By Michelle Probst, Natural Resource Educator
As we enter the holiday season, there is one holiday that simply cannot be missed—World Soils Day. On Dec. 5th of every year, we set a day to appreciate soil and focus on the importance of healthy soil. As a soil scientist, I jump for joy that everyone is talking about soil! Soil health has become a common phrase in recent discussions on the environment and agriculture.
We normally think of the critical role soils play in supporting plant growth, which is very important, but we cannot forget other important functions that soil provides such as filtering pollutants, cycling nutrients, regulating water, and sequestering carbon. All these functions are critical in our environment and thinking about soil management with a soil health perspective, gives us the ‘tool’ for managing soil for more than just plant growth.
Soil’s ability to sequester (or store) carbon has made soil become quite the popular topic in our discussion of ways to combat the climate crisis. Through photosynthesis, carbon from the atmosphere is absorbed into plants. Plants then use that carbon to grow roots and shoots and release microscopic amounts of carbon from the roots into the soil–this is also known as root exudates. Microbes that live in the soil use organic matter like root exudates and dead plant matter as food and in return, release CO2 back into the atmosphere (also known as decomposition). While this process may seem circular–CO2 enters the soil and then leaves the soil–soil can protect organic matter from decomposition by forming soil aggregates around organic matter. Soil aggregates are particles of sand, silt and clay that are held together through root exudates–when you pick up a handful of soil and it falls apart into little pieces, you are looking at soil aggregates. Carbon that is protected by soil aggregates can be stored in the soil for long periods of time–years, even decades! However, when soil aggregates are broken up or disturbed through practices like tillage, this exposes the carbon and it is then decomposed by microbes in the soil. So when we are thinking about soil’s role in combating the climate crisis, we want to manage soils in a way that helps increase and protect soil aggregates.
For the best way to protect aggregates in our soil, we can look to nature for the solution–our native ecosystems. Prior to colonization, Dane County was dominated by prairies and oak savannas. These ecosystems contain many diverse root systems that increase the amount of carbon into the soil, while protecting the carbon from decomposition by forming stable soil aggregates. Dane County has seen the value in restoring prairies and oak savannas because of its ability to store carbon. The Dane County Natural Areas Program works to restore and sustain natural communities, and has many active restoration projects.
While soil can certainly be a solution in mitigating the climate crisis, it shouldn’t be our only solution. As our climate warms, decomposition rates will increase and carbon that was protected in the soil could be easily decomposed by microbes and return to the atmosphere. Most of our soil carbon is stored in our arctic regions as permafrost, and permafrost is thawing with climate change. This thawing will release even more carbon into our atmosphere.
Soil is a complex and fascinating ecosystem, and it performs many functions that make life possible. One of those important functions is sequestering carbon. By enhancing and protecting aggregates in the soil, the soil has the ability to store more carbon. As we continue to develop solutions to our climate crisis, protecting our soil is a tool in our toolbox. December 5 is World Soils Day so take the time to learn about and admire the ground you’re on–it helps make life possible!
Dr. Alexandra (Sasha) Kravchenko, “Soil Carbon Storage in Agriculture Fields” https://soilhealthnexus.org/soil-carbon-storage-in-agricultural-fields/
Adam F. A. Pellegrini, Jennifer Harden, Katerina Georgiou, Kyle S. Hemes, Avni Malhotra, Connor J. Nolan, Robert B. Jackson. Fire effects on the persistence of soil organic matter and long-term carbon storage. Nature Geoscience, 2021
USDA-NRCS, 2008, Soil Quality Indicators