A comprehensive review of approaches, challenges, and future directions for advancing nitrous oxide emission modeling

Nitrous oxide (N2O) is a potent greenhouse gas contributing to global warming. Numerous models have been developed and widely applied to simulate long-term N2O emissions at large scales, particularly within agroecosystems. This review systematically evaluated the current state of modelling approaches for simulating N2O emissions. 15 empirical models were categorized into two groups, and the limitations and targeted improvements of each group were discussed. Among the 73 process-based models reviewed, 51 models partition N2O from nitrification using a constant value or a fixed parameter within a range of 0.0003–0.2. Similarly, 16 models partition N2O from denitrification with a constant value or fixed parameter ranging from 0.002 to 0.9. These ranges are narrower than those reported in previous studies. Future research is needed to accurately quantify these ranges and categorize values based on climate, soil properties, and crops. 8 of the collected process-based models simulate N2O through a sequential nitrate reduction approach, while 27 models apply a partitioning ratio for N2O from denitrification. Both strategies rely on soil environmental factors (e.g., soil nitrogen, carbon, soil temperature, moisture, and pH), which are typically derived from small site-specific datasets. Future large meta-analyses could help develop more robust equations that better represent the effects of environmental factors on N2O emissions from denitrification. This review highlighted that despite differences in structure, most models share common strategies for simulating N2O emissions.