Nori’s Stance on Soil Sampling

Why soil sampling isn’t (yet) a silver bullet for soil carbon credits

We have all frequently heard that carbon markets are the wild west. However, true wildness is found in what we’re building these markets upon: soil carbon dynamics.

One of the most commonly asked questions we get at Nori is “How do you estimate carbon changes in the soil?” While our answer is fairly straightforward — “Through biogeochemical modeling that is calibrated and validated by soil samples” — the process by which soil organic carbon stock changes can be estimated is anything but simple.

In the world of soil carbon, there are two main schools of thought behind how to estimate soil carbon: direct measurement or biogeochemical modeling. At Nori, we believe that the future of carbon markets will include direct measurement estimations of carbon. Though currently, these direct measurements are not yet standardized, scalable, or accessible enough to meaningfully be incorporated into voluntary carbon markets. So for now, we depend on biogeochemical modeling to inform our carbon credits. This article explains:

1. The common means of direct soil measurement and the gaps we find in this approach;
2. Why Nori currently uses biogeochemical modeling to achieve scientifically sound estimates that enables flexibility to scale; and
3. What we believe needs to be in place before direct measurement is openly incorporated into voluntary carbon markets.

Estimating Soil Carbon

Let’s begin with direct measurement of soil organic carbon. This is most commonly achieved through taking soil samples directly from fields on a regular basis to build site-specific trends of soil organic carbon stock changes. Taking soil samples for carbon is often compared to sampling for nutrients: go out to each field in the fall, pull a few composite cores, send them to the lab, and use the results to make recommendations. Decades of research have defined the how and why of nutrient sampling. Nutrient sampling has the benefit of a standardized methodology (from how deep to pull cores, to which assays are used to analyze nutrient compositions), an understanding of nutrient usage and movement in the soil profile, and accessibility for all types of farmers and agronomists to pull these samples anywhere throughout croplands. The end result is simple: if numbers fall within a given range, apply “x” amount of fertilizer.

The same is not true with soil sampling for carbon. Yes, we have data to inform us of soil carbon dynamics, defined tests for measurement (e.g. dry combustion, loss of ignition, etc.)¹, and we understand some of the details, such as the importance of taking bulk density to understand the scale². These data have led to understanding carbon dynamics in agricultural soils, informed modeling efforts, and are used as guideposts to understanding the effects of agronomic practices on soil carbon dynamics.

But unlike soil sampling for nutrients, the majority of these learnings are nested within research institutions and are not yet translatable from academia to applied agronomics. The last thing we want to do is ask farmers to set aside land and run replicated experimental design trials across their operations for the next ten years. We do not want to pass on the experimentation to the farmer and we also do not want to pass on the cost. At the current price of $15/carbon credit, the cost of soil sampling is neither something we can ask the growers to absorb, nor do we believe we should absorb it ourselves, as we do not find the data from sampling valuable to own. Nori is a carbon removal company, not an agricultural one, and as a policy, we never want to own any farm data, and we believe that that information belongs to the farmer.

We cannot scale carbon sampling to a point where it is as accessible as nutrient sampling because we do not have the same depth of science to back it up. There are ways to overcome this, such as through a massive deployment of soil sampling across a given region. However, effective implementation of such an effort is expensive — requiring consistent data collection, access to labs, correct assays, tight statistical design, and appropriate analysis. Which raises the question: who is going to pay for this large scale, consistent data collection? Larger agricultural companies are already investing in such endeavors. They have the resources to fund the sampling and can benefit directly from the learnings of owning that data.

Due to these limits, we won’t simply “do soil sampling” to check a box. That said, we believe that soil sampling is very important to build a robust, long-lasting voluntary marketplace. We believe in soil sampling that is done well, and we need it to be reliable and accessible before incorporating it into our marketplace.

Quantification approach

Given our stance of not yet incorporating direct measurements of carbon, how does Nori currently create reputable, science backed carbon credits? In sum:

1. We are very conservative in our quantification; and
2. Our carbon credits have a scientifically reasonable length of time that the carbon will remain in the ground.

