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How long does Carbon stay in the soil?

How long carbon stays in the soil depends on a variety of factors, including the type of soil, the amount of carbon that is added, and the management practices that are used. In general, however, carbon in soil organic matter carbon can remain in the soil for decades, while other forms, such as Carbonates, may persist for centuries or even millennia.

One of the key factors that influences how long carbon can be sequestered in soil is the form that it takes. For example, carbon that is in the form of charcoal or other types of biochar can remain in the soil for hundreds or even thousands of years, while other types of carbon may be more easily decomposed by soil microbes and released back into the atmosphere as carbon dioxide.

Other factors that can influence the length of time that carbon stays sequestered include temperature, moisture, and soil pH. In general, cooler temperatures and higher levels of moisture tend to slow the decomposition of organic matter and promote the accumulation of carbon in the soil.

In addition, management practices such as reduced tillage and the use of cover crops can help to promote the sequestration of soil carbon, which can in turn help to mitigate climate change by reducing the amount of carbon dioxide in the atmosphere.

In summary, these are some of the factors that can affect how long carbon stays sequestered in the soil:

  • Soil type: Carbon can persist in soil for longer periods of time if the soil is well-drained and has a high clay content;

  • Climate: In cold and wet climates, carbon can remain in soil for longer periods of time than in warm and dry climates;

  • Land management practices: The way land is managed can have a significant impact on how long carbon remains in soil. For example, tilling soil can release carbon into the atmosphere, while the use of cover crops can help sequester carbon in soil; and

  • Depth of soil: The deeper the carbon is buried in soil, the longer it is likely to remain there.

Soil Carbon Sequestration Process

The process of soil carbon sequestration is as follows:

  • Carbon starts as purely organic matter from decaying crop residues, resides close to the surface (within approximately 10 centimetres) and is in the process of cycling rapidly.
  • Over time, it forms more complex humic substances that are bound into the soil aggregate structure. Humic substances are the organic component of soil, formed by the decomposition of leaves and other plant material by soil microorganisms.
  • As the humic structure of carbon becomes more complex, it also becomes more resistant to degradation. It can reside at a greater depth and, under the appropriate management, can persist in the soil for hundreds of years.

For an explanation of how carbon gets stored in the soil, see our other FAQ questions, including What is Carbon Sequestration and how does it work?

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