Effects of non-conventional substrates and treated wastewaters on plants cultivated in soilless systems and controlled conditions

Agriculture is facing critical challenges due to climate change. Particularly, the increase of CO₂ and temperature are altering weather events, compromising the quality and availability of freshwater and fertile soil for agricultural purposes. Concurrently, global population growth demands increased agricultural output, often in regions with diminishing natural resources. Therefore, these conditions require the urgent need for sustainable agriculture practices that optimize resource efficiency, minimize environmental degradation, and ensure food security for future generations. This PhD thesis investigates the use of innovative sustainable approaches to reduce freshwater consumption and fertile soil utilization for the production of different horticultural crops. Particularly, this study examines the suitability of (i) non-conventional substrates in pot cultivation, such as the use of marine remediated sediments, biochar-enriched substrates, (ii) treated wastewater as irrigation source, and (iii) advanced soilless techniques such as hydroponic and aeroponic systems in controlled environments. The use of remediated marine sediments as alternative substrates was evaluated for crops like wild strawberry (Fragaria vesca L.) and basil (Ocimum basilicum L.). Different sediments concentrations (e.g., 12.5, 25, 50 and 100 % v/v) were added to a peat-based substrate. Findings highlighted the capability of remediated sediments to replace peat- based substrates while maintaining or enhancing crop quality. Wild strawberry grown in these substrates demonstrated comparable or superior fruit quality, achieving high levels of sugars, organic acids, and sensory attributes under controlled water regimes. Similarly, two different basil cultivars (‘Valentino’ and ‘Genovese’) showed an increased germination rates and biomass grown in sediment-based media, aligning with sustainable cultivation principles. Biochar-enriched substrates were tested for their effects on tomato (Solanum lycopersicum L.) and rocket salad (Eruca vesicaria (L.) Cav.). Different biochar mixtures in a peat-based medium were investigated (from 5 to 70 % v/v of biochar). Biochar enhanced plant biomass in tomato, while higher concentrations (> 30%) reduced fruit yields. Moderate biochar concentrations (10–20 %) proved to be a sustainable alternative to peat, improving substrate properties and supporting fruit quality without introducing contaminants. Regarding rocket salad, biochar content up to 40 % did not affect seed germination. Moderate biochar concentrations (~20%) enhanced plant biomass, nutrient content and reduced nitrate levels in rocket leaves by 26–30%, addressing a key quality and safety concern. Hydroponic and aeroponic systems demonstrated significant water and nutrient use efficiency. Rocket salad grown with urban treated wastewater (diluted 1:1 v/v) in aeroponics achieved high yield and quality while mitigating nitrate accumulation and heavy metal uptake. Different treated wastewaters (urban and mixed) irrigation was shown to be a viable replacement for freshwater in hydroponics when diluted (30 and 20%, respectively), reducing environmental strain and supporting circular economy goals. Conversely, undiluted treated wastewaters negatively impacted rocket salad growth and yield. However, hydroponics and aeroponics proved to be reliable technique for baby leaf cultivation, offering precise control of growth conditions, resulting in enhanced resource use and improved crop performance. This research highlights the potential of integrating marine remediated sediments, biochar- enriched substrates, as well as treated wastewater in hydroponic and aeroponic systems into agricultural practices. These approaches contribute to optimize resources, enhanced crop quality, and minimized environmental impact, providing a robust framework for sustainable agriculture and advancing global efforts toward food security and environmental conservation.