Carbon footprint assessment for irrigated and rainfed maize (Zea mays L.) production on the Loess Plateau of China

Abstract

Although irrigation increases maize yield, its environmental costs, especially those associated with greenhouse gas (GHG) emissions, remain unclear. This study evaluated the differences and mitigated potentials of carbon footprint in irrigated and rainfed maize systems, based on a survey of 120 farmers and a life cycle assessment (LCA). The results indicated that the GHG emission of irrigated system was 5.33 Mg CO2 eq ha−1, 40% higher than that in rainfed system, mainly due to the increased consumption of electricity and increased fertiliser application (especially nitrogen). However, the average yield in irrigated system was 10.0 Mg ha−1, 2.1 times that of rainfed system (4.7 Mg ha−1), and therefore the carbon footprint was lower by 37%. Fertiliser production, transportation and application contributed 85–95% to the carbon footprint in rainfed system and 79–86% in irrigated system, while the electricity used for irrigation accounted for 9–16% of the carbon footprint in irrigated system. Grouping assessment found that higher yield and lower carbon footprint existed in win–win group in both systems. In addition, scenario analysis shows that the carbon footprint could be reduced to 362 kg CO2 eq Mg−1 for rainfed system and to 285 kg CO2 eq Mg−1 for irrigated system by optimising crop, fertiliser, and water management. In conclusion, the irrigated system could produce more grain with a lower carbon footprint even though it required more energy, water and fertilisers in this study. And the carbon footprint could be further cut down through optimised integrative management in both rainfed and irrigated systems.