a IPCC(1997)

b Emission Factor for year 1999

c Sneath et al (1997)

d Chickens, turkeys, geese, ducks and guinea fowl.

e Factor quoted assumes animal lives for a year. Emission calculation assumes animal lives for 6 months.

1 43% of animals graze on good quality pasture, rest confined

Gestation period 281 days

Digestible Energy 65%

Methane conversion rate 6%

Ash content of manure 8%

2 Weight assuming annual growth of 1% from 1990.

1 Digestible Energy 65%

Ash content of manure 8%

Methane producing capacity of manure 0.24 m³/kg VS

2. IPCC(1997) default (48 kg/head/y) used since calculated factor is very close to default and the difference under the Tier 2 method will not affect the accuracy of the emission factor at the required level of precision.

a IPCC (1997)

Animals are assumed not to give rise to nitrous oxide emissions directly, but emissions from their wastes during storage are calculated for a number of animal waste management systems (AWMS) defined by IPCC. Emissions from the following AWMS are reported under the IPCC category, manure management.

• Flushing Anaerobic Lagoons. These are assumed not to be in use in the UK.
• Liquid systems
• Solid storage and dry lot
• Other systems (farmyard manure, poultry litter, stables)

According to IPCC(1997) guidelines, the following AWMS are reported in the Agricultural Soils category

• Daily spread
• Pasture range and paddock

Emissions from the combustion of poultry litter for electricity generation are reported under power stations.

The IPCC (1997) method for calculating emissions of N₂O from animal waste management systems can be expressed as:

N₂O_(AWMS) = 44/28 . å N_T . Nex_(T) . AWMS_(T) . EF_(AWMS)

where

N₂O_(AWMS) = N₂O emissions from animal waste managment systems

(kg N₂O/yr)

N_T = Number of animals of type T

Nex_(T) = N excretion of animals of type T (kg N/animal/yr)

AWMS_(T) = Fraction of Nex that is managed in one of the different

waste management systems of type T

EF_(AWMS) = N₂O emission factor for an AWMS (kg N₂O-N/kg of Nex in AWMS)

The summation takes place over all animal types and the AWMS of interest. Animal population data is taken from MAFF Statistics (MAFF, 2000b). Table A44 shows emission factors for nitrogen excretion per head for domestic livestock in the UK (Nex) based on balances by Smith (1998). The UK methodology assumes that 20% of the total N emitted by livestock volatilises as NO_x and NH₃ and therefore does not contribute to N₂O emissions from AWMS. This is because in the absence of a more detailed split of NH₃ loss occurs prior to major N₂O losses. Hence the Nex factors used in the AWMS estimates and those reported in Tables A44 and A45 exclude the fraction of N volatilising. Hence they are 20% less than if they were reported on the same basis as the ‘total’ Nex factors reported in the IPCC Guidelines.

Nex factors for dairy cattle take account of the assumed growth in the average cow weight by 1% per annum and are shown in Table A45. The conversion of excreted N into N₂O emissions is determined by the type of waste management system used. The distribution of waste management systems for each animal type (AWMS_(T)) is given in Table A46. Table A47 gives the N₂O emission factor for each animal waste management system (EF_(AWMS)). These are expressed as the emission of N₂O-N per mass of excreted N processed by the waste management system.

Emissions from grazing animals (pasture range and paddock) and daily spread are calculated in the same way as the other AWMS. However, emissions from land spreading of waste that has previously been stored in liquid systems, other systems, solid storage and dry lot are treated differently. These are discussed in the section on Organic Fertilizer.

2 Nex factors exclude 20% N volatilising as NO_x and NH₃

3 Estimate for year 1999

4 Sneath et al, (1997)

5 Factor quoted assumes animal lives for a year. Emission calculation assumes animal lives for 6 months.

1 Nex factors exclude 20% N volatilising as NO_x and NH₃

b Poultry Litter, Stables

c ADAS(1995a)

d Sneath et al (1997)

e Agricultural Economics Unit Exeter University (1996)

f Tucker (1997)

Table A47 Nitrous Oxide Emission Factors for Animal Waste Handling Systems^a

b Reported under Agricultural Soils

Direct emissions of nitrous oxide from agricultural soils are estimated using the IPCC recommended methodology (IPCC, 1997) but using some recently derived UK specific emission factors. This involves estimating contributions from:

(i) The use of inorganic fertilizer

(ii) Biological fixation of nitrogen by crops

(iii) Ploughing in crop residues

(iv) Cultivation of histosols (organic soils)

(v) Spreading animal wastes on land

(vi) Manures dropped by animals grazing in the field

In addition to these, the following indirect emission sources are estimated:

(vii) Emission of N₂O from atmospheric deposition of agricultural NO_x and NH₃.

(viii)Emission of N₂O from leaching of agricultural nitrate and runoff.

Descriptions of the methods used follow.

