GEO 101, Tuesday, April 22, 2014
More than you ever wanted to know about soil
If you did not take Exam 3, please see me or
email me after class, you need to take it before
Thursday.
Dirt: loose earth
Soil ≠ Dirt
any foul or filthy substance
soil that is out-of-place
Soil: that portion of the earth that supports growth
of plants and has developed over time via
soil forming processes
Soil varies geographically
Processes in the soil
Soil has layers called “horizons”
Addition
deposition of material on surface
gain in organic matter
True Soil
A
Regolith
Transformation
weathering of rock
decomposition of organic matter
O
E
Simplified Soil Profile
A-horizon
Zone of leaching (depletion)
“eluviation”
B-horizon
Zone of accumulation
“illuviation”
Depletion
loss of dissolved or suspended matter
C-horizon
Altered parent material
Translocation
vertical movement from one part of soil to another
D (or R)-horizon
Unaltered parent material
Size of individual soil particles
Inorganic
Material
Clay
Silt
Elements of
earth’s crust,
comes from
broken up
rocks
Sand
Pin head
1
Water in the soil
Electrical
charges hold
How is it held?
Water held by
capillary action
is available
to plants
How much can soil hold?
Gravitational
(drains through)
What makes it available?
Soil
particle
water tightly:
adhesion
Capillary water
Deep watering encourages
plants to grow roots down
into capillary zone.
Shallow watering
encourages shallow roots.
Capillary fringe: water rises by
capillary action into this zone
Water table:
top of saturated zone
How much water can soil hold and yield?
Small particles
High porosity
Low permeability
Large particles
Low porosity
High permeability
Depends on:
Porosity = volume of spaces between particles
Permeability = how easily water can move through soil
2
Available water held between field capacity and wilting point
Low porosity
High permeability
Water held loosely
Percentage water by weight
Clay
High porosity
Low permeability
Water held tightly
Available water
Adhesion water
tightly held
Sand
4
5
7
8
9
Acid
Nutrient
availability
10
Ammonia
Baking soda
6
Loam (mixture of different size particles)
High porosity
High permeablity
Best for plants
43%-32%=11%
water
Milk of Magnesia
25 to 30%
water
Normal rain
Vinegar
3
Clay
Loam
12%-3%=9%
water
Lemon juice
Sand
Gravitational
water drains
away
Water is
important
carrier of
nutrients.
Air in soil
Occupies same pore space as water
Some air is critical
11
Basic
(Alkaline)
Nutrients
are most
available
when soil
pH is
neutral
Plant growth
Organic matter in soil
Undecomposed plant material
Bacterial transformation  humus
Improves soil structure
Improves water storage capacity
Provides food for earthworms and microbes
Restores minerals to soil
What plant community uses is recycled,
rest is eventually leached away
3
Do teacher evaluations here
Please use a blue or black ink pen, not a pencil.
Soils described by 3 properties
1. Color
Mark answers with an X in the box.
If you make a mistake, darken in the whole “wrong”
box and mark an X in the correct box.
Answer questions on front and back.
Remember to fill in the comment section.
Also use this if you want to express yourself further
about me or any other professor you have
www.ratemyprofessors.com
2. Texture =
3. Structure
Shape of clumps (peds)
how they are arranged
% sand
% silt
% clay
Columnar
Blocky
Platy
Granular
Pedology:
study of soils
Platy
structure can
cause
“hardpans”…
impermeable
layers
Describe
color
texture
structure
of each horizon
4
In many places there is no true soil
Soil Formation Factors
Climate
Organic activity
Relief
Parent material
Time
“CLORPT”
Climate’s effects on soil
Global climate map looks like global soil map
Soil Profiles
A
Arctic soil
B
Temperature and water
affect the rate of chemical
reactions.
Breakdown of parent
material rapid in warm wet
climates.
Climate’s effects on soil
Global climate map looks like global soil map
Climate affects organic material in soil, function of
production versus decay rates & vegetation type
Organic raw material production in humid climate
Destruction of org. matter in aerobic environment
Tropical soil
C
Soils of the World
Degrees F 
D
5
Vegetation type affects organic matter in soil
Organic matter in soil, metric tons per hectare
Forest standing
crop ≈ 202 tons
Prairie standing
crop ≈ 7 tons
180
240
360
150
90
Total in soil = 184 tons
excluding large roots
Total in soil = 345 tons
Relief: difference between highs and lows
shape of the land
Plants control nutrients...what they use is recycled
If nutrient not used by plants, it is leached from soil if
there is enough precipitation.
Organic activity also includes soil microbes, fungi,
worms, burrowing rodents, ants
Thin soil due
to erosion
Well
drained
soil on
hilltop if
not steep
Deep, poorly
drained soil
Parent Material affects soil
Time
Takes hundreds –
thousands of years soil
Young soils have poorly developed
horizons
Mature soils have well developed
horizons
Old soils have overdeveloped “problem”
horizons with dense crusts or
hard-pans in “B”
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