Assessing the environmental impacts of soilless systems: a comprehensive literature review of Life Cycle Assessment studies

Purpose Soilless cultivation systems (SCS) are farming cultivation methods using inert or organic substrate in place of soil. These systems are considered promising from an environmental sustainability perspective, as they can reduce the amount of water, fertilizers, and other substances harmful to the environment. The aim of this study is to consolidate the current knowledge of environmental impact assessment in the soilless systems context and shed light on the methodological choices regarding the LCA method implementation. Methods A three-step research method was employed, starting with the identification of the nomenclature of SCS via an overview of the literature, followed by a review of reviews where Life Cycle Assessment (LCA) has been identified as the most used method to assess the environmental performance of a system. Such a preliminary step served for the third step, which allowed the creation of a search query combining the various soilless techniques and LCA. From Scopus and Web of Science, 56 articles were selected, and methodological data was extracted according to FLAVIA-LCT framework. Data was then analyzed using Excel and VOSviewer. Systematic analysis was preceded by a bibliometric and network analysis, as well as by a technical analysis of the systems found in the selected articles. Results and discussion Drip irrigation in conjunction with solid substrates, mostly perlite, is the most common SCS method, while tomatoes and lettuce are the most studied crop species. Most systems set in a rural environment had commercial orientations, while urban systems had mostly experimental ones. Most of the assessed systems are set in Spain. Attributional LCA models are most prevalent, with mass-related functional units (FUs) and cradle-to-farm gate system boundaries. The production phase is the most impactful, with electricity, fertilizers, and structure materials being the main contributors. Conclusions LCA studies displayed common methodological choices concerning attributional model, FUs, and system boundaries, reflecting a main focus on production. Consequential approaches were limitedly applied, and, in these cases, assumptions were often made for transportation and material lifespan due to data unavailability. Sensitivity analyses were only performed by half of the selected articles. Finally, the findings highlight that attention should be given to alternative crop species, innovative techniques, and substrates.