Recently though, he stood in a sea of green to consider how a shower of charged particles might affect lettuce.
He had been invited to one of the largest commercial greenhouses in Quebec to help the growers rethink the energy of agriculture. Inside the building, encased by glass walls and covering more ground than four soccer fields, thousands upon thousands of lettuce plants floated on polystyrene mats in a hydroponic, or no-soil, growing system. The crop was nearly ready to be picked, packaged and shipped. Reuter’s task was to use physics to help the company, Hydroserre Inc. in Mirabel, reduce its carbon footprint.
To that end, the company is interested in finding new ways to fight pathogens and to deliver fertilizer to the growing plants. Many fertilizers contain ammonia, which is produced from nitrogen (necessary for plant growth) and hydrogen using a chemical reaction called the Haber-Bosch process. This process revolutionized agriculture in the early 20th century by making mass production of fertilizer possible. However, the process yields hundreds of millions of metric tons of carbon dioxide each year.
“Ideally, we want a fertilizer that’s renewable,” Reuter says. And to make it truly green, it should be created at the farm, making transport, another carbon emitter, unnecessary. Reuter and a growing number of chemists, physicists and engineers think they can see how to make that happen. These researchers are working toward future farms that are truly sustainable, where the energy from renewable sources like wind or solar is harnessed to make an efficient fertilizer on-site. They hope to realize this vision by exploiting plasma.
Reuter might seem an unlikely consultant for an agricultural challenge. After all, his expertise is in the physics of plasma, one of the four fundamental states of matter, along with solids, liquids and gases.
Plasma is remarkably common. In fact, most matter seen in the known universe — more than 99.9 percent, according to astrophysicists — is in a plasma state. Lightning produces plasma. So do those inexpensive novelty lamps in museum gift shops. Switch on the power, and an electrode at the sphere’s center produces a high voltage that interacts with the gas sealed inside the glass to form tendrils of colored plasma that radiate outward. Touch the glass, and the plasma tendrils seem to reach toward your fingers.
The sun is a ball of plasma and gas. The solar wind is a stream of plasma that peels off the sun . When that wind collides with the protective, plasma-rich magnetic cushion that envelopes Earth, the interactions produce rivers of light seen in the aurora borealis and aurora australis.
Plasma is also a workhorse of modern technology. Engineers use it to etch the millions of tiny transistors found on the chips in today’s computers, cars and musical birthday cards. The pixels in plasma televisions contain gas that forms a plasma, sealed inside tiny cells sandwiched between two glass plates, and neon signs and fluorescent lights glow because of plasma. Some former astronauts even predict that plasma engines will someday propel us to Mars.
How technology will revolutionize the agriculture industry in 2021- 2022
But what exactly is plasma? It’s a soup of electrons with their negative charges, positive ions and neutral atoms that also produces electromagnetic fields and ultraviolet and infrared radiation. Plasma comes about when gas gets super energized — by heat or an electric current, for example — and electrons are freed from atoms.
Plasmas occur naturally or can be human-made. When produced by high temperatures, such as in the sun, it’s called “hot plasma,” while the plasma created in a plasma ball and other room-temperature, low-pressure environments is called “cold plasma.” Plasma balls make it easy to see: They’re filled with a gaseous mixture that includes one of the very stable, noble gases, like argon, xenon, neon or krypton. Plasma makes up those glowing tendrils that reach out from the center. The high-frequency current excites electrons that then separate from the atoms of gas. Many agricultural experiments include a mix of noble gases and air to yield ions of nitrogen and oxygen.
Scientists have long been interested in plasma’s biological implications. In the late 19th century, the Finnish physicist Karl Selim Lemström observed that the width of growth rings in fir trees near the Arctic Circle followed the cycle of the aurora borealis, widening when the northern lights were strongest. He hypothesized that the light show somehow encouraged plant growth. To artificially emulate the northern lights, he placed a metal wire net over growing plants and ran a current through it. Under the right conditions, he reported, the treatment produced larger vegetable yields.
For decades, scientists have known that exposure to plasma can safely kill pathogenic bacteria, fungi and viruses. Small studies in animals also suggest that plasma can prompt the growth of blood vessels in skin. In his research, Reuter studies ways to harness these properties to inhibit new infections in wounds and expedite healing or treat other skin conditions. But more recently, he and other physicists have been working on ways to use the power of plasma to improve food production.
Experiments conducted in the last decade or so have tested a mix of ways to apply plasma to seeds, seedlings, crops and fields. These include plasma generated using noble gases, as well as plasma generated from air. In some cases, plasma is directly applied through plasma “jets” that stream over the seeds or plants. Another approach uses plasma-treated water that can do double duty: irrigation and fertilization. Some studies have reported a range of benefits, from helping plants grow faster and bigger to resisting pests.
“Even in this very, very early stage of research that we’re at with plasma, which has really only come into its own in the last 10 to 15 years, we’re seeing very promising data,” says plant pathologist Brendan Niemira at the Food Safety and Intervention Technologies Research unit at the U.S. Department of Agriculture’s Eastern Regional Research Center in Wyndmoor, Pa. He’s a fan of the approach: On Zoom, Niemira’s avatar shows an almond basking in an eerie, purple plasma glow.
The challenge now, he says, is to figure out whether plasma can deliver at the level of hectares of crops. “Can we make it work in a field environment [to] deliver an advantage that can be integrated into grow systems in the future?”
Nested within that challenge are many others, including finding a way to deliver plasma to plants on a large scale, confirming benefits reported in lab studies and showing that plasma is better than current methods. And, finally, figuring out what the charged soup of plasma is actually doing to plants.
Recent advances became possible, Niemira says, largely because in the 1990s and early 2000s, scientists developed efficient and cost-effective ways to generate cold plasmas by streaming high-energy electrons into a gas. Those electrons would collide with gas molecules, knocking off electrons and producing charged particles. Since then, he says, there’s been something of a rush to test plasma on plants at all stages of growth and with a range of strategies.
