『Abstract
　Literature reports on N2O and NO emissions from organic and mineral agricultural soil amended with N-containing fertilizers have reached contradictory conclusions. To understand the influence of organic manure (OM) and chemical fertilizer application on N2O and NO emissions, we conducted laboratory incubation experiments on an agricultural sandy loam soil exposed to different long-term fertilization practices. The fertilizer treatments were initiated in 1989 at the Fengqiu State Key Agro-ecological Experimental Station and included a control without fertilizer (CK), OM, mineral NPK fertilizer (NPL), mineral NP fertilizer (NP), and mineral NK fertilizer (NK). The proportion of N emitted as NO and N2O varied considerably among fertilizer treatments, ranging from 0.83％ to 2.50％ as NO and from 0.08％ to 0.36％ as N2O.Cumulative NO emission was highest in the CK treatment after NH4⁺-N was added at a rate of 200 mg N kg^-1 soil during application of fertilizers significantly reduced NO emission by 54-67％. In contrast, the long-term application of NPK fertilizer and OM significantly enhanced N2O emission by 95.6％ and 253％, respectively, compared to CK conditions. The addition of NP fertilizer (no K) significantly reduced N2O emission by 25.5％, whereas applications of NK fertilizer (no P) had no effect. The difference among the N-fertilized treatments was due probably to discrepancies in the N2O production potential of the dominant ammonia-oxidizing bacteria (AOB) species rather than AOB abundance. The ratio of NO/N2O was approximately 24 in the CK treatment, significantly higher than those in the N-fertilized treatments (3-11), and it decreased with increasing N2O production potential in N-fertilized treatments. Our data suggests that the shift in the dominant AOB species might produce reciprocal change in cumulative NO and N2O emissions.

Keywords: Nitrous oxide; Nitric oxide; Nitrification; Ratio of NO/N2O; Ammonia-oxidizing bacteria』

1. Introduction
2. materials and methods
　2.1. Study site and sampling
　2.2. Soil analysis and enumeration of ammonia-oxidizing bacteria
　2.3. Laboratory incubation
　2.4. Statistical analysis
3. Results
　3.1. general soil properties
　3.2. AOB population
　3.3. Changes in NH4⁺ and NO3^- concentration
　3.4. N2O emissions
　3.5. NO emission and ratio of NO/N2O
　3.6. Chemical production of N2O and NO
4. Discussion
　4.1. Effect of organic manure and mineral fertilizer on N2O production potential
　4.2. Effect of organic manure and mineral fertilizer on NO production potential and ratio of NO/N2O
5. Conclusion
Acknowledgements
References