Nitrous oxide emissions from soil: A review of cropping practices and their consideration in process-based models

Nitrous oxide (N₂O) is a major anthropogenic greenhouse gas. Agriculture represents its largest source, but the estimation, projection and mitigation measures pose considerable challenges. We conducted a secondary meta-analysis to synthesize and quantify the impact of various agricultural practices on observed N₂O emissions. In addition, we synthesized how various process-based crop models considered these impacts and related processes when modeling N₂O emissions in order to identify research gaps. We examined 134 field experiments and 108 modeling articles on N₂O emissions. The application of biochar, nitrification and/or urease inhibitors, reduced fertilizer rates, controlled-release/coated fertilizers, deep fertilizer placement compared to surface application, and drip irrigation compared to broadcast surface irrigation consistently reduced observed N₂O emissions (7-29%). In contrast, crop residue addition compared to removal increased N₂O emissions. Many crop models already account for some of the practices, such as crop rotations, organic amendments, irrigation, fertilizer management in terms of rates, timing and sources, and, to a lesser degree, placement. Tillage practices are included in several models, but the considered approaches vary. Other important practices to increase fertilizer efficiency, such as the use of nitrification and urease inhibitors, are only included in a few models. While no modeling studies have explicitly assessed the liming effects on N₂O emissions, biochar effects were only represented indirectly through carbon dynamics rather than nitrogen transformations. Overall, model improvements are necessary to accurately quantify N₂O emissions associated with current agricultural practices, thereby contributing to the design of sustainable cropping systems that minimize the trade-off between climate change mitigation and crop productivity.