Materials and MethodsLife Cycle Ass

Materials and Methods
Life Cycle Assessment Approach for N Fertilizer Chain .We used a life cycle assessment approach to estimate GHG emissions due to the main components of the N fertilizer chain in China, primarily using Chinese-specific parameters rather than IPCC tier 1 default values. According to the International Organization for Standardization’s International Standard ISO 14042 (34), the life cycle of N fertilizer should be conducted from “cradle to grave.” Therefore, we include GHG emissions associated with mining of fossil fuel used for fertilizer production, transport of fossil fuel, fertilizer synthesis, fertilizer transport and distribution, and gaseous emissions (direct and indirect) when fertilizers are applied to farmland (Fig. 1).