Evaluation of N2O emission from rainfed wheat field in northwest agricultural land in China

The net greenhouse gas (NGHG) emissions and net greenhouse gas intensity (NGHGI) were investigated via the determination of nitrous oxide (N₂O) emission in loess soil under rainfed winter wheat monocropping system during 3 years of field study in Northwest China. Five treatments were carried out: control (N₀), conventional nitrogen (N) application (NCₒₙ), optimized N application with straw (SNOₚₜ), optimized N application with straw and 5% of dicyanodiamide (SNOₚₜ + DCD), and optimized N rate of slow release fertilizer with straw (SSRFOₚₜ). Over a 3-year period, the NGHG emissions were achieved 953, 1322, 564, and 1162 kg CO₂-eq ha⁻¹, simultaneously, and the NGHGI arrived 158, 223, 86, and 191 kg CO₂-eq t⁻¹ grain in NCₒₙ, SNOₚₜ, SNOₚₜ + DCD, and SSROₚₜ grain, respectively. Contrasted with conventional farming system, optimized farming methods reduced 32% of N fertilizer use without significant decrease in grain yield, but brought about 38% increase in N₂O emissions, up to 28% gained in soil CH₄ uptake. Thus, it was observed that the straw incorporation performs noticeable increased in N₂O emissions in the winter wheat cropping season. Among the optimized N fertilizer rates compared with the SNOₚₜ treatment, the SNOₚₜ +DCD and SSROₚₜ treatments decreased in N₂O emissions by approximately 55% and 13%, respectively. Additionally, the N₂O emission factor across over a 3-year period was 0.41 ± 0.08% derived from N fertilizer, and it was half of IPCC default values for upland corps. It is expected possibly due to low precipitation and soil moisture with the monocropping system. The 25% higher in the amount of rainfall (almost 300 mm in 2013–2014) during a cropping season underwent into 1–2-fold increase in N₂O emissions from N-fertilized plots. As the statistical differences among annual cumulative emissions coincided with that during winter wheat growing season, it can be concluded that crop growing season is a vital important period for the determination of N₂O emissions from under rainfed monocropping system.