Earth’s Resources

Chapter Fifteen: Soil and Fresh Water Resources

• 15.1 Soil

• 15.2 Water Resources

Investigation 15A

• What resources do we use and how can we conserve them?

Natural Resources

15.1 What is soil?

• In nature, humus refers to the material that is produced by the bacterial decay of plant and animal matter, also known as organic matter.

15.1 What is soil?

• Soil is the portion of Earth’s surface that consists of organic matter mixed with sediment.

• Soil is a natural resource that is needed to support life on Earth.

15.1 What is soil?• There is a big difference between “dirt” and

“soil.”• We use the word “dirt” to mean particles

and dust that we don’t want around. • Soil contains humus as well as particles of

weathered rock including sand, silt, and clay.

• Water, air, and living organisms are also important components of soil.

15.1 How soil forms

• Soil is part of the rock cycle.

• Factors that affect soil formation include:– climate, – type of parent rock or mineral, – presence of living organisms, – topography, and – time.

15.1 Layers of soil

• A soil profile is a cross-section that shows the different layers (or horizons) of soil in the ground.

• Young (or immature) soil does not have as many layers as mature soil.

Which soil horizon is the first to form?

15.1 Types of soil• There are 12 soil types, or orders.• Soil classification is based on the following

properties:– How much the soil horizons are developed– Composition of different soil horizons– Amount of organic material – Amount of weathering and leaching of minerals – Presence of calcium carbonate subsurface– Location below grasslands or forests– Presence of clay that shrinks and swells when mixed

with water– Presence of permafrost – Presence of volcanic ash

15.1 General terms for soil types

• Focus on three types of soil: pedocal, pedalfer, and laterite.– Pedocal forms in dry or semi-dry climates

and is rich in calcium.– Pedalfer forms in humid climates and is high

in aluminum and iron.– Laterite forms in tropical climates that have a

lot of rains so it is leached of most of its elements.

15.1 Erosion and agriculture

• Soil that contains a mixture of sediments, humus, air, and water is ideal for growing crops.

• More soil is lost each year through erosion than is formed by nature.

15.1 Erosion and agriculture

• This soil profile shows the layer of topsoil on a farm in Iowa.

• Due to farming, Iowa’s average topsoil depth has decreased from 14–18 inches to only 6–8 inches.

15.1 Erosion and agriculture• The Natural Resources Conservation Service

recommends managing construction projects so that erosion is minimized, intercepting surface runoff so that less soil is lost, planting ground cover, and improving farming techniques.