1. Soil Formation

2. Soil Formation Vocabulary
Humus
Horizons (A, B, C, R)
Soil Profile
Litter
Leaching

3. Soil Formation
Soil is the end result of weathering and erosion which provides nutrients and an environment for plants.
Soil forms as rock is broken down by weathering and mixes with other materials on the surface.
Soil is constantly being formed whenever bedrock is exposed.

4. Soil Composition Composition of Soil
Organic Matter 5%
Air 25%
Water 25%
Silt 18%
Sand 18%
Clay 9%
Composition of Soil
Soil is a mixture of rock particles, minerals, decayed organic material, air and water.
The type of rock particles and minerals depend on two factors; (1) the bedrock that was weathered and (2) the type of weathering.
The decayed organic material in soil is called humus (formed from decaying plants and animals).

5. Observing Soil A Horizon B Horizon C Horizon
When we take a sample of soil, very often we take a “core” sample.
A Horizon
B Horizon
This is a cross sectional view of the soil, usually obtained by drilling into the ground and removing just a small cylinder of soil.
C Horizon
Unweathered Bedrock

6. Soil Horizons
A soil horizon is a layer of soil that differs in color and texture form the layers above or below it.
The A horizon is made up of topsoil - a crumbly, dark brown soil that is a mixture of humus, clay and other minerals.
The B horizon is often called subsoil – usually consisting of clay and other particles washed down from the A horizon, but little humus.
The C horizon contains only partially weathered rock.

7. Need to Know
-Dissolved minerals move down into the lower horizons through a process of leaching.
-Litter is the leaves, twigs and other organic(living) material that can be changed to humus.
Soil Profile is all the different horizons.