Download The Nature of Soil

The Nature of Soil
Essential Question:
What are the characteristics of soil?
How does the composition of soil vary?
What is Soil?
Soil is the loose, weathered material on
Earth’s s surface in which plants can grow
 Soil is created from broken down bedrock
 Bedrock is the solid layer of rock beneath
the soil
 When this rock is exposed, it gets weathered
or broken down into small particles that
forms soil

What is soil made up of?

Soil is made up of:
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Rock/mineral fragments
Decayed Organic matter
Air
Water
Rock/Mineral fragments are broken down into small particles
such as clay, silt, and sand
 Most decayed organic material comes from plants, but also
from animals when they die
 Eventually, this turns into humus, a dark-colored substance
that forms as plants and animals decay
 Humus contains nutrients that plants need to help them
grow
 Good soil has an equal mix of humus and weathered rock

Different types of Soil:
Soil texture (how it feels) can vary
depending on the particle size in the soil
 Sand feels coarse and grainy, while clay feels
smooth and silky
 Soil texture is important for plant growth:

◦ Sandy soils allow water to quickly drain, so plants
may not get enough water
◦ Clay soils hold a lot of water, so plants may drown
from too much water

Good soil should have equal parts of sand, silt,
and clay
How does soil form?
Soil forms as rock is broken down by
weathering and mixes with other material on
the surface.
 Soil is constantly being formed whenever
bedrock is exposed and weathered.
 Plants and animals add organic matter to rock
fragments
 Organic Matter is the remains of once
living organisms (plants and animals)

What is a soil profile?
As soil develops it forms layers known as
horizons
 Horizons are the different layers of soil
that differs in color and texture from the
layer above or below it
 All of the horizons together form a soil
profile

What is a Soil Profile?
O Horizon: layer of loose leaves and organic
debris at the surface of the soil
A Horizon: the top layer of soil, usually covered
with litter, or leaves, twigs, and other organic
material
B Horizon: the subsoil layer. Lighter in color due to
less humus and is less fertile.
C Horizon: the parent rock. Mostly weathered rock
and is bottom of the soil profile. It is most like the
bedrock material.
Bedrock: solid rock below soil
What is Leaching?
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Leaching is the removal
of minerals that have been
dissolved in water
When it rains, the water
picks up minerals and
carries them down from
the A Horizon to the B
Horizon.
C Horizon will hardly
ever have minerals in it
How do living organisms affect soil?
Some organisms make humus, the material
that makes soil fertile
 Other organisms mix the soil and make space
for water and air
 Plants contribute most of the organic remains
that form humus

◦ Litter is the loose layer of dead plant leaves and
stems of the soils surface

Decomposers are the organisms that break
down the remains of dead organisms (fungi,
bacteria, worms, etc)
What factors affect soil?

Factors affecting soil formation include:
◦ Climate
◦ Slope of land
◦ Types of Rock
◦ Types of Vegetation
◦ How long the rock has been weathered