To explore the effect of biochar on greenhouse gas emissions and the carbon footprint of a corn farmland ecosystem under drip irrigation with film in an arid region, biochar treatments with different application rates[0 (CK), 15 (C15), 30 (C30), and 45 t·hm-2 (C45)] were established. The seasonal changes in soil greenhouse gases (CO2, N2O, and CH4) and their comprehensive warming potential in the maize farmland ecosystem were monitored for two consecutive years after a one-time application of biochar. The carbon emissions caused by agricultural production activities and their carbon footprint were estimated using the life cycle assessment method. Compared with that in CK, the cumulative CO2 emissions in the crop growing season decreased by 17.6%-24.7%, the cumulative N2O emissions decreased by 71.1%-110.4%, and the global warming potential decreased by 19.5%-25.9%. In the second year of the crop growing season after biochar application, the cumulative CO2 emissions were reduced by 19.2%-40.6%, the cumulative N2O emissions were reduced by 38.7-46.7%, and the comprehensive warming potential was reduced by 19.7%-40.5%. For two consecutive years, the treatment of C15 and C30 increased the cumulative absorption of CH4 to different degrees, whereas the treatment of C45 significantly decreased the cumulative absorption of CH4. C15 and C45 were the treatments with the least carbon footprint per unit yield in the current and the succeeding year of biochar application, and their carbon footprint per unit yield was 10.1% and 26.2% lower than that of CK, respectively. Soil greenhouse gas emissions showed the most contribution to the carbon footprint of the maize farmland ecosystem (38.1%-59.2%), followed by nitrogen fertilizer production (19.8%-33.4%), electric energy production (6.7%-8.8%), and plastic film mulching (4.4%-7.4%). Biochar contributed 5.7%-13.8% to the ecosystem's carbon footprint. The application of 30 t·hm-2 biochar had a better effect on carbon reduction, carbon fixation, and yield increase in the farmland ecosystem. Improving the biochar production process and transportation route, increasing nitrogen use efficiency, and developing water-saving and energy-saving irrigation technology are important ways to reduce the carbon footprint of farmland ecosystems in arid regions.
Keywords: biochar; carbon footprint; global warming potential; greenhouse gas; life cycle assessment; water-saving irrigation.