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Topic 5 Part 1
soil
What is soil and why do
we care about it?
 complex mixture:
 weathered mineral
materials from rocks
 partially decomposed
organic molecules
 Ecosystem services
Soil formation
 Many factors contribute to this LONG process
 ClORPT
 Help determine soil type
Temperature and Moisture
influence the speed of chemical
reactions, which in turn, control
how fast rocks weather and dead
organisms decompose.
Soils develop fastest in warm,
moist climates, and slowest in
cold and arid ones.
The shape of the land and the direction in
faces makes a difference in how much
sunlight the soil gets, and how much water it
keeps.
Deeper soils form at the bottom of a hill than at the top because
gravity and water move soil particles down the slope.
Just like you inherited some characteristics
from your parents, every soil inherits traits
from the material from which it formed.
Soils that form in limestone bedrock are rich in calcium,
Soils that formed from materials at the bottom of lakes
are high in clay.
Time
Older soils differ from younger soils because they
have had longer to develop
EXAMPLE: In the Northern U.S., soils tend to be younger, because
glaciers covered the surface during the last ice age, which kept soils
from forming. In the southern U.S., there were no glaciers. There,
the soils have been exposed for a longer time, so they are more
weathered.
Soil Texture
 Ratio of soil particle size determines some soil
properties
Determining soil type
Soil Properties: Porosity
 Affects water infiltration, water holding capacity,
aeration, workability
Soil Properties: Chemical
 Cation exchange capacity (aka nutrient holding
capacity)
SOIL Profile
Soil Profiles in Different Biomes
mollisols
aridisols
Mosaic
of closely
packed
pebbles,
boulders
Alkaline,
dark,
and rich
in humus
Weak humusmineral mixture
Dry, brown to
reddish-brown, with
variable accumulations
of clay, calcium
carbonate, and
soluble salts
Desert Soil
(hot, dry climate)
Clay,
calcium
compounds
Grassland Soil
(semiarid climate)
Soil Profiles in Different Biomes
alfisols
oxisols
Forest litter
leaf mold
Acidic
lightcolored
humus
Humus-mineral
mixture
Light, grayishbrown, silt loam
Iron and
aluminum
compounds
mixed with
clay
Tropical Rain Forest Soil
(humid, tropical climate)
Dark brown
firm clay
Deciduous Forest Soil
(humid, mild climate)
Soil Properties: Biotic
 surface = algae
 top few cm of soil =
 bacteria & fungi
 roundworms, segmented
worms, mites, insects
 farther down: burrowing
animals--gophers,
moles, insect larvae,
worms
 even farther: some
plant roots
Soil Community
Soil Community -- Mycorrhizae
mycorrhizal symbiosis mutualism between plant
roots & fungi
Redwood seedlings with (right)
and without (left) mycorrhizae.
Pine seedling showing how
mycorrhizal roots from one
tree spread to inoculate other
tree roots.