Refining regional estimates of N₂O emissions from agricultural soils: A modelling study from Austria

Agricultural soils are a major source of nitrous oxide (N₂O), yet estimates of these emissions vary depending on the accounting method applied. The Intergovernmental Panel on Climate Change (IPCC) defines a tiered framework: Tier 1 uses activity data combined with global default emission factors, Tier 2 refines these estimates using emission factors calibrated for national conditions, and Tier 3 employs detailed process-based models or measurement systems that explicitly represent soil, climate, and management effects. Austria currently applies Tiers 1 and 2 in its national greenhouse gas inventory. This study compares these approaches with the Tier 3 model LandscapeDNDC to refine regional estimates of N₂O emissions from agricultural soils. Calculations were conducted for six selected production regions across Austria over a ten-year period. Using the National Inventory approach, estimated regional median N₂O emissions ranged between 3.3 and 3.8 kg N₂O ha^-1 yr^-1, which was 36-342% higher than the Tier 3 model results. LandscapeDNDC indicated that grassland soils are more prone to N₂O emissions than cropland soils, whereas the National Inventory estimates showed little difference between intensive land use types. This comparison highlights the trade-offs between the two approaches: National Inventory methods (Tier 1, 2) are simple and scalable, they produced higher and less spatially differentiated N₂O estimates than those from the LandscapeDNDC model (Tier 3), which is data- and computation-intensive but explicitly represents site-specific drivers such as soils, climate and management. Our results support prioritising investment in developing and implementing Tier 3 reporting tools, alongside with existing National Inventory methods, to better characterise uncertainty, increase transparency and enhance the policy relevance of mitigation strategies.