Nitrogen science for sustainable food systems and climate change mitigation

Nitrogen (N) is essential for global food production, yet its inefficient use leads to widespread environmental degradation and contributes significantly to climate change. This focus issue of Environmental Research Letters brings together a comprehensive set of studies that advance our understanding of N dynamics across scales, from field-level processes to global systems, and across sectors including agriculture, industry, and policy. The contributions provide new insights into nitrogen use efficiency, emissions, and flows through detailed subnational and national assessments, alongside methodological advances in N budgeting and accounting frameworks. Several studies address critical uncertainties in N cycling, particularly in relation to denitrification and nitrous oxide (N _2 O) emissions, highlighting gaps in measurement and modeling capabilities. Emerging integrated monitoring and modeling initiatives—including SmartField, canN _2 Onet, and N _2 Onet—demonstrate the potential for harmonized systems that improve measurement, verification, and reporting of N _2 O emissions across scales. Scenario analyses and long-term assessments of agro-food systems reveal the potential for substantial reductions in N losses through structural transformations, including dietary shifts, enhanced circularity, and improved system integration. Other contributions present underexplored opportunities for nutrient recycling, such as the recovery of N from human excreta, and examine the economic trade-offs and policy implications of N use on a global scale. Collectively, the studies emphasize the need for integrated, multi-scale approaches to N management that combine improved monitoring, robust modeling, cross-sectoral accounting, and coordinated governance. This focus issue provides a foundation for advancing N science and developing effective strategies that reconcile food production with environmental sustainability and climate change mitigation.