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

Abstract

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.