2018 ASHS Annual Conference

Tipburn on lettuce has an adverse effect on its market value. Tipburn is a common issue with some cultivars of hydroponically grown lettuce in Nutrient film techniques (NFT). Inability to uptake calcium at a faster rate has been reported to cause tipburn. We investigated the yield and degree of tipburn of three lettuce cultivars ‘Red butter’, ‘Green butter’, and ‘Oak leaf’ of Salanova ^® series under varied EC and pH levels. We also investigated the effect of application of calcium chloride (CaCl₂) as a foliar spray using the lettuce cultivar ‘Green butter’. For the experiment with EC treatments, the plants were grown at a constant pH of 5.8, and four EC levels: 1.4, 1.6, 1.8 or 2.0 mS∙cm. For the experiment with pH treatments, the plants were grown at a constant EC of 1.8 mS/cm and four pH levels 5.8, 6, 6.2 or 6.4. For the experiment with CaCl₂ foliar sprays were applied at a concentration of 0, 400 or 800 mg∙L-1 Ca a week after transplanting into NFT channels. The solution pH and EC was managed at 5.8- 6.0 and 1.8 mS∙cm. During the EC trial, the maximum yields were observed at or above 1.8 mS/cm for ‘Green butter’ (263 ± 14 g per head), and ‘Red butter’ (202 ± 8 g), and above 1.6 mS∙cm for ‘Oak leaf’ (183 ± 6 g). Tipburn symptoms were less at 1.4 mS∙cm for ‘Green Butter’ while other cultivars were not highly susceptible. The yield of ‘Green Butter’ was 75g less at 1.4 mS∙cm compared to 1.8 mS∙cm. During the pH trail, the maximum yields were observed at pH 6.0 and 6.2 for all cultivars. There was no variation in tipburn symptoms across pH levels. Preliminary investigations with once a week CaCl₂ foliar sprays was found ineffective in controlling tipburn. A twice a week application of 800 mg∙L^-1 Ca, showed promising results in controlling the tipburn as compared to other treatments. The yield with the 800 mg∙L^-1 CaCl₂ spray, however, was 25g less than 0 and 200 mg∙L^-1 CaCl₂. Reducing EC of the fertilizer solution below 1.4 mS∙cm or twice a week application of 800 mg∙L^-1 Ca in the form of CaCl₂ can control tipburn of the lettuce cultivars evaluated. Application of CaCl₂ provided a better control as the symptom of tipburn was minimal and the impact on yield was minor as compared to reducing EC.