Carbon

Carbon

Carbon, more specifically, carbon dioxide (CO2), is the subject of a lot of debate these days.  Global climate change, global warming, and myriad other topics all seem to center on this topic.  I don’t intend to engage in these debates.  For the most part, the required science and engineering are far above my paygrade.

Sequestration

What I can talk about is the part plants play in sequestering carbon, which can potentially be part of the solution to some of the problems associated with excess CO2 in the atmosphere.

Carbon - Soil

Plants require at least 16 different elements to remain healthy.  We are all familiar with the big three, Nitrogen, Potassium, and Phosphorus (N-P-K).  The other 13 or so are rarely talked about unless our plants begin to show some problems related to a lack of these elements.  What is rarely talked about are Carbon and Hydrogen. 

Plants don’t get the carbon or hydrogen they require from the soil.  These two vital elements are captured from the air and, during the photosynthesis process, turned into compounds that the plant uses to produce vegetation, fruit, and the carbohydrates (sugars) that are exuded into the soil by the roots.  Bacteria and fungi consume these exudates in return for other nutrients required by the plant.  It is a symbiotic relationship.

Carbon and Soil regeneration

Carbon - Soil regeneration

These carbohydrates (CH2O) are sequestered in the soil biome as organic materials.  Some researchers divide these organic materials into two categories protected and unprotected.  The unprotected category is unstable in the soil and is returned to the atmosphere as CO2.  The protected category remains relatively stable in the soil, over time.  It is the bacteria and fungi in the soil that are responsible for the bulk of the protected category.  Thus, building the soil biome is a viable means of sequestering carbon in the soil.  Why is this important?

CO2 and Soil

Carbon dioxide is the gas most associated with global warming.  It is chief among the so-called greenhouse gases.  It is estimated that the soil biome holds 1500 Gt (gross tons) of Carbon in the top meter of the soil.  This sequestered carbon is much greater than the estimated 560 Gt of carbon held in the biotic pool and twice what is estimated in the atmosphere.  Clearly, the sequestration of carbon in the soil is of greater importance than has been previously guessed.

Modern agricultural practices, most especially the practice of regularly tilling to control weeds and prepare fields for planting, is a major contributor to the release of CO2 into the atmosphere.  Tilling destroys the soil biome in the top layers of the soil.   As these soil biome organisms die, they release their stored carbon into the atmosphere as carbon dioxide.  Without the soil biome organisms in the soil, carbon sequestration falls dramatically.

Tilling – The Carbon Problem

Some researchers believe that in the heavily tilled agriculture areas of the US, the soil may have lost as much as 30 – 55% of its sequestered carbon back into the atmosphere, which represents a dramatic loss as well as a huge opportunity.  These exploited soils represent areas with huge potential for carbon sequestration.  Changes in agricultural practices will be needed to promote this opportunity. 

Adopting no-till practices on cropland, as well as other regenerative soil management practices, are believed to be the biggest and most available means of mitigating climate change.  The soil remains the largest carbon sink.  It is a challenge for all of us to understand the role of carbon in the soil and how it can be a key component in the control of climate change.

Soil carbon sequestration with continuous no-till management of grain cropping systems in the Virginia coastal plainhttps://www.sciencedirect.com/science/article/pii/S0167198708000895

Soil Carbon Sequestration Impacts on Global Climate Change and Food Security, https://science.sciencemag.org/content/304/5677/1623

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