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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.

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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

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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