In order to find the effective mitigation means and lead dairy farming systems to low-carbon development, it is important to estimate greenhouse gas (GHG) emissions from dairy farming systems accurately. The paper developed an methodology to estimate the GHG emissions from dairy farming systems based on the life cycle assessment (LCA), combined with the specific situation of China's dairy farming systems, and the method was applied to estimate GHG emissions of a typical large-scale dairy farming system at the suburb in Xi'an city. The results showed that the large emission sources were enteric fermentation, feed production and processing, waste storage, accounting for 48.86%, 18.97% and 16.39% of the total emissions, respectively. The main compositions of greenhouse gas were CR4, N2O, accounting for 55.56% and 26.9% of the entire system. The emission per kg of raw milk corrected by protein and fat (FPCM) was 1.52 kg CO2-eq, which is lower than the average global emissions from mixed feeding systems, but higher than that of the European countries. So, there was big potential possibility to mitigate emissions. Emissions from individual sources could be reduced by improving the feed, manure management, field management and other measures, but the contribution to emission reduction of the entire system should be evaluated based on LCA. It is suggested to evaluate mitigation measures based on LCA to obtain the more effective emission reduction measures for the system.%准确评估奶牛养殖系统温室气体排放量是寻求有效减排措施和引导奶牛养殖业低碳发展的基础.该文应用生命周期评价方法,结合中国奶牛养殖业现状,建立了奶牛养殖系统温室气体排放量评估方法;并以此方法分析了西安郊区典型的规模化奶牛场的奶牛养殖系统温室气体排放特点和排放量.结果表明,该奶牛养殖系统主要的温室气体排放环节是奶牛肠道发酵CH4排放、饲料生产与加工、粪便贮存,其排放量分别占整个系统的48.86％、18.97％和16.39％.主要排放的温室气体是CH4、N2O,排放量分别占整个系统的55.56％和26.9％.该奶牛养殖系统每生产1 kg按脂肪和蛋白质纠正的原奶(FPCT)的温室气体排放量(以CO2当量计)为1.52 kg,低于全球平均的混合饲养模式原奶生产的排放量,而高于欧洲国家原奶生产的排放水平,说明减排潜力还很大.通过改善饲料、改进粪便管理模式和肥料田间管理等措施均能够减少单个环节的温室气体排放量,而不同措施对整个系统减排的贡献率还应通过生命周期评价方法进行分析.因此,建议开展不同减排措施下的生命周期评估,以获得对系统减排更有效的措施.
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