Application of the Cereal Unit in a new allocation procedure for agricultural life cycle assessments

The results of life cycle assessments (LCA) can be significantly affected by the choice of allocation procedure because different allocation approaches lead to a wide range of results. Agricultural systems are particularly sensitive due to their co-products being used in various sectors and accounted for at several allocation steps. If the allocation procedures for different products from the same agricultural system are not aligned to one another, methodological inconsistencies might occur. Parts of the environmental burden might be either unaccounted or doubly accounted for. As a consequence, the overall environmental burden of the agricultural system is not properly assessed. The Cereal Unit (CU) has been used as a common denominator in German agricultural statistics for decades and is mainly based on the nutritional value for livestock. Products and co-products not intended for livestock feeds are also covered. More than 200 CU conversion factors are provided for vegetable and animal products and co-products occurring during their processing. To calculate the CU, the specifically aggregated metabolizable energy content is calculated for each feed material and normalized using barley as a reference (1 kg barley = 12.56 MJ specifically aggregated metabolizable energy). The CU approach can be applied to other regions without prohibitive efforts. In this paper, we derive an allocation approach that is based on the CU as an existing unit for agricultural products. The new CU allocation approach is tested and compared to established allocation approaches for wheat, barley, soybean, rapeseed, sugar beet and sunflower. The CU allocation generates results between the approaches of mass, energy and economic allocations. For instance, the allocation shares between wheat grain and wheat straw are as follows: mass allocation 56% (grains)144% (straw), energy allocation 55%/45%, economic allocation 77%/23% and CU allocation 75%/25%. We demonstrate that the CU is an appropriate unit for the description of agricultural products and can serve as the basis for an agriculture-specific allocation approach in LCA. CU allocation may help to address agricultural allocation problems and might lead to more robust LCA results for products and services originating from raw agricultural materials. We recommend further testing and future application of this new allocation approach. (C) 2014 Elsevier Ltd. All rights reserved.