SOURCE CATEGORY 4B – MANURE MANAGEMENT 1 Source category description

This category reports emissions of CH4 from animal manures as well as N2O emissions from

their manures arising during its storage.

6.3.2

Methodological issues

6.3.2.1 Methane emissions from animal manures

A more detailed description of the method used and emission factors can be found in

Annex 3, Section A3.6.

Methane is produced from the decomposition of manure under anaerobic conditions. When manure is stored or treated as a liquid in a lagoon, pond or tank it tends to decompose anaerobically and produce a significant quantity of methane. When manure is handled as a solid or when it is deposited on pastures, it tends to decompose aerobically and little or no methane is produced. Hence the system of manure management used affects emission rates. Emissions of methane from animal manures are calculated from animal population data (Defra, 2011a) in the same way as the enteric emissions.

The emission factors for manure management are calculated following IPCC Tier 2 methodology but using default IPCC data to estimate the required volatile solids (VS) and methane producing potential (Bo) parameters for each livestock type (except for dairy and

beef cows, where a Tier 2 calculation is used to determine VS, and deer where no IPCC data are available). The emission factors were calculated for each livestock type based on the VS, Bo, AWMS breakdown and methane conversion factors according to manure

management type (IPCC 2000, Equation 4.17).

Recent revisions to the activity data concerning manure management practices in the UK ammonia emissions inventory, and the greater level of detail contained within that inventory, were incorporated in the revised spreadsheet model of the GHG inventory. These data derive from a number of sources, including published ad-hoc surveys (e.g. Smith et al., 2000c, 2001a, 2001b; Sheppard 1998, 2002; Webb et al., 2001) and, more recently, relevant data from the Farm Practices Survey for England. We now include a time series for AWMS. For dairy cows, the calculations are based on the population of the ‘dairy breeding herd’ which is defined as dairy cows over two years of age with offspring. The emissions for beef cows and other cattle are calculated from the IPCC Tier 2 procedure.

6.3.2.2 Nitrous Oxide emissions from Animal Waste Management Systems

Animals are assumed not to give rise to nitrous oxide emissions directly, but emissions will arise from N excreted by livestock. Emissions from manures 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 Manure Management IPCC category:

• Flushing anaerobic lagoons. These are assumed not to be in use in the UK.

• Liquid systems (i.e. slurry)

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• Other systems (poultry manure without bedding and poultry manure with bedding (poultry litter); IPCC 2000 Good Practice Guidance)

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

• All applied animal manures and slurries

• Pasture range and paddock

Emissions from the combustion of poultry litter for electricity generation are reported under power stations. Emissions occurring during storage of poultry litter that will later be used for energy generation are included in the agricultural inventory.

Emissions of N2O from animal waste management are calculated using country-specific data

for AWMS breakdown and N excretion and IPCC default emission factors for the specific AWMS.

6.3.3

Uncertainties and time-series consistency

The Tier 1 uncertainty analysis in Annex 7 provides estimates of uncertainty according to IPCC source category.

Emissions are calculated from animal population data and appropriate emission factors. The animal population data are collected in the June annual census, published by Defra. This is a long running publication and the compilers of the activity data strive to use consistent methods to produce the activity data. The time-series consistency of these activity data is very good dueto the continuity in data provided.

6.3.4

Source-specific QA/QC and verification

This source category is covered by the general QA/QC procedures which are discussed in

Section 6.9.

6.3.5

Source-specific recalculations

A number of changes were made to the calculation of emissions from manure management. A Tier 2 methodology was introduced for CH4 emissions from manure management for all

livestock categories except deer (previously Tier 2 was used only for Dairy and Beef cows and Tier 1 for all other livestock). AWMS breakdown for all livestock categories (and sub- categories) were revised according to recent survey data and historic survey data as used in the UK NH3 emission inventory. Emissions of CH4 and N2O from poultry litter storage prior to

incineration have now been included (previously, emissions from any poultry litter destined for incineration were unaccounted). The combined effect of these changes was a reduction in the emission from manure management of 490 Gg CO2 eq.

6.3.6

Source-specific planned improvements

Emission factors and activity data will be kept under review including the use of more detailed emission factors and activity data to allow estimation of the effect of future mitigation policies.

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