A global synthesis of soil denitrification: Driving factors and mitigation strategies

Dinitrogen (N-2) and nitrous oxide (N2O) produced via denitrification may represent major nitrogen (N) loss in terrestrial ecosystems. A global assessment of soil denitrification rate, N2O/(N2O+N-2) ratio, and their driving factors and mitigation strategies is lacking. We conducted a global synthesis using 225 studies (3367 observations) to fill this knowledge gap. We found that daily N loss through soil denitrification varied with ecosystems and averaged 0.25 kg N ha(-1). The average emission factor of denitrification (EFD) was 4.8%. The average N2O/ (N2O+N-2) ratio from soil denitrification was 0.33. Soil denitrification rate was positively related to soil water filled pore space (WFPS) (p < 0.01), nitrate (NO3-) content (p < 0.05) and soil temperature (p < 0.01), and decreased with higher soil oxygen content (p < 0.01). N-2 emissions increased with latitude (p < 0.05), WFPS (p < 0.01) and soil mineral N (p < 0.05) but decreased with soil oxygen content (p < 0.05). The N2O/(N2O+N-2) ratio increased with soil oxygen content (p < 0.01) but decreased with organic carbon (C) (p < 0.05), C/N ratio (p < 0.01), soil pH (p < 0.05) and WFPS (p < 0.01). We also found that optimizing N application rates, using ammonium-based fertilizers compared to nitrate-based fertilizers, biochar amendment, and application of nitrification inhibitors could effectively reduce soil denitrification rate and associated N-2 emissions. These findings highlight that N loss via soil denitrification and N-2 emissions cannot be neglected, and that mitigation strategies should be adopted to reduce N loss and improve N use efficiency. Our study presents a comprehensive data synthesis for large-scale estimations of denitrification and the refinement of relevant parameters used in the submodels of denitrification in process-based models.

Automated summary

Soil denitrification can lead to significant nitrogen loss, and the denitrification rate is positively correlated with soil water content, nitrate content, and temperature, with an average emission factor of 4.8% and an average N2O/(N2O+N-2) ratio of 0.33. Latitude, water content, soil mineral nitrogen, and soil oxygen content affect N-2 emissions, while soil oxygen content, organic carbon, C/N ratio, soil pH, and water content affect the N2O/(N2O+N-2) ratio. Optimizing nitrogen application, using ammonium-based fertilizers, applying biochar, and using nitrification inhibitors can effectively reduce soil denitrification rate and N-2 emissions.