We Study Soil Because It’s A(n) Great integrator: all parts of ecosystem Producer and absorber of gases Medium for plant growth Medium of crop production

We Study Soil Because It’s A(n)Great integrator:all parts of ecosystem

Producer andabsorber of gases

Medium for plant growth

Medium of crop production

Home to organisms(plants, animals and others)

Waste decomposer

Snapshot of geologic, climatic, biological, and human history

Source material for construction, medicine, art, etc.

Filter of water and wastes

Essential natural resource

SOIL: Make it Work for You!

Soil Forming FactorsParent Material

Topography

(The first four factors over) Time

Climate

Biota

These five factors work together to create a unique soil profile made of layers called horizons.


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)

What is “Soil?”


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


Texture: the mineral components Consistency & Structure: How the

mineral components are put togetherBulk DensitySoil Moisture

Physical Characteristics of Soil:


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”


Soil Texture: Relative Size Comparison of Soil Particles

frisbee

Silt(feels floury)

dime

Clay(feels sticky)

beachball

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)

(< 0.002 mm, USDA)

(< 0.002 mm, ISSS)


SiCL

% Sand

% Silt%

Cla

y

S LSSL

L SiLSi

CL

SiC

C

SC

SCL

0

100

100

100 0

0Triangle Key:S = sand or sandySi = silt or siltyC = clayL = loam or loamy

Soil Texture Triangle


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.

Effects of Soil Texture:


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!).


Soil ConsistenceLoose*

Extremely FirmFirm

Friable

* Soils with “single grained” structure always have loose consistence.


With Structure: Granular Blocky Platy Prismatic Columnar

Without Structure Single Grained Massive

Soil Structure: the shape that the soil takes based on its physical and chemical properties. Possible choices of soil structure are:


With Structure: Without Structure Single Grained:

• beach sand Massive

• solid mass with no shape

Soil Structure:


Soil Structure: with StructureGranular Block

y

Prismatic

Columnar

Platy


Single Grained Massive

Soil Structure: without Structure



Bulk Density: a measure of soil compaction

To calculate Bulk Density:

1 cm. (so, there is 1 cubic centimeter of soil)

Sample is made of Solids andPore Spaces

1.33 gms.

Volume = 1 cm3

Weight = 1.33 gms

Bulk Density = Weight of Soil

Volume of Soil

Bulk Density = 1.33

1

Bulk Density = 1.33 gms / cm3


Bulk Density & Compaction Zones

8 inches

1.43

0 inches

7 inches

9 inches10 inches

Depth Bulk Density (grams / cm3

1.90

1.87

1.84

1.80

1.60

Plow Layer

Compacted Zone

Uncompacted subsoil


Basic Soil Components

Soil Particles: Mineral and Organic

Pore Spaces: location of air and water

Soil Moisture: some terms and concepts Field CapacityField Capacity: water that remains in soil

beyond the effects of gravity. Permanent Wilting PercentagePermanent Wilting Percentage: amount of

water after the permanent wilting point is reached.

Available WaterAvailable Water: amount of water in the soil between the field capacity and the permanent wilting percentage.



Relationship between soil texture and water availability

Sand SandyLoam

SiltLoam

ClayLoam

Clay

Inches of Water Per ft. of Soil

1

2

3

4


At Saturation At “Available Water

Soil at Different Moisture Levels:

Pore Space Water on soilparticle surfacePore Spaces are filled with

water


Soil at Different Moisture Levels:

At Permanent Wilt Compacted

No water remains attached to soil particles

Pore spaces are collapsed

Compacted ZoneImpermeable Layer


HH22OO HH22OO

Non-Compacted

Compacted

Sand Over Clay

HH22OO HH22OO

Impermeable Layer


HH22OO HH22OOPerched Water Table

Clay Over Sand


Wet & Dry LayersHH22OOHH22OO

Soil Sandwiches


Patchy Soil Moisture HH22OOHH22OO

Soil Salads


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.


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 areaStructures modify soil saturation, contact

areas, and volume contact/unit area



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

Controlling Surface Drainage

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



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

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


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.

Characterization and Sampling Options

Soil Pit Exposed Profile (road cut)


Chemical bondingpHNutrient AvailabilityCation Exchange Capacity (CEC)


Soil Chemistry

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.”


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.



Chemistry Made Simple: The Atom

Hydrogen

(+)-

The Nucleus = positive charge

The Electron = negative charge


Chemistry Made Simple: The Atom

Hydrogen

(+)-

The Nucleus = positive charge

A Water Molecule


H2O(+)

(+)

(+)

Hydrogen Hydrogen

Oxygen

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


What happens when an anion meets a cation?Anions have a negative charge (-):

Cations have a positive charge (+):

When they meet, they combine to become a molecule, the simplest compound:

NaCl (sodium chloride = salt).

Chlorine: Cl-

Sodium: Na+



Cation ChemicalSymbol

Ionic Form

Hydrogen H H+

Potassium K K+

Sodium Na Na+

Magnesium Mg Mg++

Calcium Ca Ca++

Anion ChemicalSymbol

Ionic Form

Chloride Cl Cl-

Nitrate N NO3-

Magnesium Mg H2PO4-

Common soil cations and anions, their chemical symbols and ionic forms


The Chemistry of Clay:

Clay Particle

- - --

--

-------------- - - - - - -

Clay particles carry negative charges


With Magnets

-

-

+

-Unlikes Attract

Likes Repel

In Soil

CLAY

NH4+Ammonium

CLAY

K+Potasium

CLAY

NO3

-

Nitrate

+-

+ +

Water ionizes: it falls apart into ions.

H2O H+ + OH-

Called the self ionization of water.Only a small amount.

The Strange Properties of Water:


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)

What is pH?:



Possible pH Ranges Under Natural Soil Conditions

black walnut: 6.0-8.0

Most desirable

carrot: 5.5-7.0

cucumber: 5.5-7.0

spinach: 6.0-7.5tomato: 5.5-7.5

white pine: 4.5-6.0

Verystrong

Strong Moderate Slight Slight Moderate StrongVery

strong

Neutral

Acid Basic

3 4 5 6 7 8 9 10 111 2 12 13 14

Most agricultural soils

Extreme pH range for most mineral soils

cranberry:4.2-5.0

apple: 5.0-6.5

-

--

-

Mg+2

H+Mg+2

K+

H+ Ca+2

Ca+2

PO4-3

-

--

--

-

-

-

--

-

--

-

-Al+3

-

-

-

K+

Clay Particle

NO3-

NO3-

Soil reactions in neutral to high (alkaline) pH conditions


Clay and organic particles have a negative charge

-

--

-

H+

H+Al+3

K+

H+ Al+3

Al+3

PO4-3

-

--

--

-

-

-

--

-

--

-

-Al+3

-

-

-

K+

Clay Particle

NO3-

NO3-

Soil reactions in low (acid) pH conditions


Clay and organic particles have a negative charge

Soil Texture and physical nature of the soil Water availability:

soil texture bulk density

Soil Chemistry: Charged elements / molecules & soil particles pH and nutrients

Physical and Chemical Characteristics of Soil: what does it all mean to you?


Documents

We Study Soil Because It’s A(n) Great integrator: all parts of ecosystem Producer and absorber of gases Medium for plant growth Medium of crop production