Effect of co-application of straw and various nitrogen fertilizers on NO emission in acid soil.

In order to explore the alteration of N transformation and NO emissions in acid soil with the co-application of straw and different types of nitrogen (N) fertilizers, an incubation experiment was carried out for 40 days. There are totally five treatments in the study: (a) without straw and N fertilizer (N0), (b) straw alone application (SN0), (c) straw with NHCl (SN1), (d) straw with NaNO (SN2), and (e) straw with NHNO (SN3). NO emissions, soil physicochemical properties, and abundance/activity of ammonia-oxidizing archaea (AOA) were measured. The results showed that the combined application of straw and N enhanced NO emissions, particularly, SN2 and SN3 treatments. Moreover, the soil pH was lower in co-application treatments and the average decreasing rate was 9.69%. Specially, the pH was lowest in the SN1 treatment. The results of correlation analysis indicated a markedly negative relationship between pH and NO, as well as a negative relationship between pH and net mineralization rate. These findings suggest that pH alteration can affect the N transformation process in soil and thus influence NO emissions. In addition, the dominant AOA at the genus level in the SN2 treatment was Nitrosopumilus, and Candidatus nitrosocosmicus in the SN3 treatment. The reshaped AOA structure can serve as additional evidence of the changes in the N transformation process. In conclusion, as the return of straw, the cumulation of NO from arable acid soil depends on the form of N fertilizer. It is also important to consider how N fertilizer is applied to reduce the possibility of N being lost in the soil as gas.