Characterization of Nitrous Oxide Emissions from Global Cropping Systems and Grasslands.

Nitrous oxide (N₂O) emissions from the agricultural  sector contribute about 80% of the global anthropogenic N₂O emissions and can affect the trend of the net global warming potential (GWP) because of its much higher GWP than that of CO₂ and CH₄. We compiled historical experimental observations of N₂O emissions at both growing season and annual scales from global cropping systems and grasslands and characterized the N₂O emission rates associated with manageable variables. The results demonstrate substantial variations in N₂O emission rate not only with nitrogen fertilizer type, fertilization rate and method, but also with soil organic carbon content level and cropping system, particularly fertilized pasture. The growing season emission rate can more realistically reflect the uncertainty of human activity-induced emissions in comparison to the annual emission rate and therefore can be more useful for policy-makers to develop mitigation strategies. Our results also suggest that applying low emission fertilizers and optimizing the application rate based on both cropping system and soil conditions could feasibly mitigate fertilizer-derived N₂O emissions and be critical for sustaining the agriculture that relies increasingly on N fertilization. More studies are needed to figure out to what extent the application of both N inhibitors and less N₂O emitted-N fertilizers can be expanded and to determine their impacts on soil quality and environmental health.