Inside China's attempt to boost crop yields with electric fields
In greenhouses across China, scientists are exposing lettuces and cucumbers to powerful electric fields in an attempt to make them grow faster. Can electroculture work?
21 August 2019
By Donna Lu and David Hambling
AT FIRST blush, the huge commercial greenhouse on the outskirts of Beijing doesn’t seem unusual. Inside, lettuces sit in neat rows and light pours in through the glass above. But there is a soft hum and an intense feeling in the air, almost as if a thunderstorm is on the way. The most obvious sign that this is no ordinary growing space is the high-voltage electrical wiring strung over the crops.
This place may be different, but it is far from unique. Over the past few years, greenhouses like this have sprouted up across China, part of a government-backed project to boost the yield of crops by bathing them in the invisible electric fields that radiate from power cables. From cucumbers to radishes, the results are, apparently, incredible. “The overall quality is excellent,” says Liu Binjiang, the lead scientist on the project. “We’re really entering a golden age for this technology.”
Using electricity to boost plant growth – not by powering heaters or sprinkler systems, but simply by exposing plants to an electric field – is an old idea. It is also controversial. Electroculture was tested in Europe many decades ago and found wanting, with the results too inconsistent to be any use. The mechanism was also mysterious: no one knew how or why electric fields might boost growth. So what exactly is going on in China’s new greenhouses? Can you really improve agriculture through the power of electric fields – and if so, how?
It was Finnish physicist Karl Selim Lemström who introduced the world to the idea of electroculture in the 1880s. He was studying the northern lights in Lapland when he noticed that trees grew well there in spite of the short growing season. He suggested it might be because of the electrical field produced by charged particles rushing into Earth’s atmosphere to create the aurora. Lemström carried out tests with plants growing under electric wires and achieved mixed results. In one experiment conducted in a field in Burgundy, France, he saw that “carrots gave an increase of 125 per cent and peas 75 per cent”.
In 1896, a reporter for the North American Review breathlessly described Lemström’s work and that of rivals in France and Russia, writing: “Gardens that have been stimulated by the atmospheric electricity… have increased their growth and products by fifty per cent. Vineyards have been experimented upon, and the grapes produced have not only been larger in size and quantity, but richer in sugar and alcohol. The flowers have attained a richer perfume and more brilliant colours.”
Before long the results were replicated in the UK. The botanist J.H. Priestley reported a 17 per cent increased yield of cucumbers with Lemström’s technique, while physicist Oliver Lodge cultivated a large field of wheat with wires strung above it and saw a 24 per cent boost in the grain harvest. The words in the North American Review seemed to ring true: “It is difficult to explain why the electric current so marvellously affects the growth of plants, but the fact that such stimulation does occur cannot be denied.”
At the end of the first world war in 1918, the UK set up the Electro-Culture Committee, a group of scientists and farmers, and asked it to find out whether electroculture was worth pursuing. The committee experimented through the 1920s with wheat, oats, peas and potatoes, but the results were frustratingly inconsistent. This, together with the cost of electricity, eventually doomed electroculture. “Increases of 20 per cent can hardly be considered economic even if obtained in most years,” said the committee’s final report in 1936. Nevertheless, the scientists seemed to think the effect was real, if erratic.
The US Department of Agriculture conducted some experiments at Arlington Experimental Farm, near Washington DC, but these, too, were difficult to interpret. Many patents were taken out, but the technique never took off in the US either.
“Plants may take applied electric fields as a signal of impending rainfall”
Research in electroculture slowed to a trickle for some 50 years. Then, in the 1980s, Liu began looking into the technique as a researcher at the Inner Mongolia Agricultural University in Hohhot, China. He says he had been fascinated by the effect of lightning on soil nutrients, and began looking into whether electricity boosted the growth of wheat and barley. Around this time, the Chinese government began giving out grants in agricultural science, allowing him to expand his study.
Liu began developing what he calls the “space electric field” method. There is usually a natural vertical electric potential gradient in the air of about 100 volts per metre. Liu began setting up experiments in greenhouses where that was increased to between 700 and 20,000 volts per metre. Electrical wires were strung above the crops and the field emanated from these. He began seeing impressive improvements in crop yields: increases in lettuce and cucumber by up to 40 per cent, and similar improvements for potato, radish and fennel. Liu worked with a company in the southern Chinese city of Shenzhen to develop a commercial generator to power the wires in 2000. Within a few years, electroculture greenhouses were being set up in Beijing, Dalian and Tianjin.
