Question

The $\text{O}_\text{a}$ sub-horizon denotes-}

• A. Organic horizon with highly decomposed organic matter
• B. Organic horizon with intermediately decomposed organic matter
• C. Organic horizon with least decomposed organic matter
• D. Organic horizon without decomposed organic matter

Hint:

Remember the prefixes: "i" for initial (fibric/least), "e" for intermediate (hemic), and "a" for advanced (sapric/highest) decomposition.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The "O" master horizon represents organic soil layers dominated by fresh or partially decomposed plant and animal residues. Sub-horizons are designated by lowercase suffix letters to specify the degree of organic decomposition.

Step 2: Detailed Explanation:
According to USDA soil taxonomy, three main types of organic material are differentiated in the O horizon:
- \(\text{O}_\text{i}\) (fibric): Least decomposed organic material where original plant fibers are easily identifiable.
- \(\text{O}_\text{e}\) (hemic): Intermediately decomposed organic material.
- \(\text{O}_\text{a}\) (sapric): Highly decomposed organic material where original tissue fibers cannot be recognized.

Step 3: Final Answer:
Therefore, the \(\text{O}_\text{a}\) sub-horizon denotes an organic horizon containing highly decomposed organic matter.