New technology could help farmers keep better tabs on soil health

By Alexander Servantez

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.”