Final report: Review of New Zealand Specific FracGASM and FracGASF Emissions Factors

Abstract

FracGASM and FracGASF are important factors within national nitrous oxide (N₂O) emissions inventories. These factors represent the proportions of manure-N and fertiliser-N respectively that are released into the atmosphere, principally as ammonia, NH₃, to become indirect sources of N₂O when re-deposited on land surfaces elsewhere. Currently the NZ N₂O inventory uses the IPCC defaults of 0.2 and 0.1 for FracGASM and FracGASF respectively. The use of 0.2 for FracGASM in New Zealand’s N₂O inventory recently came under the scrutiny of the ‘Expert Review Team’ (ERT) of the United Nations Framework Convention on Climate Change (UNFCCC) secretariat. Amongst other things, the ERT encouraged NZ to: “investigate a country-specific FracGASM or document why the IPCC default value is considered appropriate for New Zealand conditions”. This current review forms part of that investigation. In this review we have attempted to locate and scrutinise all (mostly field-based) studies of relevance to the magnitudes of FracGASM and FracGASF as used in NZ’s current N₂O inventory. Following a brief introduction (section 1) sections 2 and 3 focus on the factors influencing the production and emission of NH₃(g) and NOx(g) from soils and also provide an overview of the techniques employed for their measurement. Sections 4 and 5 then focus respectively on international and local (NZ) studies of relevance to FracGASM. In section 6 we review international and NZ data on NH₃(g) emissions from mainly urea and diammonium phosphate fertilisers and then follow that in section 7 with a review of NOx emissions from animal excreta and fertiliser applied to pasture. Section 8 summarises all major findings and recommendations.