Carbon footprint of synthetic nitrogen under staple crops: A first cradle‐to‐grave analysis

• Published in: Global change biology 2024-04, Vol.30 (4), p.e17277-n/a
• Main Authors: Abdo, Ahmed I., Sun, Daolin, Yang, Kai, Li, Yazheng, Shi, Zhaoji, Abd Allah, W. E., El‐Sobky, El‐Sayed E. A., Wei, Hui, Zhang, Jiaen, Kuzyakov, Yakov
• Format: Article
• Language: English
• Subjects: Anthropogenic factors; Biodiesel fuels; Biofuels; Biological fertilization; Biomass; Carbon; Carbon dioxide; Carbon footprint; Cereal crops; Climate change; Crops; Fertilization; Fertilizer application; Fertilizers; Food; Food conversion; food supply chain; Footprint analysis; GHG emissions; global warming; Grain; Grain crops; Human food; Life cycle; Life cycle analysis; Life cycle assessment; Life cycles; Livestock; Livestock feed; Livestock feeds; Mitigation; Nitrogen; nitrogen agronomic efficiency; Plant biomass; soil and plant systems; synthetic nitrogen; Transport
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.17277

More than half of the world's population is nourished by crops fertilized with synthetic nitrogen (N) fertilizers. However, N fertilization is a major source of anthropogenic emissions, augmenting the carbon footprint (CF). To date, no global quantification of the CF induced by N fertilization of the main grain crops has been performed, and quantifications at the national scale have neglected the CO2 assimilated by plants. A first cradle‐to‐grave life cycle assessment was performed to quantify the CF of the N fertilizers' production, transportation, and application to the field and the uses of the produced biomass in livestock feed and human food, as well as biofuel production. We quantified the direct and indirect inventories emitted or sequestered by N fertilization of main grain crops: wheat, maize, and rice. Grain food produced with N fertilization had a net CF of 7.4 Gt CO2eq. in 2019 after excluding the assimilated C in plant biomass, which accounted for a quarter of the total CF. The cradle (fertilizer production and transportation), gate (fertilizer application, and soil and plant systems), and grave (feed, food, biofuel, and losses) stages contributed to the CF by 2%, 11%, and 87%, respectively. Although Asia was the top grain producer, North America contributed 38% of the CF due to the greatest CF of the grave stage (2.5 Gt CO2eq.). The CF of grain crops will increase to 21.2 Gt CO2eq. in 2100, driven by the rise in N fertilization to meet the growing food demand without actions to stop the decline in N use efficiency. To meet the targets of climate change, we introduced an ambitious mitigation strategy, including the improvement of N agronomic efficiency (6% average target for the three crops) and manufacturing technology, reducing food losses, and global conversion to healthy diets, whereby the CF can be reduced to 5.6 Gt CO2eq. in 2100. Nitrogen fertilization should be considered when addressing the triple challenges: food security, climate change, and environmental degradation. Nitrogen (N) fertilizers contributed to the global warming by 7.4 Gt CO2eq. from the grain crop production and consumption, which is expected to augment substantially by 2100, responding to the increment in food demand. This carbon load of the N fertilization can be reduced by one‐fourth through improving the manufacturing technology of N fertilizers, increasing the N agronomic efficiency, reducing losses, and converting to healthy diets.