivation involves roughgeneralizations and assumptions based on limited information. One assumption that bears particular scrutiny isthat all of NLEACH experiences a groundwater or drainage ditch phase, sufficient for 0.015kg N2O -N/kg
NLEACH to be converted to N2O. Note that EF5-g accounts for 60 percent of the magnitude of EF5. All of
NLEACH is assumed to survive the groundwater phase and subsequently to enter rivers. In other words, all N2O
observed in groundwater and agricultural drainage ditches is assumed to be produced by nitrification. However,Minami and Oshawa (1990) found that N2O in drainage ditch water may have been derived partly from sediment
denitrification, and Groffman et al., 1999 suggest that significant additional N losses may occur in the riparianzone between groundwater and rivers. Furthermore, the assumption of annual turnover of nitrogen in
groundwater neglects deep aquifers, which may act mainly as a long-term sink for leached N.
EF5, as described above, in which groundwater is treated as a chimney which emits 60 percent of the N2O
associated with leached N, may be conceptually inconsistent with FRACLEACH, as derived from the massbalance studies described in Section 2.2.2.1. These studies generally quantify the fraction of leached N by
dividing N loading in rivers by agricultural inputs. Often, a large fraction of leached N appears to be channelled
more or less directly to rivers, bypassing the groundwater phase. When groundwater is considered in these massbalance studies, it is often mentioned mainly as a sink for the 30 percent or more of agricultural N inputs that
otherwise cannot be accounted for. To be more conceptually consistent with FRACLEACH, the IPCC
methodology should consider defining emission factors which distinguish between water-borne agricultural N
that flows directly into rivers versus drains through groundwater and riparian zones. In the latter case, theamount of NLEACH should be reduced to account for N removal that occurs before the river stage. This
discussion suggests that a uniform EF5 may not be appropriate for all leached agricultural N and may create themisleading impression that leaching-related N2O emissions occur primarily from groundwater. For example,

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Seitzinger and Kroeze’s estimated emission (primarily anthropogenic) of ~2 Tg N2O-N/yr from rivers, estuaries,
and coastal areas, might be extrapolated on the basis of the current EF5 to suggest an additional 3 Tg N2O-N/yrfrom groundwater. This would be difficult to reconcile with the current understanding of the N2O source and theconstraints imposed by the observed atmospheric increase (see discussion in Section 2.7).

2.2.3

Human consumption of crops followed by municipal
sewage treatment

N2O emissions associated with human sewage are reported under the Waste Sector rather than the Agricultural
Sector (IPCC Guidelines: Reporting Instructions, Tables 4 and 6). However, human sewage ultimately is derived
from agricultural nitrogen. Accordingly, the scientific basis for sewage N2O emissions was developed by the
agricultural working group and is discussed briefly below. The methodology does not consider direct N2Oemissions from sewage treatment plants. This decision was based on three studies that measured fairly negligible
N2O emissions from operating wastewater treatment facilities (Hemond and Duran 1989; Czepiel et al. 1995;
Velthof and Oenema 1993). The methodology does consider crop nitrogen that ends up as human sewage inrivers and estuaries, where it provides substrate for nitrification and denitrification. Unlike the leached andvolatilised fractions of fertiliser and manure nitrogen used to calculated N2O(L) and N2O(G), microbial N2O
production associated with human sewage is calculated from activity data that are independent of the direct andanimal emissions calculations. Sewage nitrogen is estimated based on protein consumption per capita multipliedby human population, with an assumed 16 percent N by weight of protein.

EQUATION 4NSEWAGE = PROTEIN ● FRACNPR ● NRPEOPLE
N2O(S) = NSEWAGE ● EF6
Where:
EF6:

emission factor for sewage nitrogen

FRACNPR:

0.16kg N/kg of protein

NRPEOPLE: human population from FAO data
PROTEIN:annual per capita protein consumption from FAO data (kg/person/yr)

The N2O yield (EF6) of sewage nitrogen is based on a subset of the same assumptions that go into determining
the leaching and runoff N2O yield. The main difference is that sewage N is assumed to be discharged directly torivers, bypassing the groundwater phase, thus reducing EF6 to 0.01 versus 0.025 for EF5. The sewage N2O
source is a fairly minor (~10 percent) contributor to total indirect emissions. Questions: Is the assumption of no
groundwater phase universally applicable? In some countries, might not some portion of sewage effluent end up
in groundwater, e.g., via septic tanks (Ronen et al., 1988; Ueda and Ogura, 1991). Second, could the estimate of
NSEWAGE somehow be linked to the crop N biomass assumptions used to calculate direct N2O emissions, thus
helping to validate and ensure internal consistency within the methodology (see further discussion underCompleteness, section 2.6). Finally, should the methodology consider removal of nitrogen in wastewater
treatment?

