A year of discoveries is helping one lab dig into a new era of farming

At first glance, a farm field doesn’t seem all that complicated. It’s just dirt and crops.

But amongst the landscape lies one of Earth’s most complex ecosystems—a bustling network of microbes, nutrients, roots and chemical reactions that quietly govern the health of every harvest.

For years, understanding what’s happening beneath that surface has been one of agriculture’s biggest challenges. Important soil and plant indicators, like pH, microbial activity and plant physiology, are always changing, yet notoriously difficult to track in real time.

Now, a group of researchers in the Paul M. Rady Department of Mechanical Engineering at CU Boulder have developed a low-cost electronic sensor capable of continuously monitoring soil pH, offering a new window into the hidden world below our feet. 

They believe it’s a step toward a future in which farms can constantly monitor their own soil conditions, helping growers detect changes sooner and respond with more informed decisions.

“In many cases, by the time farmers discover that something is wrong with their soil or plants, the window for effective treatment may have already passed,” said Professor Gregory Whiting, leader of the Boulder Experimental Electronics and Manufacturing Laboratory (BEEM Lab). “Monitoring these factors continuously can help us better manage agricultural land and secure our food production.”

The study, led by PhD student Juan Cisneros Barba, was recently published in the journal Scientific Reports. It marks the latest breakthrough in a prolific year for Whiting and his team, whose recent discoveries are helping farmers listen to soils, monitor living plants and enable farms of the future to gather important information.

The “master variable”

Few measurements carry more weight in agriculture than soil pH. Often called the "master variable," it influences nearly everything on a farm from nutrient availability to plant growth.

But despite its importance, Whiting says tracking pH comes with challenges.

“Traditional pH sensors are often not very well suited for soil. Think of a small glass bulb that’s fragile and needs to be recalibrated a lot,” said Whiting, who is also affiliated with the Materials Science & Engineering Program. “The measurement they provide drifts over time and changes for different environments. This requires them to be frequently and manually calibrated, which can be cumbersome.”

Because of this, the group pivoted toward a new kind of electronic sensor that uses a pH-sensitive dye called alizarin to provide more dependable readings.

The device itself isn’t necessarily new. Scientists around the world—including Whiting and his team—have been studying the technology for years. They’ve shown it works in simple settings and can be printed efficiently at low cost.

But a critical question remained: Could they reliably monitor real soil outside the lab for weeks or even months?

To find out, the researchers buried a series of electrochemical sensors in various types of soil. Some featured more organic matter while others were more sandy or muddy, with both compacted and uncompacted soils included to mimic the kinds of changing environmental conditions they would encounter in the field.

They also improved the original sensor, moving to a printed circuit board-based design that was easier to manufacture. By pairing it with an inexpensive, field-deployable readout system, the technology became more practical to distribute and use outdoors.

The results exceeded the team’s expectations. Across multiple soil types, the redesigned sensor delivered reliable, continuous pH measurements for months, while a multi-month outdoor monitoring test in soil showed stable performance without the need for constant recalibration.

For Whiting, it was the strongest evidence yet that these low-cost, battery-powered printed electronics can move beyond the lab and into real agricultural environments.

“It’s really just about usability,” Whiting said. “These things cost close to nothing to make, function with minimal human effort and can be used in various soil types, allowing the technology to actually be useful in farms.”

Illustration by Hanna Nordwall

A biodegradable breakthrough

Of course, the group’s soil pH sensor is only one piece of a much larger puzzle. 

Whiting and his team have also been working to develop devices that are able to characterize microbial activity in soils, which is an important component of soil health and is difficult to measure continuously and autonomously.

In a study led by former BEEM Lab Postdoctoral Researcher Taylor Sharpe and published earlier this year in the journal Computers and Electronics in Agriculture, the researchers showed that signals from these microbial activity sensors correlated with laboratory measurements related to soil health—including microbial biomass carbon—during a field study carried out alongside collaborators at Lancaster University and the University of Manchester.

But the technology actually grew out of a different problem.

Working with researchers at the University of California Berkeley, Whiting and his team had originally been developing biodegradable sensors to monitor soil conditions, such as nutrient  concentrations and moisture content. While networks of inexpensive sensors could be scattered across agricultural fields, widespread deployment creates other challenges.

“You’ve got all of these great devices gathering data for you, but what happens when you have to recalibrate, repair or simply remove them if they are no longer needed?” Whiting asked. “Now you have to locate and remove a large number of sensors.”

Rather than asking farmers to recover hundreds of buried sensors, the group designed devices that don't require recovery at all.

Built from biodegradable materials, the electronics finish their job and then naturally break down underground, making large-scale sensing networks far more practical and sustainable.

But along the way, their research uncovered an unexpected bonus. The rate at which the sensors broke down also offered a window into microbial activity in the soil.

Whiting and his team realized they could take advantage of that process. As microbes decomposed a biodegradable composite conductor, its electrical resistance changed. 

By tracking those changes, the researchers turned what would normally be unwanted sensor drift into a useful signal, allowing them to continuously measure microbial decomposition activity in real-time, directly in the soil using a low-cost printed sensor.

If plants could talk

The BEEM Lab’s work has also expanded beyond the soil itself.

Above ground is an equally complex system of plants feeding off the nutrients at their root tips. They are often the first to know and react to any soil issues, like pH changes or pathogens, by releasing electronic signals when they are struggling or wounded.

But similar to soil, detecting these signals can be challenging.

“One strategy is to try and attach electronics to plant tissues and measure from there. Think of a bionic plant fitted with a ‘wearable’ device,” Whiting said. “However, doing this can injure the plant, making it difficult to do continuous, long-term monitoring.”

So the team came up with a new biocompatible system that contains an adhesive gel electrode. 

Illustration by Hanna Nordwall

The novel electrode is made from an ink-jet printed, electrically conducting polymer that is incorporated onto a polyvinyl alcohol gel. It’s then stuck onto the leaf of a plant using a cellulose-based adhesive.

Then, they are able to connect the electrode to other electronic devices and monitor the plant’s electronic responses to its environment.

To put the technology to the test, the group turned to one of nature's most electrically responsive plants: the Venus flytrap.

“It’s a great test case, because when you poke those little hairs in the plant, it closes and you create an action potential that you can easily measure with the gel-based bioelectrodes,” said Whiting. “We were able to monitor the plant over two weeks and see stable responses, allowing us to determine that the electrodes weren’t damaging the plant tissues.”

The study, led by former PhD student Catherine Crichton and in collaboration with researchers at the University at Buffalo, was recently published in Nature Communications Engineering journal. It showcases a handful of alternative experiments that help illustrate the power of their new bioelectronic system.

In one of the tests, the team put a Venus flytrap in a chamber with crickets. As crickets walked into the mouth of the plant, the flytrap closed, allowing the researchers to detect insect interactions and see when a plant had caught a cricket.

In another experiment, the group hooked two Venus flytraps together in their lab. When one plant closed, they detected that electronic signal and relayed a high-voltage pulse to the other, forcing it to close, as well.

Sharpe says this kind of “interplant communication” may sound like mad science, but he believes there are real applications at play.

“Imagine plants that can function as sentinels and transmit instructions to a field full of crops, helping them respond to sudden stressors or threats,” Sharpe said. 

Going forward, Whiting and his team are looking to expand their breadth of research even further. They are currently working on projects that help identify nitrous oxide emissions on farms, measure chemical reactions in plants using their wearable electronic technology and better track microbial activity in soil.