Oxygen Nanobubble Irrigation in Protected Horticulture: Mechanisms, Evidence, and Grower Considerations

Nanobubble (NB) technology is gaining attention as a method to improve irrigation water quality and crop performance in controlled-environment horticulture (CEH). Nanobubbles are very small gas-filled bubbles characterized by high surface charge, extended stability in water, and enhanced gas-transfer properties. When air- or oxygen-enriched NB water is used for irrigation, it can increase the availability of dissolved oxygen in the root zone, thereby supporting aerobic respiration. Beyond oxygenation, NB irrigation has been associated with changes in nutrient uptake, root development, and rhizosphere microbial communities. Proposed mechanisms include enhanced oxygen delivery, improved conditions for beneficial microbes, and potential signaling effects related to reactive oxygen species (ROS), although direct causal links remain under investigation. This review synthesizes current knowledge on NB physicochemical properties, plant physiological responses, and crop-level outcomes across soil-based, soilless substrate, and hydroponic production systems, with a practical focus relevant to CEH growers. The published evidence base is concentrated in soil-based greenhouse systems in China, where the largest yield responses have been reported under intensive production conditions with mineral soils and likely represent an upper bound that does not generalize across all CEH environments. Evidence from soilless substrate systems—the preferred growing media in high-value commercial CEH production across much of Europe, North America, and Australia—remains limited. Key practical considerations for growers, remaining knowledge gaps, and priorities for future research are discussed, with the aim of providing a balanced and evidence-based resource for researchers and producers considering NB irrigation in commercial CEH.