2.3

Default versus country-specific factors

The accuracy and precision of N2O emission factors are correlated to the number of samples and the frequency
of sample collection. Because of limited sampling, even on a global scale, countries often use default factors thatare based largely on studies of temperate agriculture. Emissions factors for N2O in aquatic systems are
particularly sparse in tropical regions. In terms of temporal variability, measurement of N2O dissolved inagricultural drainage ditches and groundwater is especially important soon after fertiliser application, sinceconcentrations may change by a factor of 10 or more over an annual cycle (Dowdell et al., 1979). Although
regional, seasonal, and crop-specific emission factors are desirable, the large range of agricultural systems inmost countries and the difficulty of establishing continuous or periodic monitoring programmes may beprohibitive to obtaining such data. Among the 34 countries that reported greenhouse gas emissions fromagricultural soils, 13 used default emission factors, 9 used country-specific factors, 3 used a mix, and 9 provided
no information about which factors were used (Table 2, UNFCCC 1998/7). Again, agricultural soils are not390

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partitioned in the UNFCCC report by greenhouse gas or by direct versus indirect emissions and the relevance of
these statistics to indirect N2O emission factors is unclear.
In addition to N2O emission factors, the methodology contains a number of nitrogen partitioning factors,
including FRACLEACH, FRACGASM, and FRACGASF. As discussed earlier, total agricultural N2O emissions
are relatively insensitive to the assumed volatilisation fractions, but highly sensitive to the fraction of nitrogenassumed leached from agricultural soils and animal waste management systems. The UNFCCC 1998/7 report
does not provide detailed information about whether default or country-specific partitioning factors are currently
being used. New Zealand was cited as one Party, which used a country-specific leaching factor of 0.15, which isonly half as large as the default factor of 0.3.

2.4

Activity data

Current activity data used to calculate indirect N2O emissions include commercial synthetic fertiliser
consumption, livestock and poultry populations, data on animal waste management, crop production, partitioned
into regular and nitrogen-fixing crops, grazing animal wastes, human population, and per capita protein
consumption. The above inputs are generally available from UN/FAO yearbooks. Additional activity data that
may be useful for estimating the leaching partitioning factor include data on river discharge and water runoff(Caraco and Cole, 1998). Factors used to convert activity data into parameters needed in the methodology
include N excrement/animal/year and C/N ratios for regular and nitrogen-fixing crops. Note that the “Field
Burning of Agricultural Residues” sector of the IPCC Guidelines Workbook provides C/N ratios for a moredetailed partitioning of crops (Table 4-15). This is a duplication of effort/inconsistency that should be correctedin future versions of the workbook.
The FAO data, particularly the data on synthetic fertiliser production and consumption, are probably one of themost reliable aspects of the methodology. The choice of single year versus 3-year average FAO input data does
not appear especially critical. The United States reported a < 5 percent difference in estimated agricultural N2O
emissions between these 2 different types of activity data (Table 10, UNFCCC 1998/7).

2.5

Uncertainty

All 34 Parties reporting to the UNFCCC indicated “low” confidence in their estimates of N2O emissions fromagricultural soils. “Low” confidence indicates an uncertainty of 50 to > 100 percent (UNFCCC 1998/7). Indirect
N2O emissions are not specifically discussed in the UNFCCC report, but generally they account for the majority(~2/3) of the uncertainty in the 1996 estimated global agricultural N2O source. High uncertainty is to a large
extent inherent to biogenic processes like microbial N2O production.

2.6

CompletenessA review of 34 national inventories submitted to the UNFCCC indicates that 85% of countries reported on N2Oemissions from agricultural soils (Table 18, UNFCCC 1998/7). However, since indirect N2O emissions are notspecifically listed, the completeness of reporting in current inventories is difficult to assess. In terms of thecompleteness of the methodology itself in accounting for all agricultural N2O emissions, several additionalsources, which were considered but ultimately omitted from the 1996 methodology, should be discussed. (Thecounterpart to completeness, redundancy or double-counting, is also considered here.)

