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• Nutrient solution management controls yield and quality in floating system lettuce. • Diluting the nutrient solution slows lettuce growth but maintains plant nutrition. • High nitrogen concentration can toxically accumulate in lettuce. Lettuce is a leading greenhouse-grown vegetable highly appreciated by consumers for its nutritional properties texture and flavor. However, leafy vegetables are known to accumulate an excessive amount of nitrate and this constitutes a strong health concern in Europe. Among the factors that most affect the yield and quality of hydroponic crops, the composition and management of the nutrient solution stand out. In this work, different strategies have been studied in the management of the nutrient solution for hydroponic lettuce cultivation. Production nutritional status, and quality parameters were evaluated. The concentrations of nutrients in the nutrient solution significantly influence the harvested product, 100 to 50 % H treatment resulted in highest yields with significant increase of 14 % compared to 50 % H at 34 DAT, from the point of view of both biomass production and quality, regarding the contents of anthocyanins, chlorophylls, and calcium, constituents that add value to the product due to their importance in the human diet. A significant reduction of nitrates in lettucewas observed one (14 %) and two (22 %) weeks after modifying the nutrient solution (100 to 50 % H). After one week there was no reduction in lettuce growth. In addition, no significant reduction in the concentration of most macro- and micronutrients was observed. [ABSTRACT FROM AUTHOR]

Lettuce (Lactuca sativa L.) is a leading greenhouse-grown vegetable. However, nitrate (NO3−) accumulation in leaves remains a major issue. The aims of this research were: (i) to test the modified intermittent Nutrient Film Technique (NFT) in the cultivation of soilless lettuce in which plants are grown on peat blocks in trays and supplied with an intermittent flow of nutrient solution, and (ii) to calibrate the fertilization scheme to increase yield performance, while keeping NO3− concentration under control. Two greenhouse trials were performed between autumn 2013 and spring 2014. Results showed that a 30-day cycle is the optimum duration in terms of fresh biomass yield, both for autumn and spring cultivation. Reducing N fertilization in the last cropping days never affected NO3− concentration in leaves during autumn trial, due to unfavourable growing conditions. Conversely, suspension of fertilization 2 days before harvest had a consistent effect during the spring trial, when NO3− concentration in leaves was highly reduced (from 20 to 36%) without yield penalties. Thus, suspending fertilization 2–4 days before harvesting in intermittent NFT may reduce, on average, NO3− accumulation by 29–58% and the fertilization rate by 7–16%, respectively. Yet, growing conditions are crucial to make this system effective.

Lettuce (Lactuca sativa L.) is a leading greenhouse-grown vegetable. However, nitrate (NO3−) accumulation in leaves remains a major issue. The aims of this research were: (i) to test the modified intermittent Nutrient Film Technique (NFT) in the cultivation of soilless lettuce in which plants are grown on peat blocks in trays and supplied with an intermittent flow of nutrient solution, and (ii) to calibrate the fertilization scheme to increase yield performance, while keeping NO3− concentration under control. Two greenhouse trials were performed between autumn 2013 and spring 2014. Results showed that a 30-day cycle is the optimum duration in terms of fresh biomass yield, both for autumn and spring cultivation. Reducing N fertilization in the last cropping days never affected NO3− concentration in leaves during autumn trial, due to unfavourable growing conditions. Conversely, suspension of fertilization 2 days before harvest had a consistent effect during the spring trial, when NO3− concentration in leaves was highly reduced (from 20 to 36%) without yield penalties. Thus, suspending fertilization 2–4 days before harvesting in intermittent NFT may reduce, on average, NO3− accumulation by 29–58% and the fertilization rate by 7–16%, respectively. Yet, growing conditions are crucial to make this system effective. [ABSTRACT FROM AUTHOR]