Nutrient use efficiency and yield

Yield and quality results by crop

The strongest results in this lesson are yield and quality gains measured against non-aerated or conventionally irrigated controls. They come from different crops, systems and gases, so each is stated with its conditions.

Rice: yield and fertilizer

Field experiments with rice found that nanobubble irrigation increased yield by about 8% Wang et al., 2021. The same work reported that nanobubble treatment kept yield equal to the fully fertilized control while fertilizer application was cut by 25%, a result that points to better nutrient use efficiency (NUE).

Tomato: yield and fruit quality

In greenhouse trials, micro-nano bubble water oxygation (MNBWO) increased tomato yield by 16.9% to 19.66% compared with non-aerated controls Liu et al., 2019; Chen et al., 2023. Fruit quality improved as well: vitamin C content rose by 17.7% to 26.5% and soluble sugar content by 20.7% to 39.2%. The ranges span both studies.

Leafy crops: biomass

In subsurface drip trials with treated wastewater, oxygen nanobubble aeration increased lettuce aboveground dry biomass by 52% compared with control subsurface irrigation Baram et al., 2021. In a separate study, air nanobubbles increased aerial fresh weight of Brassica campestris, a leafy brassica, by 34.5% Ebina et al., 2013.

Root growth may contribute. Nanobubble treatment has been observed to increase total root length density in greenhouse tomato, expanding the root system's capacity to take up water and nutrients del Moral Torres et al., 2024.

Nanobubbles may carry nutrient ions to the root surface

One proposed mechanism is electrostatic. Nanobubbles suspended in water typically carry a negative surface charge, measured as zeta potential, and have a large surface area for their volume. The negatively charged gas–liquid interface attracts positively charged nutrient ions (cations) such as ammonium (NH₄⁺), potassium (K⁺), calcium (Ca²⁺) and magnesium (Mg²⁺), so the bubbles may act as carriers that bring these ions to the root surface and raise their availability Arablousabet & Povilaitis, 2024; Wang et al., 2021.

The gas matters. Ahmed et al. reported a larger negative zeta potential for nitrogen nanobubbles than for air nanobubbles, which they attributed to differences in ionization energy Ahmed et al., 2018. A stronger charge would let nitrogen nanobubbles hold more cations, which may help explain why they often promoted vegetative growth more than other gases in that work.

This carrier role is a proposed mechanism. The lesson cites no measurement of ions actually delivered to roots by bubbles.

Oxygen keeps the roots' nutrient pumps powered

Roots take up nitrogen (N), phosphorus (P) and potassium (K) partly by active transport, which needs energy in the form of adenosine triphosphate (ATP). Oxygen supply largely sets how much ATP the roots can make.

In heavy or waterlogged soils, hypoxia slows aerobic respiration and pushes roots toward anaerobic metabolism, which yields much less ATP. Keeping dissolved oxygen (DO) high with oxygen nanobubbles is proposed to sustain aerobic respiration through the tricarboxylic acid (TCA) cycle, supplying the ATP that ion pumps and transport proteins need Zheng et al., 2025; Ahmed et al., 2018.

Nutrient-uptake genes were more active in rice

Laboratory studies on rice seedlings found that nanobubble treatment upregulated genes for nutrient absorption, including OsBT (nitrate uptake), PiT-1 (phosphate transport) and SKOR (potassium transport) Wang et al., 2021. This is consistent with a genetic contribution to the higher NUE measured in the same work, although gene expression in seedlings does not by itself show how much more fertilizer a field crop takes up.

Germination depended on the gas

The effect of nanobubbles on germination varied with the gas used. In a comparison on lettuce, carrot and fava bean, nitrogen nanobubbles gave the most consistent promotion Ahmed et al., 2018. Lettuce germination reached 100% with nitrogen nanobubbles, against 85% with oxygen, 82% with air and 80% with tap water.

Air nanobubbles generated with electric fields raised lettuce germination from about 20% in the control to 96% within two days Jannesari et al., 2024. The low germination of the control makes the relative gain large.

Barley seeds submerged in nanobubble water reached 58% germination after 17 hours, twice the 28% measured in distilled water Liu et al., 2015.

Reactive oxygen species act within a window

The proposed explanation for faster germination is an "oxidative window". Liu et al. found that nanobubbles produce low levels of reactive oxygen species (ROS), including hydroxyl radicals (•OH) and superoxide anions (O₂^•−) Liu et al., 2015. Within a certain range, these act as signal molecules that loosen cell walls and allow cell elongation, both needed for germination.

Too much ROS inhibits germination. Oxygen nanobubbles produced the most ROS, which exceeded the tolerance of sensitive seeds such as carrot, so they gave no significant promotion there. Nitrogen and air nanobubbles produced moderate ROS levels that stayed within the window that stimulated germination Ahmed et al., 2018; Liu et al., 2016.