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 3,4dimethylepyrazole 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 yieldscaled 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.