Grassland renewal dominates multi-year nitrous oxide emissions in boreal legume grassland: Insights from eddy-covariance measurements

Nitrous oxide (N 2 O) emissions from agricultural soils represent the dominant source of this potent greenhouse gas, yet the interactions between management practices and environmental drivers governing these emissions remain poorly quantified, particularly across the entire grassland rotation cycle including renovation phases. We conducted three-year eddy covariance measurements of N 2 O fluxes from a legume-based grassland in eastern Finland, comparing mineral nitrogen ( N min ) and cattle-slurry digestate ( N org ) fertilization strategies across the first ( R 1 ) and second grass production years ( R 2 ), and the renovation year ( R 3 ). Annual N 2 O emissions increased through the rotation and ranged from 1.9 to 3.4 kg N 2 O-N ha −1 under N min and 2.6–5.4 kg N 2 O-N ha −1 under N org treatments. Emission factors ranged from 1.79 % to 7.56 % ( N min ) and 2.65–3.06 % ( N org ). Grassland renewal increased emissions by 55 % ( N min ) and 80 % ( N org ) relative to grass production years ( R 2 ). Environmental controls diverged between treatments: ecosystem respiration as the primary driver of N 2 O emissions under N min , while soil temperature dominated under N org . N 2 O emissions during non-growing season contributed 22–35 % of annual budgets. Grassland renovation represents the critical emission hotspot within boreal grassland rotation cycles, overriding fertilizer type effects. N org produced 37–59 % higher cumulative emissions. These findings highlight the critical importance of grassland management event and fertilizer type in N 2 O emission mitigation strategies and warrant eddy-covariance measurements for more accurate N 2 O emission inventories from boreal grasslands. • Renovation year dominates N 2 O across the three-year rotation. • Emission factor peaks in renovation (up to 7.6 % under mineral N fertilizer). • Moisture drives N 2 O under mineral N; temperature under digestate. • Non-growing-season N 2 O is substantial (22–35 % of annual total).