Evaluation of N2O emission from rainfed wheat field in northwest agricultural land in China
2020
Yang, Yue | Tong, Yan’an | Gao, Pengcheng | Htun, Yin Min | Feng, Tao
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.
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