AGRICULTURE TECHNOLOGY FLYER
Microbubbles, Ultrafine Bubbles,and Nanobubble in Agriculture,
Horticulture, and Hydroponics
Agriculture Technology Flyer
Microbubbles, Ultrafine
Bubbles, And Nanobubble In
Agriculture, Horticulture, And
Hydroponics
As an oxygen transfer package, the properties of small bubbles continue to surprise.
The challenge for many years has been in consistently generating these small bubbles, understanding that at the nanobubble size range—which we call “Ultra Fine Bubbles”—consistently and predictably generating these bubbles has been challenging.
Yet the benefit for food production stemming from these small bubbles has been known and documented for some time. As we’ll see in the examples laid out in the following pages, since 2009 the benefits of nanobubbles’ superior oxygen/air transfer efficiency has been documented in assisting not only oxygen shortages, but even improving plant seed germination, biomass growth (e.g., lettuce and spinach)1 and crop yield (e.g., tomato)2 , which improvements may be extended to hydroponically or aquaponically grown crops—with the benefit that these microbubble, ultra-fine bubble, and nanobubble applications will always be toxin and chemical-free, with no downstream consequence.
Since then, later studies have delved into a detailed understanding of processes, and findings have remained consistent in science—a recent study3 compared different sized bubbles and their effects on crop growth and benefits in agriculture, and indeed, the study found that smaller air microbubbles are more effective than their larger millibubble cousins in transferring benefits to plants. The conclusions of this 2017 study found the following:
“The results showed that microbubbles applied to the culture solution promoted the growth of spinach more than that by millibubbles. Using microbubbles, cultivars maintained a high concentration of dissolved oxygen at the middle growth stage, during which the dissolved oxygen concentration in the culture solution was reduced by the active root respiration. This result suggests that microbubbles are more effective than millibubbles in the hydroponic culture of vegetables.”
In plant and animal growth studies, as we’ll review below, Nanobubbles have superior oxygen and air transfer efficiencies and benefits, and have been demonstrated as a vector to improve biomass growth in hydroponic applications as well as in soil agriculture. Moreover, benefits have been proven in raceway and controlled aquaculture systems, and, naturally, these benefits also extend to openwater and marine aquaculture. In every case, our energy-efficient, adaptable technology, provides a chemical-free, no-fallout, zero residual solution—delivering material impact to agroindustry while also supporting biodiversity and planetary husbandry.
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Park, Jong-Seok, and Kenji Kurata. ‘Application of Microbubbles to Hydroponics Solution Promotes Lettuce Growth’. HortTechnology 19, no. 1 (January 2009): 212–15. https://doi.org/10.21273/HORTSCI.19.1.212. and Ikeura, Hiromi, Keita Tsukada, and Masahiko Tamaki. ‘Effect of Microbubbles in Deep Flow Hydroponic Culture on Spinach Growth’. Journal of Plant Nutrition 40, no. 16 (2 October 2017): 2358–64. https://doi.org/10.1080/01904167.2017.1346663.
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Wu, Yuncheng, Tao Lyu, Bin Yue, Elisa Tonoli, Elisabetta A. M. Verderio, Yan Ma, and Gang Pan. ‘Enhancement of Tomato Plant Growth and Productivity in
Organic Farming by Agri-Nanotechnology Using Nanobubble Oxygation’. Journal of Agricultural and Food Chemistry 67, no. 39 (2 October 2019): 10823–31.
https://doi.org/10.1021/acs.jafc.9b04117. -
Tamaki, Masahiko & Ikeuraa, Hiromi & Tsukadab, Keita. (2017). Effect of Microbubbles in Deep Flow Hydroponic Culture on Spinach Growth. Journal of Plant
Nutrition. 40. 00-00. 10.1080/01904167.2017.1346663.
Nanobubbles in Practice
Nanobubbles have now been documented with a number of extraordinary properties, and more continue to be uncovered. And not just in crop growth rates—a study as early as 2013 noted that “The germination rates of barley seeds dipped in water containing NBs (bubbles formed from gas mixtures of nitrogen and pure air) were 15–25 percentage points greater than those of the seed dipped in distilled water with the same concentration of dissolved oxygen (DO)4.” This was a curious result as it draws attention away from simple increased presence of oxygen—which would give a more expected conclusion. The study concludes that “nanobubbles in water could influence the physical properties of water,” which is an unexpected conclusion, but which opens further doors to benefits feasible using these artefacts.
