Allocation in field crop and livestock life cycle assessment

Main Presenter:    Nicole Bamber 

Co-Authors:   Roland Kroebel     Sally Willis-Stewart      Nathan Pelletier                                    

Field crops and livestock are important economic sectors, but are also significant contributors to a variety of environmental impacts such as greenhouse gas emissions, acidification, eutrophication, and land use [1]. Life cycle assessment (LCA) is a commonly used tool to assess the environmental impacts of supply chains, including for the agri-food sector. In LCA, allocation is used to partition these life cycle impacts when processes produce multiple co-products, such as different parts of a field crop, or multiple animal products produced from a single livestock species. The choice of allocation methods can have a large impact on the results of an LCA. However, the ISO 14044 guidelines [2] which are meant to inform these methodological choices are lacking in clarity and consistent application. Therefore, the goals of this work were 1) to assess current food sector allocation methods against the ISO guidelines, and 2) to provide recommendations for allocation methods that align with
ISO guidelines for field crop and livestock LCAs. This information can be used to appropriately model the different co-products and wastes associated with field crop and livestock production systems.
The ISO guidelines for LCA recommend to first avoid allocation of impacts by subdividing the process into multiple processes that only produce one product, or by system expansion. If this is not possible, ISO recommends to allocate impacts between co-products based on a biophysical, or causal, relationship between flows. Finally, the last option is to allocate impacts based on another kind of relationship, such as the economic value of the co-products. Despite this hierarchy, economic allocation was found to be performed the most in agricultural LCAs, often justified because it represents the motivation behind producing each co-product. However, the ISO guidelines indicate a preference for natural science-based approach, therefore we provide recommendations in line with biophysical causal pathways. Based on a review of available methods from the literature, we recommend biophysical allocation for the co-products of crop and livestock production, either based on internal causality (such
as metabolic partitioning of energy within an animal) when possible, or external causality (such as the protein or energy content of the products). We provide detailed recommendations for a representative sample of allocation scenarios in crop and livestock product systems. These can be used to enable consistent comparisons of the environmental impacts of different food production pathways, and to inform the optimization of a climate-friendly food system.

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