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Soil
Science
“Land, then, is not merely soil; it is a fountain of energy
flowing through a circuit of soils, plants, and animals.”
- Aldo Leopold, A Sand County Almanac, 1949
The Rock Cycle
IGNEOUS
ROCK
SEDIMENTARY
ROCK
METAMORPHIC
ROCK
SEDIMENT
Melt
Erode & Weather
MAGMA
What is SOIL????
The relatively thin surface layer of the Earth’s crust consisting of mineral and organic matter.
Soil is not DIRT!
Q: What’s the difference
between soil and dirt?
A.Location,
location, location!
Dirt is found under your nail,
soil is found beneath your feet
The 5 Soil-Forming Factors
• climate (water, wind, temperature)
• biology (macro- and microorganisms, plants)
• relief (topography)
• parent material (rocks/minerals)
• time
Which is the MOST important??
CLIMATE!!!
Formed from parent material (bedrock) that’s slowly broken down through
weathering processes.
What is Soil? How would you describe soil?
Color • Texture
Texture
http://www.mii.org
Why the color? http://www.msstate.edu
http://www.cs.cmu.edu
Hematite:
red
Goethite:
yellowish brown
Ferrihydrite:
reddish brown http://www.beg.utexas.edu
Calcite:
off white
http://www.pitt.edu
Quartz:
white
Organic matter:
black
http://www.organicgardeninfo.com
• Did you know ?????? There are more than 20,000
different soil types in the
United States
Soil Color Variation
Soil Composition
Water
(~25%)
Air
(~25%) Mineral
(~45%)
Humus
(~5%)
Mineral matter comes from parent material
Air & Water percents are interchangeable
Humus is organic matter!
Soil Composition continued…
Mineral Matter – Provides nutrient
minerals for plants – Provides pore space
for water & air
Older soils are: – More weathered – Lower in certain essential nutrient
minerals
Humus: black/dark brown organic material remaining after decomposition – Leaf litter, animal dung, & decaying organisms – Increases the soil’s water-holding capacity by acting
like a sponge
POROSITY = amt of soil pore spaces
Pore spaces occupy ~50% of a soil’s volume – Filled with varying proportions
of soil water and soil air
Soil Air contains the same gases as atmospheric air, but in different proportions. – More CO2 and less O2 (from organism respiration) – Some bacteria need nitrogen
(why??) – The CO2 can accelerate
weathering • CO2 + H2O H2CO3
(carbonic acid)
Porosity
Soil Composition continued…
Soil Composition continued…
As water infiltrates the soil, it can carry dissolved materials with it.
Leaching: Removal of dissolved materials from the soil by water percolating downward
Illuviation: Deposition of leached material in lower layers – Some substances completely leach out of
the soil because they’re so soluble that they migrate right down to the groundwater.
Observe this SOIL PROFILE through soil
Soil layers are
horizons and
assigned letters
O: Organic material (may be absent)
A: Topsoil - Organic
material & mineral
grains
E: Leached zone (may be absent)
B: Subsoil – rich in
clay, iron, aluminum
C: Weathered bedrock
R: Bedrock (parent material)
Soil Pedon
A horizon: organic coatings
B horizon: Iron coatings
C horizon: little coating
Soil Color by Horizon
http://nesoil.com
Fun Fact: It takes
100 to 600 years to
form an inch of
topsoil.
Soil Color – Variation by Geography
Red soils:
Southeast US
Soil Color – Variation by Geography
Brown/black soils:
Midwest
http://www.scienceclarified.com
Soil Color – Variation by Geography
White (gypsum) sands:
New Mexico
Soil Organisms
Ex: bacteria, fungi, algae, microscopic worms, protozoa, plant roots, insects, earthworms, moles, snakes, groundhogs, etc.
Soil organisms provide several Ecosystem Services (important environmental functions). – maintaining soil fertility
– preventing soil erosion
– breaking down toxic materials
– cleansing water
– affecting atmospheric composition
Earthworms & Ants: – Cycle minerals – Aerate the soil – Decomposing corpses
contribute organic matter – Assist plants in reproduction
by burying seeds
Mycorrhizae – Symbiotic relationship
between fungi and the roots of vascular plants
– Fungus absorbs nutrients from the soil, and provides it for the plant.
– Plant produces food (photosynthesis), and provides it for the fungus.
Dr.
