Hydroponic vegetable cultivation is becoming increasingly important, mainly due to faster growth and development of plants and higher yields. The quality of hydroponically grown vegetables is often questionable. In our research, we wanted to find out whether hydroponically grown lettuce is comparable to lettuce grown in soil in terms of its morphological and biochemical properties. In 2021, we conducted an experiment that took place from May to July in a laboratory field at the Biotechnical Faculty in Ljubljana. We established three growing systems: on a floating hydroponic system (Deep Water Culture), on a bed covered with black and white PE mulch (foil), and on an uncovered bed (bare soil). The experiment was laid out in 4 replicates, each with 24 plants; 12 plants were grown to technological maturity, and 12 plants were scheduled for weekly sampling. Morphological characteristics were measured on the weekly sampled plants and the technologically mature plant: weight of the aerial part (g), diameter of the rosette (cm), height of the stem (cm); and biochemical parameters: spectrophotometric measurement of the content of specific pigments, total phenolic compounds, and vitamin C content measured by liquid chromatography. The moisture content of the plants was also measured on air-dried samples. The marketable mass of rosettes at the time of technological maturity was 420±60 g in hydroponics, 369±30 g on film and 268±28 g on bare soil. Rosette lettuce in hydroponics had a characteristic longer (elongated) stem (8±1 cm) compared to lettuce on film (5±0 cm) and on bare soil (4±0 cm). The cultivation system had a characteristic effect on the content of total phenolic compounds, as rosettes grown in soil had significantly more total phenolic compounds (on bare soil 800±120 mg GAE /kg DM, on film (657±88 mg GAE /kg DM) compared to hydroponic rosettes (422±67 mg GAE /kg DM). The growing system had no significant effect on the moisture content of the lettuce plant, which ranged from 94.7 % in hydroponic system to 95.05 % in bare soil culture.
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