Targeting yield and reducing nitrous oxide emission by use of single and double inhibitor treated urea during winter wheat season in Northern Germany

Nitrous oxide (N₂O) is a powerful greenhouse gas and has an adverse effect on stratospheric ozone. Field application of synthetic N fertilizers is the largest source of global N₂O emission and different N forms (nitrate vs. ammoniacal N) may play a significant role. In addition, the use of nitrification inhibitor (NI) is considered as a reliable way to mitigate agricultural N₂O emission, whereas this effect is still debated for urease inhibitors (UI). However, the efficacy of NI or UI is still variable among different inhibitor products and environmental conditions. This study was conducted to test the efficacy of N form (calcium ammonium nitrate CAN vs. urea) and the almost unstudied UI, N-(2-nitrophenyl) phosphoric triamide (2-NPT), as well as an NI, mixture of dicyandiamide and 1H-1,2,4-triazol (DCD/TZ) and the combination of both inhibitors on N₂O emission and crop yield. The measurements were carried out in winter wheat growth season in the subsequent years of 2012–2013 in the North of Germany. No difference in cumulated N₂O emissions were observed between urea and CAN. The results confirmed the positive effect of NI (DCD/TZ) on reducing N₂O emission. Compared with untreated urea, NI addition caused ∼75 % reduction of fertilizer derived N₂O emissions within the vegetation period. The combination of UI and NI did not result in a further reduction of relative or yield-scaled N₂O emission, although it resulted in higher grain yield and nitrogen recovery. Addition of UI showed no consistent effect on N₂O emission compared to untreated urea, however in year 2013 a significant reduction of fertilizer derived emissions by ∼50 % was observed. Higher yields were observed for CAN fertilization compared to urea, though not significant. For both treatments including UI the yield effects, in particular N use efficiency, were stronger than for untreated urea and urea solely treated with NI. Therefore, the combined treatment with UI and NI was the most advantageous fertilizer solution for concomitantly achieving high yield, high nitrogen utilization efficiency and N₂O emission reduction.