关中平原饲料作物生产的碳足迹及影响因素研究

畜牧业是主要的人为温室气体排放源,而饲料作物生产是畜牧业温室气体排放的主要来源之一.研究饲料作物生产的碳足迹及减排措施对于从日粮的角度减少畜牧业的温室气体排放至关重要.因此,本文应用生命周期评价理论和IPCC(2006)田间温室气体计算方法,建立了饲料作物碳足迹评估方法,分析了关中平原饲料作物的温室气体排放特点和减排措施及潜力.结果表明:关中平原主要饲料的碳足迹(以CO_2当量计)由大到小依次为玉米0.620、苜蓿0.382、小麦麸皮0.240、青饲玉米0.217、小麦秸秆0.083和玉米秸秆0.070 kg·kg~(-1);主要排放环节是化肥生产、氮肥田间排放和灌溉,对碳足迹的贡献率分别为26.0%~33.8%、27.8%~29.6%和24.5%~39.1%.由于关中平原存在过量施肥和大水漫灌的现象,通过化肥减施和节水灌溉措施减少饲料作物碳足迹的潜力很大,但不同措施带来的实际减排量仍需通过田间实践和具体技术的生命周期评价进行验证.

Carbon footprint and its impact factors of feed crops in Guanzhong Plain

Livestock is one of the main anthropogenic sources of GHG emissions. Feed production is an important factor to affect the GHG emissions from livestock. It is therefore important to study the carbon footprint of feed crops and options for reducing the emissions of livestock based on feed ration. In order to identify the basis data of greenhouse gas emissions from feed crops, a survey about the cultivation of feed crops was carried out in Guanzhong Plain in June 2015. Based on the theory of life cycle assessment (LCA) and the GHG calculation method of IPCC (2006), the study analyzed the GHG emission characteristics and reduction potential of feed crops in Guanzhong Plain. The results showed that the carbon footprint of feed crops in Guanzhong Plain was corn grain 0.620, maize straw 0.070, wheat bran 0.240, wheat straw 0.083, silage maize 0.217 and alfalfa 0.382 kg CO_2eq·kg^-1 DM, respectively. Corn is the main component of the concentrated feed of dairy cattle, and its carbon footprint is significantly higher than that of roughage, such as alfalfa, silage corn, corn straw and wheat straw. The three main impact factors of GHG emission are chemical fertilizer production, field emission from nitrogen fertilizer, and irrigation, which contributes 26.0%~33.8%, 27.8%~29.6% and 24.5%~39.1% to carbon footprint, respectively.Under optimized fertilization conditions, the carbon footprint of corn, wheat and alfalfa could be decreased by 18.3%,22.4% and 42.1%, respectively. Irrigation as the second biggest sources of the greenhouse gas emission accounted for 26.7%~39.1% of the total GHG emission. Due to the existence of the phenomenon of excessive fertilization and flood irrigation in Guanzhong Plain, there is a significant potential to reduce greenhouse gas emission through reasonable fertilizer application and water-saving irrigation measures.