Understanding the role of carbon in agriculture – Part 1
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Just about everyone is familiar with the Old McDonald nursery rhyme. History tells us that the lyrics derive from an old folk song prevalent in the British Isles and North America hundreds of years ago. Flash forward to 2021 and carbon capture and storage is now being touted as a potential new role for old McDonald’s farm.
For some time now, the popular press has covered the ongoing debate about climate change. Some articles point to agricultural as a primary contributor to the problem. Currently, the U.S. Environmental Protection Agency (EPA) estimates agriculture and forestry together account for 10.5% of U.S. greenhouse gas emissions (0.7 million metric tons). Transportation and industry are estimated to account for about 60% of emissions (4.0 million metric tons). However, what really sets agriculture apart is its potential to remove carbon dioxide (CO2) from the atmosphere and sequester it in soil.
Science is now demonstrating that agriculture can be a primary solution to the problem of greenhouse gas emissions and climate change. As a result, farmers are now hearing terms like carbon credits, carbon financing and carbon payments. Why all the buzz now about farms being considered part of the solution to climate change? Conceptually it is quite simple—once you understand the basics of how carbon is cycled in the environment.
The issue of climate change revolves primarily around the main atmospheric form of carbon, CO2. In fact, CO2 is the metric, or currency in which changes in atmospheric radiative forcing (i.e., global warming) are measured. What does all this have to do with farming? As it turns out, the most effective way to reduce atmospheric CO2 levels is through Mother Nature’s own process of photosynthesis. A few simple, back of the envelope calculations demonstrate agriculture’s ability to assimilate CO2, which can potentially lead to carbon capture and storage. Let’s use corn, the nation’s top crop, as an example.
Corn will contain, on a whole plant basis, approximately 43% carbon (C) by weight. Additionally, the amount of C deposited by roots will be approximately 29% of the shoot biomass carbon. Using the above ballpark figures and assuming a typical mid-Michigan corn grain yield of 180 bushels per acre, we can calculate the amount of atmospheric CO2 corn will potentially assimilate during the growing season to be a whopping 34,679 pounds per acre!
The 2020 national corn growing champion 476-bushel yield, which happened to be grown in Michigan by Don Stall of Charlotte, Michigan, would have assimilated 91,707 pounds per acre CO2! Of course, this figure represents the total amount of C assimilated in the corn crop, not the amount of C “sequestered” in the soil. Much of the assimilated C is naturally recycled back to the atmosphere when an animal respires CO2 while metabolizing corn grain in its feed or soil microbes metabolize stover remaining in the field. The key to “sequestering” or successfully capturing and storing some of the assimilated carbon into the soil depends upon the farmer’s use of C-smart best management practices including minimal or no-till systems and the use of cover crops.
Carbon dynamics in the soil are complex, but these best management practices help to move and maintain soil C into a more stable form in the soil. Soil C exists primarily in organic form as soil organic matter, which is comprised of forms that decompose at different rates, the most stable of which can persist for thousands of years. With proper management, over time the C level of the soil can be raised to a new equilibrium level.
In Part 2 of this series, we will discuss the challenges of capturing and storing C in agricultural soils, which unfortunately can be a long-term process that under poor management can be easily reversed.
Hopefully you now understand that there’s really nothing new about farming’s potential to help protect the environment by capturing and storing C in the soil with the adoption of best management practices. The potential has been there since the very first farming took place. And, although they will probably not be adding “carbon” to Old McDonald’s lyrics, C sequestration will likely be of value to farms of the future in terms of emerging policy involving C credits, C financing and C payments. E-I-E-I-O.
