Ultrafine bubbles (UFBs) exhibit a number of unique physical characteristics; however, reports on plant growth enhancement by UFB application are controversial. Here, we report experiments conducted to test whether UFB technology effectively promotes plant growth. We analyzed the effects of three experimental factors: water (UFB addition), hypoxia (aeration), and fluid movement (stirring) on the growth of soybean seedlings cultured hydroponically under low and high nutrition levels in a controlled environment room under artificial lighting for 8 days. When no nutrients were supplied, positive UFB water effects were evident, but low nutrition reduced UFB water-mediated growth enhancement and high nutrition totally obliterated any growth enhancement by UFB water. We concluded that UFB water-induced growth enhancement was effective and significant under nutrient deficit stress but no growth enhancement was observed, and even negative effects were evident, under favorable plant growth conditions.

Previous research into the effects of ultrafine bubbles (UFB) on plant growth have been contradictory. To facilitate the resolution of these contradictions, the aim of the present study was to clarify the interspecific differences in growth responses among cereal/leguminous species under different levels of UFB concentrations. Seedlings of six species were grown hydroponically with three different UFB concentrations and two levels of plant nutrition to evaluate biomass and elongation growth. UFB growth promotion under zero-nutrition occurred in all species. Interspecific differences were noted in response to differing UFB concentration levels. Rice and soybean had higher above-ground biomass production at both low and high concentrations. Conversely, other crops exhibited promoted growth at only one of the concentrations. Negative effects occurred in full nutrient conditions except for root elongation. This study demonstrated that growth-promoting effects with UFB depended on the crop species being tested and the concentration of UFB used.

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