Dual Effects of Nitrification Inhibitors on N2O Emission from Agriculture.

Nitrification inhibitors show promise in decreasing nitrous oxide (N₂O) emission from agricultural systems worldwide, but they may be much less effective than previously thought. Limited studies suggest that these inhibitors may increase ammonia (NH₃) volatilization and subsequently, indirect N₂O emission while decreasing direct N₂O emission. These dual effects are typically not considered. To evaluate the effectiveness of a nitrification inhibitor as a N₂O mitigation tool, we conducted the first case study to quantify N₂O and NH₃ emissions from a vegetable farm using continuous gas flux measurements and micrometeorological techniques. We also collated the limited available results from the literature that simultaneously examined the effects of nitrification inhibitors on N₂O and NH₃ emissions. These data collectively show that nitrification inhibitors decreased direct N₂O emission by 0.2–4.5 kg N₂O-N ha^–1 (8–57%), but generally increased NH₃ volatilization by 0.2–18.7 kg NH₃-N ha^–1 (3–65%). Taking into account the indirect N₂O emission from deposited NH₃, the overall impact of nitrification inhibitors ranged from –4.5 to +0.5 kg N₂O-N ha^–1. Our results suggest that the beneficial effect of nitrification inhibitors in decreasing direct N₂O emission may be undermined or even outweighed by the concomitant increase in NH₃ volatilization.