Imagine trying to catch lightning in a bottle—quite literally. That's what some modern scientists, including Nathan Eylands, an assistant professor at the University of Minnesota, are attempting with plasma-activated water (PAW). Plasma technologies are relatively new to the horticulture industry, however, its history dates back much further. "In the early 1900s, a method called the Haber-Bosch process revolutionized agriculture," Nathan explains. "This method involves taking natural gas and combining it with nitrogen from the air—no easy feat considering nitrogen's triple-bonded stubbornness—to produce ammonia, a key ingredient in nitrogen fertilizers." However, if something sounds too good to be true, it usually is. "While this was a game-changer for agriculture, it was also an energy hog and a significant source of greenhouse gas emissions." Back in the day, there was another method in the running: plasma activation, which could also create reactive nitrogen species. However, at the time fossil fuels seemed like an endless, cheap resource, so the world went with Haber-Bosch and largely forgot about plasma activation.
In today's world, where climate change and sustainability concerns are pushing us to revisit old ideas, plasma-activated water is emerging as a promising technology that could very well be agriculture's new Swiss Army knife, as Nathan puts it.
Electrified water
Nathan describes PAW as lightning in a bottle because it's water that has been exposed to a high electrical field, ionizing the gases in the air—mainly nitrogen and oxygen—and infusing them into the water. "The result is a concoction of reactive nitrogen and oxygen species that can be used in various agricultural applications."
It turns out that this acidic, reactive water can be quite handy in horticulture. PAW possesses characteristics that have piqued the interest of growers worldwide. Not only does it contain a high concentration of dissolved nitrogen, but it also has abilities to enhance seed germination and seedling vigor, as well as amplify natural protective measures against biotic and abiotic plant stressors.
"For example, in one study by Christian Nansen at UC Davis, PAW was used to treat tomato plants plagued by spider mites," Nathan says. In that study, the mites preferred the untreated control plants over those treated with PAW. Likely attributed to increased trichome density on the leaf surface.
Tomato plants in containers in which the fertigation program was supplemented with tap water or PAW. University of California, Davis
Different uses
There are more practical applications being explored too, and Nathan's research collaborators are hard at work proving the efficacy of this 'electrified water' in several areas of controlled environment horticulture. Reactive oxygen species in water form hydrogen peroxide, giving PAW antimicrobial properties (fungicidal, bactericidal). Moreover, PAW inputs include water, air, and electricity; creating an eco-friendly product that is free of industrialized synthetic chemicals."For example, PAW could be sprayed in the greenhouse to combat powdery mildew or used in post-harvest processes to extend the shelf life of produce. Imagine a supermarket where fruits and vegetables are misted with PAW instead of pesticides."
Additionally, researchers are exploring its use in hydroponics as well. "Neil Mattson at Cornell University conducted experiments to see if PAW could replace other acids used to buffer pH levels in hydroponic systems. It worked, but it wasn't the most efficient solution yet, needing more PAW than would be practical," Nathan remarks. Still, the research is ongoing, and it's definitely too soon to draw a line.
"It's important to note that while the potential of PAW is exciting, it's still in the research phase," Nathan states. Obviously, there are economic and practical challenges to overcome. "For instance, while PAW can be effective at a pH of 5, it might not be as safe or effective at more acidic levels, where it can become harmful to biological tissues."
There's also the sustainability aspect. In a world where consumers are increasingly worried about pesticide residues and environmental impacts, PAW offers a relatively safe alternative for managing pests and diseases without introducing harmful chemicals. However, its effectiveness and economic viability still need to be proven across a range of conditions and crops.
More electrified water
As researchers continue to tinker with PAW, adjusting variables like atmospheric pressure and electrical input, we'll likely see more breakthroughs—and perhaps a few more setbacks. "We are definitely closing in on ultimately getting to an economically viable solution for growers. There's still a lot of research ahead of us, but we're getting closer to the goal every day."
This technology is becoming commercially available and adopted by large greenhouse operations around the world. If you are interested in sustainable crop production and frontier technologies and want to learn more about PAW – you're in luck. This research group, along with key cold plasma industry members met online to discuss fundamental and applied aspects of PAW. To access the recorded video of the meeting, click this link. During the meeting, participants discussed several topics including a recently conducted survey in which CEA growers were asked questions regarding their willingness to adopt PAW in their operations. Additionally, the stability of PAW over time as a function of storage conditions was discussed in detail from an analytical perspective. The meeting also includes a comprehensive presentation on how irrigation of tomato plants with PAW can boost indirect plant resistance mechanisms to spider mites – this study was recently published and is freely available online.
If you still have a hankering for more information on PAW, please visit the project website on which newsletters, meeting recordings, and other materials are becoming available: https://chrnansen.wixsite.com/nansen2/cold-plasma-1
For more information:
University of Minnesota / Department of Horticultural Science
260 Alderman, 1970 Folwell Ave, St. Paul, MN 55108, United States
[email protected]
horticulture.umn.edu