Evaluation of effectiveness of enhanced‐efficiency fertilizers as mitigation options for N2O and NO emissions from agricultural soils: meta‐analysis

Agricultural fields are an important anthropogenic source of atmospheric nitrous oxide (N₂O) and nitric oxide (NO). Although many field studies have tested the effectiveness of possible mitigation options on N₂O and NO emissions, the effectiveness of each option varies across sites due to environmental factors and field management. To combine these results and evaluate the overall effectiveness of enhanced‐efficiency fertilizers i.e., nitrification inhibitors (NIs), polymer‐coated fertilizers (PCFs), and urease inhibitors (UIs)] on N₂O and NO emissions, we performed a meta‐analysis using field experiment data (113 datasets from 35 studies) published in peer‐reviewed journals through 2008. The results indicated that NIs significantly reduced N₂O emissions (mean: ?38%, 95% confidential interval: ?44% to ?31%) compared with those of conventional fertilizers. PCFs also significantly reduced N₂O emissions (?35%, ?58% to ?14%), whereas UIs were not effective in reducing N₂O. NIs and PCFs also significantly reduced NO (?46%, ?65% to ?35%; ?40%, ?76% to ?10%, respectively). The effectiveness of NIs was relatively consistent across the various types of inhibitors and land uses. However, the effect of PCFs showed contrasting results across soil and land‐use type: they were significantly effective for imperfectly drained Gleysol grassland (?77%, ?88% to ?58%), but were ineffective for well‐drained Andosol upland fields. Because available data for PCFs were dominated by certain regions and soil types, additional data are needed to evaluate their effectiveness more reliably. NIs were effective in reducing N₂O emission from both chemical and organic fertilizers. Moreover, the consistent effect of NIs indicates that they are potent mitigation options for N₂O and NO emissions.