Enhanced efficiency nitrogen fertilizers were not effective in reducing N2O emissions from a drip-irrigated cotton field in arid region of Northwestern China

Abstract

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 (N2O) 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 N2O 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 N2O fluxes were determined. Across the two growing seasons, a single pre-plant application with ESN or SuperU significantly increased growing season cumulative N2O emissions (ƩN2O) 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 N2O emission intensity (EI) were not affected by N source. Reducing N rate from 240 to 120 kg N ha−1 significantly decreased ƩN2O by 35% in 2017 and 36% in 2018 while simultaneously reduced cotton yield in both years. The increased N2O 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 N2O 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.