Transcript Soils

Soils
Earth’s Changing
Surface
Review
 Weathering
– breaks down rock
– Mechanical
– Chemical
 Erosion
– removes the rock particles
What is soil?
 The
loose, weathered material on
Earth’s surface in which plants can
grow.
Soil
 Bedrock
- the solid layers of rock
beneath soil.
Soil Composition
 Mixture
of rock particles, minerals,
decayed organic material, water, and
air
 Humus – decayed organic material in
soil
Soil
 Fertility
of Soil – measures how well
the soil supports plan growth.
– Rich in humus has high fertility
 Why
does fertility of soil matter?
Soil Texture
 What
does soil feel like?
 Sand feels coarse and grainy
 Clay feels smooth and silky
 Soil
texture depends on the size of
soil particles.
Soil Particle size
Clay
Silt
Sand
Gravel
Less than Less than Less than 2 mm and
1/256 mm 1/16 mm 2 mm
larger
Loam
 Soil
that is made up of about equal
parts of clay, sand, and silt is called
loam.
Soil Formation
 Forms
as rock is broken down by
weathering and mixes with other
materials on the surface.
Soil Formation
 Soil
Horizons
– A layer of soil that differs in color and
texture from the layers above or below
it.
Soil Horizons
A Horizon
 Topsoil
– a crumbly, dark brown soil
that is a mixture of humus, clay, and
other minerals.
 Develops as plants add organic
material to soil and plants weather
rock.
B Horizon
 Subsoil
– clay and other particles
washed down from the A horizon,
but little humus.
Soil Types
 Thousands
of different types of soil
in U.S. alone
 Classified based on climate, plants,
and soil composition.
Living Organisms in Soil
 Some
soil organisms make humus
 Some soil organisms mix the soil and
make spaces in it for air and water.