Effects of electrical conductivity, pH, and foliar application of calcium chloride on yeld and tipburn of Lactuca sativa grown using the nutrient–film technique

Authors: SAMARAKOON, UTTARA - The Ohio State University; PALMER, JACK - The Ohio State University; LING, PETER - The Ohio State University; Altland, James

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2020
Publication Date: 7/1/2020
Citation: Samarakoon, U., Palmer, J., Ling, P., Altland, J.E. 2020. Effects of electrical conductivity, pH, and foliar application of calcium chloride on yeld and tipburn of Lactuca sativa grown using the nutrient–film technique. HortScience. https://doi.org/10.21273/HORTSCI15070-20.
DOI: https://doi.org/10.21273/HORTSCI15070-20

Interpretive Summary: Leafy green production using nutrient film technique (NFT) is the most common practice among all hydroponically grown vegetables. With this system, nutrient solution is recirculated continuously, replenishing the nutrients and dissolved oxygen during the production cycle. Commercial hydroponic fertilizer formulations consist of all the macro- and micronutrients required for plant growth with fertilizer recommendations given based on EC levels and acidity or basicity (pH) of the nutrient solution. Tipburn in lettuce is characterized by necrotic tips and margins on younger leaves, and can render crops unsalable. Tipburn is a common issue in hydroponically grown lettuce in NFT during the summer and under supplemental lighting during other seasons and results from inadequate Ca supply to the younger leaf tissues. Hydroponic solution pH and EC are known to effect yield and severity of tipburn in lettuce under various growing conditions. The objective of this research was to determine yield and degree of tipburn of three lettuce cultivars (Red Butter, Green Butter, and Red Oakleaf) of the Salanova® series in response to varying EC, pH, and foliar Ca application under summer greenhouse growing conditions. ‘Red Butter’, ‘Green Butter’, and ‘Red Oakleaf’ of the Salanova® series at four EC levels (1.4, 1.6, 1.8, or 2.0 mS·cm–1) and a constant pH of 5.8; four pH levels (5.8, 6.0, 6.2, or 6.4) and a constant EC of 1.8 mS·cm–1, or CaCl2 was applied 1 week after transplanting into NFT channels at three different concentrations: 0, 200, 400, or 800 mg·L–1 calcium (Ca). Our investigation also provides evidence for two potential nutrient management strategies to control tipburn. One is reducing the EC of the nutrient solution to less than 1.4 mS·cm–1 and the other is a twice-a-week application of CaCl2 at rates of 400 or 800 mg·L–1 Ca. Of the two techniques, application of CaCl2 provided a better control as the symptom of tipburn was minimal and the impact on yield was minor compared with reducing the EC.

Technical Abstract: Yield reduction resulting from high temperatures and tipburn are common issues during the summer for hydroponically grown lettuce using the nutrient–film technique (NFT). We investigated the yield and degree of tipburn of lettuce ‘Red Butter’, ‘Green Butter’, and ‘Red Oakleaf’ of the Salanova® series under different-solution electrical conductivity (EC) and pH levels. We also quantified the effect of foliar spray application of calcium chloride (CaCl2) on the yield and degree of tipburn using the lettuce cultivar Green Butter. For the EC experiment, the plants were grown at four EC levels (1.4, 1.6, 1.8, or 2.0 mS·cm–1) and a constant pH of 5.8. For the pH experiment, the plants were grown at and four pH levels (5.8, 6.0, 6.2, or 6.4) and a constant EC of 1.8 mS·cm–1. For the foliar spray experiment, CaCl2 was applied 1 week after transplanting into NFT channels at three different concentrations: 0, 200, 400, or 800 mg·L calcium (Ca). During the EC trial, the maximum yields were observed at or more than 1.8 mS·cm–1 for ‘Green Butter’ (263 ± 14 g/head) and ‘Red Butter’ (202 ± 8 g), and more than 1.6 mS·cm–1 for ‘Red Oakleaf’ (183 ± 6 g). The yield of ‘Green Butter’ was 75 g less at 1.4 mS·cm–1 compared with 1.8 mS·cm–1. Tipburn symptoms were less at 1.4 mS·cm–1 for ‘Green Butter’ whereas other cultivars were not highly susceptible. In pH trials, the maximum yield for all cultivars was found at pH 6.0 and 6.2. There were no differences in tipburn symptoms among all pH levels. The foliar spray treatment, twice a week at 400 or 800 mg·L–1 Ca, provided improved tipburn control, as the tipburn symptoms were minimal and the impact on yield was minor compared with reducing EC. This series of experiments found evidence in proper EC and pH management for optimum yield and tipburn control in NFT lettuce grown in summer conditions.