How Do Models Measure Carbon Credits?

To ensure farmers get the best price for their carbon impact, Corteva is working in collaboration with IndigoAg to measure and quantify carbon credits. Indigo’s approach currently reflects the best available science and is the first to be listed with the Climate Action Reserve (CAR)*. Third-party verification and issuance of credits through an independent registry results in premium pricing and gives buyers confidence that credits are legitimate.

We asked Max DuBuisson, Indigo’s Head of Sustainability Policy & Engagement, to explain how Indigo quantifies a farmer’s carbon impact.

What model does Indigo use?

Indigo uses a version of DayCent (the Daily Century Model). It was developed at Colorado State University and is probably the most widely used biogeochemical model in the world.

  • The model can simulate crop yields, soil carbon changes, nitrous oxide changes, and nitrate leaching with data from native and managed agricultural systems.
  • It has been studied for almost 40 years and has hundreds of thousands of peer reviewed papers written on it.
  • It’s also used globally for soil carbon and GHG accounting, including annual accounting for GHG removal in the U.S. due to land management, including for land use emissions for the annual U.S. GHG Inventory.

What’s the advantage to using a model versus direct soil samples?

There’s an incredible amount of variability in time and space – even within a field –  when it comes to soil carbon. I like to compare it to a bank account with lots of deposits and withdrawals. If you look at that bank account on one day, it only reflects money in the account that day. It doesn’t tell you how much was in the account the whole year, or the trend in growth or loss over time. 

To generate a carbon credit, we need to know change over time, as well as what that change would have been if new management practices weren’t adopted. We could sample the same points, year over year, but often soil carbon changes are long-term trends that require us to wait three to five years between measurements to really separate that “daily balance” from “long-term savings.” Moreover, the reality is it’s just not possible to sample every field in a large scale program – there simply aren’t enough soil sampling consultants in the U.S. to get it done.

There’s also tremendous benefit from the aggregation or grouping of many growers together. It’s like a forest project where each field is a tree, and together they can be quantified as one forest. We don’t have to take soil samples on every single field, just like you wouldn’t measure every tree in the forest. You create randomized plots and measure the trees in those plots, and those measurements are statistically representative of the whole forest. 

With modeling, we can generate credits year-over-year. Models take into account the many current and historical factors that influence carbon cycling and GHG emissions, including planting and harvest dates, yields, crop types, nitrogen inputs, irrigation, tillage depth, and weather.

How do you determine the impact of an individual farmer?

We look at the carbon impact from introducing a new practice(s) versus what your baseline carbon impact would have been if you continued historical practices. Your net impact is the difference between the two. One carbon credit is equal to one metric ton of carbon dioxide equivalent (CO2e) removal or abatement from the atmosphere.

Why are historical data important?

The soil carbon system is dynamic, and may have been trending up or down prior to the new practice adoption. Historical data gives us a starting point for the model. With three to five years of data, we can get a more accurate assessment of how the grower’s past land management impacted soil organic carbon. Once we have our baseline, we can then measure the impact of introducing new practices. 

With each new project year, we run the model to establish a baseline for that year and then again to measure the impact from new management practices used that year. This allows us to isolate things like weather that are not in a farmer’s control and just compare management practice to management practice (i.e., the positive impact of changing from what you did in the past to what you are doing now).

Why do I want credits that are verified?

Learn more about the importance of having carbon credits third-party verified in this next blog in our series.

*The Climate Action Reserve is an independent nonprofit that establishes strict standards for quantifying and certifying GHG emissions reduction projects to ensure the integrity, transparency, and financial value in the North American carbon market.

Have specific questions about your eligibility for a carbon program?