Emissions from the application of inorganic fertiliser are calculated using the IPCC (1997) methodology and IPCC default emission factors. They are given by:

N₂O_(SN) = 44/28 . N_FERT . (1-Frac_GASF) . EF₁

where

N₂O_(SN) = Emission of N₂O from synthetic fertiliser application

(kg N₂O/yr)

N_FERT = Total use of synthetic fertiliser (kg N/yr)

Frac_GASF = Fraction of synthetic fertiliser emitted as NO_x + NH₃

= 0.1 kg NH₃-N+NO_x -N / kg synthetic N applied

EF₁ = Emission Factor for direct soil emissions

= 0.0125 kg N₂O-N/kg N input

Annual consumption of synthetic fertiliser is estimated based on crop areas (MAFF, 2000b) and fertiliser application rates (BSFP, 2000).

Emissions of nitrous oxide from the biological fixation of nitrogen by crops are calculated using the IPCC (1997) methodology and IPCC default emission factors. They are given by:

N₂O_(BF) = 44/28 . 2. Crop_BF . Frac_NCRBF . EF₁

where

N₂O_(BF) = Emission of N₂O from biological fixation (kg N₂O/yr)

Crop_BF = Production of legumes (kg dry mass/year)

Frac_NCRBF = Fraction of nitrogen in N fixing crop

= 0.03 kg N/ kg dry mass

EF₁ = Emission Factor for direct soil emissions

= 0.0125 kg N₂O-N/kg N input

The factor of 2 converts the edible portion of the crop reported in agricultural statistics to the total biomass. The fraction of dry mass for the crops considered is given in Table A48.

b Burton (1982), Nix (1997) or MAFF estimates

c Hops dry mass from Brewers Licensed Retail Association(1998)

d Field beans dry mass from PGRE (1998)

The data for residue/crop is taken from IPCC (1997) defaults in the Agricultural Soils section, or derived from Table 4.17 of the Field Burning of Agricultural Residues section. Crop production data is taken from MAFF (2000b, 2000d). The total nitrous oxide emission reported also includes a contribution from improved grass calculated using a fixation rate of 4 kg N/ha/yr (Lord, 1997).

Emissions of nitrous oxide from the ploughing in of crop residues are calculated using the IPCC (1997) methodology and IPCC default emission factors. They are given by:

N₂O_(CR) = 44/28 . 2 . (Crop_O . Frac_NCRO . + Crop_BF . Frac_NCRBF )(1-Frac_R) . (1-Frac_B) EF₁

where

N₂O_(CR) = Emission of N₂O from crop residues (kg N₂O/yr)

Crop_O = Production of non-N fixing crops (kg dm/yr)

Frac_NCRO = Fraction of nitrogen in non-N fixing crops

= 0.015 kg N/ kg dm

Frac_R = Fraction of crop that is removed from field as crop

Frac_B = Fraction of crop residue that is burnt rather than left on field

EF₁ = Emission Factor for direct soil emissions

= 0.0125 kg N₂O-N/kg N input

Crop_BF = Production of legumes (kg dry mass/year)

Frac_NCRBF = Fraction of nitrogen in N fixing crop

= 0.03 kg N/ kg dry mass

Production data of crops is taken from MAFF (2000b, 2000d). The dry mass fraction of crops and residue/crop from the field are given in Table A48. Field burning has largely ceased in the UK since 1993. For years prior to 1993, field burning data was taken from the annual MAFF Straw Disposal Survey. (MAFF, 1995)

Emissions from histosols were estimated using the IPCC(1997) default factor of 5 kg N₂O-N/ha/yr. The area of cultivated histosols is assumed to be equal to that of eutric organic soils in the UK and is based on a FAO soil map figure supplied by SSLRC.

Emissions from wastes dropped by grazing animals are classified under agricultural soils by IPCC. The method of estimation is the same as that for AWMS in Section 2.12.1.3 but applying factors for pasture range and paddock.

Emissions from animal wastes used as organic fertilisers are classified under agricultural soils by IPCC. The procedure involves estimating the amount of nitrogen applied to the land and applying IPCC emission factors. For daily spreading of waste, the emission is given by:

N₂O_(DS) = 44/28 . å N_T . Nex_(T) . AWMS_(T) . EF₁

where

N₂O_(DS) = N₂O emissions from daily spreading of wastes (kg N₂O/yr)

N_T = Number of animals of type T

Nex_(T) = N excretion of animals of type T (kg N/animal/yr)

AWMS_(T) = Fraction of Nex that is daily spread

EF₁ = Emission Factor for direct soil emissions

= 0.0125 kg N₂O-N/kg N input

For the application of previously stored wastes to land, a correction is applied to account for N₂O losses during storage.

N₂O_(FAW) = 44/28 . å (N_T . Nex_(T) . AWMS_(T) - N_(AWMS) ) . EF₁

where:

N₂O_(FAW) = N₂O emission from organic fertiliser application

N_(AWMS) = N₂O emissions from animal waste managment systems as

nitrogen (kg N₂O-N/yr)

N_T = Number of animals of type T

Nex_(T) = N excretion of animals of type T (kg N/animal/yr)

AWMS_(T) = Fraction of Nex that is managed in one of the different

waste management systems of type T

The summation is for all animal types and for liquid system, solid storage and other systems where wastes are stored.

