A multi-objective framework for nitrogen management integrating N2O emissions in malting barley systems

Malting spring barley is an important commodity for Scotland’s whisky and beer industries. Meeting malting quality standards requires precise control of grain protein, which is strongly influenced by nitrogen (N) fertilization. However, N management must balance environmental impacts in addition to grain quality and profitability. Previous frameworks optimized N to reduce nitrate leaching but rarely considered nitrous oxide (N 2 O) emissions, which are critical under emerging carbon taxation policies. In this study, simulated N 2 O emissions were integrated into spatial and temporal N-rate optimization for malting spring barley using a calibrated process-based model. Ten N rates (20-200 kg N ha -1 ) were simulated across four yield-stability zones in an 11-ha commercial farm over 34 years. Emissions varied across zones and years: medium-yield zones (MYZ) emitted the least at high N rates; wet years (>470 mm) produced more N 2 O than dry years (<320 mm). Higher N inputs improved yield, grain quality, and marginal net returns (MNRav), but increased nitrate leaching and N 2 O emissions. Trade-offs occurred at 100 kg N ha -1 (N 2 O vs yield), 140 kg ha -1 (N 2 O vs MNRav, grain N concentration), and <80 kg N ha -1 (N 2 O vs nitrate leaching). Multi-objective optimization identified 120-140 kg N ha -1 as optimal, with 120 kg N ha -1 favored in wet years. These findings provide a framework for integrating greenhouse gas (GHG) metrics into site-specific N management, advancing climate-smart strategies for intensive cereal systems globally.