Effect of oxygen-nanobubbles on the growth of lettuce in hydroponics

With modern nanobubble agrotechnology, oxygen-nanobubbles (ONB) can be administered in hydroponic systems. Nanobubbles (less than 1 μm in size) possess some unique properties that, when combined with a high dissolved oxygen concentration (%DO) content of between 20 and 40 mg L^-1, are considered to improve plant health, growth, yield, and quality. The effect of ONB on the plant growth, yield, and postharvest quality of commercial lettuce cultivars (Lactuca sativa L.) grown in a nutrient film technique (NFT) was investigated in this study. ‘Chalmers’, ‘Meditation’, ‘Chicarita’, and ‘Tallio’ cultivars were transplanted and grown for 49 days in a hydroponic system. A nutrient solution with a pH of 5.8 and an EC of 1.0 dS m^-1 was maintained in the system. A glasshouse trial was set up with two treatments; ONB irrigation with a target %DO of 20 mg L^-1, and the other was control irrigation. The results showed that the root length of the four cultivars was significantly longer in ONB (average 599 mm) than in control irrigation (average 257 mm). ‘Meditation’ showed a significant difference with a 126.5% increase in root length. Under ONB irrigation, yield indicators such as the fresh weight and total leaf area were higher, with significant differences only for ‘Meditation’. In terms of storage ability, the relative weight loss of the plants under ONB was significantly lower than that under control irrigation. ONB also improved the overall health of plant roots by suppressing algae growth throughout the hydroponic system. Therefore, it is possible to conclude that ONB irrigation benefits both root growth and crop health in NFT, thereby improving lettuce postharvest quality. Further studies should focus on the effect of ONB on fruiting crops (like strawberries and tomatoes) with more extended growing periods and testing different percentages of DO.