Certified Crop Advisor Practice Exam

When organic materials decompose, most of the carbon ends up as?

1. CH4

2. CO2

3. Fixed Carbon

4. Organic Matter

The correct answer is: CO2

When organic materials decompose, a significant portion of the carbon contained within them is released as carbon dioxide (CO2). This process occurs through microbial respiration and is part of the natural carbon cycle. During decomposition, microorganisms break down complex organic compounds, resulting in the release of energy and gases, with CO2 being the most prevalent gas emitted. This process is crucial for soil health and nutrient cycling, as the CO2 released can be utilized by plants during photosynthesis, transforming it back into organic matter. While some carbon may be released as methane (CH4) during anaerobic decomposition, it is not the main product in aerobic conditions, which are often the case in well-aerated soils. Fixed carbon and organic matter refer to different forms of carbon that are not primarily the result of the decomposition process but rather indicate carbon that has been incorporated into stable soil components. Thus, the choice of CO2 reflects the most common fate of carbon during the breakdown of organic materials.