Lab in a Tube: Monitoring Soil Chemistry Without Disturbing It

A team of researchers has developed a portable and automatic laboratory that can monitor soil chemistry in real time—and without expensive components. The aim is to give us easier access to follow the processes that usually take place hidden beneath our feet.

Imagine inserting a camera into the soil and continuously getting an overview of how oxygen moves between soil particles. Or how pH changes over a day as rainwater seeps through.

It sounds like a great idea, and a group of researchers at Aarhus University thinks so too. Together with German colleagues, they are now making it possible.

They have developed a portable and automatic mini-laboratory in tube form, called MARTINIS, which can measure specific chemical parameters in the soil in situ—that is, where they naturally occur—with minimal disturbance to the living microcosm that soil truly is.

"Soil is very complex—and as soon as we dig into it, we change it," explains Associate Professor Klaus Koren from the Department of Biology at Aarhus University. "With MARTINIS, we can observe what happens over time, in high resolution, and without touching the samples."

Klaus Koren is a co-author of the paper on MARTINIS, published in Sensors and Actuators B: Chemical.

Sensor film in the soil

The system works using so-called planar optodes—thin sensors that light up or change color when exposed to specific chemical substances such as oxygen, ammonia, or pH changes. This is a well-known technology that has long been used in laboratories.

But when analyzing a soil sample in the lab, you only get data on what is present, exactly where and when the sample was taken.

"We have scaled down the lab equipment to a cylinder 25 centimeters in diameter that can be buried in the soil, allowing continuous imaging of the surrounding soil environment," explains Ph.D. student Martin Reinhard Rasmussen, who has developed the system—and whose first name, incidentally, has nothing to do with the project name.