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Difficulty: MediumSoil Formation, Profiles, and Major Vegetation Types

During soil profile development in humid regions, percolating water washes fine clay particles, iron, and aluminum oxides downward from the upper topsoil layer. In which soil profile horizon do these translocated materials primarily accumulate?

  1. The B horizon, which acts as the zone of illuviationAnswer
  2. B
    The C horizon, which consists of partially altered parent rock
  3. C
    The A horizon, where surface weathering and organic accumulation dominate
  4. D
    The R horizon, which forms the continuous unweathered bedrock basement

Answer

The B horizon, which acts as the zone of illuviation
The correct answer correctly identifies the subsoil layer as the primary site of illuviation. In a mature soil profile, downward-percolating rainwater carries fine clay particles, iron compounds, and organic material out of the top layer (eluviation) and deposits them into the subsoil below (illuviation), creating a distinct layer enriched in minerals.

Step-by-Step Solution

1
Identify the pedogenic translocational process described in the stem.
Downward movement of fine clay and oxides by percolating water is known as leaching/eluviation from topsoil.
Water moving through topsoil dissolves and suspends fine particulates.
2
Determine the destination horizon where translocated materials settle.
The subsoil layer receives and stores these deposited compounds through illuviation.
The subsoil horizon positioned immediately beneath the topsoil captures downward-migrating minerals.
3
Match the zone of illuviation to standard soil profile nomenclature.
The B horizon is designated as the subsoil accumulation layer.
Standard pedological classification defines the B horizon as the illuvial layer.

Key Concept

Soil Profile Horizons and Illuviation
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Topics

Soil Formation, Profiles, and Major Vegetation Types

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