Effect of Ultrafine Bubbles in Nutrient Solutions on the Growth of Different Lettuce Varieties Cultivated in a Controlled Plant Factory Environment

Abstract

　The growth of different lettuce varieties in response to the application of ultrafine bubbles (UFB) was investigated inside a plant factory with artificial light (PFAL). Six different types of lettuce (greenwave, frilly, green leaf, butterhead, romaine, and lamb lettuce) were cultivated under UFB and control treatments using a deep flow technique (DFT) hydroponic system. As a result, the effect of UFB treatment was found to vary depending on the type of lettuce cultivar. UFB treatment was found to promote growth in greenwave, frilly, and romaine lettuce but not in green leaf, butterhead, or lamb lettuce. Compared to the control treatment, the temperature of the nutrient solution and the dissolved oxygen (DO) concentration were higher by 1.61℃ and 59.5% in the UFB treatment, respectively. These findings suggest that an increased temperature and a high DO content during UFB generation are factors that enhance lettuce growth. Taken together, these results indicate that the application of UFB in the DFT hydroponic culture system can significantly promote lettuce growth in PFAL.