Growth, yield and quality of hydroponically cultivated green leafy vegetables as affected by nutrient solution and growing season

Lettuce (Lactuca sativa L.) var. ‘Lollo rossa’ was grown in a floating hydroponic system. Six saline treatments were used, adding different concentrations of calcium chloride (CaCl2) to the nutrient solution (mol m−3): 0, 2.5, 5, 10, 15, 20, which, respectively, corresponds to an electrical conductivity of 2.5, 3, 3.5, 4.4, 5.4, 6.3 dS m−1. In plants subjected to moderate salinity stress the growth was not affected and yields were not statistically significant; however, the data shows a slight decline in 20 mol m−3 CaCl2 treatments. Nitrate contents in the leaf decreased when the concentration of CaCl2 in nutrient solutions increased. Other quality parameters were positively affected by treatment with CaCl2, especially at moderate concentrations such as 5 and 10 mol m−3. In fact, both the content of phenols and antioxidant power increased at moderate salt concentrations and reduced in the treatment with 20 mol m−3 CaCl2. The content of chlorophyll and carotenoids were not affected by treatment even at high salt concentrations. The use of CaCl2 did not result in nutrition imbalances in plants either. In fact, the ratio K/Na remained unchanged in the various treatments, as well as the contents of microelements.