Effectiveness and key drivers of nitrification inhibitors in mitigating N2O Emissions in a cool temperate climate: A Meta-analysis

Agricultural systems are a major source of nitrous oxide (N₂O) emissions. Nitrous oxide is a potent greenhouse gas (GHG) emitted from managed grasslands and croplands, primarily as a result of nitrogen fertilization. Reducing nitrogen inputs alone can mitigate N₂O emissions, but this may compromise crop productivity. Alternative mitigation strategies are therefore required to sustain food production while reducing GHG emissions. Currently one of the most promising strategies to do that is the use of nitrification inhibitors (NIs).

Nitrification inhibitors act by suppressing the activity of nitrifying microorganisms for a period, thereby slowing the conversion of ammonium to nitrate. This reduces N₂O emissions from ammonia oxidation and the availability of nitrate for subsequent denitrification and associated N₂O emission. Fertilizers amended with NIs may improve plant nitrogen uptake and reduce nitrogen losses. In a second-order meta-analysis, Grados et al (2022) found an average reduction of 44 % in N₂O emissions when NIs are used as fertilizer amendment. However, effects may vary among studies, potentially due to variable soil and climate conditions, as well as different management (time, rate and method of application).

To obtain a more robust estimate of the effectiveness and key drivers of nitrification inhibitors under temperate conditions, we conducted a meta-analysis of studies reporting cumulative N₂O emissions from NI-amended fertilization in northern European climate. Literature was identified using Web of Science (all databases) by combining search terms related to nitrous oxide and nitrification inhibitors. The initial search yielded 9,387 references, which were filtered using exclusion terms implemented in R, followed by manual screening of approximately 100 abstracts. In total, 43 studies met the inclusion criteria and were included in the analysis.

Preliminary results based on studies from Denmark only (n= 10) show a statistically significant average decrease of 40% in N₂O emissions, when NIs are used as fertilizer amendment. However, factors such as sand content and concentration of nitrogen applied significantly affect the inhibitors mitigation efficiency.

Reference: Grados et al 2022 Environ. Res. Lett. 17 114024, DOI 10.1088/1748-9326/ac9b50