SOIL: Make it Work for You!
We Study Soil Because It’s A(n)
Medium of crop
production
Great integrator:
all parts of ecosystem
Producer and
absorber of
gases
Snapshot of
geologic, climatic,
biological, and
human history
Waste decomposer
Medium for
plant
growth
Source material for
construction,
medicine, art, etc.
Home to organisms
(plants, animals and
others)
Essential natural resource
Filter of water
and wastes
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Soil Forming Factors
Biota
Parent Material
Topography
Climate
(The first four factors over) Time
These five factors work together to create a unique soil profile made of layers called
horizons.
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What is “Soil?”
 Each discipline defines soil in a different way,
depending on how soil affects it.
 “In an engineering sense, soil is the relatively loose
agglomerate of mineral and organic materials and
sediments found above the bedrock.”
• R.D. Holtz and W.D. Kovacs (1981)
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 Physical
Characteristics
 Soil
Texture,
Consistency, &
Structure
 Soil Compaction
(Bulk Density)
 Soil Moisture
 Nutrient
Characteristics (Soil
Chemistry)
 Chemical
bonding
 pH
 Cation
Exchange
Capacity (CEC)
 Nutrient Availability
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Physical Characteristics of Soil:
 Texture: the mineral components
 Consistency & Structure: How the
mineral components are put together
 Bulk Density
 Soil Moisture
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 Soil Texture:
 The way the soil “feels” is called the soil texture.
 Soil texture depends on the amount of each size of
mineral particles in the soil.
 Sand, silt, and clay are names that describe the
size of individual mineral particles in the soil.
Sand are the largest particles and they fell “gritty”
Silt are medium sized, and they feel soft, silky or
“floury”
Clay are the smallest sized particles, and they feel
“sticky”
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Soil Texture: Relative Size Comparison of Soil Particles
beachball
frisbee
dime
Silt
(feels floury)
Sand
(feels gritty)
(2.00 - 0.05 mm, USDA)
(2.00 - 0.02 mm, ISSS)
(0.05 - 0.002 mm, USDA)
(0.02 - 0.002 mm, ISSS)
Clay
(feels sticky)
(< 0.002 mm, USDA)
(< 0.002 mm, ISSS)
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Soil Texture Triangle
100
0
Triangle Key:
S = sand or sandy
Si = silt or silty
C = clay
L = loam or loamy
C
SiC
SC
CL
SCL
L
0
S LS
SL
SiCL
SiL
100
Si
100
0
% Sand
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Effects of Soil Texture:
 Soils are more cohesive when they have more fine particles




(Clays).
Soils are more loose when the have more coarse particles
(Sand).
Different combinations of coarse and fine contents produce
different soil textures.
A loam is a mixture of sand, silt and clay: sandy clay loam is
best in landscapes.
Many other inclusions, such as cobbles, boulders.
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 Soil Consistency
 Describes the general organization of the soil.

Hold a moist sample between the thumb and
forefinger, and gently squeeze it until it falls apart.
 The soil is classified by the following categories
• Loose: You have trouble picking out a single sample and the
structure falls apart before you handle it.
• Friable: The sample breaks with a small amount of pressure.
• Firm: The sample breaks when you apply a good amount of
pressure and dents your fingers before it breaks.
• Extremely Firm: The sample can't be crushed with your
fingers (you need a hammer!).
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Soil Consistence
Loose*
Friable
* Soils with “single grained” structure always have loose consistence.
Firm
Extremely Firm
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the shape that the soil takes based on
its physical and chemical properties. Possible choices of
soil structure are:
Soil Structure:
 With Structure:
 Granular
 Blocky
 Platy
 Prismatic
 Columnar
 Without Structure
 Single
Grained
 Massive
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Soil Structure:
 With Structure:
 Without Structure
 Single
Grained:
• beach sand
 Massive
• solid mass with no
shape
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Soil Structure: with Structure
Block
y
Granular
Columna
r
Prismati
c
Platy
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Soil Structure: without Structure
Single Grained
Massive
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Bulk Density: a measure of soil compaction
Sample is
made of
Solids and
Pore Spaces
1.33 gms.
1 cm. (so, there is 1 cubic
centimeter of soil)
To calculate Bulk Density:
Volume = 1 cm3
Bulk Density =
1.33
1
Bulk Density =
1.33 gms / cm3
Weight = 1.33 gms
Bulk Density =
Weight of Soil
Volume of Soil
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Bulk Density & Compaction Zones
Depth
Bulk Density
(grams / cm3
0 inches
1.43
7 inches
8 inches
9 inches
10 inches
1.90
1.87
Plow Layer
Compacted Zone
1.84
1.80
1.60
Uncompacted
subsoil
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Basic Soil Components
Pore Spaces:
location of air
and water
Soil Particles:
Mineral and
Organic
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 Soil Moisture: some terms and concepts

