Influence of mild saline stress and growing season on yield and leaf quality of baby lettuce grown in floating system

Consumer demand has been increasing and many vegetable farmers have oriented their production plans towards baby leaf vegetables such as lettuce. The management of the nutrient solution as well as the growing conditions could significantly affect the yield and quality of leafy vegetable crops. The aim of the present work was to determine the effects of increasing the level of salinity in the nutrient solution (1, 10 or 20 mM NaCl) during two consecutive growing seasons (spring and autumn) on the yield and quality of Lactuca sativa L. var. acephala grown in floating raft culture. Increased salinity in the nutrient solution decreased marketable yield and dry biomass with more detrimental effect during the warm season. The percentage of yield reduction in comparison to the non-saline control was 7 and 20% in the spring season and 4 and 13% in the autumn growing season at 10 and 20 mM NaCl, respectively. Plants grown in the spring season exhibited higher yield and dry biomass but lower leaf quality than those grown in the autumn season. When averaged over salinity level the lipophylic antioxidant activity, total ascorbic acid, phenols and nitrate contents were significantly increased by 7.1, 20.1, 19.4 and 24.4%, respectively, in plants grown in spring as compared to autumn growing season. The floating system could be considered an efficient and low-cost tool to improve quality aspects through proper management of the salt concentration in the nutrient solution with an acceptable yield reduction.