Greenhouse gas accounting for agricultural systems consider methane and nitrous oxide emissions, carbon emissions from liming and urea use, as well as carbon stock changes, but it ignores gross flows of bio-based energy and carbon. This study compiled data for Canada’s agri-food system over the 2010-13 period, from food supply and disposition to crop processing, animal production, and crop/pasture production. The data were converted to units of energy and carbon, tracked through the agri-food system and compared in scale and conversion efficiency with Canadian crude oil recovery to the production of refined petroleum products. Results showed domestic photosynthesis-derived energy and carbon flow equivalent to 75% and 98%, respectively, of the fossil fuel-derived energy and carbon in the crude oil recovered in Canada. This magnitude is substantial since Canada is a nation with high per capita oil demand that exports over 50% of its own production. Only 14% of the agri-food energy and carbon, respectively, emerged in agri-food products, compared to 91% of the energy and carbon in crude oil that resulted in refined petroleum products. The low conversion efficiency of the agri-food system derived, in part, from 40% of bio-based energy and carbon being diverted to crop and animal residues or waste. Per unit of energy in end products, the other energy inputs (e.g. electricity, fuels) needed to support the agri-food system were 5.3-folds higher in the agri-food system than in the crude oil to products system. This study highlights the need to develop strategies to better utilize the energy and carbon flows of the agri-food system, thereby reducing fossil energy use and greenhouse gas emissions associated with human activities.

用于农业系统的温室气体考虑了甲烷和一氧化二氮的排放，石灰和尿素使用的碳排放以及碳储量的变化，但它忽略了生物能源和碳的总流量。这项研究汇总了2010-13年间加拿大农业食品系统的数据，从食物的供应和处置到作物加工，动物生产以及作物/牧草生产。将数据转换为能量和碳的单位，通过农业食品系统进行跟踪，并将规模和转换效率与加拿大原油回收与精炼石油产品的生产进行比较。结果表明，加拿大回收的原油中，国内光合作用产生的能量和碳流量分别相当于化石燃料产生的能量和碳的75％和98％。由于加拿大是一个人均石油需求量大的国家，其出口量超过其本国产量的50％，因此这一幅度非常可观。农业食品产品中仅产生了14％的农业食品能源和碳，而产生精炼石油产品的原油中能源和碳却只有91％。农业食品系统的转换效率低，部分原因是40％的生物基能源和碳被转用于作物和动物残留物或废物。每单位最终产品中的能源消耗，支持农业食品系统所需的其他能源输入（例如电力，燃料）比原油到产品系统高5.3倍。这项研究强调了制定策略以更好地利用农业食品系统的能量和碳流量的必要性，