Enhanced efficiency nitrogen fertilizers were not effective in reducing N_2O emissions from a drip-irrigated cotton field in arid region of Northwestern China

摘要

Drip irrigation is an effective water-saving strategy for crop production in arid regions. However, limited information is available on how fertilizer nitrogen (N) management affects soil nitrous oxide (N_2O) emission under drip irrigation. A two-year (2017-2018) field experiment was conducted in arid northwestern China to test management options of fertilizer N to reduce N_2O emission and improve NUE of cotton (Gossypium hirsutum L.) under drip irrigation. Treatment included a factorial design of rate (120, 240 kg N ha~(-1)) and source of N fertilizer (Urea, polymer-coated urea-ESN, stabilized urea with nitrification and urease inhibitors-SuperU), and an unfertilized Control. Urea was split-applied with irrigation water (fertigation) whereas ESN and SuperU were all side-banded at pre-plant. Crop yield and N uptake, soil mineral N concentrations, soil temperature and moisture, and N_2O fluxes were determined. Across the two growing seasons, a single pre-plant application with ESN or SuperU significantly increased growing season cumulative N_2O emissions (∑N_2O) by 29-47% and applied N-scaled emission factor (EF) by 57-83% compared to urea fertigation, irrespectively of application rate. In contrast, cotton yield, agronomic NUE, apparent N recovery (ANR), and yield-based N_2O emission intensity (EI) were not affected by N source. Reducing N rate from 240 to 120 kg N ha~(-1) significantly decreased IN_2O by 35% in 2017 and 36% in 2018 while simultaneously reduced cotton yield in both years. The increased N_2O emissions with ESN and SuperU were attributed to greater availability of inorganic N resulted from one-time application at pre-plant and higher soil temperature. We concluded that fertigation with urea at the recommended rate is the best option to ensure agronomic productively and agronomic NUE with minimal risk of N_2O emissions. In contrast, the benefit of enhanced efficiency N fertilizer is limited and recommendation on using of these products is challenging for arid croplands under drip irrigation.