Field Capacity: water that remains in soil
beyond the effects of gravity.
 Permanent Wilting Percentage: amount of
water after the permanent wilting point is
reached.
 Available Water: amount of water in the soil
between the field capacity and the permanent
wilting percentage.
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Relationship between soil texture and water
availability
4
Inches
of
3
Water
Per ft. 2
of Soil
1
Sand Sandy Silt
Clay
Loam Loam Loam
Clay
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Soil at Different Moisture Levels:
At Saturation
Pore Spaces are filled with
water
At “Available Water
Water on soil
Pore Space particle surface
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Soil at Different Moisture Levels:
At Permanent Wilt
No water remains
attached to soil particles
Compacted
Pore spaces are collapsed
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Compacted Zone
Impermeable Layer
H2O
H2O
NonCompacted
Compacted
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Sand Over Clay
Impermeable Layer
H2O
H2O
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Clay Over Sand
Perched Water Table
H2O
H2O
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Soil Sandwiches
Wet & Dry Layers
H2O
H2O
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Soil Salads
H2O
Patchy Soil Moisture
H2O
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Summary of Water Movement:
 Rate depends on:
 pore
space (structure) and consitence
 particle sizes (texture) and particle size distribution.
 Changes in bulk density:
 changes
water movement (e.g. compaction).
 may result in perched water tables through creating
an impermeable layer.
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Surface Drainage (Run-Off)
 Severity of slopes
 Angle and length of slopes
 Soil or surface type
 Presence or absence of vegetation
 Total surface area of drainage basin
 Must
include structural surface area
 Structures modify soil saturation, contact
areas, and volume contact/unit area
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Controlling Surface Drainage
 Divert run-off from adjacent




sites
Stabilize slopes with synthetic
materials,
mulches or
vegetation
Break up straight line flows,
slows velocity
Construct sediment fences
Line drainage channels with
coarse
aggregates
 Contoured beds and or terracing
 Re-vegetation mats

Organic vs. synthetics
 Run strips parallel to slope
 Soil modifications;
 Replace high bulk density
soils
 Incorporate OM or
aggregates
 Break up soil surface crusts
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Altering Subsurface Drainage
 Deep plowing (sub-soiling) can damage tree
roots where landscape is established, utilities,
impractical for small sites
 Avoid abrupt changes in soil type
 Incorporate OM or large quantities of
aggregates
 Huge variety of drains
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 Large Subsurface Drains


Concrete pipes
• Usually for heavy traffic
or very large drains
• High handling and
transportation costs
Large diameter - 12” to 24”
diameter metal culverts
• Preferred under vehicular
traffic
• Damaged ends hinder
linking
• Expensive
 Smaller Subsurface Drains

Ceramic tiles, out moded
 Corrugated plastic pipe
• Cheap, light, flexible
• Perforated - areas of collection of
release
• Non-perforated - transport areas

Avoid clods contacting during
installation
• Cover on 3 to 4 sides with 3” to 4”
of aggregates
• Cover with back-fill, preferably
12”+
 Topsoil in non-roads, road
bed material in traffic areas
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French Drains
 Old-fashioned, but very effective
 Numerous variations;
 With
or without pipes
 Covered or exposed
 Often connected to the surface with water permeable
material
 Essentially a trench filled with aggregates
 Always slope to a lower elevation!
 Very useful for draining contained planting sites
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Soil Horizons:
 Horizon “A” = topsoil



Specified by texture, OM
content, available nutrients and
drainage characteristics.
Critical to landscape success.
Should be removed prior to
construction and stock piled on
site
• Incorporate 1/3 into sub-soils after
construction to create smoother
transition zone
• Sharp transition between topsoil
and subsoil creates perched water
tables.
 Horizon “B” = transition
zone

Constitutes much of the
exposed soil in areas where
construction has occurred and
in some formerly cultivated
portions of Ohio
 Horizon “C” = true subsoil


Little or no soil development.
Often contains accumulated
soluble salts, lime, etc. beneath
cultivated areas.
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Characterization and Sampling Options
Soil Pit
Exposed Profile (road cut)
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Soil Chemistry
 Chemical bonding
 pH
 Nutrient Availability
 Cation Exchange Capacity (CEC)
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 What is “chemistry?”

