Chapter 12Chapter 12

Soil ResourcesSoil Resources

Chapter Overview QuestionsChapter Overview Questions

What is soil? What is soil? How is soil formed?How is soil formed? What are the major components of soil?What are the major components of soil?

BiosphereBiosphere

AtmosphereAtmosphere Membrane of air around the planet.Membrane of air around the planet.

StratosphereStratosphere Lower portion contains ozone to filter out most of Lower portion contains ozone to filter out most of

the sun’s harmful UV radiation.the sun’s harmful UV radiation. HydrosphereHydrosphere

All the earth’s water: liquid, ice, water vaporAll the earth’s water: liquid, ice, water vapor LithosphereLithosphere

The earth’s crust and upper mantle.The earth’s crust and upper mantle.

SOIL: A VALUABLE RESOURCESOIL: A VALUABLE RESOURCE

Soil is a Soil is a SLOWLYSLOWLY renewed resource that provides renewed resource that provides most of the nutrients needed for plant growth and most of the nutrients needed for plant growth and also helps purify water. IB considers soil to be also helps purify water. IB considers soil to be nonrenewable resource because it takes hundreds nonrenewable resource because it takes hundreds to thousands of years to replace a few inches.to thousands of years to replace a few inches. Soil formation begins when bedrock is broken down by Soil formation begins when bedrock is broken down by

physical, chemical and biological processes called physical, chemical and biological processes called weatheringweathering..

Mature soilsMature soils, or soils that have developed over a , or soils that have developed over a long time are arranged in a series of horizontal long time are arranged in a series of horizontal layers called layers called soil horizonssoil horizons..

SOIL: A VALUABLE RESOURCESOIL: A VALUABLE RESOURCE

Figure 3-23Figure 3-23

Fig. 3-23, p. 68

Fern

Mature soil

Honey fungus

Root system

Oak tree

Bacteria

Lords and ladies

Fungus

Actinomycetes

Nematode

Pseudoscorpion

Mite

RegolithYoung soil

Immature soil

Bedrock

Rockfragments

Moss and lichen

Organic debrisbuilds upGrasses and

small shrubs

Mole

Dog violet

Woodsorrel

EarthwormMillipede

O horizonLeaf litter

A horizon

Topsoil

B horizonSubsoil

C horizon

Parent material

Springtail

Red Earth Mite

Layers in Mature SoilsLayers in Mature Soils

Infiltration: the downward movement of water Infiltration: the downward movement of water through soil.through soil.

Leaching: dissolving of minerals and organic Leaching: dissolving of minerals and organic matter in upper layers carrying them to lower matter in upper layers carrying them to lower layers.layers.

The soil type determines the degree of The soil type determines the degree of infiltration and leaching.infiltration and leaching.

Soil Profiles of the Soil Profiles of the Principal Terrestrial Principal Terrestrial

Soil Types Soil Types

Figure 3-24Figure 3-24

Fig. 3-24a, p. 69

Mosaic of closely packed pebbles, boulders

Weak humus-mineral mixture

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

Desert Soil(hot, dry climate)

Grassland Soilsemiarid climate)

Fig. 3-24b, p. 69

Tropical Rain Forest Soil(humid, tropical climate)

Acidic light-colored humus

Iron and aluminum compounds mixed with clay

Fig. 3-24b, p. 69

Deciduous Forest Soil(humid, mild climate)

Forest litter leaf moldHumus-mineral mixtureLight, grayish-brown, silt loamDark brown firm clay

Fig. 3-24b, p. 69

Coniferous Forest Soil(humid, cold climate)

Light-colored and acidic

Acid litter and humus

Humus and iron and aluminum compounds

Some Soil PropertiesSome Soil Properties

Soils vary in the size Soils vary in the size of the particles they of the particles they contain, the amount contain, the amount of space between of space between these particles, and these particles, and how rapidly water how rapidly water flows through them.flows through them.

Figure 3-25Figure 3-25

Fig. 3-25, p. 70

0.05–2 mmdiameter

High permeability Low permeability

WaterWater

Clayless than 0.002 mm

diameter

Silt0.002–0.05 mm

diameter

Sand

Soil is a non-renewable resourceSoil is a non-renewable resource

Soil formation takes a very long time.Soil formation takes a very long time. Under the best conditions (wet, temperate Under the best conditions (wet, temperate

climate) only a few millimeters of soil are climate) only a few millimeters of soil are formed each year.formed each year. This is only after initial chemical and physical This is only after initial chemical and physical

weathering has occurred.weathering has occurred. Soil use often exceeds soil formation.Soil use often exceeds soil formation. Soil should be considered a non-renewable Soil should be considered a non-renewable

resource.resource.