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Introduction to Soils

Objectives

• Explain what soil is and where it comes from

• Define a soil body

• List examples of the five soil-forming factors

• Explain how soils develop

Terms to know:

• Alluvial Fan • Alluvial Soil • Chemical Weathering • Colluvium • Delta • Ecosystem • Eolian Deposit • Floodplains • Frost Wedging • Gracial Drift • Glacial Outwash • Glacial Till • Igneous Rock • Lacustrine • Leaching • Levee • Loess • Marine Sediment • Metamorphic Rock

• Mineral Soil • Organic Soil • Parent Material • Pedology • Pedon • Physical Weathering • Polypedon • River Terrace • Root Wedging • Sedimentary Rock • Soil Genesis • Soil Series • Talus • Topography • Topsoil • Weathering

What is soil?

• Soft material that covers earth

• Provides a place for growth of plant roots

• Vital part of ecosystem

Study of Soils

• Pedology

– Is the study of soil

• Soil Genesis

The Soil Body

• Ped – smallest unit of soil (chunk)

• Pedon

– Small body of soil (1M x 1M x 1.5 M)

• Polypedon

– Collection of pedons

• Soil Series

– Polypedons mapped into units

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Formation of Soils

• All soil begins with solid rock

– Parent Material

• Weathering- refers to the changing of the original material to new materials. Two kinds:

• Physical

• Chemical

Physical Weathering

• Temperature

• Water

• Wind

• Other Factors

– Plants

Chemical Weathering

• Changes the chemical makeup of rock and breaks it down.

– Solution

– Hydrolysis

– Hydration

– Dissolution

– Oxidation-reduction

Plant Roles

• Root Wedging

– Roots can exert up to 150 pounds per square inch of pressure

Rocks and Minerals

• Parent materials

– Igneous

– Sedimentary

– Metamorphic

Igneous

• Cooling and solidification of molten materials

• Granite contains:

– Feldspar, quartz and other minerals

• Basalt

– Softer, finer grained

– Weathers more quickly

– Less acidic

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Sedimentary Rock

• Overlays about ¾ of igneous crust

• Loose materials like mud or sand deposited

• Slowly cemented by chemicals or pressure

– Sandstone

– Limestone

Metamorphic Rock

• Formed when igneous and sedimentary rocks are subjected to great heat and pressure.

– Limestone to Marble

Five Factors of Soil Formation

• Parent Material

• Time

• Climate

• Organisms

• Topography

Parent Material Delivery Method

• Lacustrine - Glacial

• Eolian - Wind

• Alluvial - Water

• Colluvium - Gravity

Lacustrine - Glacial

• Glacial Drift- general term for materials deposited as glaciers melted and shrunk between glacial periods.

• Glacial Till- accumulations of unsorted, unstratified mixtures of clay, silt, sand, gravel, and boulders.

• Glacial Outwash- glacial drift deposited in water flowing away from a melting glacier. Outwash is sorted by the running water.

– Lacustrine- glacial deposits in bottom of lakes.

Eolian - Wind

• Eolian Deposits - Parent material that was carried by wind.

– Loess- Wind deposited silty materials

• Some of the best soils

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Alluvial - Water

• Alluvial soils- soils whose parent materials were carried and deposited in moving fresh water. – Alluvial fans-form below hills and mountain ranges.

– Levee-coarse material deposited following a flood.

– Floodplain-area where water is slow moving and debris settles.

Alluvial Continued

– River Terrace-changes in elevation where a river flows. Old floodplain is a terrace.

– Marine sediments- form in the ocean. (Sandy)

– Deltas-form where rivers flow into ocean. Very small particles settle at the mouth of the river.

Colluvium - Gravity

• Colluvium- Parent materials move simply by sliding or rolling down a slope.

– Talus- sand and rocks that collect at a the foot of a slope.

– Avalanches, mudslides and landslides are other examples.

Other Information

• Volcanic Deposits – ash blown out of a volcano and deposited nearby.

• Mineral Soils-less than 20% organic material

• Organic Soils-contain 20% or more organic material. (MN, WI, FL)

Time

• Soils change over time – Aging

– Young soils are a thin layer over parent material.

– Over 100 of years weathering carries materials deeper into soil, changing the soil profile.

– Biological processes tend to increase ntirogen content and reduce phosphorus

Time Continued

– Mature soils are generally productive but less productive than young rich soils.

– Aging process is not static, dramatic events reset the clock. • Fire • Landslide • Avalanche

– Forest invading prairie = a new type of soil

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Climate

• Cause Physical and chemical weathering of rock

• Main effects are temperature and rainfall

• Temperature affects speed of chemical reactions in soil. Higher temps = faster reactions.

– Tundra= slow soil development

– Rainforest= faster reactions

Climate Continued

• Temperature = Organic Matter

– Warmth more vegetation

– Warm speeds decay, more rain speeds leaching

• Rainfall affects soil development mainly by leaching

– Moves materials deeper into the soil

– Leached materials are lime, clay, plant nutrients and chemicals

Organisms • Things that live in soil

– Plants, insects, burrowing animals and microbes • Grasslands = high organic content

(fibrous roots)

• Forest= surface materials that don’t mix in – Type of tree changes mix

• Desert=least organic matter

– Vegetation affects location of nutrients in soil

Organisms Continued

• Burrowing animals

– Bring sub soil to the surface

• Earthworms

– Create large deep pores

– Speed organic matter decay

• Nitrogen fixing bacteria

Humans?

• Are now considered part of the “normal” organisms that effect soil.

• However our actions can be so rapid, dramatic and different from other life forms… we may be the 6th factor.

• Effects Range: Simple as deposition of air pollutants to the destruction of earthmoving during road construction.

Topography

• The soil’s position in the landscape, influences soil development mainly by affecting water movement. – Water runs off slopes, making them drier.

– Water collects in low areas, making them moister.

• Water movement affects: – Leaching

– Chemical reactions

– Types of vegetation

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Topography Continued

• Slope effects vary according to a number of characteristic…

– Steep or shallow

– North facing vs. south facing

• Water may carry away soil as fast as it is formed.

– Thin layer at top of hill

– Thick layer at the base

So Should You Care About Soil?

Assignment

• http://ngm.nationalgeographic.com/print/2008/09/soil/mann-text

• Read article • Write a report about the article

– Answering the question: What are 3 factors causing soil loss. Your report should include an explanation of the 3 types of soil loss and what do YOU think we should do about it. This is an opinion paper.

– 500 Word Minimum – Calibri, 12 pt, double spaced, 1” margins – Email to Ms. Griffith by 11/25/11 at 11:59 pm