2.6.1

Formation of N 2 O from NH 3 in the atmosphere

Dentener and Crutzen (1994) proposed that oxidation of HN3and subsequent reaction of the intermediate NH2
radical with NO2 could lead to a production of 0.6±0.3 Tg N2O -N/yr. They parameterised natural HN3emissions
from vegetation using a highly uncertain NH3 canopy compensation point (the atmospheric concentration above
which plants assimilate and below which they emit HN3). Without considering this compensation point, N2O
production was reduced by 55 percent. Other sources of HN3in the tropics include animal waste decomposition(both from wild and domestic animals), fertiliser application and biomass burning emissions. About half of theatmospheric N2O production may be associated with agricultural nitrogen, amounting to about 0.25 Tg N2O N/yr-1. Due to the high uncertainty of this estimate (ca. 100 percent), this source was not included in the 1997
IPCC N2O emissions inventory. Recent calculations suggest that this hypothetical source may have been
overestimated (Dentener, private communication) and confirm that it should not be included in the inventory at
this time.

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2.6.2

Food processing (and other fates)

This category currently is not included in the methodology due to lack of information. The category was
intended to encompass the potentially significant fraction of the harvested crop that is not consumed by people,
but that may eventually lead to N2O production, e.g., as landfill, compost, fuel for biomass burning, or fodder for
livestock. The default recommendation is that 45 percent of the crop is harvested. N2O production associatedwith the mineralization of the 55 percent remaining on the field is treated in the direct emissions calculation.
N2O emissions associated with the 45 percent harvested are partially accounted for through category C (sewage),(although these emissions are based on independent human population and protein consumption data and are
therefore not cross-linked to the assumed crop fate.) Future refinement of the methodology may requireestablishing internal consistency within these different emissions categories associated with the long-term fate ofcrop biomass removed from the field.
Since indirect N2O emissions from agriculture are treated by a number of different sectors (Agriculture, Energy,
Waste, Land-Use Change), inventory experts should take care to communicate with each other among these
sectors, especially when substituting country-specific partitioning factors for default values. In part, this need forcaution results from the conceptual incompleteness of the current methodology in tracking nitrogen from “cradle
to grave.” One example of a possible redundancy lies in the calculation of direct N2O emissions associated withmineralization of crop residue. Currently, the methodology assumes that 45 percent of total crop biomass isharvested and 55 percent, minus the 0-25 percent burned, is mineralised in the field. N2O emissions due tobiomass burning estimate are handled by the Land-Use Change sector rather than the Agricultural sector. In
some countries, a significant fraction of unburned crop residue may be fed to livestock. Since livestock manureis treated as an external nitrogen input, estimates of N2O from manure and mineralization of crop residue may
involve some double counting. Although this example is a fairly minor source of uncertainty (~5 percent of
direct emissions), it illustrates the desirability of developing a more complete and unified accounting ofagricultural nitrogen in future versions of the methodology (see Figure 1). Note that animal manure, in contrast
to synthetic N fertiliser (which is manufactured industrially from atmospheric N2), is derived in part fromharvested (e.g., corn, soybeans) and unharvested (e.g., rice straw) crop nitrogen and therefore is not a true
external input to the system.

2.7

Consistency with atmospheric increase

The IPCC 1997 agricultural N2O source is estimated at 6.3 (1.2-17.9) Tg N/yr. Even without the additional 1.3(0.7-1.8) Tg N/yr industrial and 0.5 (0.2-1.0) Tg N/yr biomass burning source, the mean and upper range of the
agricultural estimate significantly exceed the observed atmospheric N2O increase of 3.9 (3.1-4.7) Tg N/yr. The
N2O stratospheric sink has likely increased by 1-2 Tg N/yr due to the increased atmospheric burden of N2O.
However, even with this adjustment, the 1997 IPCC total N2O source is difficult to reconcile with the observed
atmospheric increase, which is one of the best and most precisely measured constraints available on the N2O
budget (A. Khalil, International Workshop on the Atmospheric N2O Budget, Tsukuba, Japan, 1999.). The
consistency of the agricultural N2O source estimate with the overall global N2O budget probably deserves moredetailed discussion than it has been granted so far.

3

REPORTING AND DOCUMENTATION

3.1

Current IPCC reporting guidelines

The IPCC Guidelines: Reporting Instructions are used to guide countries in the preparation and submissions ofannual greenhouse gas emissions inventories to the UNFCCC. The Guidelines establish:•

Standard tables, definitions, units, and time intervals for reporting all types of emissions;•

Necessary documentation to enable comparison of national inventories, including worksheets, major
assumptions, methodological descriptions, and enough data to allow a third party to reconstruct theinventory from national activity data and assumptions, and•An uncertainty assessment.