Indirect emissions of N₂O from the atmospheric deposition of ammonia and NO_x are estimated according to the IPCC (1997) methodology but with corrections to avoid double counting N. The sources of ammonia and NO_x considered, are synthetic fertiliser application and animal wastes applied as fertiliser.

The contribution from synthetic fertilisers is given by:

N₂O_(DSN) = 44/28 . (N_(FERT) - N_(SN)) . Frac_(GASF) . EF₄

where

N₂O_(DSN) = Atmospheric deposition emission of N₂O arising from synthetic fertiliser application (kg N₂O)

N_(FERT) = Total mass of nitrogen applied as synthetic fertiliser (kg N)

N_(SN) = Direct emission of N₂ O_(SN) as nitrogen (kg N₂O-N)

Frac_(GASF) = Fraction of total synthetic fertiliser nitrogen that is emitted

as NO_x + NH₃

= 0.1 kg N/ kg N

EF₄ = N deposition emission factor

= 0.01 kg N₂O-N/kg NH₃-N and NO_x-N emitted

The estimate includes a correction to avoid double counting N₂O emitted from synthetic fertiliser use.

The indirect contribution from waste management systems is given by

N₂O_(DWS) = 44/28. (N_(EX)/(1-Frac_(GASM)) -N_(F) ) . Frac_(GASM) . EF₄

where

N₂O_(DWS) = Atmospheric deposition emission of N₂O arising from animal wastes(kg N₂O)

N_(EX) = Total N excreted by animals

Frac_(GASM) = Fraction of livestock nitrogen excretion that volatilises as

NH₃ and NO_x

= 0.2 kg N/kg N

N_(F) = Total N content of wastes used as fuel (kg N)

The equation corrects for the N content of wastes used as fuel but no longer for the N lost in the direct emission of N₂O from animal wastes as prevously. The nitrogen excretion data in Table A40 already excludes volatilisation losses and hence a correction is included for this.

Indirect emissions of N₂O from leaching and runoff are estimated according the IPCC methodology but with corrections to avoid double counting N. The sources of nitrogen considered, are synthetic fertiliser application and animal wastes applied as fertiliser.

The contribution from synthetic fertilisers is given by:

N₂O_(LSN) = 44/28 . (N_(FERT) . (1-Frac_(GASF) )- N_(SN)) . Frac_(LEACH) . EF₅

where

N₂O_(LSN) = Leaching and runoff emission of N₂O arising from synthetic fertiliser application (kg N₂O)

N_(FERT) = Total mass of nitrogen applied as synthetic fertiliser (kg N)

N_(SN) = Direct emission of N₂ O_(SN) as nitrogen (kg N₂O-N)

Frac_(GASF) = Fraction of total synthetic fertiliser nitrogen that is emitted

as NO_x + NH₃

= 0.1 kg N/ kg N

Frac_(LEACH) = Fraction of nitrogen input to soils that is lost through leaching

and runoff

= 0.3 kg N/ kg fertiliser or manure N

EF₅ = Nitrogen leaching/runoff factor

= 0.025 kg N₂O-N /kg N leaching/runoff

The estimate includes a correction to avoid double counting N₂O emitted from synthetic fertiliser use.

The indirect contribution from waste management systems is given by

N₂O_(LWS) = 44/28. (N_(EX-N_(F) -N_(WS) ) . Frac_(LEACH) . EF₅

where

N₂O_(LWS) = Leaching and runoff emission of N₂O from animal wastes

(kg N₂O)

N_(EX) = Total N excreted by animals (kg N)

N_(F) = Total N content of wastes used as fuel (kg N)

N_(AWMS) = Total N content of N₂O emissions from waste management systems including daily spread and pasture range and paddock

(kg N₂O-N)

The equation corrects both for the N lost in the direct emission of N₂O from animal wastes and the N content of wastes used as fuel.

The NAEI estimates emissions from field burning under the category agricultural incineration. The estimates are derived from emission factors calculated according to IPCC(1997) and from USEPA (1997) shown in Table A49.

The estimates of the masses of residue burnt of barley, oats, wheat and linseed are based on crop production data (MAFF, 1999d) and data on the fraction of crop residues burnt (MAFF, 1997; ADAS (1995b)). Field burning ceased in 1993 in England and Wales. Burning in Scotland and Northern Ireland is considered negligible as is grouse moor burning, so no estimates are reported from 1993 onwards. The carbon dioxide emissions are not estimated because these are part of the carbon cycle.

a IPCC(1997)

b Larkin et al. (1985)

c USEPA(1995)

The NAEI reports an estimate of NMVOC emissions from forests, woodlands, heathland, pastures and crops in the UK. Emissions comprise of mainly isoprene, terpenes and other NMVOCs. The estimate is based on a study by Simpson et al (1999) The estimate is very approximate and the same value is used for all years.