Elements: the simplest kind of matter. They cannot
be broken down into anything simpler.
 Elements can exist alone. Nitrogen (N),
Phosphorus (P), Potassium (K), Oxygen (O), are
elements and they can be made to exist alone, but in
nature they seldom do.
 Elements tend to combine with each other. These
are called “compounds.” When they combine, it’s
called a “chemical reaction.”
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 What is “chemistry?”
Chemistry is the study of the “how” and “why”
elements combine, and break apart, through
chemical reactions.
 Soil Chemistry is simply studying how and why
compounds are formed and broken apart in the soil,
and how these chemical reactions affect plants.

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Chemistry Made Simple: The Atom
(+)
The Electron =
negative charge
The Nucleus = positive charge
Hydrogen
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Chemistry Made Simple: The Atom
-
(+)
The Nucleus = positive charge
Hydrogen
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A Water Molecule
H2O
(+)
(+)
Hydrogen
Hydrogen
(+)
Oxygen
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 What happens when an atom has too many
electrons?
 It
has a negative charge ( - )
 These atoms are called: anions
 What happens when an atom doesn’t have
enough electrons?
 It
has a positive charge (+)
 These atoms are called: cations
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 What happens when an anion meets a
cation?
 Anions
 Cations
 When
have a negative charge (-):
Chlorine: Cl
have a positive charge (+):
+
Sodium: Na
they meet, they combine to become a
molecule, the simplest compound:
NaCl (sodium chloride = salt).
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Common soil cations and anions, their
chemical symbols and ionic forms
Cation
Hydrogen
Chemical Ionic Form
Symbol
H
H+
Potassium
K
K+
Sodium
Na
Na+
Magnesium
Mg
Mg++
Calcium
Ca
Ca++
Anion
Chloride
Nitrate
Magnesium
Chemical Ionic Form
Symbol
Cl
ClN
NO3-
Mg
H2PO4-
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The Chemistry of Clay:
- - Clay Particle --------Clay particles carry negative charges
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With Magnets
In Soil
CLAY
CLAY
NH4+
Ammonium
K+
Potasium
Unlikes Attract
+
-
-
CLAY
+
Likes Repel
+
-
NO
3
Nitrate
- +
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The Strange Properties of Water:
 Water ionizes: it falls apart into ions.
 H2O  H+ + OH Called the self ionization of water.
 Only a small amount.
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What is pH?:
 It’s simply a measure of the relative amount
of H+ ions
 In the soil, it is driven by the ionization of
water: H2O  H+ + OH We us pH to measure the acidity or the
alkalinity (basicity) of a solution (a soil
solution)
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Possible pH Ranges Under Natural Soil Conditions
Neutral
Acid
Very
strong
1
2
3
Basic
Strong
4
Slight
Moderate
5
6
Slight
7
Moderate
8
9
Most desirable
Most agricultural soils
Extreme pH range for most mineral soils
apple: 5.0-6.5
spinach: 6.0-7.5
tomato: 5.5-7.5
cranberry:4.2-5.0
cucumber: 5.5-7.0
carrot: 5.5-7.0
white pine: 4.5-6.0
black walnut: 6.0-8.0
Very
strong
Strong
10
11
12
13
14
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Clay and organic particles have a negative charge
Soil reactions in neutral to high (alkaline) pH
conditions
PO4-3
NO3-
Mg+2
- -
-
- -
Ca+2
- -
- - -- H+
NO3-
Ca+2
- -
+
K
-
Clay Particle
Al+3
- -
H+
-
Mg+2
-
K+
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Clay and organic particles have a negative charge
Soil reactions in low (acid) pH conditions
PO4-3
NO3-
H+
-
-
-
- -
Al+3
- -
- - -- H+
NO3-
Al+3
- -
+
K
-
Clay Particle
Al+3
- -
H+
-
Al+3
-
K+
SOIL: Make it Work for You!
Physical and Chemical Characteristics of
Soil: what does it all mean to you?
 Soil Texture and physical nature of the soil
 Water availability:

soil texture
 bulk density
 Soil Chemistry:

Charged elements / molecules & soil particles
 pH and nutrients