Assessing the environmental impacts of cropping systems and cover crops: Life cycle assessment of FAST, a long-term arable farming field experiment

To reduce environmental impacts of cropping systems, various management strategies are being discussed. Long-term field experiments are particularly suitable to directly compare different management strategies and to perform a comprehensive impact assessment. To identify the key drivers of several environmental impacts, we analysed a six year crop rotation of the Farming System and Tillage Experiment (FAST) by means of the Swiss Agriculture Life Cycle Assessment method (SALCA). The following factors of the FAST experiment were considered: (1) cropping system (stockless conventional farming vs. organic farming), (2) tillage (intensive tillage vs. no or reduced tillage), and (3) cover crop. We analysed the effects of these three factors on the global warming potential (GWP), aquatic and terrestrial eutrophication, and aquatic ecotoxicity for two functional units, i.e. per product and per area. Potential impacts on biodiversity were also analysed. Our analysis revealed that there is not one superior cropping system, as the ranking depended on the environmental impact selected and on the functional unit. The cropping system had the strongest effect on most of the environmental impacts, and this was mainly driven by differences in N-fertilisation (amount and form) and yield. The global warming potential, for instance, was highest in both conventional systems compared to the organic systems, when emissions were calculated per area. In contrast, calculating emissions per product, there were no statistical differences between all four systems. On the other hand, due to higher nitrogen emissions related to the application of cattle slurry in the organic system, the terrestrial eutrophication of the organic systems was higher than the conventional systems, independent of the functional unit. The effects of tillage were much lower compared to the cropping system. No tillage, but not necessarily reduced tillage, and the cultivation of cover crops had the potential to reduce aquatic eutrophication. As N-fertilisation dominated many impact categories, we suggest improving the N-efficiency as a crucial leverage point to improve the environmental performance of arable farming systems.