The need for co-product allocation in the life cycle assessment of agricultural systems—is “biophysical” allocation progress?

Abstract

Purpose Several new Bbiophysical^co-product allocation methodologies have been developed for LCA studies of agricultural systems based on proposed physical or causal relationships between inputs and outputs (i.e. co-products). These methodologies are thus meant to be preferable to established allocation methodologies such as economic allocation under the ISO 14044 standard. The aim here was to examine whether these methodologies really represent underlying physical relationships between the material and energy flows and the co-products in such systems, and hence are of value. Methods Two key components of agricultural LCAs which involve co-product allocation were used to provide examples of the methodological challenges which arise from adopting biophysical allocation in agricultural LCA: (1) the crop production chain and (2) the multiple co-products produced by animals. The actual Bcausal^relationships in these two systems were illustrated, the energy flows within them detailed, and the existing biophysical allocation methods, as found in literature, were critically evaluated in the context of such relationships.Results and discussion The premise of many biophysical allocation methodologies has been to define relationships which describe how the energy input to agricultural systems is partitioned between co-products. However, we described why none of the functional outputs from animal or crop production can be considered independently from the rest on the basis of the inputs to the system. Using the example of manure in livestock systems, we also showed why biophysical allocation methodologies are still sensitive to whether a system output has economic value or not. This sensitivity is a longstanding criticism of economic allocation which is not resolved by adopting a biophysical approach. Conclusions The biophysical allocation methodologies for various aspects of agricultural systems proposed to date have not adequately explained how the physical parameters chosen in each case represent causal physical mechanisms in these systems. Allocation methodologies which are based on shared (but not causal) physical properties between co-products are not preferable to allocation based on non-physical properties within the ISO hierarchy on allocation methodologies and should not be presented as such.

Nitrogen flows on organic and conventional dairy farms: a comparison of three indicators

“…As established by numerous LCA studies, different methods give different results (see, e.g., Cederberg and Stadig 2003;de Vries and de Boer 2010;Dalgaard et al 2014;Mackenzie et al 2016), and there is no consensus on which method is most appropriate. To our knowledge, the importance of co-product handling in N indicators is not much investigated, but such efforts would be valuable.…”

Achieving Environmentally Sustainable Livestock Production

“…Most of the papers identify the efficiency of the production as a key factor to affect the emission intensity of the livestock products. To assess the possible improvements in efficiency, holistic approaches such as Live Cycle Assessment would be necessarily needed, and further methodological development in this area is still required [22]. This would be especially a challenge when linking together the three pillars of sustainability (environmental, social, and economic) in sustainability assessments of livestock production.…”

Mapping the impacts of farmed Scottish salmon from a life cycle perspective

“…viscera at the primary processor) and co-product production with several Btarget products^in other cases (such as fishmeal and fish oil at the reduction plant). Economic allocation was used as being most appropriate given the motivations of the industry at each point in the value chain and the dynamics of transitioning between waste and co-production (MacKenzie et al 2017). However, as co-product allocation is often a contentious subject and results may differ considerably according to the method chosen Ayer et al 2007), a sensitivity analysis, using mass allocation, has been included in the supporting information.…”