Application of innovative technologies on growth and quality of leafy vegetables grown under high-salinity water in a floating-disk hydroponic system

Leafy vegetables often need a high quantity of water to grow and among the most critical factors and stressors are high soil and water salinity levels and the concomitant reduction in optimum arable areas. Salinity increases by the intrusion of salts in the underground and surface water due to overfertilization and reduces the amount of available freshwater for irrigation (Kumar, 2022). In the EU, especially in the southern European Member States, most of all arable land will be affected by salinization and yields of non-irrigated crops are projected to decrease by up to 50 % by 2050 (Christopoulos and Ouzounidou, 2021). The objective of this study was to evaluate irrigation with high-salinity water (ECi= 10 dS/m) with the application of two innovative technologies for growing leafy vegetables species in four different tanks. One technology is the use of a nanobubble (NB) generator (Hephaestus Lab: https://chem.duth.gr/) and the other is an electronic water treatment system, using low-frequency radiation waves (MAXGROW: https://maxgrow.tech/). The study was conducted in the Greenhouse Laboratory of the Perrotis College/American Farm School, Thessaloniki, Greece, under a floating-disk hydroponic system, in which three leafy vegetables species (endive and two lettuce varieties, Lollo Rossa and Butterhead) were grown in four different sections/tanks, each one filled with irrigation water of different salinity: a. Control (E.C.i ~1 dS/m); b. saline water (E.C.i = 10 dS/m) enriched with NB; c. saline water (E.C.i = 10 dS/m) + MAXGROW; and d. saline water (E.C.i = 10 dS/m) + MAXGROW + NB. Various vegetable agronomic parameters (total fresh weight, height, root weight, SPAD units, etc.), plant tissue analysis (macro- and micronutrients), water parameters (dissolved oxygen, pH, EC, nutrients, temperature, size and concentration of NB, etc.), and the environmental conditions [temperature (^oC), humidity (%), PAR, and CO₂] inside the greenhouse were recorded. Additionally, quality parameters (Chlorophyll, flavanols, anthocyanins, etc.) were measured. This study will continue with evaluations in different vegetable species, growing seasons, and hydroponic systems to further assess the potential of the innovative system used in high salinity levels. The results so far showed that both water treatment devices increased yield. Finally, both innovative technologies could provide efficient energy use, low operation cost, and sustainability and mitigate high-salinity irrigation problems in crop production systems.