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Coll
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Physical Soil Properties
PHYSICAL properties:
Texture (%sand, silt, clay)
Porosity & Permeability
Ionic Charge
Texture is determined by its % sand, silt, and clay.
Texture determines the type of soil, and the soil’s properties.
Physical Property: Texture
Loam: ideal for
agricultural soil
Soil Components
http://school.discoveryeducation.com
Q: What did the shy
pebble say to the big
rock?
A. Do you think I’ll ever be
a little boulder?
Fine Texture - Clay
https://www.soils.org/lessons
Course Texture - Sand
https://www.soils.org/lessons
Soil Texture The relative portions of sand, silt, and clay-sized particles
Sand: 2.0 – 0.05 mm
Silt: 0.05 – 0.002 mm
Clay: < 0.002 mm
B
Soil Texture Diagram Practice What type of soil has:
1. 20% clay, 40% silt, 40% sand
2. 40% clay, 10% silt, 50% sand
3. 30% clay, 60% silt, 10% sand
Find the % of each particle at:
1. A
2. B
3. C
A
C
60%clay, 20%silt, 20%sand
30%clay, 40%silt, 30%sand
10%clay, 30%silt, 60%sand
(1) Loam
(2) Sandy clay
(3) Silty clay loam
Property Sand Silt Clay
Water holding Low Med-high High
Aeration Good Med Poor
Nutrient supplying Poor Med-high High
Pollutant Filtering Low Med High
Why is Soil Texture Important?
Physical: Porosity & Permeability again… Think it is important??
Definition?
– amt of soil pore spaces
Porosity
Permeability Definition?
– ability of water to percolate through
____ porosity = ____ permeability
Physical: Ionic Charge
Soil minerals are often present as ions.
Minerals ions are either positively or negatively charged.
Clay particles have mostly negative charges on their outer surfaces.
– Positively charged mineral ions are attracted to the soil particles and are held for plant use.
• potassium K+ and magnesium Mg2+
– Negatively charged mineral ions are repelled by the soil particles and are washed away from roots.
• nitrate NO3-
Physical Characteristics (review)
Why would 100% sand be undesirable for plants?
Why would 100% clay be undesirable for plants?
Answer SAND / SILT / CLAY for the following: – A soil with a lot of _____ would have good drainage,
but poor nutrient-holding characteristics.
– A soil with a lot of _____ would have poor drainage, but good nutrient-holding characteristics.
– A soil with a lot of _____ would have low porosity.
– A soil with a lot of _____ would have high permeability.
Two soil cores
Bottom of core
contains filter
paper and
cheese cloth
Demonstration
Two unknown
liquids
Pollutant #1
Pollutant #2
Demonstration
Liquids passed
through soil
cores
Leachate
collected below
What did you observe?
Demonstration
What happened to
the original liquids?
What does
a change or no change
in color mean?
To what extent did the
soil contribute to
this change?
Soil Soil
Adsorption of Organic Dyes
S+
N
NN
Cl-
O
SO
O
HO
OH
Cl
Cl
Chlorophenol red
Methylene blue
CR-
MB+
Soil
CR- CR-
CR-
CR-
MB+
MB+
MB+ MB+
MB+
MB+
MB+
MB+ MB+
MB+
Chemical Property: Acidity
Most soil pH is 4-8. Plants are happiest at 6-7.
Plants are affected by soil pH. (1) The solubility of certain nutrient minerals varies with
differences in pH • Low pH = Al & Mn are more soluble, and can be absorbed in
toxic amounts.
• High pH = some salts are less soluble, and are less available to the plants.
(2) Soil pH affects the leaching of nutrient minerals. • Acidic soil = positively charged ions are less soluble and are
unavailable for plants.
Soil Conditioners (Lime) CaCO3 or MgCO3
Soil amendment / conditioner… not a fertilizer!
Important functions: 1. Corrects soil acidity
2. Adds important plant nutrients— Ca & Mg
3. Reduces solubility & toxicity of certain elements in the soil
Al, Mn, Fe
This toxicity could reduce plant growth under acid conditions.
4. Promotes availability of major plant nutrients.
Zn, Cu, P
5. Increases bacterial activity & mutualistic relationships.
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Soil Conditioners (Compost)
Decayed organic matter
Replaces some nutrients
Improves soil structure
– The soil becomes more porous, increasing air circulation and the ability of the soil to absorb and hold moisture.