These effects have advanced to further, broader studies, and as a starting point, it’s useful to refer to a study that examined impacts across both plants and animals, presenting an overview of the sorts of surprising findings we’re now calling commonplace. In this paper we simply review some of the different applications of nanobubbles in different sectors of the agriculture and aquaculture industries.
We begin with a broad study run by a number of prominent health science authorities in Japan5. The headline findings were that:
• Air nanobubbled water (continuously circulated) significantly promoted the height, length of leaves, and aerial fresh weight of hydroponically grown Brassica campestris, a plant with subspecies ranging from turnips to field mustard, and from whose seeds Canola oil is commonly grown. In this test, there was no significant difference in pH, nitrogen, phosphorous, potassium, calcium,, and magnesium concentrations with the control group.
• For sweetfish (an East Asian species that is amphidromous, moving between coastal marine waters and freshwater lakes and rivers), after three weeks total weight of sweetfish increased from 3.0 to 6.4kg in normal water, and from 3.0 to 10.2 kg in air-nanobubble water.
• Total weight of rainbow trout increased from 50.0 to 129.5 kg in normal water, whereas it increased from 50.0 to 148.0 kg in air-nanobubble water after 6 weeks
• After 12 weeks, free oral intake of oxygen-nanobubble distilled water significantly promoted the weight (21.860.3 vs. 23.560.3 g; P,0.01) and the length (16.160.1 vs. 17.060.1 cm; P,0.001) of mice as compared to free oral intake of normal water. As for food consumption, mice drinking oxygen-nanobubble water took higher dose of food compared to that of normal water.
These findings suggest remarkable benefits for plural applications for nanobubble technologies; it will be easily noted that the organisms tested were chosen so as to be representative of a truly broad class of biological applications. As will be seen below, there are also antiseptic effects to nanobubbles, as well as soil effects for making nutrients available to not only plants (for multiple effects), but also the microbiota at the soil, to promote fertility, and even to reduce greenhouse gas emissions.
In the present paper, we’ll focus explicitly on agriculture, horticulture, aquaculture, and hydroponic applications of Nanobubbles and Ultrafine Bubbles.
Nanobubble are inherently non-toxic and don’t require chemicals, meaning that benefits are sustainable and scalable, and kinder on biodiversity and on local and downstream ecosystems
4 Liu, Shu, Yoshinori Kawagoe, Yoshio Makino, and Seiichi Oshita. ‘Effects of Nanobubbles on the Physicochemical Properties of Water: The Basis for Peculiar Properties of Water Containing Nanobubbles’. Chemical Engineering Science 93 (April 2013): 250–56. https://doi.org/10.1016/j.ces.2013.02.004.
5 Ebina, Kosuke, Kenrin Shi, Makoto Hirao, Jun Hashimoto, Yoshitaka Kawato, Shoichi Kaneshiro, Tokimitsu Morimoto, Kota Koizumi, and Hideki Yoshikawa. ‘Oxygen and Air Nanobubble Water Solution Promote the Growth of Plants, Fishes, and Mice’. Edited by Jose Luis Balcazar. PLoS ONE 8, no. 6 (5 June 2013): e65339. https://doi.org/10.1371/journal. pone.0065339.
Germination and agriculture
Nanobubbles act as biochemical, and kinetic agents, as well as vectors for the gas within their envelope—which can be CO2, Oxygen, Ozone, Nitrogen, Hydrogen, normal air, or other compounds. As such, nanobubbles can work through different media for extraordinary effects.
Nanobubble applications can work across multiple different opportunities for interaction in agriculture. Moreover, nanobubble uses are inherently non-toxic and don’t require chemical exposure to the crops, meaning that benefits are sustainable and scalable in their own right, and also kinder on biodiversity and on downstream ecosystems, which are important considerations under current thinking and approaches to agriculture. Finally, it’s important to note that certain applications have been shown to reduce methane emissions from agriculture, a potent greenhouse gas—this is an important consideration in current profiling for agricultural development.
For instance, it’s been noted that in porous soil, nanobubbles have a long retention time, suggesting that they adsorb to soil with the potential for long-term effects on soil chemistry6—these benefits accrue not only to plants, but also to microbiology in the soil; additionally the collapse of nanobubbles may generate reactive oxygen species, such as hydroxyl radicals (•OH), which can affect plant growth and seed germination7.
