Controlled-release nitrogen fertilizer application mitigated N losses and modified microbial community while improving wheat yield and N use efficiency

The extensive application of traditional fertilizer has greatly contributed to wheat yield, accompanied by massive nitrogen (N) loss and environmental pollution. Controlled-release nitrogen fertilizer (CRNF) is expected to improve N use efficiency (NUE) in agricultural systems. Unfortunately, the mechanism by which CRNF reduces N loss and its response to soil microbial communities remains unclear. In this study, common urea, polymer-coated urea (PCU), sulfur-coated urea (SCU) and urea-formaldehyde (UF) were used as materials to analyze the effects of split application of different N sources on wheat yield, NUE, soil N balance, soil bacterial diversity and functional abundance. The results showed that PCU and SCU significantly improved yield relative to urea, with an average increase of 18.20% and 15.73%, respectively. N uptake by wheat in PCU, SCU and UF was increased by 18.76%, 14.26% and 7.75% compared to that in urea, respectively. CRNF increased the mineral N content of the topsoil (0−20 cm) but decreased the mineral content in the deeper soil (40−60 cm). CRNF was observed to significantly decrease cumulative N2O emissions, as well as apparent N loss compared with urea, which was reduced by 39.45%, 30.74% and 11.68% in PCU, SCU and UF, respectively. In addition, PCU decreased soil bacterial diversity but increased the abundance of microbes involved in N cycle, such as Firmicutes, Actinobacteriota and Bacteroidota, which could regulate soil nitrate concentrations. The results indicated that split application of PCU was conducive to promoting N uptake by wheat, increasing topsoil mineral N content, reducing N leaching into deeper soil and N2O emissions, thereby alleviating N loss while increasing NUE and wheat yield.