Use of urease and nitrification inhibitors to decrease yield-scaled N2O emissions from winter wheat and oilseed rape fields: A two-year field experiment

Nitrogen fertilizers are the major source of nitrous oxide (N₂O) emissions from arable land. The addition of nitrification inhibitors to fertilizers may improve the nitrogen (N) use efficiency and reduce N₂O emissions. However, it is still unclear how crop rotations affect nitrification and urease inhibitors to reduce N₂O emissions. We conducted a field experiment with two-year winter wheat and one-year oilseed rape cultivation in Germany from 2016 to 2017. We applied five different fertilizer treatments: (1) a control treatment without fertilization (N0); (2) calcium ammonium nitrate (CAN); (3) ammonium sulfate nitrate with the nitrification inhibitor 3,4-dimethylepyrazole phosphate (ENTEC); (4) urea; and (5) urea with the urease inhibitor N-(n-butyl) thiophosphoric triamide (UTEC). Crop yield, grain and straw N content, and N₂O fluxes were measured to assess yield-scaled N₂O emissions under different treatments. We found that in all fertilized treatments, the aboveground N uptake of wheat after wheat was 199–203 kg N ha⁻¹, which was much lower than that of wheat after oilseed rape (252–271 kg N ha⁻¹). The apparent N recovery of oilseed rape (13–23%) was much lower than in wheat after wheat (63–66%). The enhanced-efficiency fertilizers increased aboveground N uptake by 0–5% compared to fertilizers without inhibitors. The oilseed rape field had the highest yield-scaled N₂O emissions (18.0, 15.1, 16.7 and 15.6 g N₂O-N kg⁻¹ aboveground N uptake in CAN, ENTEC, urea and UTEC, respectively). These results indicate that urease and nitrification inhibitors hold the potential to increase crop yield and reduce N₂O emissions. Oilseed rape straw should be carefully managed to avoid high N₂O emissions. Future research should be focused on different fertilizer level and optimized N application strategy to increase the efficiency of urease and nitrification inhibitors, for instance, by increasing the N application rate in wheat after wheat, but reducing it in oilseed rape.