Automated gas measurement reveals contrasting effectiveness of enhanced-efficiency fertilizers for reducing ammonia and nitrous oxide emissions.

Enhanced-efficiency nitrogen (N) fertilizer technologies have the potential to reduce N gas emissions, yet their effects on nitrous oxide (N2O) and ammonia (NH3) emissions are often inconsistent and context-dependent. The aim of this study was to quantify N2O and NH3 gas emissions using continuous photoacoustic infrared spectroscopy under varying N fertilizer rates, moisture regimes, and fertilizer sources in controlled incubations. Gas fluxes were measured every 48 min from fertilizer applied to bare soil in glasshouse (29 days) and laboratory (47 days) settings. Nitrous oxide emissions show N rate by moisture interactions, with emission factors ranging from 0.03% to 3.55%. Under moderate soil moisture (55% water-filled pore space [WFPS]), N2O emissions increased with N rate, whereas under high soil moisture (75% WFPS), the highest N rate (2500 kg N ha-1) resulted in unexpectedly low N2O emissions. In contrast, NH3 emissions were only observed at high N rates, regardless of moisture conditions, with emission factors around 1.1%-1.2%. Polymer-coated urea (PCU) and polymer-coated sulfur-coated urea (PCSCU) did not reduce cumulative N2O emissions relative to urea. Instead, PCU and PCSCU delayed N2O release, producing similar total emissions with altered temporal patterns. However, cumulative NH3 emissions were reduced by 81%-99% with the use of coated fertilizers. These findings suggest that while coated fertilizers help mitigate NH3 losses, their effectiveness in reducing overall N emissions is highly dependent upon environmental conditions and application methods.