1. Chapter 12
Soil Resources

2. Chapter Overview Questions
What is soil?
How is soil formed?
What are the major components of soil?

3. Biosphere Atmosphere Stratosphere Hydrosphere Lithosphere
Membrane of air around the planet.
Stratosphere
Lower portion contains ozone to filter out most of the sun’s harmful UV radiation.
Hydrosphere
All the earth’s water: liquid, ice, water vapor
Lithosphere
The earth’s crust and upper mantle.

4. SOIL: A VALUABLE RESOURCE
Soil is a SLOWLY renewed resource that provides most of the nutrients needed for plant growth and also helps purify water. IB considers soil to be nonrenewable resource because it takes hundreds to thousands of years to replace a few inches.
Soil formation begins when bedrock is broken down by physical, chemical and biological processes called weathering.
Mature soils, or soils that have developed over a long time are arranged in a series of horizontal layers called soil horizons.

5. SOIL: A VALUABLE RESOURCE
Figure 3-23

6. Wood sorrel Oak tree Organic debris builds up Lords and ladies
Dog violet
Rock
fragments
Grasses and
small shrubs
Earthworm
Millipede
Fern
Moss and
lichen
Honey
fungus
O horizon
Mole
Leaf litter
A horizon
Topsoil
B horizon
Bedrock
Subsoil
Immature soil
Regolith
Young soil
C horizon
Figure 3.23
Natural capital: soil formation and generalized soil profile. Horizons, or layers, vary in number, composition, and thickness, depending on the type of soil. (Used by permission of Macmillan Publishing Company from Derek Elsom, Earth, New York: Macmillan, Copyright © 1992 by Marshall Editions Developments Limited)
Pseudoscorpion
Mite
Parent
material
Nematode
Root system
Actinomycetes
Red Earth
Mite
Fungus
Mature soil
Bacteria
Springtail
Fig. 3-23, p. 68

7. Layers in Mature Soils
Infiltration: the downward movement of water through soil.
Leaching: dissolving of minerals and organic matter in upper layers carrying them to lower layers.
The soil type determines the degree of infiltration and leaching.

8. Soil Profiles of the Principal Terrestrial Soil Types
Figure 3-24

9. Desert Soil (hot, dry climate) Grassland Soil semiarid climate)
Mosaic of closely packed pebbles, boulders
Weak humus-mineral mixture
Alkaline,
dark,
and rich
in humus
Dry, brown to reddish-brown with variable accumulations of clay, calcium and carbonate, and soluble salts
Figure 3.24
Natural capital: soil profiles of the principal soil types typically found in five types of terrestrial ecosystems.
Clay, calcium compounds
Desert Soil
(hot, dry climate)
Grassland Soil
semiarid climate)
Fig. 3-24a, p. 69

10. Tropical Rain Forest Soil (humid, tropical climate)
Acidic
light-colored humus
Figure 3.24
Natural capital: soil profiles of the principal soil types typically found in five types of terrestrial ecosystems.
Iron and aluminum compounds mixed with clay
Tropical Rain Forest Soil
(humid, tropical climate)
Fig. 3-24b, p. 69

11. Deciduous Forest Soil (humid, mild climate)
Forest litter leaf mold
Humus-mineral mixture
Light, grayish-brown, silt loam
Figure 3.24
Natural capital: soil profiles of the principal soil types typically found in five types of terrestrial ecosystems.
Dark brown firm clay
Deciduous Forest Soil
(humid, mild climate)
Fig. 3-24b, p. 69

12. Coniferous Forest Soil
Acid litter and humus
Light-colored and acidic
Figure 3.24
Natural capital: soil profiles of the principal soil types typically found in five types of terrestrial ecosystems.
Humus and iron and aluminum compounds
Coniferous Forest Soil
(humid, cold climate)
Fig. 3-24b, p. 69

13. Some Soil Properties
Soils vary in the size of the particles they contain, the amount of space between these particles, and how rapidly water flows through them.
Figure 3-25

14. 0.05–2 mm diameter 0.002–0.05 mm diameter less than 0.002 mm diameter
Sand
Silt
Clay
0.05–2 mm
diameter
0.002–0.05 mm
diameter
less than mm
diameter
Water
Water
Figure 3.25
Natural capital: the size, shape, and degree of clumping of soil particles determine the number and volume of spaces for air and water within a soil. Soils with more pore spaces (left) contain more air and are more permeable to water than soils with fewer pores (right).
High permeability
Low permeability
Fig. 3-25, p. 70

15. Soil is a non-renewable resource
Soil formation takes a very long time.
Under the best conditions (wet, temperate climate) only a few millimeters of soil are formed each year.
This is only after initial chemical and physical weathering has occurred.
Soil use often exceeds soil formation.
Soil should be considered a non-renewable resource.