Eight years organic amendment application alters N₂O emission potential by increasing soil O₂ consumption rate

Organic amendments are efficient measures that can be employed to increase both nitrogen use efficiency and soil organic carbon (SOC) content. However, the long-term effects of such measures on soil N₂O emission and the associated underlying mechanisms are still unclear. Here, we sampled soils that were part of two long-term trials after eight years of different amounts and types of organic amendment addition, and investigated the response of soil N₂O emissions to different types of mineral N addition under oxic condition. Further, we selected two soil samples with a large difference in SOC content and investigated the responses of soil CO₂, N₂O, NO, and N₂ emissions as well as O₂ consumption to NH₄⁺, NO₃^-, and nitrification inhibitor addition under limited O₂ diffusion condition and anoxic condition. Results showed that long-term organic amendments significantly increased SOC content, while the stimulated effect on N₂O and N₂ emissions owing to increased SOC contents was more pronounced with NH₄⁺ addition under limited O₂ diffusion condition than under oxic or anoxic conditions. Further, in all treatments under limited O₂ diffusion condition, soil O₂ concentration and N₂O production showed significant inverse relationships, suggesting that O₂ directly regulates N₂O production. We speculated that the decrease in O₂ availability with higher SOC contents owing to enhanced soil respiration, instead of the increased supply of electron donors, is primarily responsible for the stimulated N₂O emissions. This implied that practices which reduce limited O₂ diffusion conditions might help to minimize the stimulated N₂O emissions from increased SOC content.