These effects have been shown to have extraordinary results to crop growth and development. A recent study8 confirmed that Nitrogen and Phosphorous became more bioavailable to plants after exposure to oxygen nanobubbles, leading to a 23% increased yield in soil-cultivated tomatoes (as well as increasing soil microbial biomass, activity, and diversity), while
another study9 postulated that air nanobubbles at the plant root can help in the attraction of Potassium and Calcium, magnesium and other nutrients, coupled with direct exchange of oxygen at the root, showing in hydroponic lettuce “significant increases in growth—2.1 times greater fresh leaf weight and 1.7 times greater dry leaf weight than controls with conventional aeration.”Moreover, “nanobubble and “micro bubble surfaces may help roots absorb nutrient salts because micro bubbles attract ions dissolved in nutrient solutions10.
These outcomes suggest that on soil agriculture, simple air nanobubbles can help plants absorb nutrient salts even as nanobubbles are adsorbed to the soil substrate, with evident benefits not only to the target crops, but also to the microbiology associated with root functions
These studies confirmed that nanobubble oxygenation improved fertiliser mineralization, enhanced microbial activity and diversity—creating a yield increase of 23% using organic practices, which would offset yield losses commonly attributed to the transition from traditional farming using chemical fertiliser to organic farming using organic fertilisers11, or, by the same token, can limit, or eliminate, the cost or carbon footprint of large scale chemical fertilisation while maintaining equivalent yields and supporting biodiversity.
7 Park, Jong-Seok, and Kenji Kurata. ‘Application of Microbubbles to Hydroponics Solution Promotes Lettuce Growth’. HortTechnology 19, no. 1 (January 2009): 212–15. https://doi.org/10.21273/HORTSCI.19.1.212.
8 see Takahashi, M. 2005. z Potential of micro- bubbles in aqueous solutions: Electrical properties of the gas-water interface. J. Phys. Chem. B 109:21858–21864.
9 Forster, D.; Andres, C.; Verma, R.; Zundel, C.; Messmer, M. M.; Mäder, P. Yield and economic performance of organic and conventional cottonbased farming systems–results from a field trial in India. PLoS One 2013, 8, (12), e81039.
10 see Takahashi, M. 2005. z Potential of micro- bubbles in aqueous solutions: Electrical properties of the gas-water interface. J. Phys. Chem. B 109:21858–21864.
11 Forster, D.; Andres, C.; Verma, R.; Zundel, C.; Messmer, M. M.; Mäder, P. Yield and economic
Other staple crops
In the case of barley, nanobubbles “induced the expression of genes related to cell division and cell wall loosening”, thereby speeding
the sprouting of the plant12. This example confirms the effect documented in other studies regarding the germination benefits of nanobubbles.
Another study on barley seed germination also concluded that the application of nanobubbles “had a positive effect on the germination rate of seeds.13” In this experiment two different varieties of barley were treated with oxygen nanobubbles, and germination rates were 10-20% higher than the control group.
However, different gases perform with different varietals:
“Different plants, including lettuce, carrot, fava bean, and tomato, were used in germination and growth tests. The seeds in water-containing nanobubbles exhibited 6–25% higher germination rates. Especially, nitrogen nanobubbles exhibited considerable effects in the seed germination”.14
The growth of stem length and diameter, leaf number, and leaf width were promoted by NBs with different gases, but not air; this effect was thought to stem from the generation of exogenous reactive oxygen species by nanobubblers and higher efficiency of nutrient fixation or utilization by the plants15. By any measure, these are important results to consider, particularly when we understand that the raw materials necessary for these results come from readily accessible gases and water only, and our nanobubble generator, and can be scaled as required at marginal costs.
12 Liu, Shu, Seiichi Oshita, Saneyuki Kawabata, and Dang Quoc Thuyet. ‘Nanobubble Water’s Promotion Effect of Barley ( Hordeum Vulgare L.) Sprouts Supported by RNA-Seq Analysis’. Langmuir 33, no. 43 (31 October 2017): 12478–86. https://doi.org/10.1021/acs.langmuir.7b02290.
13 Purwanto, Ya, Nn Maulana, Sobir, Sulassih, and N Naibaho. ‘Effect of Ultrafine Bubbles Water on Seed Germination’. IOP Conference Series: Earth and Environmental Science 355, no. 1 (1 November 2019): 012073. https://doi.org/10.1088/1755-1315/355/1/012073.
14 Ahmed, Ahmed Khaled Abdella, Xiaonan Shi, Likun Hua, Leidy Manzueta, Weihua Qing, Taha Marhaba, and Wen Zhang. ‘Influences of Air, Oxygen, Nitrogen, and Carbon Dioxide Nanobubbles on Seed Germination and Plant Growth’. Journal of Agricultural and Food Chemistry 66, no. 20 (23 May 2018): 5117–24. https://doi.org/10.1021/acs.jafc.8b00333.