The science is clear³ that soil carbon does not accumulate in a linear manner and that any given measurement is highly dependent on that year’s weather. Therefore, years of data are needed to estimate trends and avoid over-issuing carbon credits based on the first few years of carbon gains. At this stage, biogeochemical modeling is our best tool to both understand carbon trends and to get carbon markets started. Modeling is not a new tool for building understanding of scientific principles and market trends and, therefore, the most important question to ask is: what is the most scientifically rigorous and data backed modeling platform? Our third-party carbon quantification tool meets USDA Blue Book standards for greenhouse gas accounting where the soils data comes from SSURGO, weather data from NOAA, and the crop specific models were built in numerous academic institutions.

We acknowledge that these tools are fairly elementary and do not fully capture the intricacies of modern farming, but we need to start somewhere. Similarly, the application of fertilizer began with elementary tools to make fertilizer recommendations that resulted in blanket applications — and we are now using precision agriculture technologies that help us understand fertilizer needs on a per acre basis. With carbon markets, we can’t start at precision ag levels of granularity coming out the gate. But we do need to start somewhere.

Using these models allows us to estimate the effects of changing agronomics on soil carbon dynamics. By starting with these straightforward, inexpensive tools, we can get the marketplace going. The price of carbon in the Nori market is relatively inexpensive, and we want farmers to start seeing an economic benefit to their regenerative, stewardship-minded practices. By using modeling as our initial carbon quantification tool, we can be both backed by science and work in a farmer forward manner that keeps farmer data in the hands of the farmer.

At Nori, we are the first to say that we are operating in uncharted waters. And yet we strongly believe that the best way to get more information is to move forward. Because we care about getting things right, we are taking a very conservative approach to our quantification. To ensure the conservative nature of our issuances, on average, each of our issuances are based on soil organic stock gains that are about 30% less than what the model predicts as the annual average of carbon gains on a per project basis. Of our projects, we are averaging about 0.5 tonnes of carbon sequestered per acre per year, which lines up with the academic understanding of carbon flux gains in the topsoil of agricultural land⁴ ⁵.

Nori will stand behind the transaction between buyer and supplier to ensure our product is held to clear, achievable, and high standards.

Our regenerative agriculture carbon credit, the Nori Regenerative Tonne, represents approximately one tonne of carbon removed and retained in a reservoir (soil, in this case) for a minimum of 10 years. Each supplier signs our Regenerative Tonne Agreement allowing us to track that the carbon sold stays in the ground for a minimum of 10 years. We define a 10 year period of carbon retention because this is a scientifically appropriate time estimate for carbon to remain in the soil and it is a practically reasonable amount of time to hold a supplier accountable for their carbon storage.

Our Regenerative Tonne agreement ensures that the purchaser of the carbon credit has full guarantee that the carbon they have bought is held to our clear standards of 1 Regenerative Tonne being equivalent to 1 tonne CO2e stored for a minimum of 10 years.

How Soil Sampling Can Scale

We have built in many buffers to our system so that our marketplace can eventually be accessible to all farmers, and they do not take on the financial burden of figuring out the science through long term soil sampling. As we grow, Nori will not turn a blind eye to the need for a more robust understanding of the science of soil organic carbon stock changes. And modeling will not be the only tool we rely upon. By creating a marketplace that is an economic driver for soil carbon to be part of farm management decisions, research effort and money will start to flow towards understanding soil organic carbon dynamics.

In fact, the money and resources are already starting to flow towards soil carbon research. Larger agricultural companies are already investing in this pursuit. Much as the Encirca sampling from Corteva (formally Pioneer) helped inform the best management practices for fertilizer, soil sampling at Corteva can help us understand carbon dynamics under a wide variety of soil types and management practices.

