Abstract: The objective of this study was to examine the effects of combined application of organic manure and nitrapyrin (CP) on nitrogen transformation, N₂O and NH₃ emissions, and ammonia-oxidizing bacteria and archaea (AOA and AOB) in red soil. An incubation experiment was carried out with five treatments, including no fertilization (CK), only urea, urea + CP, 60% urea + cattle manure, and 60% urea + cattle manure + CP. The results showed that the nitrapyrin addition treatments significantly increased soil NH₄⁺-N concentration and reduced NO₃^--N concentration within 36 days after incubation (P<0.05) compared to only urea and 60% urea + cattle manure treatments. Urea or urea plus manure treatment significantly increased soil potential nitrification rate and microbial biomass carbon and nitrogen (P<0.05) at seven days after incubation, which were significantly decreased by the addition of nitrapyrin. qPCR results showed that urea combined with manure application significantly increased both AOA and AOB gene abundance, while nitrapyrin application significantly reduced the gene abundance of AOA rather than that of AOB. The AOA abundance in nitrapyrin addition treatment recovered to the level in no nitrapyrin treatments at 36 days of incubation. Soil potential nitrification rate was significantly correlated with AOA and AOB (P<0.001). Reduced urea combined with manure application significantly reduced N₂O and NH₃ emissions compared with urea application alone during the  incubation, while the addition of nitrapyrin further significantly reduced N₂O emissions but increased NH₃ emissions. NH₄⁺ and pH were the key factors affecting the abundance of AOA and AOB gene. AOA contributed more to N₂O emissions than AOB in this red soil. In conclusion, nitrapyrin combined with urea or organic manure application could mitigate N₂O emission, but increase the risk of NH₃ volatilization.

Key words: acid red soil, nitrapyrin, N₂O, NH₃, real-time quantitative PCR.