How Does Soil Pull Carbon out of the Atmosphere?

Amidst concerns about catastrophic climate change, carbon sequestration is all the rage these days. Carbon sequestration is basically the process of pulling carbon out of the atmosphere and storing it natural reservoirs such as soil. Below ground, soil a counts for about 46% of total terrestrial carbon sequestration. How does it work?

The Simple Answer: Microbes Lock It Up

The simple answer is: microbes absorb the carbon and hold it. The process starts with photosynthesis, when plants “inhale” carbon dioxide from the atmosphere and use it to make sugars.

Then, they send 3040% of their hard-earned sugars down into the soil as offerings their microbial allies. They literally give it away because those microbes are so valuable and vital to them, but more on that later.

The microbes (mainly soil fungi, and to a lesser extent, bacteria, protozoa, nematodes) take the carbon and “lock it up” in the form of recalcitrant organic matter or they store it within their bodies, mainly in fungal networks.

Through this ancient natural process, carbon is pulled from the atmosphere and stored away in the soil. That is, until a human comes along and disturbs or tills that soil and releases the carbon back into the air again.

If you want to understand a few more details about this process (in plain language), read on.

Image courtesy of Dirt to Dinner

Paying Farmers to Fight Climate Change?

Soil is finally making headlines these days and I’ve got to say, any ecological farmer or soil scientists is happy to see people starting to care about the humble Earth beneath their feet.

The problem is that the mainstream public has very little understanding of soil. People are quick to praise the idea of paying farmers to fight climate change (this is the key marketing point of both “regenerative farming” and the related “climate farming” or “carbon farming”).

The Biden Administration has proposed farm-based carbon credits as a way to encourage reduced carbon emissions and increase carbon sequestration on agricultural land.

Only problem? Scientists haven’t quite mastered a reliable method for measuring soil carbon sequestration over any significant amount of land (imagine trying to find the carbon across thousands of acres of land with soil many yards deep).

Furthermore, it is conveniently ignored that the majority of farms (especially industrial corn & soy monocultures) will have to undertake a MAJOR shift in their farming practices to even “break even” with their carbon emissions, let alone drawdown carbon from the atmosphere.

That’s because most soils have been degraded into dirt, especially in the United States. Dirt absolutely cannot sequester carbon.

Photo by Ivan Bandura on Unsplash

Soil vs. Dirt

At its core, soil is a living ecosystem much like a tropical rainforest but even more diverse and complex.

Soil is full of living, breathing organisms. These organisms are both macroscopic (you can see them with the naked eye), like earthworms, spiders, voles, and even groundhogs, as well as microscope (you cannot see them without microscope).

Unfortunately, vast amounts of soil are being turned to dirt on a daily basis. I use the term “dirt” to describe degraded lifeless soil that can no longer function as a thriving ecosystem.

Dirt cannot provide the vital soil ecosystem services like making plant nutrients, filtering and storing water, preventing erosion, or carbon sequestration, to name a few.

Modern agriculture has used all manner of synthetic herbicides, pesticides, fumigants, and heavy machinery to “kill” the soil. In turn, they have become reliant on these chemicals, as well as synthetic fertilizers, to continue growing crops in dirt that is devoid of microorganisms.

While dirt typically has very few microorganisms (mostly disease-causing bacteria), there are billions and billions of beneficial or neutrally harmless microorganisms in a single pinch of healthy soil. These microbes are the ones that fuel carbon sequestration.

Healthy living soil at Singing Frogs Farm in Sebastopol, CA | Image courtesy of author

Microorganisms are Carbon-Based

Although bacteria and other soil microbes are made of carbon, their bodies are relatively small and short-lived. Fungi do the bulk of the heavy carbon lifting because their networks are so large and carbon-rich.

Fungi can have a carbon to nitrogen ratio of 1000:1 . For reference, bacteria have an average carbon to nitrogen ratio of around 5:1, meaning they are a lot more nitrogen-rich.

Without getting too in the weeds, it will suffice to say that microorganisms are carbon-based (just like every living thing on Earth). Bacteria, protozoa, and nematodes play a small role in the soil carbon cycle, but fungi are absolutely loaded with carbon and they make large-scale CO2 drawdown possible.

