Ammonia volatilization emission factors matching the fertilizer EFs for the industry/system
Indirect nitrous oxide (N2O) emissions from ammonia volatilization, nitrate leaching and run-off were first included in the Australian National Greenhouse Gas Inventory (NGGI) methodology in 2005.
The first implementation assumed that the fraction of synthetic fertiliser N volatilised as ammonia (NH3-N) and nitrogen oxide (NOx-N) (FracGASF) was based on the IPCC default emission factor (EF) of 0.1 Gg N/Gg applied i.e. 10% of all N fertiliser applied was deemed to be lost as ammonia.
This default method also assumed that 100% of this ammonia was then deposited on agricultural land, using the IPCC default emission factor for N2O from N fertiliser of 0.01 (Gg N2O-N/Gg N) i.e. assuming that 1% of this deposited nitrogen was then lost as N2O.
Following two successive national N2O research programs in Australia, where emissions of nitrous oxide from varying soils, climates, agricultural systems and nitrogen inputs were quantified, a series of industry-specific Tier 2 emission factors were published and adopted into the NGGI.
These revised EFs (Gg N2O-N/ Gg N) were: Irrigated pasture 0.004; Irrigated crop 0.0085; Non-irrigated pasture 0.002; Non-irrigated crop 0.002; Sugar cane 0.0199; Cotton 0.0055; Horticulture 0.0085.
The Australian Agriculture Inventory Expert Advisory Panel then discussed the logic of assuming that ammonia emitted and then re-deposited into these systems would have an EF of 0.01, while fertiliser N entering the same soil as ammonia would have the industry-specific EF as listed above.
As the highest ammonia deposition rates are found within a few hundred meters of the emission source, the EFs applied for ammonia deposition were therefore considered to be related to the source of the N.
The NGGI was therefore updated so that the EFs applied for atmospheric deposition are the same as those applied for direct N2O emissions from N fertiliser applied to that system, as listed above.