Step by step directions for calculating indirect N2O emissions from volatilisation and leaching are given in
Workbook Section 4.6, steps 6-8, of the IPCC Guidelines. Directions for calculating indirect N2O emissions
from field burning of agricultural residue are given in section 4.5. Directions for calculating indirect N2O

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emissions from sewage and biofuel burning of manure are presented in the Waste and Energy sections,
respectively.
Indirect N2O emissions from volatilisation and leaching are reported in Table 4 of the Reporting Instructions of
the IPCC Guidelines. (Sewage N2O emissions are reported separately in Table 6.) Unfortunately, directemissions and indirect emissions in Table 4 are lumped into one line labeled “Agricultural Soils.” This
consolidation of the reported source hinders transparency and analysis of national emissions inventory reports(UNFCCC/SBSTA/1998/7). Furthermore, it is a misnomer with respect to indirect N2O emissions, since ~85%of these emissions is estimated to occur from aquatic systems rather than soils.

4

INVENTORY QUALITY

4.1

Introduction

Inventory quality assurance and quality control (QA/QC) is a process integral to the development of a credible
inventory. A well-developed and well-implemented quality assurance programme fosters confidence in the final
inventory results regardless of the purpose and goal of the inventory. A successful quality assurance programmeis two-fold requiring agricultural producer/government level procedures and external review and audit activities.
The internal QC activities are designed to ensure accuracy, documentation, and transparency. The external
review process is designed to minimize errors that occur in the preparation of emissions inventories, and reduceor eliminate potential inherent bias.

4.2

Internal inventory quality assurance systems

Inventory agency review (QA) of agricultural inputs
Before accepting fertiliser consumption, crop production, and livestock population and production data, theinventory agency should carry out an assessment of data quality and auditing procedures. This type of review
requires cooperation with agricultural producers and suppliers to obtain enough information to verify thereported emissions, as discussed above. The assessment should include identification of potential bias in themethodology and recommendations for improvement.
Inventory agency QC on compiling national emissions
In addition to a thorough quality assessment of the standard input data discussed above, the inventory agency
should investigate additional country-specific information which could be used to replace default emissions
factors or to provide independent cross-checks on the N2O emissions estimated by the default methodology. This
information would include, among other things:•

Fraction of nitrogen applied as synthetic and organic fertiliser lost to leaching;•

Dissolved N2O concentration in groundwater, rivers and estuaries contaminated by human and agricultural
waste;•

Correlations between N2O, NO3- and or O2 in above areas;•

Fraction of sewage and agricultural waste discharged directly to rivers and estuaries, versus allowed toinfiltrate groundwater;•

Turnover time of groundwater in contaminated aquifers, and•River runoff rates.

4.3

External inventory quality assurance systems

External QA activities include a planned system of review and audit procedures conducted by personnel not
actively involved in the inventory development process. The key concept is independent, objective review toassess the effectiveness of the internal QC programme, the quality of the inventory, and to reduce or eliminate
any inherent bias in the inventory processes. Several types of external reviews, or audits, may be appropriate forN2O emission inventories.

