2 Soil Horizons and Profiles Free Online FlashCards

What is a soil horizon?

A soil horizon is a layer, generally parallel to the land surface, that differs from neighboring layers in properties such as color, texture, structure, or composition.

What does a soil profile describe?

A soil profile is the vertical sequence of horizons at a particular location.

Is O–A–E–B–C a required sequence in every soil profile?

A common simplified sequence is O–A–E–B–C, sometimes above R, but it is a guide rather than a required sequence.

What characterizes the O horizon?

The O horizon consists of organic material, such as leaf litter and partly decomposed plant remains. It may be at the surface or buried, and is not present in every soil.

What are typical features of the A horizon?

The A horizon is mineral soil near the surface, commonly mixed with organic matter by organisms and roots; it is often darker than underlying mineral layers.

What process typically distinguishes an E horizon?

The E horizon is a zone of eluviation, where moving water removes some materials, often clay, iron, or organic matter. This can leave it relatively pale.

What commonly happens in the B horizon?

The B horizon is a subsurface zone altered by soil-forming processes. Materials from above may accumulate there through illuviation, and minerals, structure, or color may also change.

What is the C horizon?

The C horizon is relatively little-altered parent material beneath the more developed soil; it may consist of weathered rock or transported deposits.

What does the R horizon represent?

The R horizon is hard bedrock beneath the soil. It is included in the profile description but is not itself soil.

Which processes help create differences between soil horizons?

Weathering breaks down minerals, organisms add and transform organic matter, and moving water can remove, alter, or deposit materials.

What local factors contribute to variation among soil profiles?

Soil horizons vary with climate, organisms, landscape position, parent material, and time.

What visible features help distinguish soil horizons?

Compare horizon depth and thickness, color, texture, structure, roots, stones, and boundary sharpness. Chemical and mineral properties may require laboratory analysis.