How Does Soil Sequester Carbon?

Author: Lois Eaton 11/23/2020
 

I used to think that the important role plants played in carbon sequestering was holding the carbon in their structures and then later releasing it to the soil when they die.  Now I am happy to know that living plants are also conduits for carbon from the air to the soil.  In a nutshell covering bare earth with seeds to grow into plants will make a huge contribution towards pulling carbon out of the air where it is a key component of climate change.  Once it is in the plant and then in the soil unless the soil is left bare or tilled, the carbon will stay in the soil increaseing the soil’s nutritive value.   The elephant in the room is the need to pull carbon out of the air for climate change mitigation.  We are long pass being able to slow climate change just by reducing the amount of carbon we are putting into the air.  We now need to do both, rapidly.

farm

https://www.nature.com/scitable/knowledge/library/soil-carbon-storage-84223790/ 

I learned about plants as conduits for carbon when I was researching how regenerative farming works.  So, what is it that carbon does in the soil and why, how does it stay there, and how is it released back into the atmosphere?

Carbon in the soil is in the form of organic matter from plants that have died or carbon the plants deposited in the soil while alive 

A Brief Overview of Earth’s Energy Source

First a perspective aside – why understanding carbon’s many roles in our lives matters.  It is good to remember that all our energy comes from the sun whether as oil, wind, solar, wood burning etc.  Whether fuel is for our machines or fuel for living bodies such as humans.   The original and only energy source is the sun.  Even wind is from the sun.  The sun heats the earth unevenly, causing air movement between the different areas of temperature.  That wind sometimes blows gently and sometimes with the force of a hurricane. Wind is one of the few forms of fuel or energy that does not have a carbon component.

https://www.nationalgeographic.com/science/earth/earths-atmosphere/wind/ 

In the ocean dead plankton (miniature plants and animals) falling to the ocean floor millions of years ago became today’s oilfields.

https://energyeducation.ca/encyclopedia/Oil_formation

Of course, we eat plants and animals.  The animals grow because they eat plants.  So, we circle back to the sun providing us with energy for our bodies, all life on our planet and our world of machines and most of this energy has a carbon component in it.  

Carbon Soil Connection to Agriculture

When we think of organic matter in our soils, we think of it as the stuff that makes soil highly nutritious for growing plants.  There may be a disconnect for us between the fertility of soil and the carbon in it, as carbon is so often characterized as the villain of our time.   Yet much of a soil’s nutrition is tied into the carbon in it.  As humans till the soil, we expose the carbon to the soil-air interface.  Here the carbon is released back into the air, where it quickly morphs into carbon monoxide.  We have somehow sidestepped understanding how much carbon is in the soil which has led us to not understanding how much we release back into the air through tilling. 

https://www.soilcc.ca/ggmp_feature_articles/2004/2004-02.php

https://www.usnews.com/news/articles/2016-08-04/could-no-till-farming-reverse-climate-change

There are two things humans can do to increase the amount of carbon sequestered in our soils: 

  • don’t till, instead drill seeds into the ground, 
  • also plant every inch of exposed soil 
    • so the plants can pull carbon out of the air and sequester it in the soil
    • and so the bare soil doesn’t release carbon slowly back into the air
  • avoid cutting down trees, especially old growth forests.

Current Practices

Seems simple to me.  Instead, humans clear-cut trees on lots to build a house rather than fitting the house to the lot to minimize the number of trees cut.  We continue to cut old growth forests and slash many trees in the forest for which logging companies have no use.  The reasons are purely economic – a lot of board feet in big old trees and many sawmills would need to be retooled to accept second growth trees.  It is easier to get at the trees with financial value if the nuisance trees are not standing in the way.  Yet leaving the trees standing as much as possible will make a significant difference to mitigating climate change.

Another disruptive human practice is messing with the soil.  Farmers and gardeners still till the soil, turning it over in the spring massively increasing the amount of carbon released to the air to become carbon monoxide  Tilling the soil has a tarnished record down through history of bankrupting soils of essential nutrients – carbon and moisture – with disastrous impacts on civilizations.   Articles are written on the connections between the collapse of civilizations and the degradation of their soils for food production. 

https://www.sciencedaily.com/releases/2013/11/131104035245.htm 

Part of the history of agriculture is the timeline of more efficient tools and machines to till the soil.  Although we now have airconditioned, computer-directed tractors pulling strings of multiple discs tilling multiple rows at a time – the science of tilling has hardly changed since the ancient civilizations.  

https://www.farmmanagement.pro/a-short-history-of-tilling/

Science is changing our agricultural practices as it discovers what is going on in the soil and tilling’s impact on the nutritious value of the soil.

Science has discovered the following advantages of no-till agriculture:  

  • improved soil structure and environment for all the micro creatures that change dead plants into forms useful to living plants, 
  • locking nutrients into the soil rather than exposing them to surface where they can be blown away, washed away, or leaked back into the atmosphere once again becoming carbon monoxide.
  • keeps moisture in the soil instead of bringing it to the surface to evaporate

Plant the Planet

One other thing is needed, however.  Bare, untilled soil is still gradually transferring water and carbon back into the atmosphere.  We need plants on soil to block these carbon and water loses to the air.  We need to plant every square inch of soil that we can, to multiply the carbon sequestering impact of plants.  Plants will soften water’s impact on the ground for gradual absorption rather than becoming run-off carrying away topsoil and water.  

Critically for climate change, plants pull carbon out of the air, use it themselves and then let it flow through their roots into the soil.  Now that we understand that once in the soil, bacteria and other micro creatures transform the carbon into a form plants can use, or it just hangs around safely secured away from air exposure, we know the value of protecting this process.  Finally, when the plants die, they decompose into more carbon.

Imagine the volume of carbon sequestering a towering Douglas Fir captures in its layers of multiple boughs with fingers of needles from each branch.  So much more than a newly planted sapling.  

Our Wonderfully Simple and Effective Role

What each of us can do to mitigate climate change through carbon sequestering in the soil.

  • Write letters to our provincial government saying 
    • NO to old growth forest harvesting
    • Time to do a tune up on forestry practices
  • Write letters to Regional Districts and Town Councils requesting vegetation policies that regulate 
    • which trees can be cut down, 
    • the payment required for each tree cut down, 
    • the requirement for replanting.  
      • (Although new plants and trees are much less efficient at sequestering carbon than old growth trees at least replanting requirements begin to address the ravaging of our land)
  • Plant every inch of bare soil on your land, 
    • grow plants on your balconies, 
    • participate in community gardens, 
  • write letters requesting more community gardens and forests set aside as parklands. 

It is amazing to think how efficient the combination of plants and soil are in addressing the overload of carbon in our atmosphere.  

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It is our elected officials that most critically need to here from us.  They are the ones who represent our needs and can provide the leadership for change. 

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