Sustained nitrogen release and nitrogen-cycling functional genes jointly shape NH₃-N₂O loss trade-offs under...

Simultaneously mitigating ammonia (NH₃) volatilization and nitrous oxide (N₂O) emissions without compromising crop productivity remains a critical challenge in sustainable nitrogen management. Drawing on a long-term field experiment established in 2013, this study integrated multi-year gaseous nitrogen loss measurements with metagenomic sequencing to assess the performance of polymer-coated fertilizer (PCF) and sulfur-coated fertilizer (SCF) relative to conventional urea (CU) in intensive maize production. Both coated urea treatments substantially suppressed NH₃ losses relative to CU, with PCF achieving consistent reductions of 72.3%-92.8% and SCF showing more variable reductions of 28.8%-89.7%. However, sustained nitrogen release from coated urea concurrently stimulated N₂O production, with increases of 8.3%-114.3% under PCF and 15.5%-88.9% under SCF. Critically, NH₃ mitigation substantially outweighed the N₂O penalty, enabling PCF to reduce the combined NH₃ and N₂O losses by 39.8%-69.5% and yield-scaled losses by 45.9%-70.9%, respectively, while enhancing crop yield by 4.7%-11.2%. Soil enzyme assays and metagenomic analyses suggested that NH₃ suppression was associated with reduced urease activity and enrichment of archaeal ammonia oxidation and downstream nitrification genes under PCF, whereas elevated N₂O emissions were correlated with sustained soil inorganic nitrogen replenishment that appeared to override concurrent declines in denitrification genes. These findings suggest that PCF reduces the combined NH₃ and N₂O losses while sustaining crop productivity, although the N₂O penalty outweighed the climate benefit of NH₃ mitigation in three of four years. The net environmental performance of controlled-release fertilizers therefore depends on the indicators evaluated and was associated with nitrogen release dynamics and the corresponding functional gene networks.