Assessing nitrous oxide mitigation efficiency of three nitrification inhibitors with synthetic and organic fertilisers in Eastern Denmark

The use of nitrification inhibitors (NIs) with fertilisers holds the potential to reduce nitrous oxide (N₂O) emissions and optimise nitrogen use efficiency (NUE). However, this potential of NIs needs to be quantified across diverse field conditions to comprehensively assess the influence of management practices, crop types, fertilisation strategies, climatic conditions, annual variations, and soil types. In 2020, a field experiment was conducted using spring barley, followed by a similar experiment with winter wheat in 2021, aimed at studying N₂O mitigation, crop nitrogen uptake and crop yield effects of three additives containing commercially available NIs: 3,4-dimethylpyrazole phosphate (DMPP), nitrapyrin (NP), and a mixture of 1,2,4-triazole and 3-metylpyrazole (TM) together with synthetic (ammonium sulphate nitrate (NS), urea ammonium nitrate (UAN)) and organic (pig slurry (PS)) fertilisers. DMPP was applied with NS and PS, while NP and TM were applied with UAN and PS. Fertilisers were applied during early spring in both years, following the recommended optimal rate of synthetic fertiliser and PS. Control treatments included fertilisers applied at the same rate without NIs and no fertiliser. N₂O fluxes were assessed throughout the growing seasons of both years utilising manual static flux chambers. The study found that N₂O emissions were significantly reduced from PS with DMPP (by 77 %) and TM (by 67 %), and that DMPP significantly reduced N₂O emissions from NS (by 60 %) in 2021. Crop yield and N uptake were increased with NIs in both years. These findings suggest that DMPP and TM effectively reduce N₂O emissions from both PS and synthetic N sources. Notably, the mitigation effects were more pronounced in PS compared to synthetic N. Nonetheless, the efficiency of N₂O reduction through these nitrification inhibitors varied depending on crop type and specific management conditions.