[Effects of Different Nitrogen Application Measures on NO Emissions in Wheat-maize Rotation System].

To investigate the response of NO emissions from farmland soil to different nitrogen application measures and the factors affecting it in the wheat and jade rotation system in North China, we analyzed the results of the one-time application of fertilizer in the following six treatments： without fertilization （CK）, conventional nitrogen application （urea, one instance of follow-up fertilization, U1）, optimized nitrogen application （20% nitrogen reduction, one instance of follow-up fertilization, U2）, one-time fertilization of controlled-release doped fertilizers （50% urea + controlled-release urea 50%, nitrogen reduction 20%, SRU1）, controlled-release fertilizer one-time fertilization （nitrogen reduction 20%, SRU2）, and inhibitor-type controlled-release fertilizer one-time fertilization （nitrogen reduction 20%, ISRU）, and the differences in NO emission fluxes and soil physicochemical properties were determined. The results showed that soil NO emission fluxes were dynamic during the wheat and jade crop rotation, and the NO emission peaks of the CK, U1, and U2 treatments appeared in the corn season at 4-7d of basal fertilizer and 6-10d of fertilizer, and out of the wheat season its emission peaks appeared in the basal fertilizer at 4-8 d and 6-9 d of fertilizer. The emission peaks of SRU1, SRU2, and ISRU appeared in the basal fertilizer at 10-21 d, 12-20 d, and 12-20 d of fertilizer, respectively, in the corn season and the wheat season. At 21 d and 12-20 d, the application of controlled-release fertilizer significantly reduced the peak and frequency of NO emission. Compared with those in U1, the NO emission fluxes of the U2, SRU1, SRU2, and ISRU treatments were significantly reduced by 8.5%, 20.0%, 33.8%, and 43.6%, respectively, and the NO emission fluxes were higher in the corn season than in the wheat season, which accounted for 58.1%-65.1% of the whole crop rotation cycle. Yield was reduced by 5.9% and 1.9% for the U2 and SRU1 treatments and increased by 1.7% and 7.0% for the SRU2 and ISRU treatments, respectively, compared to that in U1. In the maize season, the ISRU yield increased by 14.6%, the environmental benefit was $581, and the net economic benefit increased by up to 18.6% compared to that in U1, whereas the wheat season showed a decrease in yield and net economic benefit, which resulted in a one-time application of the inhibitor controlled-release fertilizers being more suitable for the maize season. Correlation analysis of NO emission fluxes with the physicochemical indices of soil properties revealed that NO was correlated with moisture, ammonium N, nitrate N, and microbial carbon and nitrate N and nitrogen. NO and moisture, ammonium N, nitrate N, and microbial amount of carbon and nitrogen were significantly positively correlated. Thus, the one-time application of inhibitor-type controlled-release fertilizers played a positive role in reducing labor inputs and environmental benefits, and it could be an effective method of N fertilizer management for maize cultivation in North China.