Purpose

The purpose of this commentary is to call for consistent and improved methodology for agricultural carbon footprint (CF) studies.

Methods

The methods of published agricultural CF studies were compared to identify areas of inconsistency. Organic agriculture has been proposed as an approach to reduce net agricultural greenhouse gas (GHG) emissions and sequester carbon. Therefore we used organic agriculture as a focal system to explore the impact on CF estimates of using inconsistent boundaries, soil emission accounting, and emission factor (EF) tiers.

Results and discussion

Studies of agricultural CF use inconsistent boundaries and most use EFs based on national averages or regional models. As a result the local and farm-to-farm variability of EFs are obscured and the comparability of CFs from different studies is dubious. We propose three principles for agricultural CF calculation: use of consistent broad agricultural system CF boundaries, incorporation of soil emissions and sequestration, and development and use of fine-scale EFs for agricultural inputs. The potential use of organic practices in GHG mitigation efforts, along with the annual inspection process for certified organic farms, justify the future use of organic farms as a longitudinal national or international study population using the proposed principles.

Conclusions

Using different boundaries, or generalized vs. site-specific EFs, can give not only different levels of precision but also fundamentally different answers. Policy based on averaged data or incomplete estimates may be misdirected. To support effective policy and individual decision-making that reduce GHG emissions and/or sequester more carbon, accurate and consistent assessments of the GHG emissions of agricultural practices and systems at a finer temporal and spatial scale are needed.

中文翻译：

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改善农业系统的碳足迹：边界，层级和有机农业

目的

本评论的目的是呼吁对农业碳足迹（CF）研究进行一致且改进的方法。

方法

比较了已发表的农业CF研究方法，以确定不一致的区域。已经提出有机农业作为减少农业净温室气体（GHG）排放和隔绝碳的方法。因此，我们以有机农业为重点系统，探讨了使用不一致的边界，土壤排放核算和排放因子（EF）层对CF估算的影响。

结果与讨论

农业CF使用边界不一致的研究，大多数使用基于国家平均值或区域模型的EF。结果，EF的局部和农场间差异被掩盖了，来自不同研究的CF的可比性令人怀疑。我们提出了农业CF计算的三项原则：使用一致的广泛农业系统CF边界，纳入土壤排放和固碳，以及开发和使用用于农业投入物的小规模EF。在减缓温室气体的努力中可能使用有机做法，以及对经过认证的有机农场进行年度检查，证明了使用拟议原则将有机农场作为国家或国际纵向研究人群的未来用途是合理的。

结论

使用不同的边界或广义的EF与特定于站点的EF，不仅可以提供不同级别的精度，而且可以提供根本不同的答案。基于平均数据或不完整估计的策略可能会被误导。为了支持减少温室气体排放和/或封存更多碳的有效政策和个人决策，需要在更精细的时间和空间范围内对农业实践和系统的温室气体排放进行准确，一致的评估。