15 Ibid
Rice
Nanobubble research has uncovered a number of interesting properties for nanobubbles in the cultivation of rice, a global staple crop; effects which work from the seedling to the harvest stage.
Recent field experiments16 show that air nanobubbles increased yields by almost 8% over fields that are using normal fertilisation as control, and equivalent yields using 75% fertiliser. This equates to an enormous economy in fertiliser use for equivalent yields, with a documented improvement in crop resilience, biodiversity benefits, and materially lower carbon and downstream nitrification footprint.
• At the seedling stage, using air, plant height and root length in laboratory testing increased by around 26%and 52% respectively, with a 10 minute nanobubble treatment eight times per day.
• In growth, it was found that “three genes responsible for nutrient absorption were significantly more highly expressed in the roots of rice treated with NBs.” This resulted in an increased absorption of Nitrogen, Phosphorous, and Potassium.
• The nanobubbles demonstrably “activated nutrient absorption related genes”, which in turn increased the plant’s adaptability to environmental stress—ultimately resulting in higher yields.
In the field, uptake of nutrients was noted to the extent that “improvement in nutrient absorption
capacity in the crop plants is likely to be an important factor by which nanobubbles promote rice yield and reduce fertiliser use by approximately 25%.”17 Moreover, the plants naturally became more resilient to stress, which is a powerful finding in the face of climate uncertainties facing growers.
According to statistics from the Food and Agriculture Organization of the United Nations (FAO), there were 16,713 million ha of rice paddy worldwide in 2018 which used about 120 kg/ha fertilizer. As rice production is projected to increase by 40% by 2030 to meet the demand of population expansion18, fertilizer use is also likely to grow in future. If fertilizers can be used more efficiently by applying methods such as nanobubble irrigation, this would dramatically reduce the chemical load on farmland, as well as soil degradation and environmental pollution—not only at the site, but also downstream.
Another field study went further, to analyse whether the introduction of nanobubbles could have other effects on the nutritional qualities, and yields, of rice. This study19 started from the position that “rice normally appears to have more absorption of cadmium (Cd), a very toxic heavy metal caused by soil contamination and acidification, compared to other major cereal crops.” The concern is that this could lead to an accumulation of cadmium in rice, to deleterious human health consequences. The study proceded to study the effect of hydrogen nanobubbles on rice in the field, and returned surprising findings on yields, and on cadmium accumulation.
• The average length and width of the grains in HNW-treated group was about 11.4% and 15.1%greater than those from the control sample.
• Grain thickness showed pronounced improvement by 37.5%
• These elements combined to yield an increase in thousand-grain-weight of about 23.8%
• Cadmium accumulation, a toxic heavy metal caused by soil contamination and acidification, prone to accumulate in rice, “was significantly reduced, reaching 52% of the control group.”
It’s important to note that normal applications of hydrogen to soils are usually short-lived, or as bound to other chemicals. Both of these traits are not useful in agricultural applications, where biodiversity of soils can be affected by the accumulation of carrier elements (e.g. magnesium hydride—an H2-releasing material), or where processes are better suited to a slower release of hydrogen; hydrogen nanobubbles bridge these concerns very well, as bubbles stay in their substrate for a long time, and no other chemicals are involved.
In this study, no chemical fertilisers or pesticides were applied, and hydrogen nanobubble water was applied once a week (about 3 tons per 150m2), as from booting stage to harvest stage. Even in this frame, the increased yields from modest applications of hydrogen nanobubbles were important.
16 Wang, Ying, Shuo Wang, Jingjing Sun, Hengren Dai, Beijun Zhang, Weidong Xiang, Zixin Hu, Pan Li, Jinshui Yang, and Wen Zhang. ‘Nanobubbles Promote Nutrient Utilization and Plant Growth in Rice by Upregulating Nutrient Uptake Genes and Stimulating Growth Hormone Production’. Science of The Total Environment 800 (December 2021): 149627. https://doi.org/10.1016/j.scitotenv.2021.149627.
17 Ibid
18 Khush, Gurdev S. ‘What It Will Take to Feed 5.0 Billion Rice Consumers in 2030’. Plant Molecular Biology 59, no. 1 (September 2005): 1–6. https://doi.
org/10.1007/s11103-005-2159-5.
19 Li, Longna, Jun Wang, Ke Jiang, Yong Kuang, Yan Zeng, Xu Cheng, Yuhao Liu, Shu Wang, and Wenbiao Shen. ‘Preharvest Application of
Hydrogen Nanobubble Water Enhances Strawberry Flavor and Consumer Preferences’. Food Chemistry 377 (May 2022): 131953. https://doi.org/10.1016/j.
foodchem.2021.131953.
