44 | New Scientist | 24 August 2019
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unpublished results showing that electrodes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.
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, saysCOURTE
SY
OFLIUBI
NJI
AN
G“ Lettuce and
cucumber yields
increased by up
to 40 per cent”
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. ❚Donna Lu is a reporter for New Scientist.
David Hambling is a freelance journalist
based in LondonIn China, scientists
are exposing crops
to electric fields