We would like to emphasize that the approach must not be confused
with the already known and established system-expansion approach.
Whereas system expansion affects the system boundary during all
stages of LCA, our approach is clearly limited to adapting the system
boundary at the level of the crop rotation when performing the LCI. Furthermore,
an essential component of this new approach is an allocation
step using the Cereal Unit allocation approach. Alternative agriculturespecific-allocation
approaches might be suitable as well. This allocation
step takes place as well within the LCIA. Here, the sum of all inputs of the
crop rotation is allocated to their respective outputs using Cereal Units.
Thus, no additional effort occurs for performing the next steps of LCA,
and the functional unit and reference flow of the LCA remain unaffected.
Today, in many LCAs, environmental burdens are allocated mainly to
the ‘main’ products, e.g. wheat grain. The relevant functions of coproducts
are poorly considered in some cases, e.g. the use of wheat
straw as animal bedding in animal production, as fiber in animal nutrition
or as a soil amendment to increase soil quality. Intentionally or unintentionally,
co-products' functions are often disregarded. In the case of
some political incentives, this might be an active choice, but it is unclear
if side effects such as indirectly setting incentives that decrease soil
quality were understood in the political decision process. From an LCA
perspective, in the worst case, this could be partially caused by the
lack of proper modeling of agricultural reality in LCA methodology.
The present work shows a way to close this gap. Co-products' functions
are inherently included within this approach, because allocating all
inputs among all outputs is an elementary component of the method.
There is a logical relation between the amount of inputs, e.g. amount
of fertilizers, that is needed to produce a certain quantity (yield) of agricultural
outputs with a certain quality (composition). For some agricultural
products, more input is needed to produce higher quality or
quantity of outputs. A proper attribution of the inputs used between
the agricultural outputs is needed, and account should be taken to quality
of the individual outputs. This classical allocation problem can be
solved by the Cereal-Unit-allocation approach for agricultural systems,
because the Cereal Unit is mainly based on the nutritional value of agricultural
products to animals. Thus, products with a greater nutritional
value and greater benefit to animal nutrition get more inputs – and
thus more environmental burden – assigned to them. In other words,
the Cereal Unit is used to introduce the performance principle, based
on animal nutritional value, to the attribution of environmental burdens
within agricultural LCAs. The basis of that principle can be justified by
the animal nutritional value as a biophysical principle, which is additionally
encouraged by the fact that a vast majority of global agricultural
area is used to feed animals (FAO, 2009), which serves as a basis for this
approach