Download Soil Formation and Composition

Soil Formation and
Composition
Biotic (living)
Abiotic(nonliving)
1. Make a table and list 5 examples of each
Soil Formation
Soil is the loose, weathered material on
Earth’s surface in which plants can
grow. It is formed wherever bedrock is
exposed.
Bedrock is the solid layer of rock
beneath the soil. It weathers when it is
exposed at the surface.
Soil Composition
Soil is more than just weathered rock.
Soil is a mixture of rock particles, minerals, decayed organic
materials, air, and water.
All soil is NOT the same - it depends on the bedrock that it was
weathered from and the type of weathering.
The dead organic material is broken down by decomposers to
form humus by decomposition.
Humus helps create spaces in soil for air and water.
Soil Formation and Composition
2. Draw the flowchart and fill it in as you go through it.
Water
Oxygen
Acid
Carbon dioxide
Living organisms
Wind Heat
Rain
Cold
Hail
ice
Mechanical
Rock
weathering
Smaller rock
particles
Chemical weathering
Soil
Mix with other
materials on the
surface
Particles with
different mineral
make up
Soil Texture
Soil texture depends on the
size of the individual soil
particles.
Soil particles range in size
from gravel to clay particles
too small to be seen by the
unaided eye.
The sand, silt, and clay shown here have been enlarged.
Soil Texture and Plant Growth
 Soil that is mostly clay is heavy
and dense which allows them
to hold a lot of water. Is this
good? No, plants may “drown”
from a lack of air.
 Sandy soil has a coarse texture
and water will drain quickly. Is
this good? No, plants may die
from a lack of water.
 Loam - The perfect soil.
“Permeable” is “Porous,” but
“Porous” May Not Be “Permeable”
 A pore is a space in rock, soil, or sediment that is
not occupied by mineral matter and that allows the
passage or absorption of fluids.
 The word comes from Latin porus, Greek poros,
where it means “passage.” A thing that is porous is
having pores, and porosity is the condition of being
porous.
Porosity is the ratio of the
volume of openings (voids)
to the total volume of
material. Consists of the
spaces between the grains
Permeability is a measure of the
ease with which fluids will flow
though a porous rock, sediment, or
soil.
The larger the pore space or the
greater their number, the
higher the porosity.
Although a rock may be highly
porous, if the voids are not
interconnected, then fluids within
the closed, isolated pores cannot
move.
The more tightly packed the
grains are, the lower the
porosity.
Soil Horizons
A soil horizon is a layer of soil that differs in
color and texture from the layers above or
below it.
They form over long periods of time. Think
centuries not decades.
It can take a hundred years for just a few
centimeters of soil to form.
Soil Horizons - C
The C horizon forms 1st
as bedrock weathers and
rock breaks up into soil
particles.
Soil Horizons - A - Topsoil
The A horizon develops from the C horizon
when plant roots weather the rock mechanically
and chemically.
Plants also add dark,
organic material to
the soil that is a
mixture of humus,
clay, and other
minerals
Soil Horizons - B - Subsoil
The B horizon develops as rainwater
washes clay and minerals from the A
horizon to the B horizon. Contains little
humus.
Rate of Soil Formation
Depends on the climate and type of
rock.
Occurs most rapidly in warm, wet
climates.
Limestone weathers more quickly than
granite in warm, wet climates.
Soil Horizons
3. As the topsoil and subsoil develop, what happens to
the bedrock?
4. Make a sketch of the three horizons and label each.
5. Which living things
contribute most of the
organic materials that
form humus?
6. How do
decomposers
contribute to the
formation of soil?
Life in Soil
The leaves, roots, and
stems of plants are a major
source of humus.
7. What role do
earthworms play in the
formation of soil?
8. Which organisms break up hard, compacted soil and mix humus through it?
 Fertile soil is rich in
nutrients that plants need,
such as nitrogen and
phosphorus.
 As plants shed leaves they
form a loose layer of litter
on the ground. Dead
plants add to litter and
over time decay to form
humus.
 Burrowing animals break
up hard, compacted soil
and add nitrogen when
they excrete waste.
Life in Soil
Main Decomposers
Fungi - molds & mushrooms,
grow on and digest plant
remains
Bacteria - microscopic, attack
dead organisms and their
waste
Protists
Earthworms - mix humus to
aerate the soil. They also eat
soil and eliminate it as waste
that are enriched in nutrients.
Soil Formation and Composition
9. Draw the
flowchart in your
notebook and fill
in the blanks.
consists of
is made of
above the
is made of
above the
is made of
above the