Optimising electrical conductivity, pH and cultivar selection to enhance yield and nutritional quality of hydroponic lettuce (Lactuca sativa)in subtropical environments

The present study was carried out during 2022–23 and 2023–24 at ICAR-Central Institute for Subtropical Horticulture, Lucknow, Uttar Pradesh to evaluate the combined effects of electrical conductivity (EC), nutrient solution pH and cultivar on growth, yield and quality of hydroponic lettuce (Lactuca sativa L.) under subtropical conditions. The experiment was laid out in a factorial completely randomised design (F-CRD) comprising three EC levels (1.8, 2.0 and 2.2 dS/m), three pH levels (5.5, 6.5 and 7.5) and seven lettuce varieties [Bingo (C1), Tango (C2), Lollo Rosso (C3), Grand Rapids (C4), Summer Star (C5), Romaine (C6) and Black Rose (C7)] arranged in three replications. The results revealed that increasing EC significantly improved vegetative growth, biomass, yield and quality traits, with EC 2.2 dS/m recording maximum yield, antioxidant capacity, carotenoids and ascorbic acid. Nutrient solution pH markedly influenced nutrient uptake and performance, with pH 6.5–7.5 proving superior depending on EC level. Cultivars responded differentially; ‘Bingo’ produced the highest yield while ‘Black Rose’ exhibited superior nutritional quality. Significant EC × pH × cultivar interactions highlighted the need for cultivar-specific nutrient management. Overall, EC 2.2 dS/m at pH 7.5 was optimal for high productivity and quality of hydroponic lettuce under subtropical environments.