SubSoilsTitle

module_02 Carbon Transformations and Organic Matter
lesson_01 How do the products of decomposition differ in aerobic versus anaerobic environments?
objective Be able to differentiate the products of aerobic versus anaerobic decomposition.

Aerobic products Organic material added in well-aerated soil is decomposed by a large group of microorganisms and soil fauna like earthworms. Click here to view the lesson on soil biology.  Approximately three fourths of the carbon in these materials may be released as carbon dioxide during decomposition ( oxidation). Complex carbon structures like lignin resist degradation and may become part of the stable soil organic matter.

Anaerobic products In anaerobic decomposition, methane is an important carbon product in addition to carbon dioxide. Organic acids and alcohols are transition products which accumulate in submerged soil because their decomposition to carbon dioxide and methane is slow. Other products unique to anaerobic decomposition like ammonium and hydrogen sulfide will be discussed in upcoming modules for nitrogen and sulfur.

Click the row or column headers in the table below to compare the aerobic and anaerobic decomposition products.

Significance
of methane

Both carbon dioxide and methane are identified as contributors to the greenhouse effect.  The diagram below depicts how methane produced in the submerged soil escapes into the atmosphere. Click Next in the diagram to view the various pathways of methane. 

Did you know?

Methane facts
Compared to carbon dioxide, methane is 25 times more potent in absorbing radiation reflected from the earth’s surface over a 100 year time period. (2007 IPCC Report)

Estimates for methane from rice production range from 20 – 60 Tg/yr which is 5 to 10% of the total global methane emission (Biogeochemistry of Submerged Soils - Guy Kirk 2004).

• Other human sources of methane include energy production, coal mining, petroleum and industry, landfills, ruminant animals and biomass burning.

• The largest natural source is wetlands followed by termites, oceans, wild animals, and others.

Next lesson

What are the advantages and disadvantages of adding organic materials to soil? To find out, proceed to the next lesson.

 

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