Revised emission factors for estimating direct nitrous oxide emissions from nitrogen inputs in Australia’s agricultural production systems: a meta-analysis

A meta-analysis of N2O emission observations from Australian agriculture (2003-2021) identified 394 valid emission factors (EFs). Industry based EFs for synthetic N fertiliser (excluding those derived from EEFs) ranged from 0.17% (non-irrigated pasture) to 1.77% (sugar cane), with an average Australia-wide EF of 0.70%. The revised EF for the non-irrigated cropping (grains) industry effectively doubled from 0.20% to 0.41%. Emission factors were independent of topsoil organic carbon content, bulk density and pH. Urea was the most commonly applied N source with an average EF of 0.72% compared to urine (0.20%), dung (0.06%) and organo-mineral mixtures (0.26%). The EF for synthetic N fertilisers in rainfed environments increased by 0.16% for every 100 mm over 300 mm MAR. For each additional 50 kg N ha-1 of synthetic fertiliser, EFs increased by 0.13%, 0.29% and 0.43% for horticulture, irrigated cropping and high rainfall (> 600 mm MAR) non-irrigated cropping respectively. The application of EEFs regardless of N source, significantly reduced the Australia-wide EF to 0.19%. Pairwise comparisons of DMPP and urea applications returned significant reductions in the EF of non-irrigated cropping systems of 80%, 55% in horticulture and 84% in irrigated cropping. Incorporation of the revised EFs into the 2020 National Greenhouse Accounts produced a 12% increase in direct N2O emissions from the application of synthetic N fertilisers.

JRC.D.3 - Land Resources and Supply Chain Assessments