Closing the denitrification gap: applying the 15N gas flux method with an artificial atmosphere in conventional and regenerative agriculture

Introduction: Denitrification is an elusive process that remains notoriously difficult to measure under field conditions, yet it plays a crucial role as the only natural terrestrial sink for reactive nitrogen, especially in agricultural systems where large amounts of fertilizer are applied. Direct measurements of N2 fluxes over extended periods remain rare in the literature due to technical challenges. Methods: In this study, we quantified and characterized denitrification emissions under two contrasting land-use practices—conventional and regenerative (unfertilized) agriculture—using a recently developed custom method combining a 15N isotopic tracer with an artificial atmosphere (improved 15N Gas Flux method). We conducted nine field campaigns over one year to (i) assess method applicability, (ii) derive a first annual estimate of denitrification, (iii) understand controls on denitrification dynamics, and (iv) trace denitrification‐driven losses of applied synthetic nitrogen fertilizer in conventional agriculture. Results: Our method successfully detected denitrified N2 fluxes in 90% of measurements and yielded annual budgets of 22.12 and 2.41 kg N ha‐1 yr‐1 in the conventional and regenerative fields, respectively. Soil moisture and nitrate availability (particularly under fertilized conditions) were the main controls on the denitrification product ratio (N2O/(N2O + N2)). We estimated that 11% of applied fertilizer nitrogen was lost via denitrification in the conventional field, with 7.3% of this loss emitted as N2O rather than N2. Discussion: These results underscore the role of fertilization management in shaping denitrification dynamics and its potential to act as a sink for reactive nitrogen, while modulating N2O emissions.