Final answer:
In an Allophanic Soil profile, the O horizon is the topmost layer while the A and B horizons represent the topsoil and subsoil, respectively. The C horizon is the soil base, consisting of parent material and is closest to the bedrock.
Step-by-step explanation:
The Allophanic Soil profile typically features a distinctive sequence of soil horizons. The O horizon is the topmost layer composed of organic matter, often referred to as humus, which provides nutrients and enhances moisture retention. The A horizon, also known as topsoil, follows below the O horizon and is characterized by a mixture of organic and inorganic substances, where important microbial processes and plant production occur. Below the A horizon lies the B horizon or subsoil, which is a denser layer of the soil profile. It accumulates fine materials that have moved downward from the A horizon and can contain nodules or layers of minerals like calcium carbonate. The C horizon or soil base is the deepest layer, consisting of parent material and broken-down organic and inorganic matter, often lying over bedrock.