Question

Which of the horizons of a soil profile represents the zone of accumulation of clay, sesquioxides, humus alone or in combination?

• A. A horizon
• B. B horizon
• C. C horizon
• D. E horizon

Hint:

Think of E for Exit (Eluviation/Loss).
Think of B for Build-up (Illuviation/Accumulation).
The B horizon is where the "goodies" from the topsoil end up!

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
This question asks for the master horizon in a soil profile where materials leached from upper layers eventually settle and concentrate. This process is known as illuviation.
Detailed Explanation:

• Soil Horizons Overview:
A soil profile is a vertical section consisting of master horizons: O (organic), A (surface/mineral), E (eluviated), B (subsoil/illuvial), C (parent material), and R (bedrock).

• Process of Eluviation vs. Illuviation:
Eluviation: The washing out of fine soil components (clay, iron, organic matter) from an upper layer. This primarily happens in the A and E horizons.
Illuviation: The deposition or accumulation of these washed-out materials into a lower layer.

• Characteristics of the B Horizon:
The B horizon is officially defined as the zone of illuviation.
Over time, percolating rainwater carries clay, iron/aluminum oxides (sesquioxides), and humus down from the A or E horizons.
These materials are "trapped" in the B horizon, often giving it a distinct color (redder or browner due to iron) and a denser, more clayey texture.

• Distinction from Other Options:
A horizon: Zone of organic matter addition and initial leaching.
E horizon: Maximum zone of leaching (loss), hence it looks bleached or light-colored.
C horizon: Unconsolidated material that has undergone little to no pedogenic activity; it is the parent material.

Step 2: Final Answer:
The B horizon is the designated zone of accumulation (illuvial horizon) in a soil profile.