Methane emissions
Beyond the above-noted study on germination and growth of rice, a further study20 on rice fields tested oxygen nanobubbles for oxidation properties in a flooded paddy soil.
This application was found to decrease soil methane (a powerful greenhouse gas) production by 20-28% versus control water, and increased oxygen concentration at shallow soil depths—conducive to healthy plant growth.
Reviewing these studies, air nanobubbles seem to have definite long-period improvement benefits to rice growth, and supplemental dosing of oxygen nanobubbles demonstrably help in reducing methane emissions from rice paddies. Alongside these benefits, there are evident biodiversity benefits to soil health, and downstream contamination, from a lower application of chemical fertilisation.
20 Minamikawa, Kazunori, and Tomoyuki Makino. ‘Oxidation of Flooded Paddy Soil through Irrigation with Water Containing Bulk Oxygen Nanobubbles’. Science of The Total Environment 709 (March 2020): 136323. https://doi.org/10.1016/j.scitotenv.2019.136323.
Soil microbial activity
Nanobubbles are likely to improve soil microbial activity, diversity and community by increasing nutrient availability and oxygen content in the soil21. This was also borne out through a field study of sugar cane production, where harvests were increased through the long-term improvement of soil microbial activity stemming from nanobubble treatment22.
This study in sugar cane was a two-year field experiment mixing groundwater and air nanobubble, looking to target changes in the soil rhizosphere and observe shifts in soil microbial activity. The results of the test indicated that nanobubble irrigation directly affects soil microbial communities and soil fertility, and “indirectly promoted sugarcane yield.” This improvement in yields was strongly supported by “a better
nutritional content of nanobubble irrigated soils and changes in the bacterial community23.”
Moreover, this study confirms that over a longer period, nanobubble treatments sustainably improve soil health without resorting to long-term fertiliser input—with the known consequences to biodiversity, soil health, and downstream and groundwater residual contamination.
21 Op. cit. Wu, Yuncheng, Tao Lyu, Bin Yue, Elisa Tonoli, Elisabetta A. M. Verderio, Yan Ma, and Gang Pan. ‘Enhancement of Tomato Plant Growth and Productivity in Organic Farming by Agri-Nanotechnology Using Nanobubble Oxygation’. Journal of Agricultural and Food Chemistry 67, no. 39 (2 October 2019): 10823–31. https://doi.org/10.1021/acs.jafc.9b04117.
22 Zhou, Yunpeng, Felipe Bastida, Bo Zhou, Yifei Sun, Tao Gu, Shuqin Li, and Yunkai Li. ‘Soil Fertility and Crop Production Are Fostered by Micro-Nano Bubble Irrigation with Associated Changes in Soil Bacterial Community’. Soil Biology and Biochemistry 141 (February 2020): 107663. https://doi.org/10.1016/j.soilbio.2019.107663.
23 Ibid.
Other agriculture
Regarding specialty agriculture, it’s well known that fertiliser applications can have a negative effect on some of the attractive traits of fruit—for example aromas. It’s also well known that applying nitrogen to strawberries will improve yields, but will negatively affect aromatic and flavour compounds in the fruit24. In consideration of this, a specialised study on hydrogen nanobubble applications to strawberries25 identified interaction with particular esthers (e.g. ethyl hexanoate), acids (e.g.hexanoic acid), and soluble sugars (including fructose, glucose, and sucrose) in a way that treatment “significantly contributed to strawberry flavour.” Moreover, the study found that nanobubbles “may alleviate the negative effects of fertilisers on strawberry fruit aroma.” Hydrogen nanobubbles were found to have increased the contents of the three noted sugars, even when fertilisers were applied to improve grower yields. Moreover, although control strawberries with fertiliser treatment have lower texture and chewiness, hydrogen nanobubbles were “found to increase the texture and chewiness quality as a result of increased firmness,” indicating that pre-harvest hydrogen nanobubble treatment “may be beneficial to the transportation and storage of strawberries.26”
Nanobubbles increased sugar contents in strawberries, even when fertilised for higher yields—this offset the normal negative effects on fruit quality from chemical fertilisation.
The challenges of over-fertilisation affecting flavour of the crop are also known in tomatoes, yet higher yields are a primary concern for the agriculture industry.
Following from the advantages of hydrogen and the promotion of biomass in soybean, spring wheat, barley, and canola27, and looking at nanobubbles as a vector for the hydrogen effects, another study28 considered an application of hydrogen nanobubbles to cherry tomatoes in soil. It found that hydrogen nanobubbled water “increased soil available nitrogen, phosphorous and potassium consumption regardless of fertiliser application.” The study’s conclusion was that hydrogen nanobubbled water not only exhibited fertilisation effects on yield—implying an available reduction in the use of conventional fertilisers—but also improved fruit quality, all at a lower carbon footprint.
