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

Dinitrogen (N 2 ) and nitrous oxide (N 2 O) produced via denitrification may represent major nitrogen (N) loss in terrestrial ecosystems. A global assessment of soil denitrification rate, N 2 O/(N 2 O+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 ( EF D ) was 4.8%. The average N 2 O/(N 2 O+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 (NO 3 - ) 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 N 2 O/(N 2 O+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. • We used 225 studies (3367 observations) to conduct a global assessment of soil denitrification rate, N 2 O/(N 2 O+N 2 ), and their driving factors and mitigation strategies. • 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. • Soil denitrification rate and N 2 O/(N 2 O+N 2 ) were highly related to soil properties. • 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.