2022 Volume 60 Issue 4 Pages 195-204
Previous studies have reported that ultrafine bubbles (UFBs) can promote plant growth. However, the optimum application of UFBs has not been sufficiently clarified yet. In this study, we investigated the optimum UFB content index for lettuce cultivation. Content index (CI) was defined as the product of the pass numbers (Pn) and dilution ratio (D) and taken to be indicative of UFB density; where Pn was the number of times water was passed through the UFB generator. UFB treatment comprised three different Pn: 10 passes (P1), 25 passes (P2), and 100 passes (P3). Six UFB treatments were conducted for each Pn in six D treatments as: control, UFB 10%, UFB 30%, UFB 50%, UFB 75%, and UFB 100%. The results confirmed that there was an appropriate level of CI to accelerate the growth of lettuce in a hydroponic solution, that is, a UFB CI of 7.5―30 and 18.75―30 in the nursery and cultivation stages, respectively. However, lettuce growth was significantly smaller on CI of 100. In addition, DPPH and NBT tests were conducted to measure the total antioxidant capacity (TAC) and superoxide radical on lettuce. TAC and superoxide radical accumulation were influenced by the UFB content index.
