Chapter 5
Soil Materials and Formation
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Soil Makeup, Origins, and Use
• Soft material covering Earth’s surface
• Formed by heating, cooling, water, wind,
decomposing plant/animal material
• Provides place for plant’s roots to grow;
food and water for plants; home for small
animals
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Soil Body
• Top—where atmosphere or shallow water
begins
• Bottom—farthest reach of deepest rooted
plants
• Pedon—section of soil (usually about
3' x 3' x 5' deep) used to study soil makeup
of particular area
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Soil Formation
• All soil begins with solid rock, which is
broken into smaller pieces by weathering
– Physical: temperature, water, wind, root wedging, other
factors
– Chemical: dissolution, hydrolysis, hydration, oxidationreduction
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Rocks of Earth’s Crust
• Igneous—formed by cooling and
solidification of molten materials deep in
Earth
• Examples:
– granite (made of feldspar, quartz, other minerals):
harder, coarse-grained
– basalt: softer, fine-grained
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Rocks of Earth’s Crust (continued)
• Sedimentary—formed by loose materials
like mud or sand being deposited by water,
wind, other agents
– slowly cemented by chemicals and/or pressure into rock
– overlays 3/4 of igneous crust
• Examples: sandstone, limestone
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Rocks of Earth’s Crust (continued)
• Metamorphic—igneous or sedimentary
rocks subjected to great heat/pressure
– limestone subjected to great heat and pressure changes
to marble
– soils arising from metamorphic parent materials
resemble soils from original sedimentary or igneous
rock
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Soil-Forming Factors
• Five traditional factors
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parent material
time
climate
organisms
topography
• One additional factor: humans
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Parent Material
• Rock or other material in which soil is
formed; limestone most common
• Affected by glaciers, wind, water, gravity,
volcanic deposits, organic deposits
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Time
• Young soils—low in nitrogen, high in
phosphorus
• Mature soils—generally productive
• Old soils—high in nitrogen, low in
phosphorus, become more severely
weathered, more highly leached, often less
productive
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Climate
• 1st effect—physical and chemical
weathering of rock
• 2nd effect—temperature and rainfall
– higher temperature, faster chemical reaction
– rainfall leaches lime, clay, plant nutrients, other
chemicals
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Organisms
• Plants, insects, microbes
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grassland soil: highest organic matter
forest soil: less organic matter
desert soil: least organic matter
vegetation also affects location of nutrients and other
ions in the soil
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Topography and Human Factor
• Topography—soil’s position in landscape
influences soil development mainly by
affecting water movement
• Human—rapid, dramatic, and different from
other factors
– Examples: air pollution and earth moving
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Soil Horizons and Profile
• Horizons—layers where additions, losses,
translocations, transformations happen
• Profile—vertical section through soil
extending into unweathered parent material
that exposes all horizons
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Horizons
• Master
— A: topsoil; B: subsoil; C: parent material
• Other
— O: organic layer—generally undisturbed
— E: greatest eluviation, or loss by leaching
— R: underlying hard bedrock
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.