Using nitrification inhibitors to mitigate agricultural N O emission: a double-edged sword?

Nitrification inhibitors show promise in decreasing nitrous oxide (N O) emission from agricultural systems worldwide, but they may be much less effective than previously thought when both direct and indirect emissions are taken into account. Whilst nitrification inhibitors are effective at decreasing direct N O emission and nitrate (NO ) leaching, limited studies suggest that they may increase ammonia (NH ) volatilization and, subsequently, indirect N O emission. These dual effects are typically not considered when evaluating the inhibitors as a climate change mitigation tool. Here, we collate results from the literature that simultaneously examined the effects of nitrification inhibitors on N O and NH emissions. We found that nitrification inhibitors decreased direct N O emission by 0.2-4.5 kg N O-N ha (8-57%), but generally increased NH emission by 0.2-18.7 kg NH -N ha (3-65%). Taking into account the estimated indirect N O emission from deposited NH , the overall impact of nitrification inhibitors ranged from -4.5 (reduction) to +0.5 (increase) kg N O-N ha . Our results suggest that the beneficial effect of nitrification inhibitors in decreasing direct N O emission can be undermined or even outweighed by an increase in NH volatilization.