Greenhouse gas emissions from synthetic nitrogen manufacture and fertilization for main upland crops in China

Background A significant source of greenhouse gas (GHG) emissions comes from the manufacture of synthetic nitrogen (N) fertilizers consumed in crop production processes. And the application of synthetic N fertilizers is recognized as the most important factor contributing to direct N2O emissions from agricultural soils. Based on statistical data and relevant literature, the GHG emissions associated with synthetic N manufacture and fertilization for wheat and maize in different provinces and agricultural regions of China were quantitatively evaluated in the present study. Results During the 2015-2017 period, the average application rates of synthetic N for wheat and maize in upland fields of China were 222 and 197 kg ha(-1), respectively. The total consumption of synthetic N on wheat and maize was 12.63 Mt year(-1). At the national scale, the GHG emissions associated with the manufacture of synthetic N fertilizers were estimated to be 41.44 and 59.71 Mt CO2-eq year(-1) for wheat and maize in China, respectively. And the direct N2O emissions derived from synthetic N fertilization were estimated to be 35.82 and 69.44 Gg N2O year(-1) for wheat and maize, respectively. In the main wheat-cultivating regions of China, area-scaled GHG emissions were higher for Inner Mongolia, Jiangsu and Xinjiang provinces. And for maize, Gansu, Xinjiang, Yunnan, Shannxi and Jiangsu provinces had higher area-scaled GHG emissions. Higher yield-scaled GHG emissions for wheat and maize mainly occured in Yunnan and Gansu provinces. Conclusions The manufacture and application of synthetic N fertilizers for wheat and maize in Chinese croplands is an important source of agricultural GHG emissions. The current study could provide a scientific basis for establishing an inventory of upland GHG emissions in China and developing appropriate mitigation strategies.