Note that the yield outputs were remarkable:
• Compared to normal water irrigation (9.50 t ha-1), total yield of cherry tomatoes in the treatment of hydrogen nanobubbles without fertilizers was 13.27 t ha-1 (39.7% increase)
• Hydrogen nanobubble plus fertilizers yielded (15.38 t ha-1), and increased yield by 26.5% in comparison with normal water with fertilizers
• Yield from hydrogen nanobubbles without fertilizers was even higher (9.1%) than normal water plus fertilizers (12.16 t ha-1).
Nanobubble treatment not only had fertilisation effects, meaning less fertiliser was needed, but also improved fruit quality.
Another study29 specifically looked at how air nanobubbles at different concentrations affected laboratory growth of wheat, rice, maize, soybean, cowpea, and adzuki bean—all major food crop species. Results were not homogenous across the varietals, with wheat, rice, cowpea, and adzuki bean showing growth promotion with low nanobubble concentrations, with less effect at high concentrations. At high concentrations, maize and soybean were promoted.
One of the considerations stemming from analysis of this study is that air UFBs may have limited benefits for some species in nutrient-rich environments, such as hydroponic environments. Clear benefits were observed in conditions of nutrition stress, meaning that nanobubbles can act as an insurance for variable crop growing conditions.
Nanobubbles have shown material benefits in conditions of nutrient or water stress, thereby acting like an insurance to growers over weather or cultivation shortcomings
Supporting these observations, if we specifically look at soybeans in a hydroponic environment, air nanobubble enhancement was found to be effective and significant under nutrient stress, but not under favorable plant conditions30. Indeed, under favorable nutritional environments, root biomass was not observed to be greater than from control water—possibly because the plant finds no need to expend energy in root development.
24 Cvelbar Weber, Nika, Darinka Koron, Jerneja Jakopič, Robert Veberič, Metka Hudina, and Helena Baša Česnik. ‘Influence of Nitrogen, Calcium and Nano-Fertilizer on Strawberry (Fragaria × Ananassa Duch.) Fruit Inner and Outer Quality’. Agronomy 11, no. 5 (18 May 2021): 997. https://doi.org/10.3390/agronomy11050997.
25 Li, Longna, Jun Wang, Ke Jiang, Yong Kuang, Yan Zeng, Xu Cheng, Yuhao Liu, Shu Wang, and Wenbiao Shen. ‘Preharvest Application of Hydrogen Nanobubble Water Enhances Strawberry Flavor and Consumer Preferences’. Food Chemistry 377 (May 2022): 131953. https://doi.org/10.1016/j.foodchem.2021.131953.
26 Ibid.
27 See Dong, Z., L. Wu, B. Kettlewell, C. D. Caldwell, and D. B. Layzell. ‘Hydrogen Fertilization of Soils - Is This a Benefit of Legumes in Rotation?: Hydrogen Fertilization and Crop Growth’. Plant, Cell & Environment 26, no. 11 (November 2003): 1875–79. https://doi.org/10.1046/j.1365-3040.2003.01103.x.; and Golding, Amber-Leigh, and Zhongmin Dong. ‘Hydrogen Production by Nitrogenase as a Potential Crop Rotation Benefit’. Environmental Chemistry Letters 8, no. 2 (June 2010): 101–21. https://doi.org/10.1007/s10311-010-0278-y.
28 Li, Min, Yingying Zhang, Chenxu Cai, Longna Li, Shu Wang, Yuhao Liu, Yan Zeng, Xu Cheng, and Wenbiao Shen. ‘Hydrogen Fertilization Improves Yield and Quality of Cherry Tomatoes Compared to the Conventional Fertilizers’. SSRN Electronic Journal, 2022. https://doi.org/10.2139/ssrn.4064621.
29 Iijima, Morio, Kaito Yamashita, Yoshihiro Hirooka, Yoshikatsu Ueda, Koji Yamane, and Chikashi Kamimura. ‘Promotive or Suppressive Effects of Ultrafine Bubbles on Crop Growth Depended on Bubble Concentration and Crop Species’. Plant Production Science 25, no. 1 (2 January 2022): 78–83. https://doi.org/10.1080/1343943X.2021.1960175.