Image courtesy of Soil Food Web

Plants “Inhale” CO2, Make Carbs, and Then Give It Away

As you may remember from grade school biology, photosynthesis is how plants make their own food.

Plants transform sunlight, water, and carbon dioxide into carbohydrates like glucose (C6H12O6), which is a carbon-based molecule. They are doing this day-in and day-out, using the carbohydrates to fuel their growth.

Surprisingly, however, scientists have discovered that plants are also actively funneling their carb-rich gold down into the soil at an astonishing rate. Plants share up to 40% of their energy with the microorganisms living in their root zone (known as the rhizosphere).

As soil microbiologist Dr. Elaine Ingham describes it, plants are pumping out “cakes and cookies” to the doorsteps of their microbial friends.

These carbohydrate-rich sugars are called root exudates, and they are the currency through which carbon is transformed from CO2 in the atmosphere to stable carbon in the soil.

Image courtesy of https://biochar.co.uk/soil-carbon-sequestration/

Symbiosis with “Germs”

But why the hell would plants give away 30–40% of the carbs they just worked so hard to make? Because most microorganisms have symbiotic relationships with plants. They work together in mutually beneficial relationship!

In the same way that mainstream medicine has convinced us that microorganisms are “bad germs” that cause disease, conventional industrial agriculture has indoctrinated farmers to believe that bacteria and fungi are plant pathogens that need to be sprayed or fumigated.

Ironically, both of these twisted philosophies on microbes fuel the multi-trillion dollar pharmaceutical and agricultural chemical industries.

Plants are symbiotically working with so-called “germs”. It is actually in the plant’s best interest to share its “cakes and cookies” (root exudates) with the microbes in its root zone.

The plant also communicates with the microbes about what nutrients it needs. In return, the microbes will eagerly bring back mineral nutrients and water to to the plant. They act as both an extension of the root zone and an on-demand food truck.

Microorganisms are nature’s fertilizer factories that have been mining minerals and nutrients from rocks and organic matter for thousands of years before humans ever invented synthetic fertilizers.

By the way, organic matter is just decayed poop and dead plants or animals. The Earth would be (disturbingly) covered in dead bodies if we didn’t have soil microbes to break them down and “feed” them to plants. Microbes help form organic matter. Organic matter and the bodies of fungi are where the carbon “gold” is stashed away.

Photo by Liam Briese on Unsplash

Fungal Networks Lock up Carbon

Fungi are some of the most fascinating organisms on Earth, and they are the superheroes of carbon sequestration. The largest organism on Earth is, in fact, a fungus in Oregon that is as large as 1,665 football fields and estimated to be 2,000–8,000 years old.

You might think of fungi as mushrooms, but mushrooms are just the short-lived “fruiting body” of a fungus. Most of their body is underground in long extensive networks called mycelium.

The mycelium is made up of hyphae, which are like tiny threads weaving through miles and miles of soil. When fungi receive those “cakes and cookies” (root exudates) from plants, they use the carbon to thicken the walls of their hyphae.

Fungal hyphae are thread-like white “roots” of a fungus

Like a Carbon Pump

So the simplest way to make sense of soil carbon sequestration is to think of it as a carbon pump. Plants absorb atmospheric carbon and pump it down into the soil where it can be stored for hundreds to thousands of years by fungal hyphae.

This is why planting and protecting forests (which are extremely rich in fungal networks) has long been seen as the best way to “fight climate change”.

What is the Soil’s Carbon Storage Potential?

Atmospheric carbon levels are currently at about 410 ppm, the highest they’ve been in the last 450,000 years (based on ice core samples). The United Nations says a “safe” level of atmospheric carbon is 350 ppm.

So, we need to remove about 60 ppm of carbon, or about 450 billion tons of CO2, from the atmosphere. Is soil up for the task?

We don’t really know. Like I said in the introduction, scientists haven’t precisely mastered techniques for measuring soil carbon sequestration because the soil ecosystem is so dynamic (always changing) and vast.

A 2019 report from the Intergovernmental Panel on Climate Change claims that global croplands and grasslands could capture and store up to 8.6 gigatons of CO2 per year.

Dr. David Johnson at New Mexico State University has shown that, with biological farming techniques, we could sequester 20 tons per hectare per year with fungal-dominated compost.

