Nitrogen fertilizer management for mitigating ammonia emission and increasing nitrogen use efficiencies by 15N stable isotopes in winter wheat

Abstract Chemical nitrogen (N) fertilizer is essential for achieving high yield in winter wheat. However, the over–use of N fertilizer not only significantly reduces N use efficiencies (NUEs) but also leads to serious environmental concerns. An efficient N fertilizer management is thus urgently required for mitigating NH3 volatilization and increasing grain yield and NUEs of wheat. A 3–year field study using 15N stable isotopes was conducted to evaluate the fate of 15N–labelled fertilizer and to investigate the NH3 flux, grain yield, yield–scaled NH3 emissions and NUEs of various N application rates under two different application techniques comprising split–N method (basal N plus top–dressed N application) and pre–plant–only (without top–dressed N). Daily NH3 fluxes peaked within one week after basal N fertilizer application. Total NH3 volatilization, NH3 emission factor (EF) and yield–scaled NH3 emission were enhanced significantly with an increase in N application rates. Pre–plant–only N method greatly increased total NH3 volatilization, NH3 EF and yield–scaled NH3 emission by 43%, 58% and 63%, respectively, compared with split–N method when averaged across N application rates and years. The residual 15N in soil and the unaccounted 15N losses were greater under pre–plant–only N method and under high N application rate compared with split–N method and under low N application rate, respectively. Higher values of unaccounted 15N loss (nearly 50% of the total N applied) and residual 15N (27% of the total N applied) were the major contributors to lower NUEs, that could be predominantly attributed to the higher NH3 emission under elevated N application rate and pre–plant–only N method. Considering the overall environmental impact and yield performance, 120 kg N ha–1 in combination with split–N method could be recommended for improving the overall economic return and mitigating environmental pollution to ensure cleaner production of winter wheat.