Transcript 0.002 mm
Soil Composition –
What Dirt is Made of
Rock particles
Minerals
Dead, decaying plant and
animal material (humus)
Bacteria, fungi and other
microbes
Worms and insects
Air
Water
1. Why is Dirt Important?
Soil contains the minerals and
nutrients that plants need to
grow.
Soil provides shelter for
plants and animals.
Soil absorbs, stores, and
filters water.
Profile = Layer of soil also called horizon.
Litter (hummus) – dead leaves, grass,
and waste material
A. Topsoil – rock pieces, nutrients,
water, air and decaying matter (most
animals live here)
B. Subsoil – rock fragments, water and
air. (less plant/animal matter)
D. Bedrock – rock that makes up
Earth’s crust.
Example Sizes:
Particle size affects:
PERMEABILITY.
How freely water can flow/move
through soil is called
AS soil particle size increases,
water flow increases meaning that
permeability increases.
High permeability means soil
CAN’T hold moisture.
Soil Texture -
A way of classifying soil that
depends on particle size.
Examples: loam, sand, clay, silt
Most plants grow best in loam
soil = sand/silt/clay
Texture affects the amount of
water a soil can hold.
Packed soil, like red clay, does not
let water move through very
easily.
One grain of clay is SUPER small.
Loose soil, like gravel, lets water
pass through very easily.
–
One grain of gravel is a BIG rock.
pH of Soil -
Soils can be basic or acidic.
Most plants grow best in soils
with a pH between 5-7
If soil is too acidic, lime can be
added to make it more basic.
Soil Formation:
Soil forms as rock is broken
down by weathering and then
mixes with other materials on
the surface of Earth’s crust.
Types of weathering: heat,
cold, water (rain) and yes, air
(O2 and CO2).
How do rocks break into
smaller pieces?
Freezing and thawing breaks apart
bedrock
Plant roots wedge between rocks and
break them
Acid rain/chemicals break down rocks
Animals help grind rock into smaller
pieces.
Break down of dead organisms add to the
mixture.
Nutrient Depletion:
Soil becomes less fertile –
If farmers replant crops over and
over with out fertilizing soil, the
crops use nutrients faster than
decomposers can supply.
Erosion:
Movement of rock and soil by wind,
water and gravity.
Are all soils the same?
Soil type affects which type of
plants/animals can live there.
Factors that affect soil type are:
Types of plants
Climate
Time
Slope of the land