Question

Carbon content in organic matter is ________________

• A. 72%
• B. 58%
• C. 24%
• D. 84%

Hint:

Connect the 58% carbon content to the conversion factor 1.724 (\(1 / 0.58 \approx 1.724\)) used to estimate soil organic matter from organic carbon measurements.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Soil organic matter (SOM) consists of plant and animal residues at various stages of decomposition.
Determining the exact chemical composition of organic matter is essential for estimating carbon stocks and soil fertility.

Step 2: Detailed Explanation:
While the composition of soil organic matter can vary slightly depending on the origin of the organic residues, it is highly consistent on average:
- Organic carbon constitutes approximately \(58\%\) of soil organic matter by weight.
- This consistent proportion is the basis of the classic "Van Bemmelen factor" (or Bemmelen-Pratt factor) of \(1.724\).
- To calculate the total organic matter percentage in a soil sample from its measured organic carbon content, the following formula is used:
\[ \text{Soil Organic Matter (\%)} = \text{Soil Organic Carbon (\%)} \times 1.724 \]
- The factor is derived directly from the carbon proportion:
\[ \frac{100}{58} \approx 1.724 \]
- Therefore, \(58\%\) is the globally accepted average value for carbon content in soil organic matter.

Step 3: Final Answer:
The average carbon content in soil organic matter is 58%.