On the academic side, the amount of grant funding towards soil carbon research and regenerative agriculture has increased, with over $21 million dollars from the USDA alone being invested in research in soil health and climate smart agriculture⁶. From this recent research in soil carbon we have already learned how to better stratify soil sampling in ways that are more accessible to a full farm audit⁷ and the development of frameworks to aggregate and standardize soil sampling for those outside academia⁸. On the private industry side, Agricarbon, a UK based carbon company, is creating an approach to cheaper, standardized soil sampling and tackling bulk density at scale (something that is fickle, and speaking from experience, simply not fun to take). TopSoil, an app created to help farmers profit from soil health, is building out the understanding of leading and lagging indicators of soil carbon, pushing the needle forward on our understanding of helping farmers better understand their soil dynamics.

The above list only includes those that are taking in-field soil samples, which are absolutely necessary for ground truthing our understanding. And beyond those, there are many, many companies looking to help us estimate and even measure soil carbon changes through remote sensing and scanning technology.

Understanding how all these players fit into the carbon market space will need three things:

1. Standardization — It is important to have clarity that a carbon credit is a carbon credit is a carbon credit and that we have a clear understanding of how the data works so that these tools minimize uncertainty, rather than add to it.
2. Accessibility — Until carbon credits reach a certain price point, the financial burden of this research should not be on the shoulders of the farmers.
3. Scalability — Gathering ground-truthed data can’t reasonably operate like a replicated experimental design. We need to scale carbon understanding and sampling in a manner similar to how nutrient sampling was scaled for the industry. And, by understanding how some of the ways that nutrient sampling scale had missteps, we can learn from that and scale more effectively, sustainably-minded, and farmer-focused.

If the science and tools of scaling soil sampling can achieve standardization, accessibility, and scalability, we are eager to incorporate these tools into our carbon marketplace. We are moving forward in a way that is meaningful, not checking boxes that are arbitrary, and staying in line with the innovative ways to measure soil carbon directly. For now, we are estimating carbon through what we believe is the most scalable and scientifically robust tool — biogeochemical modeling. We need good science to scale great carbon markets, but we also need great carbon markets to fund good science in soil organic carbon changes.

Want to learn more about Nori’s approach to carbon credits? Read our methodology and learn more about our science-backed carbon credits.

References

1. A comparison of some methods for soil organic carbon determination by Y.K. Soon and S. Abboud
2. https://soilhealthlab.cals.cornell.edu/testing-services/soil-health-analysis-packages/
3. A review of soil carbon dynamics resulting from agricultural practices by Farhat Abbas, Hafiz Mohkum Hammad, Wajid Ishaq, Aitazaz Ahsan Farooque, Hafiz Faiq Bakhat, Zahida Zia, Shah Fahad, Wajid Farhad, and Artemi Cerdà
4. Management of cover crops in temperate climates influences soil organic carbon stocks: a meta-analysis by Shelby C. McClelland, Keith Paustian, and Meagan E. Schipanski
5. How does tillage intensity affect soil organic carbon? A systematic review by Neal R. Haddaway, Katarina Hedlund, Louise E. Jackson, Thomas Kätterer, Emanuele Lugato, Ingrid K. Thomsen, Helene B. Jørgensen, and Per‑Erik Isberg
6. USDA Invests $21.7M in Research Innovations to Improve Soil Health and Climate Smart Agriculture and Forestry (United States Department of Agriculture)
7. Farm-scale soil carbon auditing by J.J. de Gruijter, A.B. McBratney, B. Minasny, I. Wheeler, B.P. Malone, U. Stockmann
8. Soil organic carbon is not just for soil scientists: measurement recommendations for diverse practitioners by S. A. Billings, K. Lajtha, A. Malhotra, A. A. Berhe,M.-A. de Graaff, S. Earl,J. Fraterrigo, K. Georgiou,S. Grandy, S. E. Hobbie, J. A. M. Moore, K. Nadelhoffer, D. Pierson,C. Rasmussen, W. L. Silver, B. N. Sulman, S. Weintraub, W. Wieder