Effect of different growing media in hydroponic culture on the yield and biological quality of lettuce (Lactuca sativa var. capitata)

There is increasing interest among vegetable growers in hydroponic production of lettuce. Growing medium and fertilization are the most effective ways of controlling and improving the yield and nutritional value of vegetable crops. The aim of this study was to determine the effect of different growing media on the yield and biological value of lettuce cultivated in spring period. Organic medium NDASH coconut fiber and mineral medium - rockwool were compared to 'nutrient film technique' growing system (NFT). In the study two butterhead lettuce cultivars and one of batavia lettuce cultivar (Lactuca sativa var. capitata) were included. The experiment was carried out in the greenhouse with controlled microclimate. At about five days before harvest, the nutrient solution was replaced to water to reduce nitrate concentration in the leaves of lettuce. Marketable yield of the plants grown in the experiment was compared. Dry matter, total soluble solids (TSS), nitrate (NO₃), P, K, Ca, chlorophyll a and chlorophyll b, SPAD, total carotenoids contents and leaf color parameters L* (lightness), a* (greenness) and b* (yellowness) were determined. The highest yield of lettuce was obtained in NFT growing system, compared to coconut fiber and rockwool growing media. Plants growing in coconut fiber slabs were characterized by the lowest content of dry matter and chlorophyll a and b. The differences between cultivars were also observed. After 5-day treatment of the plants with water, the biggest decrease of nitrate content was found in the leaves of lettuce grown in the NFT system. It can be concluded that growing medium used in hydroponic cultivation of lettuce affects its yield and the product quality.