The motivation wasn’t just to increase yields, though. In China, there is widespread public wariness about food safety, following several high-profile incidents in which illegal pesticides were found on produce. Fruit and vegetables are almost never eaten raw or unpeeled out of concern over harmful chemicals. Because of this, there was interest in electroculture as a possible alternative to pesticides.
In 2013, Liu, now based at the Dalian City Academy of Agricultural Sciences, introduced a second electroculture technique called “charged cultivation”. This involves overhead wires again, but this time the current they generate runs through the plants, says Tong Yuxin at the Chinese Academy of Agricultural Sciences (CAS), which is supporting Liu’s work. Touch the plants, and you would get a mild shock. This effect drives insects away, says Liu. The electric field also removes microorganisms from the greenhouse air, he says, because when an electric field is discharged, it produces radicals, chemical species that can kill airborne bacteria. A report from CAS this year looking at electroculture says the yields of crops are generally increased by 30 per cent.
It isn’t easy to assess the scientific validity of Liu’s work. He and his colleagues haven’t published much of their research in international journals, though he has published more than 100 papers in China. New Scientist asked several Chinese-speaking plant scientists to look at these. They found the research unconvincing. “The statistics were generally weak and replications were not clear,” says plant scientist Yang Aijun at CSIRO, Australia’s national science agency.
Yet Liu isn’t the only researcher working on electroculture. Erika Bustos at the Centre of Research and Technological Development in Electrochemistry in Querataro state, Mexico, has been exploring its effects on Arabidopsis thaliana. This small flowering plant is a member of the same family as cabbages and is often used as a botanical guinea pig. In a 2016 study, Bustos set up trays of the plants and stuck electrodes in the soil at either end to create an electrical circuit. It was a small trial and a different method to Liu’s, but the plants did grow faster and thicker, as long as the current wasn’t cranked up too high. Bustos says she and her colleagues also have unpublished results showing that electrodes in the soil can increase the yield of wheat and maize by up to 85 per cent.
Grow with the flow
Let’s assume something is going on. How could this effect work? We know that plants make use of electricity. Some plant cells build up and release electric charge by moving ions like calcium and magnesium around their cells. It is thought that this plays a role in signalling throughout the plant, and some people even suggest that electrical signals could form the basis of plant memories. We have recently also discovered that tomato plants pass electrical signals to each other through the soil via their roots. This shows the flow of electricity is important to plants. It is harder to see how an external electric field would boost their growth.
“Lettuce and cucumber yields increased by up to 40 per cent”
There is one good reason why it might, at least according to ideas developed in the 1990s by Andrew Goldsworthy, a now-retired plant scientist who worked at Imperial College London. His suggestion was that it would be beneficial for plants to ramp up their growth following a thunderstorm when there is a lot of rain. Rather than the standard 100 volts per metre electrical field gradient in the atmosphere, a storm can produce a gradient of several hundred volts per metre or more. Goldsworthy reasoned that plants might have evolved to sense the change in field. He conducted experiments with tobacco plants in 1991 in which he showed that applying a weak external field changed the pattern of calcium ion currents in the plants. He reckoned this might be how they sensed electric fields.
If he was right, it might explain why the electroculture experiments in the early 20th century were so mixed. The plants would have taken the applied electric fields as a signal of impending rain, and when it didn’t come, that might have affected them negatively.
Still, this is all conjecture. Biophysicist Ellard Hunting at the University of Bristol, UK, says there is no detailed understanding of how growth might be enhanced by electric fields. “The mechanisms that underpin these observations remain largely elusive,” he says. “But there is definitely a very interesting interaction between plants and their electrical environment – time will tell how this might actually benefit agriculture.”
Jean Yong at the Swedish University of Agricultural Sciences in Uppsala takes a more optimistic view. “In a nutshell, plants do respond to electrical fields,” he says. It is logical, he says, that an electric field could speed up the flow of crucial nutrient ions like nitrate or calcium. “But there is no concrete or published data to prove the phenomenon.”
Although economics did for electroculture in the early 20th century, electricity is now far cheaper and less polluting. Yet even with that stumbling block removed, there are plenty of other ways to boost crop yields, from adding more fertiliser to increasing the carbon dioxide in greenhouses. How electroculture compares is unclear for the moment. If it does turn out to be a good option, the evidence might well come from those greenhouses scattered across China, where the charged air quietly hums above the greenery.