Cattle and swine manure nitrous oxide emissions

Summary

This methodology represents nitrous oxide (N₂O) emissions associated with the management and storage of buffalo, cattle and swine manure. The data and calculation methodology is sourced from the IPCC, as published in Volume 4, Chapter 10 - Emissions from Livestock and Manure Management and Volume 4, Chapter 11 - N2O Emissions from Managed Soils, and CO2 Emissions from Lime and Urea Application of their 2006 IPCC Guidelines for National Greenhouse Gas Inventories.

The methodology

Emissions model

Nitrogen (N) found within the excretions of livestock manure contributes to N₂O emissions both directly and indirectly. Direct emissions arise from the processes of nitrification and denitrification. Nitrification is the transformation of N-containing compounds (ammonia (NH₃) => nitrite (NO₂^-) => nitrate (NO₃^-)) which occurs under aerobic conditions (i.e. in the presence of oxygen). Denitrification is the subsequent transformation to N₂O which occurs only under anaerobic conditions. As such, direct N₂O emissions require both aerobic and anaerobic conditions in succession. Indirect emissions result from the vaporization of N-containing compounds (primarily NH₃ and mono-nitrogen oxides, NO_x) as well as through runoff and leaching into soils. Indirect emissions depend primarily on time.

This emissions methodology is based upon factors which describe both the direct and indirect pathways of manure-N (i.e. manure-associated nitrogen). Direct emissions are based upon the typical daily rates at which manure-N is produced by livestock, and the rates at which this N is converted directly into N₂O-N (i.e. nitrous oxide-associated nitrogen). Indirect emissions are based upon the typical fractions of excreted N which are volatilised and the rates at which this volatilised N is converted into N₂O-N.

Quantities of N₂O-N are then converted into N₂O emission quantities on the basis of their relative molecular masses.

Annual emission rates (e.g. kg / year) for a population or sub-population of livestock are calculated by multiplying the unit emissions rates (i.e. per animal or liveweight) by the total size of the livestock population which is under consideration.

This methodology represents the IPCC Tier 1 approach.

Model data

The rate at which N₂O is emitted ultimately depends on the nitrogen (N) and carbon (C) content of manure, and the duration of storage and type of treatment. As such, emissions factors for a broad range of scenarios are provided within this methodology. A total of 765 specific scenarios are represented, differentiated by geographic region (e.g., North America, Middle East), livestock type (e.g., buffalo, dairy cattle, market swine), manure management type (e.g. composting, anaerobic digester) and subtype (e.g. static pile, natural aeration).

Each scenario is represented by several data values, including the typical livestock mass, daily N excretion rates, direct and indirect N to N₂O-N conversion factors, and the fraction of manure-N typically volatilised. In addition, this methodology uses two general constants for deriving emissions quantities from N₂O-N:

• molecular mass ratio of N₂O and N: the factor for converting a N₂O-N quantity into N₂O (44/28)

• global warming potential of N₂O: the factor for converting a N₂O emissions quantity into CO₂e - the quantity of CO₂ which would exert the same atmospheric warming effect.

Activity data required

N₂O emissions are directly proportionate to the total liveweight of the livestock population kept. This can be specified either directly, or by using the total population of the livestock under consideration, in which case the methodology will calculate the total liveweight based on the typical mass of individual animals.

Calculation and results

This emissions calculated by this methodology represent those attributable to the specified population of livestock over a period of 1 year.

The methodology calculates two emissions quantities: (1) the absolute quantity of N₂O associated with the livestock population; and (2) N₂O emissions expressed in terms of CO₂e.

Additional information

Nomenclature

Following IPCC advice, the term manure is used collectively to include both dung and urine (i.e., the solids and the liquids) produced by livestock.

Incomplete data

Data on the fraction of manure N lost through volatilisation is not provided for all combinations of livestock type and manure management practices in the IPCC source documentation. Where possible, CarbonKit returns the sum of both direct and indirect N₂O emissions. Otherwise, the returned values represent direct emissions only.

Related methodologies

Analogous methodologies are also available focussing on poultry, fur-bearing and other livestock N₂O emissions associated with manure management.