Yosuke Hikosaka

The growth characteristics and physiological activities of leaves and roots of lettuce cultivated in dry-fog aeroponics with different flow rates of nutrient dry-fog (FL, 1.0 m s⁻¹; NF, 0.1 m s⁻¹) were investigated under a controlled environment for two weeks and compared to lettuce cultivated using deep-flow technique (DFT). The growth of leaves of FL and DFT was not different and was significantly higher than that of NF. The amount of dry-fog particles adhering to the objects was higher in FL than in NF, so that the root growth in NF was significantly higher than that of FL. The respiration rate of roots was significantly higher in dry-fog aeroponics, but the dehydrogenase activity in the roots was significantly higher in DFT. There were no differences in the contents of chlorophyll and total soluble protein in the leaves or the specific leaf area. Photosynthetic rate and stomatal conductance were higher in dry-fog aeroponics. The contents of nitrate nitrogen, phosphate and potassium ions in the leaves were significantly higher in DFT, but the content of calcium ions was significantly higher in FL. Thus, changing the flow rate of the dry-fog in the rhizosphere can affect the growth and physiological activities of leaves and roots.

Growth characteristics of lettuce cultivated using a novel “dry-fog” hydroponic technique were investigated and compared to lettuce cultivated using deep flow technique (DFT) as the prevailing hydroponic technique. Dry-fog hydroponics is an aeroponic technique that sprays a very fine foggy nutrient solution with an average droplet diameter of less than 10 μm into the root zone. The roots extend into the chamber filled with dry-fog of the liquid fertilizer and absorb water and nutrients from the dry-fog that fills the rhizosphere. This soilless culture system needs less water than any other hydroponic technique, and no differences were found in growth and harvest quality of plants between the two tested sytems. For dry-fog culture, root growth was encouraged and root hair significantly developed to catch the foggy nutrient solution efficiently. The contents of ascorbic acid, nitrate nitrogen, Ca+ and chlorophyll of leaves were not significantly different between the two hydroponic cultures. However, respiration rate of roots and photosynthetic rate of leaves significantly increased with dry-fog culture. Because the amount of water around the roots is less with dry-fog, horticultural crops are expected to grow well with this novel hydroponic technique which optimizes the growth and quality of plants with water-saving hydroponics.