Sustainable Transportation Energy Pathways (STEPS)
Available online at: http://dx.doi.org/10.1016/j.biombioe.2013.08.008
Murphy, Colin and Alissa Kendall (2013) Life Cycle Inventory Development for Corn and Stover Production Systems Under Different Allocation Methods. Biomass and Bioenergy in press
Agricultural residues, particularly corn stover, are a promising feedstock for bioenergy systems. To analyze these systems in a life cycle framework, environmental impacts from cultivation and harvest must be allocated to the resulting products, corn grain and stover. This paper explores three approaches to allocation for corn and stover: economic and energy-based allocation, as well as a subdivision approach, which assigns to stover only those additional activities caused by its harvest.
This study develops a life cycle inventory for corn production based on average U.S. agronomic data and then applies the three allocation methods to produce a life cycle inventory for stover. This inventory contains over 1100 environmental flows and is available in the online Supplementary material. This analysis shows that economic allocation and subdivision assign the least impact to stover (14–15%), energy-based allocation the most (30%). One hectare of corn and stover production emits approximately 2.5 tonnes of carbon equivalent and requires approximately 23 GJ of fossil energy.
Value-based allocation methods, like energy and economic allocation, may be most appropriate when they reflect the goals of the production system. In addition, value-based methods are typically simple to apply, and thus may be more transparent for those interpreting a study. Subdivision, as applied in this study, reflects the consequences of changing the existing corn production systems, may require more data, and might be most appropriate for near-term prospective analyses; such as those that question whether adding cellulosic ethanol production to existing corn production systems yields environmental benefits. Thus, the selection of an allocation approach should hinge on the intent of the study.
Keywords: Corn stover, Life cycle inventory; Allocation; Feestock; LCA; Co-products