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Crop residues are of crucial importance to maintain or even increase soil carbon stocks and fertility, and thereby to address the global challenge of climate change mitigation. However, crop residues can also potentially stimulate emissions of the greenhouse gas nitrous oxide (N 2 O) from soils. A better understanding of how to mitigate N 2 O 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 N 2 O emissions due to crop residue application to agricultural fields. Our study shows that crop residue removal, shallow incorporation, incorporation of residues with C:N ratio > 30 and avoiding incorporation of residues from crops terminated at an immature physiological stage, are measures leading to significantly lower N 2 O emissions. Other practices such as incorporation timing and interactions with fertilisers are less conclusive. Several of the evaluated N 2 O 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 N 2 O emissions without strong negative side-effects, which require further research. These are: a) treatment of crop residues before field application, e.g., conversion of residues 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 of residues 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., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

Crop residue incorporation is a common practice to increase or restore organic matter stocks in agricultural soils. However, this practice often increases emissions of the powerful greenhouse gas nitrous oxide (N 2 O). Previous meta-analyses have linked various biochemical properties of crop residues to N 2 O emissions, but the relationships between these properties have been overlooked, hampering our ability to predict N 2 O emissions from specific residues. Here we combine comprehensive databases for N 2 O emissions from crop residues and crop residue biochemical characteristics with a random-meta-forest approach, to develop a predictive framework of crop residue effects on N 2 O emissions. On average, crop residue incorporation increased soil N 2 O emissions by 43% compared to residue removal, however crop residues led to both increases and reductions in N 2 O emissions. Crop residue effects on N 2 O emissions were best predicted by easily degradable fractions (i.e. water soluble carbon, soluble Van Soest fraction (NDS)), structural fractions and N returned with crop residues. The relationship between these biochemical properties and N 2 O emissions differed widely in terms of form and direction. However, due to the strong correlations among these properties, we were able to develop a simplified classification for crop residues based on the stage of physiological maturity of the plant at which the residue was generated. This maturity criteria provided the most robust and yet simple approach to categorize crop residues according to their potential to regulate N 2 O emissions. Immature residues (high water soluble carbon, soluble NDS and total N concentration, low relative cellulose, hemicellulose, lignin fractions, and low C:N ratio) strongly stimulated N 2 O emissions, whereas mature residues with opposite characteristics had marginal effects on N 2 O. The most important crop types belonging to the immature residue group - cover crops, grasslands and vegetables - are important for the delivery of multiple ecosystem services. Thus, these residues should be managed properly to avoid their potentially high N 2 O emissions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)