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Soil Formation

Introductory Soil Science

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Weathering

• Soil is form by weathering

• The parent material (the rocks) is broken down into small particles

• The type of soil formed affects which vegetation can be grown

• This affects the continued formation because of which organic material and nutrients are added into the soil

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Where does Soil Come from?• Nature

makes little rocks out of big rocks until the particles are grain sized.

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Factors affecting soil formation

1. Parent material

2. Climate

3. Organisms

4. Topography (Relief)

5. Time

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Parent Material

• Igneous rocks– Hard and consolidated material containing

quartz and feldspar.– Example is granite

• Sedimentary Rock

• Metamorphic rocks

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Igneous Rock

• Volcanic activity occurs when magma, molten rock below the earth’s surface, rises to the surface through pipes and fissures (fractures) in the earth’s crust. The three major types of magma solidify to form volcanic rocks. Rocks formed from silica-rich magmas contain abundant quartz and feldspar, light-colored (white, pink, gray) minerals.

http://enterprise.cc.uakron.edu/geology/natscigeo/Lectures/igneous/volcano2.htm#igrx

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Igneous Rock

Basalt

Granite

Black Canyon of the Gunnison

http://enterprise.cc.uakron.edu/geology/natscigeo/Lectures/igneous/volcano2.htm#igrx

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Parent Material

• Sedimentary rocks– From unconsolidated material that has been

transported and deposited by agents such as rivers, wind, gravity, seas and lakes

• Metamorphic rocks – Such as marble, gneiss and slate– Igneous or sedimentary rocks that have been

changed under extreme heat and pressure

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• The soils physical and chemical properties are dependent on the type of rock from which it was formed.

• Mineral composition of rocks differ

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Organic Matter is mixed with the

decomposed rock material.

• Dead plant and animal matter is combined with the decomposed rock.

• Natural forces decompose the solid rock into ever increasing smaller pieces.

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Break Down

• Glacial Ice– Transported soils– Mixed soils– Washed away in melt water

• Wind• Water

– Alluvial soils – parent materials moved by fresh water to form sediments

– Marine sediments – form in the ocean

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Climate• Physical and chemical weathering• Temperature

– Over 60o more activity– More vegetation– Faster decay

• Rainfall– Leaching– Dry – high in salts– Grasslands – high organic matter; dense roots– Arid – low organic matter

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Organisms

• Plants, insects and microbes

• Grassland – fibrous root systems

• Keep organic matter high

• Forests – leaves fall, don’t mix with soil

• Arid – little vegetation

• Insects, animals and microbes dig and forage in the soil and deposit material

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Topography

• Slopes – vulnerable to erosion; esp. wind

• Lowlands – flooding and poor drainage

• Changes water movement and soil temperature

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Soil Profile

• A vertical section through the soil extending to the parent material

• Soil horizon – a section that differs in some physical or chemical way

• Master Horizons– A horizon – thin top layer ‘topsoil’, enriched with

organic matter– C horizon – parent below A– B horizon – subsoil, chemicals leached out of A

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Time

• Young soil – Low nitrogen, high phosphorus– AC soil profile

• Older soil– More organic matter– Leaching will carry material deeper forming an

ABC soil profile– Higher nitrogen, lower phosphorus– More acidic and leached

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Molisol

http://www.soils.umn.edu/academics/classes/soil2125/doc/s5chp2.htm

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Entisol

http://www.soils.umn.edu/academics/classes/soil2125/doc/s5chp2.htm

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Aridisol

http://www.soils.umn.edu/academics/classes/soil2125/doc/s5chp2.htm

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Composition of a Good Planting Soil:

• 45% mineral matter,

• 5% organic matter,

• 25% air &

• 25% water.

• bb

25% air

25% water5 % organic matter

45% mineral matter

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Why isn’t compacted soil a good soil for plants?

• There is no room for either water or air.

Air

WaterOrganic Matter

Mineral Matter

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Where Do Most of the Soils of Western Colorado Come From?

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The Four Counties of the Tri-River Area.

• Mesa• Delta• Montrose• Ouray

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The Most Common Soil in Western Colorado is Mancos Shale.

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• Mancos shale is a sticky ,clay mudstone, deposited in a shallow marine environment, 65-100 million years ago.

• Mancos shale at Hanksville Utah.

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The Grand Valley was covered by this shallow sea that advanced and retreated many times leaving a

4000 foot thick salt laden clay soil.

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Today Mancos Shale Extends from Fruita to Ridgway.

• Mancos shale is actually found from New Mexico to Wyoming and from the Rockies across Utah.

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The Mancos Layer Extends East to Glenwood Springs

• The Mancos shale is part of a large syncline that extends to Glenwood Springs.

• The red rocks in the Glenwood Springs area are part of the Maroon formation.

Mancos Shale

Maroon F

ormatio

n

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Grand Valley Soils

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How Have Natural Processes, Enhanced by Humans, Improved the Mancos Shale?

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The Three Rivers of the Tri-River Area

• Colorado

• Gunnison

• Uncompahgre

• b

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Erosion Causes the Rivers to Transports Large Volumes of Sediments.

• a

• b

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Diversion of Rivers

• The diversion of rivers improves soil by carrying river loam to the native soils.

Diversion Dam of the Grand Valley Canal at Palisade, CO.

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The Silt Laden Irrigation Water is then Delivered to the Fields.

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It Is Not Uncommon to Clean Six Inches of Silt from Irrigation Ditches Each Year.

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The River Loam is then Incorporated into the Mancos Shale thus Enriching the Soil.

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In addition to River Loam, Organic Matter is also Tilled into the soil.

• Farmers have been improving the soils of western Colorado for over a hundred years.

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Water that Improves the Soils of Mesa County.

Colorado River

Gunnison River

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Water sheds that make Mancos Shale Productive from Delta to Ridgway.

• A. Surface Creek

• B. Gunnison River

• C. Uncompahgre

river

A

B

C

Ridgway

Delta

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Grand Valley Soil

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Soils of Delta and Montrose

• Mancos shale extends from Fruita to Ridgway.

Delta

Ridgway

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Sandy Soil

• Sandy soil forms when natural forces such as wind, rain, expansion and contraction and chemical reactions make little rocks out of big ones.

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Thick Layers of Sandy Soil form at the Base of the Uncompahgre Uplift.

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Sandy Soil

• The sandy soil in our area is the result of the decomposition of sandstone.

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The Uncompahgre Uplift is a Series Sandstone Layers.

• The sandy soils along the base of the Uncompahgre are the result of the erosion of the sandstone layers that comprise this uplift.

• The Uncompahgre plateau was uplifted during the Late Cretaceous and Early Tertiary periods. Approx. 100 million years ago. (A.W. Taylor, Ph. D)

Erosion of these sandstone layers form the sandy soils along the base of the uplift.

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Sandstone Layers that form Sandy Soil.

• Chinle, Wingate, Kayenta, Entrada, Summervile Morrison, Burro Canyon and Dakota are the sedimentary layers that have eroded over the last 100 million years to form the sandy soils of the Grand Valley.

Chinle

Kayenta

Wingate

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The Uncompahgre Plateau Extends from

Fruita to Ridgway.

• The various sedimentary layers that

contribute to sandy soils.

These layers were eroded away as a result of the uplift.

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