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AbstractThis study presents a greenhouse gas (GHG) life cycle assessment of 1 tonne of wheat transported to port in south‐western Australia, including emissions from prefarm, onfarm and postfarm stages. The prefarm stage included GHG emissions from agricultural machinery, fertiliser and pesticide production. The onfarm stage included GHG emissions from diesel use, liming and nitrous oxide (N2O) emissions from N fertiliser applications. The postfarm stage included grain storage and transportation to the port. GHG emissions decreased from 487 to 304 kg carbon dioxide (CO2) equivalents when we used regional‐specific data for N2O emissions instead of the IPCC default value for the application of synthetic N fertilisers to land (1.0%). Fertiliser production in the prefarm stage contributed significantly (35%) to GHG, followed by onfarm CO2 emissions (27%) and emissions from transportation of inputs and wheat (12%). N2O emissions from paddock represented 9% of the total GHGs emitted. We recommend utilising regionally specific data for soil N2O emissions, rather than international default values, when assessing GHG for agricultural production systems.

Acknowledgements The authors are grateful to M. Scholes, D. Plaza-Bonilla, S. Menendez, P. Merino, S.C. Maris, H. Heller, D. Savvas, C. K. Kontopoulou, who were contacted and kindly supplied any missing information necessary for the meta-analysis. Special thanks to J.P.C. Eekhout for preparing Fig. 1 and F. Estellés for providing the basic data for the calculation of the fertilization in Spain. Also thanks to two anonymous reviewers for their helpful comments. M. L. Cayuela was supported by a 'Ramon y Cajal' research contract from the Spanish Ministry of Economy and Competitiveness. Thanks to Fundación Séneca, Agencia Regional de Ciencia y Tecnología de la Región de Murcia for support (grant number 19281/PI/14). Australian studies included in the meta-analysis were funded by the Australian Government, the Grains Research and Development Corporation, and the Department of Agriculture and Food WA. ; Peer reviewed ; Postprint ; Postprint ; Postprint ; Postprint ; Postprint