Nitrogen fertilizer management for mitigating ammonia emission and increasing nitrogen use efficiencies by ¹⁵N stable...

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.