Controlled root‐zone temperature effect on baby leaf vegetables yield and quality in a floating system under mild and extreme weather conditions

Abstract

BACKGROUND A floating system is a suitable low‐cost hydroponic method for growing baby leaf vegetables. Among other, an important characteristic of the system is the use of large volume of nutrient solution which is characterized by high heat capacity. The aim of this study was to evaluate the effect of different root‐zone temperatures on baby leaves of lettuce and rocket plants grown in a floating system under mild (spring) or extreme environmental conditions (summer and winter). RESULTS Root‐zone temperature was recorded in two tanks, one powered by a photovoltaic system and one where root‐zone temperature was not controlled – this was used as a control tank. Photosynthetic parameters, yield, nutritional quality, and mineral composition were determined. In both baby leaf vegetables, during extreme weather conditions, yield was higher in the tanks with controlled root‐zone temperature conditions than the control (+18.9% for rocket, and + 31.4% for baby lettuce), while quality parameters and chemical composition were not significantly affected. Stomatal conductance and net photosynthesis values were positively affected only during summer. On the other hand, control of root‐zone temperature under mild weather conditions had no significant effect on baby lettuce and rocket. CONCLUSION Control of the root‐zone temperature could be a useful tool to improve productivity for baby lettuce and rocket crops cultivated in floating systems under extreme weather conditions. © 2020 Society of Chemical Industry

Exploitation of Liquid Digestate as the Sole Nutrient Source for Floating Hydroponic Cultivation of Baby Lettuce (Lactuca sativa) in Greenhouses

“…Transpiration rate values were similar in both 5 and 10% liquid digestate treatments, and significantly higher than control and both 20% liquid digestate treatments for baby lettuce (Figure 4b). Slightly higher transpiration rates were reported by Karnoutsos et al [11] for non-heated cultivation in Hoagland solution during the winter season. Stomatal conductance did not show any significant difference in baby lettuce plants except for the treatment with 20% liquid digestate, with or without pH adjustment (Figure 4c).…”

“…For the above reasons, floating hydroponic systems are gaining increased attention today for the production of leafy vegetables. Floating systems are among the most simple, convenient, and low-cost hydroponic methods used for the production of high-quality baby leaf vegetables [10,11]. Moreover, when applying floating hydroponic techniques, the end products are cleaner, without substrate traces [12].…”

Epigenetic and Physiological Responses to Varying Root-Zone Temperatures in Greenhouse Rocket

“…The temperature inside the tanks was measured by PT−100 type sensors (Resistance thermometer Pt100, Uteco SA, Athens, Greece). More details can be found in [ 42 ]. An RZT of 22 °C is considered root-zone heating.…”

“…Furthermore, a root-zone temperature (RZT) of 20 °C was found to be appropriate for yield, high photosynthetic rate, and high mineral concentrations in rocket, even though the concentration of plant metabolites was not as high [ 41 ]. We have recently found that the management of RZT conditions leads to higher yields, making root temperature a useful tool for the increase in productivity of rocket [ 42 ]. However, during winter, the preservation of optimal RZT is achieved with the use of fossil fuels, which are expensive and have a high environmental impact, in Mediterranean greenhouses.…”

Strategic Successive Harvesting of Rocket and Spinach Baby Leaves Enhanced Their Quality and Production Efficiency

“…Upon the first true leaf formation, trays were thinned up to one plant per cell, and afterwards, they were placed in two metallic tanks (2 m length × 0.8 m width × 0.24 m height) per crop, filled with 200 L Hoagland solution (100% strength) each [20]. In both tanks of each crop, pH was constantly adjusted to 6.8 ± 0.3, electrical conductivity (EC) was constantly adjusted to 2.8 ± 0.3 mS/cm, while water temperature was fluctuating between 6 and 15 • C. Rocket and lettuce baby leaves were reported to have optimum production at 20 • C root zone temperature [21]. Therefore, 6-15 • C falls within the favorable root zone temperatures, while they are typical for the experiment's period.…”