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Crop residues are important inputs of carbon (C) and nitrogen (N) to soils and thus directly and indirectly affect nitrous oxide (N2O) emissions. As the current inventory methodology considers N inputs by crop residues as the sole determining factor for N2O emissions, it fails to consider other underlying factors and processes. There is compelling evidence that emissions vary greatly between residues with different biochemical and physical characteristics, with the concentrations of mineralizable N and decomposable C in the residue biomass both enhancing the soil N2O production potential. High concentrations of these components are associated with immature residues (e.g., cover crops, grass, legumes, and vegetables) as opposed to mature residues (e.g., straw). A more accurate estimation of the short‐term (months) effects of the crop residues on N2O could involve distinguishing mature and immature crop residues with distinctly different emission factors. The medium‐term (years) and long‐term (decades) effects relate to the effects of residue management on soil N fertility and soil physical and chemical properties, considering that these are affected by local climatic and soil conditions as well as land use and management. More targeted mitigation efforts for N2O emissions, after addition of crop residues to the soil, are urgently needed and require an improved methodology for emission accounting. This work needs to be underpinned by research to (1) develop and validate N2O emission factors for mature and immature crop residues, (2) assess emissions from belowground residues of terminated crops, (3) improve activity data on management of different residue types, in particular immature residues, and (4) evaluate long‐term effects of residue addition on N2O emissions. [ABSTRACT FROM AUTHOR]

This article presents the detailed data of the soil characteristics, field management, amount and N content of below- (roots +crown) and aboveground (stubble and herbage) grass mixture, red clover and red clover grass swards at the end of the 3rd production year, together with fluxes of greenhouse gas emissions (N 2 O, CO 2 , CH 4 ) and soil air composition (CO 2 , N 2 O, CH 4 , N 2 and O 2 ) of a field experiment in Norway. These data supplement the findings presented in the research article " Roots and other residues from ley with or without red clover: quality and effects on N 2 O Emission Factor in a partly frozen soil following autumn ploughing"(Bleken et al. 2022). For understanding of the effects of incorporating ley above- and belowground residues on cumulative greenhouse emissions refer to article from this research., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships which have or could be perceived to have influenced the work reported in this article., (© 2022 The Author(s).)

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.)