The Effect of Different Methods of Replacing Supplemental Nutrient Solution in Floating Hydroponic System on Growth and Physiological Characteristics of Three Lettuce Cultivars

The present experiment aimed at comparing three methods for replacing nutrient solution in a floating hydroponic system with three lettuce cultivars. The experiment was carried out as factorial based on a completely randomized design. The factors included the three replacement method of the nutrient solution (total replacement, replacement based on EC of nutrient solution, and replacement based on the plant demand) and cultivars (Chinese lettuce, Badbane Ghermez lettuce and Kazeroon lettuce). In all three cultivars of Chinese lettuce, Badbane Ghermez and Kazeroon, the highest root fresh weight, shoot fresh weight, and yield were observed in plants that were fed by total nutrient solution replacement method, while the vegetative traits of the plants which had been fed based on the EC of the nutrient solution had the lowest value of PI index in Chinese and Kazeroon lettuce cultivars tended to reduce 19.6 and 23.5% respectively, by nutrition based on the EC and the plant demand. The concentration of phenolic compounds and antioxidants activity of lettuce in nutrition conditions based on the EC of the nutrient solution compared to the other two methods increased and Badbane ghermez lettuce had more phenolic compounds and antioxidants activity compared to the other two cultivars. Therefore, although complete replacement of nutrient solution had a positive effect on the growth and physiological characteristics of lettuce cultivars, but increasing the antioxidant properties and reducing water and fertilizer consumption in the other two methods of production is also very important.