– Makes the soil more spongy!
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Soil supports
life
http://www.Istockphoto.com
L. Clarke and Corbis, 2008
Why is Soil Important?
Fun Fact: 1 teaspoon of
good soil contains more
than 1 million bacteria!
Fun Fact: There are more
living organisms in a cubic
foot of soil then all of
China!
Fun Fact: There are more
living organisms in a cubic
foot of soil then all of
China!
Dr. Greg Pillar, Queens College
Soil stores important nutrients
http://www.lesco.com/
Phosphorus (P)
Nitrogen (N)
Potassium (K)
Calcium (Ca)
Magnesium (Mg)
Dr. Greg Pillar, Queens College
Soil Holds Water
Dr. Greg Pillar, Queens College
Soil provides support for buildings
http://www.pbase.com Dr. Greg Pillar, Queens College
Soil
Soil filters, buffers, detoxifies….
http://extension.missouri.edu Dr. Greg Pillar, Queens College
Inputs/Outputs
Are these Soil Inputs or Soil Outputs?
Mass Movements (landslides, etc)
Precipitation
Parent Material
Leaching
Infiltration
Uptake by Plants
Organic Matter
Energy
I
I
I
I
O
I
O
O
Transfers/Transformations Recall:
Transfers simply MOVE things… they reorganize the soil!
Transformations CHANGE things… they alter the soil’s makeup in some way.
Are these Soil Transfers or Transformations?
Decomposition Erosion
Deposition Weathering
Nutrient Cycling
transfer
transfer
transformation
transformation
transformation
Soil Pollution Part II
Soil Pollution = any physical or chemical change in soil that adversely affects the health of plants and other organisms living in and on it.
Many soil pollutants… – ARE MOBILE!
• move into groundwater, surface water, or air
– ARE PERSISTENT! • seep into tiny cracks called micropores and adhere to the
soil particles
– COME FROM FERTILIZERS / PESTICIDES! – CAN ACCUMULATE!
Sustainable Agriculture practices can help… …more on this later…
Salinization of Irrigated Soil Irrigation water soaks through the soil area where the plant roots grow, adding to the existing water.
The additional irrigation water causes the underground water-table to rise, bringing salt to the surface. When the irrigated area dries & the underground water table recedes, salt is left on the surface soil.
Each time the area is irrigated this salinity process is repeated.
ALL IRRIGATION WATER CONTAINS SOME DISSOLVED SALTS.
Salinization of Irrigated Soil
Extra water flows through the
soil, mixing w/ salt underground,
and bringing it to the surface.
This is in Australia – occurred not from
irrigation, but from lack of water-loving plants.
Irrigation salinization is basically
the same concept, and the ground
would look just like this.
Effects of Salinized Soil on Plants
Normally, the water
concentration inside
plant cells is lower than
that in the soil resulting
in a net movement of
water into the root cell.
When soil contains a
high amount of salt, its
relative water
concentration can be
lower than the water
concentration inside
cells. This causes water
to move out of the roots
into the soil, even when
the soil is wet.
Soil Remediation Until recently, the only way to remove soil contaminants was to…
Why is this a bad thing to do?? – Impractical, kills all beneficial organisms,
creates waste, expensive…
DIG IT UP
& INCINERATE IT!
Soil Remediation Techniques
Dilution – Add lots of water; leach out pollutants
Vapor extraction – Inject air into soil to remove volatile organic
compounds
Bioremediation – Use microorganisms to degrade organic
contaminants (oil, sludge)
Phytoremediation – Use plants to absorb contaminants such as salts or
heavy metals.
Extraction well
Pollutant low sorption potential = not attracted to soil
easily washed away Pollutant high sorption potential = not easily washed
Water
DILUTION: Pump & Treat / Soil Washing
GROUND LEVEL
… But what’s the problem here?
Source Identification and Removal !!!!
How can this problem be fixed???
GROUND LEVEL
Bioremediation (Bioventing)
12 - 32
15.06.b
Activities that Threaten Soil
Removing vegetation
Overgrazing
Soil contamination
Erosion Control
• Agricultural: 10% of the worlds best agricultural land damaged due to soil erosion and overuse over last 50 years.
- contour plowing
- no-till agriculture (no plowing)
- terracing slopes
- crop rotation - fallow
Preventing Soil Erosion
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