Transcript Soil Formation

Soil
Formation
Soil Formation Vocabulary
Humus
 Horizons (A, B, C, R)
 Soil Profile
 Litter
 Leaching

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.
Soil Composition


Soil is a mixture of rock
Composition of
particles, minerals, decayed
organic material, air and water.
Silt 18%
The type of rock particles
and minerals depend on
two factors; (1) the
bedrock that was
weathered and (2) the
type of weathering.
Soil
Air 25%
Sand 18%
Water 25%
Clay 9%
Organic Matter 5%

The decayed organic material in soil is called humus
(formed from decaying plants and animals).
Observing Soil

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When we take a sample of
soil, very often we take a
“core” sample.
This is a cross sectional
view of the soil, usually
obtained by drilling into
the ground and removing
just a small cylinder of
soil.
A Horizon
B Horizon
C Horizon
Unweathered
Bedrock
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.
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.