Three Decades of Soil N2O Research-Insights and Gaps.

Nitrous oxide (N2O) is a potent greenhouse gas (GHG) whose atmospheric concentration continues to rise, largely driven by nitrogen (N) inputs to agricultural soils. Over the past three decades, research on soil N2O emissions has advanced substantially, yet key uncertainties still constrain mitigation efforts. Here, we synthesize developments in measurement techniques, process understanding, microbial ecology, and modelling from the 1990s to the present, and identify critical gaps for future research. Advances in high-frequency measurements, laser spectroscopy, and isotopic approaches have revealed the importance of temporal "hot moments" and spatial "hotspots," challenging earlier assumptions based on sparse sampling. Concurrently, molecular and multi-omic tools have transformed our understanding of the microbial drivers of N2O production and consumption, highlighting the role of community composition, truncated pathways, and previously overlooked N2O-producing and reducing organisms. Process-based models have evolved from research tools into policy-relevant frameworks underpinning GHG inventories, with emerging integration of data assimilation, ensemble modelling, and artificial intelligence. However, despite these advances, persistent challenges remain in linking scales, reducing uncertainties, and translating mechanistic insights into scalable mitigation strategies. Closing these gaps offers a unique opportunity to translate decades of scientific progress into next-generation mitigation strategies that align agricultural productivity with climate stabilization goals.