Download Ch. 12 Part 1

Chapter 12
Soil Resources
Chapter Overview Questions
 What
is soil?
 How is soil formed?
 What are the major components of soil?
Biosphere
 Atmosphere

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.
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.
SOIL: A VALUABLE RESOURCE
Figure 3-23
Oak tree
Wood
sorrel
Lords and
ladies
Fern
O horizon
Leaf litter
Dog violet
Grasses and
small shrubs
Earthworm
Millipede
Honey
fungus
Mole
Organic debris
builds up
Rock
fragments
Moss and
lichen
A horizon
Topsoil
B horizon
Subsoil
Bedrock
Immature soil
Regolith
Young soil
Pseudoscorpion
C horizon
Mite
Parent
material
Nematode
Root system
Mature soil
Red Earth
Mite
Springtail
Actinomycetes
Fungus
Bacteria
Fig. 3-23, p. 68
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.
Soil Profiles of the
Principal Terrestrial
Soil Types
Figure 3-24
Mosaic of
closely
packed
pebbles,
boulders
Weak humusmineral mixture
Desert Soil
(hot, dry climate)
Dry, brown to
reddish-brown
with variable
accumulations
of clay, calcium
and carbonate,
and soluble
salts
Alkaline,
dark,
and rich
in humus
Clay,
calcium
compounds
Grassland Soil
semiarid climate)
Fig. 3-24a, p. 69
Acidic
light-colored
humus
Iron and
aluminum
compounds
mixed with
clay
Tropical Rain Forest Soil
(humid, tropical climate)
Fig. 3-24b, p. 69
Forest litter leaf
mold
Humus-mineral
mixture
Light, grayishbrown, silt loam
Dark brown
firm clay
Deciduous Forest Soil
(humid, mild climate)
Fig. 3-24b, p. 69
Acid litter
and humus
Light-colored
and acidic
Humus and
iron and
aluminum
compounds
Coniferous Forest Soil
(humid, cold climate)
Fig. 3-24b, p. 69
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
Sand
0.05–2 mm
diameter
Silt
0.002–0.05 mm
diameter
Water
High permeability
Clay
less than 0.002 mm
diameter
Water
Low permeability
Fig. 3-25, p. 70
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.