Arizona Soils and Their Importance

What is the world’s most valuable natural resource?

What is one of the world’s most extensive natural resource?

Soil is!

Why is soil the world’s most valuable natural resource?

• Food – plants depend on soil to grow, animals depend on plants to live

• Water holding capabilities• Pollution filter• Temperature control• Habitat for plants and animals• Many important biological processes

carried out here

Soil

• Minerals derived from rocks

• Organic material derived from life

The 5 C’s of Arizona• Copper• Cotton• Citrus• Cattle• Climate (tourism)

How many of these depend at some level on soil?Cotton- it grows in soil

Citrus- grows in soil also

Cattle- eat what grows from soil

Climate- some aspects of Arizona’s tourism industry depend on soil (plants, animals, food)

Some other Arizona C’s

Cacti- dependant on soil

Canyons- soil developed from them but not dependant on soil

Cactus wren- dependant on plants which are dependant on soil

What is soil?

• The unconsolidated mineral or organic material on the immediate surface of the earth that serves as a natural medium for the

growth of land plants

What makes a soil?

1. Soil starts as a rock2. Weathering breaks down the rock

-Heat, water, freezing, wind, plant roots3. Rock particles (sand, silt, and clay)

separate into horizons through further weathering

Development of soil

Development of soil

Soil Air

• Air is trapped between grains • Air diffuses through soil to and from the

atmosphere• Provides organisms with O2 and other

gasses• Removes CO2 and other gasses released

by organisms

Soil Water

• Water is trapped between grains • Water percolates down through soil• Minerals and organic molecules dissolve

in the water• Dissolved materials are leeched

downward

Alluvial Fan Soil

Soils

Alluvial Fan Soil

Soil Horizons

• Organic Horizon-O• Topsoil-A (organic and

mineral)

• Pale Soil-E (leeched)

• Subsoil-B (leechate)

• Quiet Horizon-C(sand & gravel)

• Bedrock-R (solid rock)

What people typically think

of soil

What typical desert soil is

like-Black organic matter from plants near surface

-Loose, lots of space for air and water

-Not as complicated

-Tan to red in color

-Organic matter from plants nearly absent

-A lot more complex

Soil from near Oracle, Arizona

• Parent material deposited by running water

• Arid climate• Steep topography,

alluvial fan• Desert scrub vegetation• Time: 2 million years

Source: CD from Environmental Science:Toward a Sustainable Future, 9/e, Richard T. Wright

Desert Soils• Coarse textures = high water infiltration• Fine textures = low water infiltration

Desert Soils• Cryptobiotic crusts

– Microscopic algae, lichens and mosses

– Easily destroyed by trampling and off-road vehicles

– Current area of research

Desert Soils

• Desert pavement

Desert Soils• Desert varnish

Desert Soils• Desert pavement

Distribution of soil

Plants and soil

Plant roots

Soil Bacteria

• Decomposers• Mineralizers

Rooting structure

Soil interactions