Measuring electric current in soil could provide answers on soil health


Date:
August 19, 2021
Source:
Washington State University
Summary:
Researchers have developed a way to assess soil health by measuring
the electric current produced by its tiniest microbes. They used
a probe originally developed to measure the electrochemical signal
of microbes in aquatic environments, and tested it on healthy and
unhealthy soil samples to measure microbial metabolism and other
indicators of soil health. This proof-of-concept research could
someday lead to a simple, real-time test for farmers to determine
whether soil is productive.



FULL STORY ========================================================================== Washington State University researchers have developed a way to assess
soil health by measuring the electric current produced by its tiniest
microbes.


==========================================================================
The team used a probe originally developed to measure the electrochemical signal of microbes in aquatic environments, and tested it on healthy
and unhealthy soil samples to measure microbial metabolism and other
indicators of soil health. This proof-of-concept research, published
in Journal of Electrochemical Society, could someday lead to a simple, real-time test for farmers to determine whether soil is productive.

"Soil underpins all the food we eat, and most of it is degraded
worldwide," said Maren Friesen, an associate professor in the Departments
of Plant Pathology and Crop and Soil Sciences and a co-author on the
study. "One of the biggest barriers to improving soils is not being able
to have rapid, real-time measurement to develop appropriate management strategies for them. This sensor has the potential to be able to do
real-time measurements not just of the structure of the soil but how
it's actually functioning. It would be a huge advance in the field."
"I believe this is one of our most significant works and will have a high impact on soil health determination," said Haluk Beyenal, professor in the
Gene and Linda Voiland School of Chemical Engineering and Bioengineering
and corresponding author on the paper.

Other co-authors on the study include postdoctoral research fellow
Abdelrhman Mohamed, and graduate students Eduardo Sanchez and Natalie
Sanchez.

Soil health is critically important to agriculture and crop success
worldwide, but measuring it is not straightforward. Farmers and
researchers use soil chemistry, nutrient analysis, texture and pH
measurements to gain understanding of soil's physical and chemical
properties. While that information can be valuable, it doesn't always
reflect how productive the soil actually is.



========================================================================== That's because a key to soil productivity is how microbes function,
said Friesen. Billions of bacteria, fungi and other organisms play
critical roles in nutrient mobilization and provisioning, defense against pathogens and plant growth. But, until now, there has been no simple,
real-time way to measure the microbial activity.

"What makes a soil beneficial for a plant is that it is alive and contains
all these bacteria and fungi," she said.

In the new paper, the WSU research team was able to measure current
through the soil to determine microbial activity, and distinguish healthy
and unhealthy soils.

The researchers used a probe that they developed a few years
ago to measure the electrochemical signal of microbes in aquatic
environments. Similar to how humans eat and breathe, microorganisms
take in food and then use electrons liberated during metabolism for
their energy. Finally, microbes give these electrons to an acceptor
molecule such as oxygen. The probe the team developed replaces these
acceptor molecules with an electrode. Using this electrode, they can
then measure the electric current and get an idea of the magnitude of
microbial activity.

"We are able to measure metabolic rate of the microbes by capturing
electrons that are released as a part of metabolism," said Mohamed,
a postdoctoral researcher in the Voiland School. "We're watching the
microbes breathe in the soil." The two soil samples the researchers
used were collected from the R.J. Cook Agronomy Farm and looked nearly identical to each other in terms of their soil composition. They were
both collected from plots that had not been tilled, were relatively
high in organic matter, and had the same pH and soil type. But, the
researchers had data showing that one of the soils had been significantly
more productive in its wheat yield than the other.



==========================================================================
The researchers found that the more productive soil produced an electric current while the less productive soil produced almost no current --
about 1% of the more productive soil.

"There was a really dramatic difference in the amount of current
generated," said Friesen.

They also found another difference between the two soils in the open
circuit potential measured in the soil. When they added sugar to stimulate metabolic activity, the researchers also observed the electrochemical
signals change in the healthy and unhealthy soil samples converging,
which suggests that the sugar addition stimulated the microbial activity
in both soil types.

"We could see that in a couple of days, the microbes in the soil started
to respire," Mohamed said.

With just the two soil samples compared initially, the researchers say
their idea is still just a proof of concept. They have many additional questions, such as what the creatures are doing to generate current
and what specific microorganisms might be in the samples to create
productive soil.

"We have two different signals, but what do they really tell in terms
of the fundamental parameters of the soil?" said Mohamed. "Both
parameters tell slightly different things, and we need to work on
their interpretation." They also want to test a lot more soils,
including in actual farm fields rather than in the controlled setting of
a laboratory. They hope to eventually develop a portable probe that could
be inserted directly into the soil to provide real- time information.

"In terms of working towards a just society with sustainable global
food production, I feel this has the potential to be a game-changing technology," Friesen said.

========================================================================== Story Source: Materials provided by Washington_State_University. Original written by Tina Hilding. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Abdelrhman Mohamed, Eduardo J. Sanchez, Natalie S. Sanchez, Maren
Friesen, Haluk Beyenal. Electrochemically Active Biofilms as an
Indicator of Soil Health. Journal of The Electrochemical Society,
2021; DOI: 10.1149/1945-7111/ac1e56 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210819102654.htm

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