In the zone of eluviation, where constituents are leached out of the A Horizon and deposited to form hardpan or caliche, what is this deposition associated with?

• A. They are leached out of the B Horizon
• B. They are deposited in the C Horizon
• C. They are extracted as organic material
• D. They are leached out of the A Horizon and deposited to form hardpan or caliche

Answer: (D)

The key idea is that materials dissolved or carried downward by water in the eluviation zone are removed from the upper horizons and can accumulate lower in the profile when conditions favor precipitation and cementation. When those leached constituents, especially calcium carbonate, precipitate and cement the soil mass, they form a hard, compact layer called a caliche or hardpan. This deposition is the feature described, tying the downward movement of eluviated materials to the creation of a cemented layer near the surface in arid or semiarid climates. The other possibilities don’t match the process as well: the materials aren’t simply deposited in a deeper C horizon, nor are they retained as organic material, and the statement is describing the formation of the hardpan/caliche itself rather than a different kind of deposition.