Nitrification inhibitors mitigate N2O emissions more effectively under straw-induced conditions favoring denitrification

Abstract The application of reactive nitrogen (N) in the form of synthetic/organic fertilizers plays a central role in supporting a larger human population, but also contributes to global warming through the emission of nitrous oxide (N 2 O). The use of nitrification inhibitors (NIs) has repeatedly been shown to minimize N 2 O emissions; however, their effectiveness in reducing N 2 O emissions varies greatly under different environmental conditions. A better understanding of how and to what extent NIs can mitigate fertilizer-related soil-borne N 2 O emissions under a range of different conditions is required. In the present study, we carried out a soil incubation experiment in a fully automated continuous-flow incubation system under conditions favoring either nitrification- or denitrification-derived N 2 O emissions. Additionally, the abundance of AOB amoA , and AOA amoA genes was quantified and N 2 O isotopic signatures were analyzed. We mixed a common NI (PIADIN ® ) with mineral fertilizer (ammonium sulfate) and examined the N 2 O mitigation potential of the NI in a fertilized sandy soil (low denitrification potential) and a sandy soil mixed with wheat straw (high denitrification potential) at 70% water holding capacity (WHC). In non-NI treatments, the addition of straw led to a drastic increase of CO 2 and N 2 O emissions compared to the non-straw-amended soils, suggesting stimulated microbial activity and higher denitrification rate. The NI reduced N 2 O emissions in the straw-amended treatment by 41%, whereas in the treatment without straw this was only 17%. With the combination of N 2 O isotopic signatures and functional gene abundances, fungal denitrification was considered to be the major process contributing to the higher N 2 O fluxes specifically in straw-amended soils. Overall, our study indicated that NI can be used as an effective method for mitigating N 2 O emissions in cropland specifically when the denitrification potential is high, e.g. in moist N-fertilized and straw-amended soils.