CTTC 2026 Recap: Seeing Beneath the Surface with the Subterra Green

We've been sampling soils the same way for decades. Pull a core, ship it to a lab, wait for results, repeat. It works, but it has limits. A handful of samples across a large field gives you data points, not a picture. And when it comes to soil organic carbon, the story underground is far more complex than a few numbers can tell.

That's exactly the problem S4 Mobile Laboratories set out to solve.

At the 2026 Conservation Tillage & Technology Conference, S4 Mobile Laboratories' Principal Scientist Linda Barrett presented the culmination of nearly two years of grant-funded research.

What Is the Subterra Green, and How Does It Work?

The Subterra Green is S4's field instrument built around one core idea: measure soil in the ground, not in a lab. A half-inch fiber-optic probe is inserted directly into the soil, shining light at many wavelengths, both visible and near-infrared, and measuring what reflects back. That reflected light creates a unique spectral signature at each depth. The instrument reads it, and a machine learning model trained on thousands of paired field-and-lab measurements translates that signature into a prediction of soil organic carbon content and bulk density in real time.

No soil cores. No sample handling. No lab wait times.

Why Depth Matters More Than You Think

Traditional soil testing typically captures what's happening in the top few inches. But soil organic carbon doesn't stop there. The Subterra Green takes measurements approximately every centimeter on the way down to 30 cm, then at wider intervals to 90 cm, generating 30 to 40 data points per insertion. The result is a full depth profile: a chart showing exactly how carbon content shifts from the surface all the way down through the soil column.

That depth profile matters for a reason most surface samples miss entirely. Carbon stored deeper in the soil profile is often older, more stable, and more significant from a climate perspective. If you're thinking about carbon credits, soil health benchmarking, or long-term productivity, that deeper picture changes the conversation.

From a Single Probe to a 3D Map of an Entire Field

One probe insertion tells you a lot. But the real power of the Subterra Green comes from what happens when you use hundreds of them.

In one case study Linda walked through at CTTC, the team conducted 169 probe insertions across roughly 12 acres of an agricultural field, a grid pattern spanning nearly a kilometer in each direction. Each insertion produced a full depth profile. Then, using a process called spatial interpolation, all of those individual profiles were combined into a 3D data cube: a complete model of soil organic carbon content at any location in the field, at any depth down to 90 cm.

The results revealed something that no traditional sampling approach would have caught. When Linda overlaid the carbon map with elevation data and topographic wetness index,a measure of where water naturally concentrates as it flows across the surface, the relationship was clear. Areas that naturally funnel more water showed different carbon distributions than drier, higher-ground areas nearby. The topography of the field was quietly shaping soil carbon patterns that standard sampling grids would average right over.

Why Soil Organic Carbon? Why Now?

The Soil Health Institute recently identified soil organic carbon as its number one indicator of soil health above all others. That designation isn't arbitrary. Organic carbon is the backbone of soil organic matter, driving nutrient cycling, water retention, and biological activity. Fields with higher organic carbon tend to be more productive, more resilient to drought, and more responsive to management changes.

There's also a growing economic dimension. Carbon credit markets are expanding, and accurate, verifiable carbon measurement at depth is quickly becoming a prerequisite for participation. The Subterra Green with its ability to deliver lab-comparable accuracy at a fraction of the cost, is positioned precisely at that intersection of agronomy and opportunity.

Practical, Accessible, and Built for the Field

The Subterra Green was designed from the ground up to be used by people who aren't soil scientists. The instrument is portable, operates without chemicals or sample extraction, and delivers results in the field rather than days later from a lab. For farmers exploring carbon sequestration, for CCAs advising on soil health programs, and for conservation professionals managing long-term land stewardship, that accessibility isn't a nice-to-have, it's the point.

Linda's presentation at CTTC 2026 made one thing clear: we now have the tools to understand our soils at a level of detail that was simply out of reach before.

📹 Watch Linda's full session available now with CCA continuing education credits through July 1st, 2026.