Theory question 207
Soils(a) What is soil profile? (b) Draw a well labelled diagram of soil profile. (c) Describe the characteristics of the three zones of soil profile.
Show the model answer
(a) A vertical section of the soil from the surface down to the parent rock, showing its layers (horizons).
(b) Diagram with title showing humus/leaf litter at top, A horizon (topsoil), B horizon (subsoil), C horizon (weathered parent material) and bedrock, all labelled.
(c) A horizon (topsoil): dark, rich in humus and organisms, most roots, zone of eluviation (nutrients washed down).
B horizon (subsoil): lighter colour, zone of illuviation where washed-down iron, aluminium and clay collect; may form hardpan; few roots.
C horizon: partly weathered parent rock, little organic matter, source of the minerals for the layers above; lies on solid bedrock.
Label every horizon in the diagram.