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Third party audit by an accredited organization, expert, independent third party
An audit of the documentation and calculations ensures that each number is traceable to its origin. Most of theinformation used in estimating indirect N2O emissions from agriculture is generally available worldwide throughthe United Nations Food and Agricultural Organization (FAO) yearbooks.
Expert (peer) review
A detailed peer review would be appropriate when a procedure for determining N2O emissions is first adopted orrevised. Such a review generally would not be needed on an annual basis. However, to ensure that themethodology is as rigorous as possible, and that the data and assumptions used reflect the best available
information, default factors and emission factors should be revisited as needed if significant restructuring occurs
in a Party's agricultural system (e.g., changes in fertilization practices, irrigation, sewage management, livestock
production systems, etc.).
Given the large uncertainties in both FRACLEACH and EF5 discussed in section 2.2.2, one of the best ways tobuild more confidence into the estimate of N2O (L) might be to cross-check the methodology against
independent calculations. One possible cross-check is the method of Seitzinger and Kroeze (1998), who describe
a formula for estimating the amount of dissolved inorganic nitrogen that is exported by rivers as a function offertiliser use, human population, atmospheric N deposition, and water runoff, which can be validated to someextent by empirical data. Seitzinger and Kroeze (1998) have shown that this formula is practical for global-scale
analysis on a watershed basis. However, it cannot be used to calculate N leaching from agriculture on a national
scale without modifications to the model. Moreover, this method does not provide an independent estimate of
fractional N2O yields, although it perhaps can help narrow the uncertainty in FRACLEACH, since it involves a
validation of model N loading in rivers against measured values.
A second possible cross-check on predicted N2O emissions from estuaries is the semi-empirical gas-transfer
method (Nevison et al. 1995; Bange et al., 1996), in which measured surface N2O supersaturation in coastal
regions are multiplied by gas transfer factors to estimate flux to the atmosphere. The latter calculation is global
by nature, and is probably best performed by an expert group rather than by individual Parties.
As an example of the cross-check, the IPCC methodology predicts that only 10% (EF5-e/EF5) of leachingemissions occurs from estuaries. Using Seitzinger and Kroeze's (1998) estimate that 75% of N loading toestuaries is anthropogenic, Bange et al.'s estimate of 2.3-3.6 Tg N2O -N/yr from estuaries, would imply that a
total of 17-20 Tg N2O -N/yr is emitted from leaching-related sources! The Bange et al. estimate clearly appears
too high, but a higher resolution semi-empirical gas-transfer calculation focused on estuaries could help clarify
the leaching source and validate the IPCC methodology estimate.
Stakeholder review
Review by government and private agricultural organizations can provide a useful check on the methodology
assumptions and default parameters. In some cases, sensitive issues concerning food production/security may be
involved. Confidentially with respect to private businesses is probably not a major concern.
Public review
Some countries make their entire inventory available for public review and comment. This process may result ina range of comments and issues broader than those from other review processes.

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QUESTIONS FOR PAPER ON DIRECT N2O EMISSIONSAND WORKSHOP DISCUSSIONS
Some of these may infringe on the direct and animal emissions categories, but since these are intricately related
to indirect emissions (i.e., a reduction in direct emissions often means an increase in indirect emissions), they
deserve mention here.
1) While N2ODIRECT uses the reduced inputs FSN and FAW, the entire synthetic fertiliser (NFERT) andanimal (NEX) nitrogen inputs are subject to 30 percent (default) leaching. In calculating N2O(L), should
FSN=NFERT (1-FRACGASF) be used instead of NFERT? And should FAW = (NEX • (1-(FRACFUEL +FRACGRAZ + FRACGASM))) be used instead of NEX? These substitutions reduce N2O(L) to 0.9 rather
than 1.6 Tg N2O-N/yr. (Furthermore, should not FAW be calculated rather as FAW = NEX • (1FRACGASM)(1-FRACFUEL-FRACGRAZ)?) In theory, FRACGAS(F,M) represents immediate
volatization of NHx and NOx after deposition. It seems like double counting to assume that the volatized
fractions (the entire amounts of which are subject to EF4) can also be leached.
2) Can the observed N2O/NO3- ratio in groundwater be translated directly into an N2O emission factor? This is
an important question because EF5-g accounts for 60 percent of the leaching emission factor, and is aprincipal reason why EF5 is so much larger than the other emission factors (and consequently, why themethodology is highly sensitive to the assumed leached fraction). If not, is there a better approach for
determining EF5?
3) What sort of independent methods can be used to validate the standard methodology estimates?
4) The methodology is admittedly complex and the logic may appear convoluted to inventory experts who do
not understand its basis. Parties are encouraged to substitute country-specific factors for default factors.
However, could these substitutions lead to problems of omission or double-counting if experts do notunderstand the logic of the methodology? For example, if a country uses a large value of FRACBURN to
reduce its direct N2O emissions associated with mineralization, it must be careful to account for theincreased biomass-burning N2O emissions.
5) The example of sewage nitrogen being calculated from human population and protein consumption, rather
than linked to crop harvest, illustrates the lack of complete internal consistency of nitrogen tracking within
the methodology and as well as the difficulties of accounting for N2O emissions under separate categories ofagricultural, waste, and energy-related emissions. Can the methodology be revised to meet its original goalof a complete “cradle to grave” accounting of nitrogen? Would this help eliminate confusion and overlap?
6) Is such a complex approach really necessary or justified? Does it all come out in the wash anyway (forexample, the methodology is fairly insensitive to assumptions about volatilised fractions of fertiliser andmanure)?
7) Does the increased precision of EF1 (0.0125) versus EF4 (0.01) have an unintended and artificial impact on
the total agricultural emissions estimate, or does the higher value of EF1 reflect a meaningful distinction?

Indirect N2O Emissions from Agriculture397