Soil Nitrous Oxide Emissions by Atmospheric Nitrogen Deposition over Global Agricultural Systems

Agricultural soil is the main source of nitrous oxide (N₂O) emissions which contribute to global warming and stratospheric ozone depletion. In recent decades, atmospheric nitrogen (N) deposition has increased dramatically as an important agricultural soil N input, while its effect on soil N₂O emissions in the current and future climate change remains unknown. Here, we conducted a thorough analysis of the effect of N deposition and climate change on soil N₂O emissions as well as their trends. Soil N₂O emissions induced by N deposition accounted for 25% of global cropland soil N₂O emissions. Global soil N₂O emissions over croplands increased by 2% yr^-1 during 1996-2013, of which N deposition could explain 15% of the increase. The emission factor of N deposition was ∼7 times that of N fertilizer plus manure (∼1%) through a more direct way, since N deposition including nitrate (NO₃^-) and ammonium (NH₄⁺) could be directly used for nitrification and denitrification. By 2100, N deposition will increase by 80% and cropland soil N₂O emissions will increase by 241% under the RCP8.5 scenario in comparison with the 2010 baseline. These results suggest that, under the background of increasing global N deposition, it is essential to consider its effects on soil N₂O emissions in climatic change studies.