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Fast development of farming practices in China is projected to result in additional carbon emissions and thus affect farmland ecosystems' environmental performance. Based on 454 farm surveys on the North and Northeast China Plain, the carbon footprint (CF) of two farmland ecosystems (irrigated system for wheat and maize on the North China Plain and rainfed system for maize on the Northeast Plain) were assessed and emission reduction pathways explored by quantifying greenhouse gas emissions of agricultural inputs and farm practices during the entire crop growing seasons with an agricultural footprint model. The results demonstrated that the GHG emissions from wheat and maize rotation in the irrigated system were 7.63 t CO 2 eq ha -1 and 3.17 t CO 2 eq ha -1 for single season maize in the rainfed system. While energy consumption accounted for 12.5%-21.3% of the carbon footprint in both systems, the group assessment found that the largest difference in GHG emissions between the high and low emission groups came from mechanical energy consumption. Approximately 50.6% and 39.2% of the mechanical carbon footprint of wheat and maize, respectively, were caused by irrigation practices in the irrigated system. Regarding the rainfed system, where 46.6% of mechanical carbon emissions were generated by maize tillage operations. In addition, scenario analysis indicated that the mechanical carbon footprint could be reduced to 56 kg CO 2 eq t -1 for NCP-wheat and 26 kg CO 2 eq t -1 for NCP-maize, respectively, by optimizing yields and irrigation practices in irrigated systems and that the mechanical carbon footprint of NEP-maize could be reduced to 25 kg CO 2 eq t -1 by optimizing yields and tillage practices in rainfed systems. Therefore, improvement in mechanization in irrigation and tillage practices can contribute to reduce GHG emissions in China. Water-saving irrigation technology is recommended in irrigated area and conservation tillage is recommended in rainfed agricultural area to reduce carbon footprints., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Dongyu Cai reports financial support was provided by the National Key Research and Development Program of China. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The adsorbed CO 2 molecules can be easily activated to CO 2 * species by accepting electrons, which subsequently react with the activated H* species to generate the formate or CO intermediate species. Then, the generated intermediate species can be deeply hydrogenated to produce CH 4. The Co0 species and oxygen vacancies on the xCo/MnO catalysts surface both act as the active centers to catalyze the CO 2 hydrogenation reaction. The Co loading can deeply affect the CO 2 hydrogenation reaction by affecting the concentration of oxygen vacancies, metal-support interaction and the basic site numbers on the prepared xCo/MnO catalysts, which are critical to the formation of active centers and the CO 2 adsorption ability of the xCo/MnO catalysts. [Display omitted] • xCo/MnO catalysts with high CO 2 hydrogenation performances can be prepared. • The Mn 1-y Co y O solid solution can be formed in the prepared xCo/MnO catalysts. • Co0 species are the main active centers for CO 2 hydrogenation. • The basic and hydrogenation active sites can be regulated by Co loading. CO 2 hydrogenation technology has great potential for mitigating the greenhouse effect and creating a green economy. The development of catalysts plays a key role in the progress of CO 2 hydrogenation technology. In this study, the xCo/MnO catalysts for CO 2 hydrogenation reaction were prepared by the impregnation method using MnO x as the catalyst support. And the effects of the Co loading on the CO 2 hydrogenation performances of the prepared xCo/MnO catalysts were investigated. The active Co0 species on the xCo/MnO catalysts surface are the main active centers for the CO 2 hydrogenation reaction, and the medium basic sites on the xCo/MnO catalysts are the main CO 2 adsorption sites. The MnO x support possesses a large number of medium basic sites, which can enhance the CO 2 molecules adsorption ability of the xCo/MnO catalysts. An effective regulation of the basic and hydrogenation active site numbers on the xCo/MnO catalysts surface can be achieved by changing the Co loading amount, which in turn can affect the CO 2 molecules adsorption, activation and hydrogenation abilities of the xCo/MnO catalysts. Moreover, the Mn 1-y Co y O solid solution was found to be formed in the prepared xCo/MnO catalysts, which is conducive to the dispersion of metal Co nanoparticles on the MnO surface and the generation of oxygen-deficient sites. The CO 2 desorption amount on the 12Co/MnO catalyst reached 1.76 mmol/g, which provided the catalyst with strong CO 2 adsorption and activation abilities, enabling it to exhibit great CO 2 hydrogenation performance. Under the conditions of atmosphere and 420 °C, the CO 2 conversion and CH 4 selectivity on the prepared 12Co/MnO catalyst reached 57.5 % and 78.8 %, separately. Furthermore, the CO 2 conversion was able to consistently remain at the initial 57.5 %, and the CH 4 selectivity was maintained above 70.0 % in the 10 times CO 2 hydrogenation cycle tests on the 12Co/MnO catalyst. Our study highlights the potential of using MnO x as catalyst support in the CO 2 hydrogenation reaction, and the findings will provide convenient for the future studies. [ABSTRACT FROM AUTHOR]