A Q&A with 3 practitioners of soil carbon monitoring
by Cristel Zoebisch, deputy director of policy
Before we can pay farmers for sequestering carbon in their soils, we need to measure it in a cost-efficient and scalable way, so for this issue, I sat down with three different experts in soil carbon monitoring. Our conversation spanned the private sector, historically underserved farmers, and academic institutions in hopes of better understanding how Congress and USDA might design programs to measure soil carbon.
The below interview has been edited and abridged for clarity.
Q: Walk me through what measuring soil carbon looks like for you today.
Laura van der Pol: Measuring soil is like giving every kid in school an instrument to play at the same time and comparing the sound before and after a music lesson. Each kid’s song will likely be indistinguishable from chaos — to hear any change, you’d have to listen to the notes separately. Measuring soil carbon is similar: We use stratification to find comparable ranges of soil carbon and responses to change.
Chris Tolles: To measure soil carbon conventionally, you use a stainless steel cylinder to remove soil from the earth, and ship it to a lab where it’s incinerated, to oversimplify. This process is called dry combustion and it provides organic carbon as a percentage of the mass.
From that same sample, you measure density. Denser soil equals more carbon. We also measure volume: a field boundary in acres multiplied by sampling depth. Combine all of these measurements and we have total organic carbon stock as a mass.
Briana Alfaro: We measure soil health as a proxy for soil carbon. This means getting our hands into the soil, conducting in-field assessments and sending soil samples to a lab. Assessments include water filtration rates, the slake test, soil color test, soil hardness, and soil respiration, among others. It’s about creating an ecosystem that welcomes carbon back to the land.
Q: What are the major barriers to measuring soil carbon? How has that specifically showed up in your work?
BA: The barriers are time, technical assistance, and cost. Two years ago, I traveled to five farms led by farmers of color to perform soil assessments. The farmers reported positively on the soil health work but also admitted they weren’t likely to do it themselves had I not been there. Since that trip, one farmer has gone on to incorporate soil assessments yearly, with an emphasis on soil management.
We try to keep costs down by using materials found around the home or farm, but some are prohibitively expensive. We also look at existing assessments — that’s why we use the soil color test. Indigenous folks have been using soil color as an indicator for soil health for many, many years. Uplifting this knowledge as something devised by Indigenous folks before it was thought of as institutional knowledge is important to us.
CT: People think it’s just smashing a cylinder into the ground. There are details to get it right, and you can introduce a whole bunch of errors. So we need trained samplers and the cost of labor is high. The work itself is laborious, and when people are tired they make mistakes.
The second major barrier is the cost of analysis and lack of data infrastructure. There’s very poor standardization of [how we organize data] which means you’re often comparing apples to oranges.
LV: Soil sampling is intense — a lot of effort goes into physically obtaining the sample as well as the processing it. In my work it’s a balancing act of cost and analytical power. The best practices will measure a few different depths so that an equivalent mass of soil can be compared each time. Having multiple depths gives you more accuracy.
Q: Measurement is arduous, expensive, and difficult to stand up in practice — which needs to change. What are your ideas to make soil carbon measurement accessible?
CT: We focus on lowering costs: our technology eliminates physical sampling and lab analysis entirely via an in-field spectral probe. We let farmers and ranchers do what they do best — farm and ranch — and we do what we do best. Most tech people assume producers do their own sampling, but that’s largely not the case.
BA: We look at assessments people have already been doing. That’s why it was important for us to include the soil color test. Indigenous folks have been using soil color as an indicator for soil health for many years. Uplifting this knowledge and making it clear that this was devised by Indigenous folks before it was thought of as institutional knowledge is important to us.
LV: This may be a non-scientist thing to say, but I think that measurement may not be our best option. Requiring or paying for improved practices regardless of change in soil carbon makes sense for farmers and society.
Since there are many co-benefits to sequestration, we could use existing policy programs to protect soil integrity by rewarding improved management.
This is a more equitable solution for farmers since not all soils respond the same way to management and are beyond farmer control Plus, society receives improved air and water quality when farmers adopt management practices that restore degraded soils and increase soil carbon.
Q: You have a direct line to USDA’s Tom Vilsack and five minutes. What do you say?
BA: Make USDA programs that facilitate credit, land access and tenure, and make training equitable and accessible for BIPOC producers. Our network of BIPOC farmers are largely interested and invested in healthy soil practices and calling carbon back to the Earth. This isn’t new: Afro and Indigenous farmers have long-held relationships with the Earth and have farmed accordingly. They just need support to access the land, training, and tools to do so.
CT: Oh, there’s a lot to say. First, we need a unified soil data taxonomy and massive investments in soil carbon MRV research so we can figure out what actually works. Second, we need a proper reckoning with USDA’s historic and present role in issues of land disenfranchisement and other kinds of racist discrimination against Black and Native American agricultural producers.
LV: Using existing crop insurance programs, USDA could shield farmers from economic and environmental risk while removing barriers to crop diversification, cover cropping, and reduced synthetic inputs, etc. To do this, USDA could insure the whole farm revenue rather than a specific field or crop. Let’s define best practices as ones that prioritize the long-term viability of the soil to grow food and put carbon back where it’s beneficial — the soil. USDA is the only agency positioned to make that possible nationwide.
Q: There’s so much emphasis on agriculture as a climate solution right now — is there anything going unnoticed or unattended from your perspective that would have a big impact?
LV: One area that has potential to transform our food system are perennial grains like perennial rice and Kernza. They require fewer synthetic inputs and energy while protecting soil from erosion. Greater investment in perennial grains could be a way to address many of the ills incurred from agriculture while also helping to mitigate climate change.
CT: All of the science in the world doesn’t necessarily help us understand the cultural dimensions of what makes producers attempt practice changes related to soil carbon.
Half of American family farms lose money every year, so why invest in speculative R&D? These “soft science” questions of community, risk, and influence are woefully under-acknowledged.
BA: You can’t unlink soil health practices like perennials, agroforestry, and polycultures from land access and tenure. I ran into this when I was growing myself: I didn’t have long-term access to farm in a way that calls carbon back to the land. At least not the way I really dreamed of doing it. This is true for so many people.
Edited by Ana Little-Saña