Abstract: The excessive application of nitrogen fertilizers in agriculture increases emission of nitrous oxide (N₂O), a greenhouse gas, while the issue of low nitrogen use efficiency remains unresolved. Based on a chamber incubation experiment under constant temperature and humidity conditions, we investigated the effects of combined application of nitrification inhibitors (DCD) and denitrification inhibitors (an  acid-ester compound, referred to as PCB) on soil N₂O emission. There were four treatments: urea alone, urea+DCD, urea+PCB, and urea+DCD+PCB. The results showed that treatments with nitrification inhibitors alone and denitrification inhibitors alone reduced cumulative N₂O emission by 13.4% and 12.3%, respectively, by decreasing the AOB amoA and nirK genes, respectively. The addition of urea+DCD reduced the abundance of the AOB amoA gene by 16.7% and 22.7% on day 1 and 7 of cultivation, respectively. The addition of urea+PCB reduced the abundance of the nirK gene by 23.3% and 16.5% on day 7 and 35 of cultivation, respectively. However, the combined application of nitrification and denitrification inhibitors synergistically regulated soil nitrogen transformation by inhibiting both nitrification and denitrification, in that it reduced soil nitrification potential, soil nitrate reductase activity, the abundance of AOB amoA genes by 11.0%-29.4% and nirK genes by 8.0%-38.8%, resulting in a 19.7% reduction of N₂O emissions. Our results provide theoretical support and technical guidance for reducing greenhouse gas emissions in agriculture.

Key words: soil nitrogen transformation, nitrous oxide emission, dicyandiamide, acid-ester compound