Nutrient solution concentration and growing season affect yield and quality of Lactuca sativa L. var. acephala in floating raft culture

BACKGROUND: There is growing interest among consumers in baby leaf vegetables, mostly requested for mixed salads, both as fresh market products and ready-to-use vegetables. Fertilisation is one of the most practical and effective ways of controlling and improving the yield and nutritional quality of crops for human consumption. The optimal fertiliser concentration for baby leaf vegetables depends on the environmental conditions. The aim of the present work was to determine the effects of nutrient solution concentration (2,18, 34, 50 or 66 mequiv L-1) during two consecutive growing seasons (spring and summer) on the yield and leaf quality of Lactuca sativa L. var. acephala grown in a floating system. RESULTS: Marketable fresh yield, total dry biomass, leaf area index, macroelement (N, P, K and Mg) concentrations and nitrate and total chlorophyll contents increased in response to an increase in nutrient solution concentration, while the opposite trend was observed for root/shoot ratio and glucose, fructose, starch, total carbohydrate and protein contents. Plants grown in the spring season exhibited lower yield and growth (total dry biomass and leaf area index) but higher leaf quality (higher carbohydrate content and lower nitrate content) than those grown in the summer season. CONCLUSION: The use of nutrient solution concentrations of 37 and 44 mequiv L-1 for the spring and summer seasons respectively could be adopted in the present conditions to improve marketable fresh yield and leaf mineral content, but with a slight reduction in some nutritional parameters. (C) 2009 Society of Chemical Industry