Comparative environmental and economic life cycle assessment of hydroponic and in-field lettuce production in the UK

Most vegetables grown in the United Kingdom are imported, making the national food security vulnerable to international supply shocks. Additional constraints are posed by restrictions on the extraction and use of peat as a substrate in-field horticulture. This study aims to assess the environmental and economic performance of hydroponically grown lettuce as an alternative to peat-based in-field production, as practiced within the UK. Primary data for hydroponically produced crops used in this study were gathered from two trials at The University of Sheffield, School of Biosciences. The hydroponic system production was also compared with data for non-peat-based in-field grown lettuce, collated from secondary sources. All data were analysed using a cradle-to-gate life cycle assessment in SimaPro v.9.5 software using ReCiPe 2016 methodology with a Hierarchical Perspective. The results were expressed in 18 mid-point indicator categories, followed by an assessment of life cycle costs for the comparators. Utilising alternative analysis, we also deployed Emergy analysis and the results were expressed in the form of standard Emergy tables and ratios. Overall, results show that in-field production has lower environmental impacts and costs as compared to hydroponic systems, and that when infrastructure is excluded, energy usage has the greatest impact on hydroponic production. We discuss how this barrier may actually present an opportunity and explore the role of ‘low-input’ hydroponics and energy mixes.