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As the current method used by the IPCC (Intergovernmental Panel on Climate Change) to inventory emissions of N₂O, a potent greenhouse gas (GHG), considers nitrogen inputs from crop residues as the sole factor determining N₂O emissions, it does not take other factors into account. Yet there is irrefutable evidence that emissions vary considerably between residues with different biochemical and physical characteristics, in particular the concentration of mineral or easily mineralised nitrogen and the concentration of soluble carbon in residues, which increase the soil's potential to produce N₂O.  High concentrations of these components are associated with residues returned to the soil from plants at immature physiological stages (e.g. cover crops, grasses and legumes, and vegetable residues) as opposed to residues from plants that have reached physiological maturity (e.g. cereal straw). A more accurate estimate of the short-term effects (a few months) of crop residues on N2O emissions could involve distinguishing between mature and immature crop residues, which have markedly different emission factors. 

There is an urgent need for more targeted mitigation efforts for N₂O emissions after crop residues have been added to the soil, which requires an improved methodology for accounting for emissions. More needs to be known about N₂O emissions associated with agricultural practices in order to improve the GHG balance for agriculture.

This opinion paper stems from the work of the European ResidueGas project, coordinated by Aarhus University and involving INRAE and 9 European partners (https://projects.au.dk/residuegas). This work was supported by the FACCE ERA-GAS of the European Union's Horizon programme (n° 696356). The French grant was provided by the ANR (ANR-17-EGAS-0003).

Read: Olesen JE et al. Challenges of accounting nitrous oxide emissions from agricultural crop residues. Global Change Biology 2023, 1–10. https://doi.org/10.1111/gcb.16962

Contacts: Sylvie Recous (sylvie.recous@inrae.fr), Gwenaëlle Lashermes (gwenaelle.lashermes@inrae.fr), Pascal Thiébeau (pascal.thiebeau@inrae.fr)