Abstract: 【Objective】To conduct a comprehensive assessment of the carbon sequestration and emission reduction effect of the whole life cycle of complex integrated cropping-breeding farming system based on scientific agricultural carbon assessment method, which is the basis for the design and optimization of low-carbon farming system in China from the perspective of the whole industry chain. This study compared five system scenarios and their corresponding carbon footprint assessment frameworks for crop-livestock cycle industry chain, intending to provide scientific, reasonable and usable methodological references for the creation of low-carbon farming systems. 【Method】A carbon footprint accounting based on life cycle assessment published by ISO 14040 and greenhouse gas accounting provided by IPCC were combined in this study to construct a carbon footprint evaluation framework for the integrated cropping-breeding farming systems under the different system boundaries. The Maize-Cow-Recycling Manure model in tropical crop areas of South China was used as case to validate the effect of the proposed accounting framework. 【Result】 The assessment framework clarified that the whole chain of the integrated and separated crop-livestock models both had six accounting links, including agricultural inputs, crop cultivation, animal breeding, manure management, transportation and soil carbon sink. Furthermore, the carbon measurement logic of each link and its carbon footprint accounting method were analyzed. The case results showed that the whole-life carbon footprint of the integrated crop-livestock model was 20.73% lower than that of the separated model, showing better carbon sequestration and emission reduction effect. The assessment framework could fully reflect the "indirect emissions" of upstream agricultural production and transportation, as well as the "alternative emissions reduction" of downstream feed substitution and waste recycling after "coupling" or "decoupling" of farming. In addition, the evaluation results were more closely related to the actual production of the farming system in the integrated cropping-breeding farming system by combing the field measurement data and research data as well as the model evaluation parameters of the background system. 【Conclusion】The carbon footprint assessment framework of farming systems in the integrated cropping-breeding farming system constructed in this study was able to conduct a comprehensive carbon sequestration and emission reduction effects of the industrial chain in integrated and separated systems under the whole life cycle perspective and reasonable system boundary, which could provide directions for optimization.

Key words: carbon footprint, life cycle assessment, crop-livestock integrated system, low-carbon farming system, system boundary, accounting framework