Sensitive parameters in local agricultural life cycle assessments: the illustrative case of cereal production in Wallonia, Belgium

Abstract

Life cycle assessment (LCA) is a useful tool for investigating the environmental performance of agricultural products. For many crop-based products, the agricultural production step shows substantial impacts in LCA results. Using the illustrative case of cereal production in Wallonia, Belgium, the study uses sensitivity analyses to explore the parameters to be adjusted in priority when conducting a local LCA for crop production, taking into account uncertainties tied to input and output inventory data and impact characterization factors. The analysis investigated local specificities in the production of eight cereal crops in Wallonia. Cropping systems were modeled according to accounting data from representative farms, including areas, yields, inputs, and machinery. Sensitivity and uncertainty analyses for input parameters and methodological choices were performed. The following parameters were evaluated: the influence of the functional unit (kg, ha, €), the link between yield and LCIA results, the relevance of using up-to-date data for mineral fertilizer production, the type of mineral fertilizer, the model for direct field emission calculation, and the allocation rules. We observed that the use of several functional units embracing the multifunctional role of agriculture enables identifying crops with low impacts per kilogram, hectare, and euro at the same time. The cereal production steps with the greatest impact were mineral fertilizer production (up to 84% of the total impact, depending on crop and impact category) and emissions from the application of mineral (up to 65%) and organic (up to 94%) fertilizers. Sensitive parameters to be adjusted in priority were identified. Despite the high correlation between yield and results, simply extrapolating impacts on the basis of yield seemed mostly inappropriate. Using updated data for mineral fertilizer production reduced impacts by 6–160%. Shifting models for field emission calculation influenced acidification and eutrophication by 5–142%. Hypotheses on allocation factors affected results by 10–26%. An LCA for the production of major Walloon cereals was conducted taking into account local cropping practices and yields. The parameters relevant for conducting a regional LCA of crop production were identified and discussed in comparison with generic data and models. As LCA is an iterative process, further improvements would include the use of more specific models for direct field emission calculation. The results could serve as a reference for products using Walloon cereals and help enhance the quality of LCAs conducted for these products.