The influence of system boundaries on life cycle assessment of grain production in central southeast Norway.

摘要

This study assesses the environmental impacts from production of 1 kg barley, oat and spring wheat, in central southeast Norway by means of life cycle assessment. The results were given for twelve impact categories, selected based on relevance to the system. These categories are climate change, fossil depletion, freshwater ecotoxicity, freshwater eutrophication, human toxicity, marine ecotoxicity, marine eutrophication, ozone depletion, particulate matter formation, photochemical oxidant formation, terrestrial acidification and terrestrial ecotoxicity. The assessment covers processes from cradle to farm gate, including all farm activities related to grain cultivation, as well as the production and acquisition of machinery, equipments and buildings, diesel and oil, fertilizer, lime, seeds and pesticides. In order to reveal the importance of system boundaries, factors that are included in this study and often excluded in other studies, such as machinery manufacturing, buildings, pesticide production and use, humus mineralization and NO_X loss from use of mineral fertilizer were systematically individually omitted. The sensitivity of the LCA results to several selected parameters governing greenhouse gas emissions and climate change (CC) was evaluated by varying the parameters+or-50% of the default value. The assessment gave a CC impact of 0.79, 0.77 and 0.74 kg CO₂-eq for production of 1 kg barley, oat and spring wheat, respectively. The choice of system boundaries were found to have great impact on the results, and CC impact was reduced by more than 40% when factors that are not commonly reported in literature were excluded. This clearly demonstrates the need of comprehensive documentation of system boundaries in order to perform meaningful comparisons of environmental impact caused by grain production under different conditions. The sensitivity analysis revealed that most of the impact categories were not particularly sensitive to the parameters selected. A 50% change in the emission factor for N₂O emissions from N inputs had highest effect on CC with 11-13%. The highest overall impacts were found for the fraction of mineral fertilizer volatilized as NH₃ and NO_X, with 32-53% change in photochemical oxidant and particular matter formation, and terrestrial acidification impact categories.