Theory question 206
Soils(a) Draw a labelled diagram of a simple soil profile
(b) Describe the characteristics of any two of the zones in the soil profile drawn in (a) above. Give reasons for each characteristic
Show the model answer
(a) Vertical section labelled from top: organic layer/litter, A horizon (topsoil), B horizon (subsoil), C horizon (weathered parent material), bedrock
(b) A horizon: dark in colour because of humus from decaying plants and animals; loose and full of roots and organisms (most biological activity); zone of eluviation – leached and lighter in texture because water washes clay and minerals downward
B horizon: zone of illuviation – richer in clay, iron and aluminium washed in from above, so it is more compact and often reddish/brown; little humus because few organisms live there
C horizon: partly weathered rock fragments, coarse, little or no organic matter because it is close to the parent rock
For each zone give a characteristic and the reason for it.