Nitrous oxide emission related to ammonia-oxidizing bacteria and mitigation options from N fertilization in a tropical soil

Nitrous oxide (N 2 O) from nitrogen fertilizers applied to sugarcane has high environmental impact on ethanol production. This study aimed to determine the main microbial processes responsible for the N 2 O emissions from soil fertilized with different N sources, to identify options to mitigate N 2 O emissions, and to determine the impacts of the N sources on the soil microbiome. In a field experiment, nitrogen was applied as calcium nitrate, urea, urea with dicyandiamide or 3,4 dimethylpyrazone phosphate nitrification inhibitors (NIs), and urea coated with polymer and sulfur (PSCU). Urea caused the highest N 2 O emissions (1.7% of N applied) and PSCU did not reduce cumulative N 2 O emissions compared to urea. NIs reduced N 2 O emissions (95%) compared to urea and had emissions comparable to those of the control (no N). Similarly, calcium nitrate resulted in very low N 2 O emissions. Interestingly, N 2 O emissions were significantly correlated only with bacterial amoA , but not with denitrification gene ( nirK , nirS , nosZ ) abundances, suggesting that ammonia-oxidizing bacteria, via the nitrification pathway, were the main contributors to N 2 O emissions. Moreover, the treatments had little effect on microbial composition or diversity. We suggest nitrate-based fertilizers or the addition of NIs in NH 4 + -N based fertilizers as viable options for reducing N 2 O emissions in tropical soils and lessening the environmental impact of biofuel produced from sugarcane.