Effects of nitrification inhibitors on growing‑season N₂O emissions in Danish grain systems: evidence from multi‑site field trials

Nitrous oxide (N₂O) is an important greenhouse gas from agricultural systems. Nitrification inhibitors can potentially reduce N₂O emissions from field fertilization, but evidence from cool, wet climates under real farm conditions are limited.

Here we present results from a Danish multi-site program carried out in commercial farms across five different regions and soil classes (coarse sandy to loamy) in 2021-2025 focusing on winter wheat and spring barley. Fertilization practices included ammonium nitrate and organic fertilizers (cattle slurry, pig slurry and digestate). The organic fertilizer treatments included a synthetic “starter fertilizer” to reflect Danish practice, and organic fertilizers were only applied in regions where they predominate. The fertilizer treatments were included with and without nitrification inhibitors, primarily 3,4-dimethylpyrazole phosphate (DMPP) and in selected trials nitrapyrin.

N₂O fluxes were measured in situ using static chambers once weekly during the growing season and twice weekly for three weeks after fertilizer applications to capture short‑lived emission pulses. Air and soil temperature, precipitation and volumetric soil water content were logged at high frequency. Cumulative growing‑season emissions were derived by linear interpolation and trapezoidal integration.

Preliminary results show an average reduction in N₂O emissions of about 20-50 % across field trials with differences in efficiency of nitrification inhibitors being related to parameters such as crop type. Further data on growing‑season N₂O emission responses to nitrification inhibitors across crops, fertilizer types, and soils will be presented, and the potential and limitations of this mitigation option will be discussed.