(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.

(a) Soil profile

A soil profile is a vertical section of soil from the ground surface down to the parent rock or bedrock, showing the different layers or horizons of the soil.

(b) Well-labelled diagram of a soil profile

(c) Characteristics of the three zones of a soil profile

1. A horizon (topsoil or zone of eluviation)
   • It is the uppermost layer of mineral soil, immediately below the surface litter.
   • It contains decaying plant and animal remains which form humus.
   • It is dark in colour and is usually the most fertile horizon.
   • It is the zone of greatest biological activity, containing many soil organisms and most plant roots.
   • Soluble minerals and fine materials are washed down from this horizon by percolating water.
2. B horizon (subsoil or zone of illuviation)
   • It lies below the A horizon and contains little humus.
   • It is the zone in which clay, iron, aluminium and other mineral materials leached from the A horizon accumulate.
   • It is often reddish, brownish or yellowish because of iron compounds.
   • It is usually denser and more compact than the topsoil.
   • Only deep-rooted plants commonly extend into this horizon.
3. C horizon (parent-material horizon)
   • It consists mainly of partly weathered rock fragments and other parent material from which the soil develops.
   • It contains very little or no humus and has little biological activity.
   • It is coarser and less developed than the A and B horizons.
   • It grades downward into hard, unweathered bedrock.