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

Authors: Ransom, Curtis; LEMONTE, JOSHUA - Brigham Young University; LAMBERT, AUSTIN - Stanford University; SVEDIN, JEFFERY - Agri Northwest; HOPKINS, BRYAN - Brigham Young University

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/8/2026
Publication Date: N/A
Citation: N/A

Interpretive Summary: Nitrogen fertilizers help crops grow, but some of that nitrogen is converted into gases that can harm air quality and reduce fertilizer efficiency. “Enhanced-efficiency” fertilizers, using different types of coating material, are designed to reduce these losses and improve the amount of nitrogen available for plants to use, but their performance has been inconsistent and not well understood under different environmental conditions. In this study, we continuously measured two nitrogen gases, nitrous oxide and ammonia, after fertilizer was applied to soil under controlled moisture levels and fertilizer rates. Measurements were taken every 48 minutes over several weeks using an automated gas monitoring system. We found that nitrous oxide emissions depended strongly on both fertilizer rate and soil moisture. Surprisingly, very wet soil combined with extremely high fertilizer rates produced less nitrous oxide than expected, most likely because the soil microbes converted nitrogen all the way to harmless nitrogen gas instead. Ammonia losses mainly occurred at high fertilizer rates and were not strongly affected by soil moisture. Coated enhanced-efficiency fertilizers reduced ammonia losses by 81 to 99%, but they did not reduce total nitrous oxide emissions. Instead, they delayed when those emissions occurred. These results show that improved fertilizers can help reduce certain types of nitrogen pollution, but their overall environmental benefit depends heavily on soil conditions and how fertilizers are applied. Understanding these interactions can help farmers, researchers, and policymakers develop better strategies to reduce nitrogen pollution while maintaining crop productivity.

Technical Abstract: 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 minutes from fertilizer applied to bare soil in laboratory (29 days) and glasshouse (47 days) settings. Nitrous oxide emissions show N rate x 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 (2,500 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 to 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 to 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.