APES UNIT 4 SOIL HORIZONS

Order of Soil Horizons (Top to bottom)

O, A, E, B, C

O Horizon

Organic matter in various stages of composition at the surface of many soils composed of organic detritus in various stages of decomposition
- Leaves, needles, twigs, animal
- Leaves, litter, surface debris

A Horizon

(topsoil) Zone of overlying organic material mixed with underlying mineral material, frequently the top layer of soil
- Organic and mineral material (humus too)
- Fertility, erosion, crops, roots

E Horizon

Zone of leaching, found in acidic soils under the O Horizon or occasionally under the A horizon
- leaching of meals and nutrients

B Horizon

(subsoil) Primarily mineral material, very little organic matter

• accumulation, storage, clay, iron

C Horizon

(subsoil) Least weathered horizon, similar to parent material

• Weathered rock

Humus

Most fully decomposed organic matter in the lowest section of the O horizon