Can improved fertilization strategies reduce N2O emissions from winter wheat?

Nitrous oxide (N₂O) is a strong greenhouse gas, and its atmospheric concentration is rising. Anthropogenic N₂O emissions stem mostly from agricultural activities, especially the fertilization of fields. There is an urgent need to reduce the emissions of N₂O from agriculture, but so far well documented mitigation options remain scarce.

Here we present data from the first year of a series of field trials which aim to test if N₂O emissions from Danish winter wheat fields can be reduced by optimizing the fertilization strategy. The field trials were located at three different locations in Denmark with different soil types and climatic conditions. All treatments received 200 kg N/ha except the 0 N treatment (giving the background N₂O emissions). The treatments were: (1) ammonium nitrate split in three applications, (2) ammonium nitrate coated with a nitrification inhibitor (3,4-Dimethylpyrazole phosphate, DMPP) split in three applications, (3) ammonium sulfate coated with DMPP split in three applications, (4) liquid fertilizer split in three applications, and (5) ammonium nitrate split in four applications. Nitrous oxide emissions were measured by manual chambers throughout the growing season in 2022 (22 days of measurements).

The highest emissions and cumulative emissions were observed in the treatment with liquid fertilizer, and in two of the trials the emissions from the liquid fertilizer treatment were higher than emissions from the treatment with ammonium sulfate coated with DMPP. However, the nitrification inhibitor did not significantly decrease N₂O-emissions when compared to the same fertilizer type without inhibitor. In the treatment with ammonium nitrate split in four applications, we did not find significant reductions in N₂O emissions. Generally, nitrous oxide emissions from all sites were low (cumulative fluxes of 0.14 – 0.31 kg N₂O-N/ha for the growing season) due to a dry spring with a few peaks mainly due to precipitation events. Therefore a preliminary conclusion after the first year of field trials is that in a dry year, with low emissions, the selected fertilization strategies seem to have limited capacity for reducing N₂O emissions.