Dr. Elaine Ingham’s Soil Food Web, Inc. asserts that we could reverse global climate change via soil carbon sequestration within 15 years if there was global adoption of soil regeneration techniques that revitalize soil microbiota.

It’s Impossible to Sequester Carbon If You Till or Spray

Now that we understand how soil can be used to fight climate change, it’s time for a pop quiz:

Can farmers who use tillage or agricultural chemicals sequester carbon?

I hope you yelled “HELL NO!”

Why not? Because only living soil can sequester carbon, not dead dirt.

Tillage is the grinding and churning of soil into dust using plows or heavy machinery. You may recall that excessive tillage is what cause the Dust Bowl and subsequent Great Depression.

What most people don’t realize is we are living through another “Dust Bowl” in modern times. According to the UN, an estimated 30 soccer fields of topsoil is lost every minute globally to erosion, degradation, and tillage.

Ironically, tillage also releases CO2 emissions to the atmosphere. Tilling is the direct opposite of carbon sequestration. That’s because it churns up that organic matter (decayed dead stuff we talked about earlier) and releases all the carbon chains that had been “locked up” in there by microbes.

Tillage destroys the soil structure and kills the microorganisms. Fungi are the most vulnerable to disturbance and thus are the first to go after a tillage event. After years and years of tillage, soil eventually becomes dirt that is lifeless and incapable of carbon sequestration.

Image courtesy of Kiss the Ground

Obviously the same process applies to use of synthetic herbicides, pesticides, fumigants, or synthetic fertilizers. These agrichemicals indeterminately kill soil microorganisms, similar to taking a powerful antibiotic.

If microbiota are being sprayed or ground to dust on a regular basis (as with the conventional farming methods used across millions of acres in the United States), it doesn’t take a rocket scientist to understand that it is impossible to drawdown carbon or fight climate change with degraded lifeless soil.

Nature’s Way, or the Highway

Keep this in mind next time you hear about carbon farming credits or so-called regenerative farmers that use RoundUp to keep their fields “no-till”. Eliminating tillage and replacing it with agrichemicals is far from productive and maybe even more harmful to the soil ecology.

No-till, organic, and ecological farming methods are the only way to truly regenerate soil and harness the power of fungal carbon storage capabilities. Dr. Elaine Ingham and Soil Food Web, Inc. is leading the way in this revolution and has taught me the bulk of what I know about soil microbiology. You can learn more about their work here.

Image courtesy of Soil Food Web

Ultimately, Nature is going to do things her way. The Earth has been cycling carbon for billions of years, so the innate intelligence of the soil and ecology is not to be underestimated.

Humans are mere babies in the grand scheme of biological time. It is foolish, if not arrogant, to think that we can “out smart” Nature with machinery and synthetic chemicals and still expect to benefit from carbon cycling.

We got ourselves into this whole mess of climate change and ecological degradation, so we’ll have to get ourselves out of it. Regenerative farming and biological soil management appears to be the clearest path forward.

Aerial view of regenerative growers Singing Frogs Farm | Image © Logan Hailey and Ramblin Farmers LLC

Key Talking Points:

  1. Plants absorb carbon from the atmosphere during photosynthesis and use it to make carbohydrates and sugars. They give away 30–40% of their hard-earned (carbon-based) sugars to microorganisms in the soil as exudates.
  2. Plants act like a “carbon pump”, pumping carbon out of the atmosphere and into the soil.
  3. Fungal networks store the carbon by locking it up in their thread-like hyphae and storing it for centuries to come.
  4. Most soils are completely degraded and devoid of fungi because of tillage and synthetic agrichemicals.
  5. Conventional industrial farms cannot sequester carbon if they maintain current practices and chemical use. It is impossible for soil to drawdown carbon unless the soil food web is regenerated through no-till, organic, and ecological techniques.
  6. Fungi are what make soil carbon sequestration possible.

For more about soil, microbiome, regenerative farming + nature, follow me on Medium, YouTube, and Instagram.

Vivacious nomad-farmer-writer with a wild spark. Top writer. Regenerative farming, organic food, holistic health, microbiome, personal growth + Mother Earth.

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