Growth and physiological characteristics of leaf lettuce grown using a new aeroponic system with dry-fog spray fertigation

Abstract

We investigated the growth characteristics and physiological activity of leaf lettuce cultivated using different sizes of liquid fertilizer droplets and different rates of fog flow through the rhizosphere using a dry-fog hydroponics technique. These characteristics were subsequently compared to lettuce cultivated using deep flow technique (DFT), which is the prevailing hydroponic technique used in greenhouses. The cultivation chambers were filled with dry-fog (DF) containing droplets that average less than 10 µm in diameter or semi-dry-fog (SDF) containing droplets that average 20 µm in diameter. The plants were grown for three weeks following transplantation, and we measured the growth, respiration rate and TTC reduction ability of the roots in addition to the photosynthesis rate and the contents of total soluble protein, nitrate nitrogen and calcium ions. The amount of leaf growth increased with a slower flow rate under both DF and SDF conditions and was increased in both dry-fog aeroponic conditions compared to leaves grown in DFT. SDF with a slow flow rate increased root growth and activity and resulted in an increase in stomatal conductance and photosynthesis rate. DF with a slow flow rate also significantly increased the growth of leaves and roots, but the physiological activities were not affected. Thus, the growth and physiological characteristics of leaf lettuce cultivated using dry-fog aeroponics was improved in different ways by changing both the atomized droplet size and flow rate in the root zone.