Nitrous oxide emissions from enhanced-efficiency nitrogen fertilizers applied to annual crops in a subtropical ecosystem

In this study, we assessed the potential of enhanced-efficiency nitrogen (EEN) fertilizers for mitigating nitrous oxide (N2O) emissions and compared it with that of common urea. N2O-N emission factor (EF-N2O, % applied N emitted as N2O-N) and yield-scaled N2O-N emissions (N2O-N emitted per yield unit) for wheat, bean and black oat were determined in southern Brazil. Four EEN fertilizers were evaluated for comparison with common urea, namely: urea with urease inhibitor (Ur-NBPT), urea coated with an inorganic polymer (Ur-pol), ammonium nitrate (Nitrate), urea treated with copper and boron polymer (Ur-CuB) and control treatment with no N fertilizer. The first two EEN fertilizers were applied to all crops, the third only to wheat and the fourth to bean and black oat. None of the EEN fertilizers reduced N2O-N emissions or increased crop yields relative to common urea in winter wheat or black oat. By contrast, Ur-pol and Ur-CuB reduced N2O-N emissions in summer bean by 41 and 39%, respectively, and Ur-pol increased grain yield by 40%, relative to common urea. Although the Ur-NBPT proved efficient in decreasing soil N2O-N fluxes at an early stage, no effect was observed in the mid or long term (> 12 days) and, thus, the effect on total N2O-N emissions was not significant. Our findings testify to the potential of some EEN fertilizers for decreasing N2O-N yield-scaled emissions in summer crop seasons relative to common urea, the effect having no considerable impact under the mild winter conditions. EF-N2O-N averaged 0.87 ±  0.40% across crop seasons (ranging from 0.44 to 1.45%).