30 Iijima, Morio, Kaito Yamashita, Yoshihiro Hirooka, Yoshikatsu Ueda, Koji Yamane, and Chikashi Kamimura. ‘Ultrafine Bubbles Effectively Enhance Soybean Seedling Growth under Nutrient Deficit Stress’. Plant Production Science 23, no. 3 (2 July 2020): 366–73. https://doi.org/10.1080/1343943X.2020.1725391.
Dealing with biofilms in agriculture
Nanobubbles also support the proper and hygienic operation of supporting infrastructure for agriculture. In agricultural irrigation lines, biofouling causes considerable technical challenges, not only to animal health, but also to the proper and consistent operation of irrigation equipment, including drip irrigators. A recent study looked into the application of nanobubbles to deal with biofouling in agricultural irrigation water pipelines, without the application of chemical additives, bactericides (e.g. chlorination), or acid flushing31. Findings were that, especially when applied in early stages, the non-chemical
nanobubble treatment reduced fixed biomass by 31-52%, while also preventing buildup of mineral deposition—particularly carbonate deposits, which was an improvement over the common chlorination methods, and with fewer residual contaminants.
Nanobubbles not only improve irrigation benefits, but also help maintain irrigation lines clear, assuring blockages don’t stay a maintenance and inspection headache
31 Xiao, Yang, Sunny C. Jiang, Xiaoyao Wang, Tahir Muhammad, Peng Song, Bo Zhou, Yunpeng Zhou, and Yunkai Li. ‘Mitigation of Biofouling in Agricultural Water Distribution Systems with Nanobubbles’. Environment International 141 (August 2020): 105787. https://doi.org/10.1016/j.envint.2020.105787.
Horticulture and Post-harvest applications
Other applications can include post-harvest H2 treatments to delay senescence of fruits, flowers, and vegetables—all of these applications can have a simpler delivery, and longer effect, when coupled with nanobubbles, as in a recent study32, where an application of 5% hydrogen nanobubbled water “significantly prolonged the vase life of cut carnation flowers compared with distilled water.”Again, as in noted above, what is interesting is the use of nanobubbles as a vector for the transfer of
the gas in the nanobubble “package”. In the case of hydrogen, hydrogen nanobubbles are a vehicle for longer release and fewer residual concerns than say MgH2, which is widely used. In this experiment, 5% hydrogen nanobubble water “prolonged vase life by 51%, which was also larger than the effect of MgH2 alone (prolonged vase life by 27%).”
32 Li, Longna, Qianlan Yin, Tong Zhang, Pengfei Cheng, Sheng Xu, and Wenbiao Shen. ‘Hydrogen Nanobubble Water Delays Petal Senescence and Prolongs the Vase Life of Cut Carnation (Dianthus Caryophyllus L.) Flowers’. Plants 10, no. 8 (12 August 2021): 1662. https://doi.org/10.3390/plants10081662.
Hydroponics
Following from the above discussion on benefits of micro and nanobubbles in open-field agriculture, it would seem sensible that benefits would also accrue to controlled-environment, and hydroponic, agriculture.
As far back as 1988 it was confirmed that higher DO concentration are essential to root formation and root growth33. The extension of this to hydroponic environments became the field of aeroponics, where greater root development was logically understood as a vector to higher plant mass development. This paper found that the greatest effect was produced where O2 was consistent at the stem-water interface—which in the case of nanobubbles, is guaranteed.
Indeed, in the hydroponic space, much experimentation has been advanced in connection with increasing the oxygenation of roots in controlled-environment agriculture. The field of aeroponics is well documented, as are its complexities. Nevertheless, the positive results are not debated, at least with respect to root mass development of hydroponically grown tomatoes, as was confirmed in a 2010 study, with deep-water cultured lettuce, where even under conditions of winter-time cold temperatures (12˚C), Lactuca sativa L. cv Legacy lettuce plants grew 2.1 fold larger, and 2.3 times larger in dry weight, than in normally-aerated water34.
Moreover, it was found, in an even earlier study35, that, with respect to tomato plants, highly oxygenated plants not only showed not only “a marked increase in plant growth, as measured by shoot and root weights”, but also a resistance to colonization by pathogens—this particular experiment dealt with an introduction of Pythium F707, an isolate with filamentous non-inflated sporangia, which introduction was investigated under hydroponic conditions. It was found that oxygenated plants remained healthy throughout the experiment—in contrast to the other tested plants—showing significant decrease in root colonization by the pathogen.
Similar results were found with hydroponically grown kale, with respect to both germination and early growth36.
