Improving nitrogen fertilizer use efficiency and minimizing losses and global warming potential by optimizing applications and using nitrogen synergists in a maize-wheat rotation

Nitrogen (N) is the key nutrient for crop growth in most agricultural systems, but excessive N fertilizer appli-cations have led to very large ammonia (NH3) and greenhouse gas (GHG), especially nitrous oxide (N2O), emissions, resulting in severe air pollution and making a major contribution to global warming. To clarify the effects of improved N management on NH3 and N2O emissions and crop production, a 2-year field experiment was carried out in a maize-wheat rotation in the North China Plain (NCP), testing four optimized N management practices including reducing the fertilizer (urea) N rate and using N 'synergists' with the fertilizer. NH3 emissions were significantly reduced only by the urease inhibitor (UI) LIMUS (R), with an average reduction of 66.9 % relative to emissions from the untreated urea. At the same N rate, N2O emissions were reduced by 30.8-76.7 % by all the synergists (UI, a nitrification inhibitor DMPP (NI) and urea with a bacterial agent (UB)), and crop yields were improved by 14.4 % and 15.2 % under the UI and UB treatments, respectively. An 15N tracer experiment showed that using N synergists decreased the total N loss by 10.9-58.7 %, and significantly increased the re-covery efficiency of N (REN) by 16.9-44.8 % over the whole rotation. Reducing the N rate reduced the GWP and yield-scaled GWP (GHGI) by 10.6 % and 8.4 %, respectively. Using the N synergists, GHGI was significantly decreased by 19.2-26.7 % (P < 0.05), while GWP was reduced by 13.2-18.1 % only by the application of DMPP or LIMUS (R). Overall, the study showed that reducing N2O and NH3 emissions is important for increasing N utilization and mitigating global warming. Reducing N rate and using synergists can address the joint problems of environmental pollution and agricultural efficiency. In particular, the application of the optimal amount of urea (33% reduction over rates typically applied by farmers) amended with the urease inhibitor LIMUS (R) to maize -wheat rotations in the NCP proved to be the most effective method for the 'green' and sustainable development of agriculture and the mitigation of global warming in that region of China.