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

Agricultural soil is the main source of nitrous oxide (NO) 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 NO 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 NO emissions as well as their trends. Soil NO emissions induced by N deposition accounted for 25% of global cropland soil NO emissions. Global soil NO emissions over croplands increased by 2% yr 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 (NO) and ammonium (NH) could be directly used for nitrification and denitrification. By 2100, N deposition will increase by 80% and cropland soil NO 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 NO emissions in climatic change studies.