A review and meta-analysis ofmitigation measures for nitrous oxide emissions from crop residues

Crop residues are of crucial importance to maintain or even increase soil carbon stocks and fertility, and thereby to ad- dress the global challenge of climate change mitigation. However, crop residues can also potentially stimulate emis- sions of the greenhouse gas nitrous oxide (N2O) from soils. A better understanding of how to mitigate N2O emissions due to crop residue management while promoting positive effects on soil carbon is needed to reconcile the opposing effects of crop residues on the greenhouse gas balance of agroecosystems. Here, we combine a literature review and a meta-analysis to identify and assess measures for mitigating N2O emissions due to crop residue applica- tion to agricultural fields. Our study shows that crop residue removal, shallow incorporation, incorporation ofresidues with C:N ratio > 30 and avoiding incorporation of residues from crops terminated at an immature physiological stage, are measures leading to significantly lower N2O emissions. Other practices such as incorporation timing and interac- tions with fertilisers are less conclusive. Several of the evaluated N2O mitigation measures implied negative side- effects on yield, soil organic carbon storage, nitrate leaching and/or ammonia volatilization. We identified additional strategies with potential to reduce crop residue N2O emissions without strong negative side-effects, which require fur- ther research. These are: a) treatment ofcrop residues before field application, e.g., conversion ofresidues into biochar or anaerobic digestate, b) co-application with nitrification inhibitors or N-immobilizing materials such as compost with a high C:N ratio, paper waste or sawdust, and c) use ofresidues obtained from crop mixtures. Our study provides a scientific basis to be developed over the coming years on how to increase the sustainability of agroecosystems though adequate crop residue management.