Download Nature of the parent material will greatly influence time it takes to

Weathered Rocks from the
lithosphere are the parent
materials for soils
Types of Parent Material
•
•
•
•
•
•
Residual
Colluvial
Water
Ice
Wind
Organic material
Residual:Parent material in
place
The Castelleia series (CO)
consists of well drained soils
formed in thick
noncalcareous, stony
medium to moderately fine
materials weathered locally
from quartz, latite, or
similar rocks.
Nature of the parent
material
will greatly influence time it
takes to make soil and the
nature of the soil that is
formed
Colluvial debris:
Rocks that have fallen down
hills
Arawak series, US Virgin Islands
The Arawak series consists
of shallow, well drained,
slowly permeable soils on
summits and side slopes of
limestone hills and
mountains. They formed in
material weathered from soft
limestone bedrock.
1
•
Water:Alluvial
deposits
Sediment that is deposited by rivers
•
Water:Alluvial
deposits
Sediment that is deposited by rivers
Water:Marine (sediments deposited
by oceans)
Forkwood soil, Wyoming
The Forkwood series consists of very deep, well drained soils
formed in slopewash alluvium derived from interbedded shale
and argillaceous sandstone.
Pamunkey soil, Virginia
Soils of the Pamunkey series are very deep and well drained.
They formed in Piedmont and Coastal Plain sediments.
2
Water:Lacustrine (materials
deposited by lakes)
Glacial till:
Material
transported
by glacial ice
Pleistocene Epoch
2 million years
Glacial till: Material
transported by glacial ice
Glaciers - Loess
• Summer
– Melt water from glaciers would carry
fine particles or sediment
Eolian:
Materials transported by wind
Loess
Loess - Illinois
Peoria 25,000 - 12,000
• Winter
– Water would dry out leaving dry
sediment
– Winter winds would transport the
sediment
Roxanna 60,000 - 26,000
3
Loess - China
Loess - Washington
Lanzhou - 440,000 sq km
50 - 300 meters deep
From Gobi desert
Paloose hills in
eastern Washington
Soil series
Wallawalla
Paloose
Athena
Eolian:
Materials transported by wind
Volcanic ash
Organic:Wet areas where
accumulation> decomposition
Peat bogs
(1)Parent materials + 4 other
factors of soil formation
•
•
•
•
Climate
Topography
Time
Biota
4
We talked about rocks, rock
weathering and parent
materials
How soil is formed
Factors of soil
formation
Different scenarios
For soil formation:
Soil Science Taxonomy
• Soil as a natural body
• Each soil as a unique individual
– Developed as a result of the 5 factors of
soil formation
Solum
Regolith
Soil formation is,
simultaneously
O
Regolith-
A
weathered rock
and soil that
overlays bedrock
Solum - portion of
the regolith that
shows the
development of
layers called soil
horizons
E
B
C
•
•
•
•
•
Breakdown of old
Synthesis of new
Losses
Additions
Translocations
X
Y
Bedrock
(1)Parent materials + 4 other
factors of soil formation
•
•
•
•
Climate
Topography
Time
Biota
Climate
• Moisture
– Quantity
– Intensity
– distribution
• Temperature
Can be interrelated and interact
5
Rainfall: Intensity and
duration
Role of water
• Essential for chemical weathering
• Transport materials through horizons
• Determine type of plant cover
Effective precipitation
• Water has to go
into the soil
Temperature
• Rate of
biological
activity
Rate of
chemical
reactions
– Infiltration - not
overland flow
– Rainfall
exceeds
evaporation
Soil Development Time Line
Topography
Effect of Time
Same parent material, same climate
Organic Matter Accumulation
Structural
Development
CaCO3
Accumulation
Unweathered Loess
CaSO4
Accumulation
Time
Location, location, location
6
Toposequence
Excessively
drained
Well
drained
Poorly
drained
Biota - plants
Very poorly
drained
Type of plant :
Grass
Soil Profile
A - mollic horizon
• Dense root system
• Above ground
foliage will die
annually
• Grows where
moisture < trees
• Thick A horizon
Tree - deciduous
• Leaves high in cations (Ca, Mg, Fe..)
• Annual leaf fall
• Well developed A horizon
– Decomposed OM
– High nutrients
Deciduous •
•
•
•
Larger A horizon
More cations
Less acidic
More clay
translocation
7
Coniferous
Acidic
Tree - coniferous
• Leaves low in cations
• Little leaf fall
Thin A
• Thin A horizon
E (eluviation)
– Oi - slightly decomposed
• E horizon
– eluviation
Animals
• Pedoturbation
– Animal burrows effectively mix soil from
different horizons
Animals
• Humans
– Agricultural
practices
– Accelerate soil
loss
– Accelerate soil
formation
Animals
• Earthworms
– Soil mixing
– Soil structure
– Soil aeration
Start with a pile of rocks
• Physical and chemical weathering
– Breakdown particles
– Change mineral structure
8
Plant starts growing
• Organic matter is added to soil
surface
• Root exudates further break down
minerals
When a plant starts growing
• Organic matter from plants is a
nutrient source for other organisms
First stage of
soil formation
• Increased organic
matter in A horizon
Next stage will involve
development of a B horizon
• Cations that have been solubilized
by plant exudates, microbial
activity,and acidification will start
moving lower into the soil
• Secondary clays have been
formed in A and are also moving
down the profile
Beginning of a
B horizon
• Dark A horizon
– Organic matter
– Clays
• Something below the
A that looks different
from the parent
material
• Parent material
9