Nitrous oxide emission from croplands: biogeochemical drivers, nitrification inhibitors, policy implications, and future directions

Abstract

Abstract Nitrous oxide (N 2 O) emissions from croplands are a distinct environmental challenge because N 2 O is both a potent greenhouse gas and a major contributor to stratospheric ozone depletion. Emissions arise largely from agricultural nitrogen (N) inputs and microbially mediated nitrification and denitrification as N pools are transformed under fluctuating soil oxygen and moisture conditions. Yet N inputs are central to maintaining yield stability, ensuring an adequate food protein supply, and sustaining farm profitability. Therefore, mitigation strategies that rely predominantly on reducing N use are difficult to scale without compromising agricultural productivity. When expressed as chlorofluorocarbon-11–equivalent ozone-depleting emissions, N 2 O (179.0 kt yr −1 ) exceeds the combined emissions of legacy ozone-depleting substances and transitional hydrochlorofluorocarbons (145.7 kt yr −1 ), strengthening the case for prioritizing agricultural N 2 O within climate and ozone-protection frameworks. In this review, we synthesize current understanding of nitrification- and denitrification-derived pathways of N 2 O formation and the biological sink of N 2 O reduction to dinitrogen (N 2 ), emphasizing how fertilizer-driven shifts in N pools interact with soil to regulate pathway dominance and the N 2 O:N 2 product ratio. We then place these mechanisms in the context of 21st-century fertilizer-use trajectories and rising atmospheric N 2 O and summarize the stratospheric reactions that couple agricultural N 2 O to ozone loss. Building on these mechanistic foundations, we evaluate direct nitrification-targeted mitigation by contrasting synthetic nitrification inhibitors with emerging biological nitrification-inhibition traits and their potential integration into the cropping system. Finally, we highlight how recent Conference of the Parties negotiations and the 2024 Global N 2 O Assessment are elevating N 2 O as a priority on the climate and ozone protection agenda. We argue that durable scaling of mitigation will require outcome-based quantification, including models and measurement strategies that deliver credible seasonal-to-annual estimates with transparent uncertainty, so that management changes translate into verifiable N 2 O reductions and eligible incentives.