Starting with direct investigation of hydroponic lettuce, a 2009 study37 noted that “Fresh and dry weights of the microbubble treated lettuce were 2.1 and 1.7 times larger” than lettuces treated with normal aeration. The study’s presumption was that “the larger specific surface area of the microbubbles and the negative electronic charges on the microbubbles’ surfaces may promote growth because microbubbles can attract positively charged ions that are dissolved in the nutrient solution.” In other words, the bubbles’ aeration had a positive effect, but there was a further effect in aiding the absorption of nutrients in the hydroponic stream—implying a greater uptake efficiency of introduced nutrients at the root.
These observations were borne out very quickly, as reported by Liu in 2010, concluding that nanobubbles in water “could influence the physicochemical properties of water and that it could contribute to one of the explanations for the mechanism of NBs’ promotion effect on physiological activity of living organisms. The hydroponic experiment showed that the NBs could greatly promote the growth of barley and NMBs technology was feasible to be used in hydroponic cultivation of vegetables as a new technology in agriculture applications.”38
Of course, observations above on the improvements from micro, ultra-fine, or nanobubbles to organic or soil-grown produce can also apply to hydroponically grown crops.
33 Soffer, Hillel, and David W. Burger. ‘Effects of Dissolved Oxygen Concentrations in Aero-Hydroponics on the Formation and Growth of Adventitious Roots’. Journal of the American Society for Horticultural Science 113, no. 2 (March 1988): 218–21. https://doi.org/10.21273/JASHS.113.2.218.
34 Suyantohadi, A., T. Kyoren, M. Hariadi, M.H. Purnomo, and T. Morimoto. ‘Effect of High Consentrated Dissolved Oxygen on the Plant Growth in a Deep Hydroponic Culture under a Low Temperature’. IFAC Proceedings Volumes 43, no. 26 (2010): 251–55. https://doi.org/10.3182/20101206-3-JP-3009.00044.
35 Chérif, M., Y. Tirilly, and R. R. Bélanger. ‘Effect of Oxygen Concentration on Plant Growth, Lipidperoxidation, and Receptivity of Tomato Roots to Pythium F under Hydroponic Conditions’. European Journal of Plant Pathology 103, no. 3 (1 March 1997): 255–64. https://doi.org/10.1023/A:1008691226213.
36 Sritontip, Chiti, Wichein Phonsaeng, Nakhorn Thonglek, Chanchai Dechthummarong, and Kiyochi Yoshikawa. The Application of Micro/Nano Bubbles to Seed Germination and Seedling Growth of Chinese Kale, 2018.
37 Park, Jong-Seok, and Kenji Kurata. ‘Application of Microbubbles to Hydroponics Solution Promotes Lettuce Growth’. HortTechnology 19, no. 1 (January 2009): 212–15. https://doi.org/10.21273/HORTSCI.19.1.212.
38 Liu, Shu, Masatoshi Enari, Yoshinori Kawagoe, Yoshio Makino, and Seiichi Oshita. ‘Properties of the Water Containing Nanobubbles as a New Technology of the Acceleration of Physiological Activity’, n.d., 7. (https://bit.ly/3Do2Nvt)
Open water treatment and plant growth
Other studies have looked at the limits of nanobubbles for plant growth—in particular, one study39 looked at the effects of over-exposing plants to air nanobubbles.
This study recognised that nanobubbles, with their superior oxygen/air transfer efficiency, would be expected to assist aquatic vegetation to overcome oxygen shortages—noting that nanobubbles have been used to improve plant seed germination, biomass growth, and crop yield—as is noted in other sections of this document.
“Nanobubble technology, as an emerging and sustainable approach, has been used for remediation of eutrophication.”
“The results demonstrated that nanobubbles can enhance the delivery of oxygen to plants, while appropriate nanobubble levels will promote plant growth, excess nanobubbles could inhibit plant growth and photosynthesis.”
Unsurprisingly, growth of aquatic plants was promoted, however, for plants which are principally submerged (e.g. Echinodorus amazonicus), a lower threshold was found before the plant suffered hyperoxia stress. For Echinodorus, the threshold was found to be 1.23x107 particles/mL, therefore, in an open water installation, care should be taken for species in the ecosystem—the study’s proposal is for particles to be kept at not more than 107 particles/mL—presumably most stringently in cooler months—to prevent growth inhibition of particular species during eutrophication management and water restoration.
39 Wang, Shuo, Yunsi Liu, Tao Lyu, Gang Pan, and Pan Li. ‘Aquatic Macrophytes in Morphological and Physiological Responses to the Nanobubble Technology Application for Water Restoration’. ACS ES&T Water 1, no. 2 (12 February 2021): 376–87. https://doi.org/10.1021/acsestwater.0c00145.