Chapter 12 Soil and Agriculture

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Essential Questions Covered• What are the components of the soil?• How is soil formed?• What are some of the effects of soil erosion on the

land?• Describe the impact of human activities on the

land.• How do recycling and composting programs affect

the soil?• What impact do pesticides have on the soil?• What affect do fertilizers have on the nitrogen

cycle?

Who Cares About DIRT?

How is my food choice impacting the environment?

How come not everyone has enough food?

About 38% of Earth’s land surface is used for agriculture.

About 38% of Earth’s land surface is used for agriculture.

Section 1 Soil• Explain how soil is formed.• Describe the different layers

(horizons) of soil.• List four characteristics used to

classify soil.

What is soil made of?• Soil is made up of

minerals, organic matter, air, and water.

• Soil composition is influenced by climate, organisms, landforms, parent material, and time

Soil Composition • Soil is a thin layer

over most land that is a complex mix of rock, nutrients, decaying matter, water, air and billions of organisms…many microscopic decomposers

Why is soil important• Renewable

resource…SLOW• Depends upon

climate (1cm in 15yrs.)

• Basis of life• Filters water• Water storage• Habitat

Simplified Soil Food Web

Soil Formation•Weathering: Physical and

chemical breaking of rocks and minerals into smaller pieces

•Erosion and deposition: Pick-up, transport, and drop-off of material from one place to another

•Decomposition: Breakdown of waste, organisms, and organic material into simple molecules

Weathering of PARENT MATERIAL (ROCK)

Decomposition

Leaf Litter

Different Biomes = Different Parent Material, Climate, Organic Matter =

Different Soil

Soil Horizons• Soil horizons are

distinct layers of soil.

• A cross-section of soil horizons is a soil profile.

• “A” Most Critical

Did You Know? In general, organic matter is concentrated in the O and A horizons, making them the most critical for agriculture.

Did You Know? In general, organic matter is concentrated in the O and A horizons, making them the most critical for agriculture.

Is All DIRT The Same?

Soil Characteristics • Soil groups are

further classified according to properties such as color, structure, pH, and texture.• Soil texture is based

on particle size.

Topsoil Color a Great Quick Indicator

Dark, loamy, neutral pH are some of best soils for farming

Dark color often means lots of decayed material (nutrients)

Section 1 Review

• Explain how soil is formed.• Describe the different layers

(horizons) of soil.• List four characteristics used to

classify soil.

Section 1 Quiz

1) After a catastrophe, soil formation is the first step in•A. primary succession. •B. secondary succession. •C. a climax community.

2) Most of the nutrients in soil come fromA. chemical weathering. B. mechanical weathering. C. erosion. D. decomposition.

3) A farmer interested in raising healthy crops should look for aA. heavy clay soil with a high pH and a dark color. B. loamy soil with a low pH and a light color.C. loamy, clumpy soil with a neutral pH and a dark color. D. sandy soil with a high pH, no clumps, and a light color.

4) An example of a soil parent material isA. humus. B. volcanic rock. C. leaf litter. D. topsoil.

5) As a farmer, you would be most concerned with the quality of the soil in theA. O horizon. B. A horizon. C. E horizon. D. R horizon.

6) A rancher interested in the quality of the soil in her pasture might use which aspect of soil as a quick indicator of the pasture’s overall fertility?A. color B. smell C. structure D. pH E. Taste

7) Short Answer: If you were to travel to the desert in Arizona, you might find Horizon Layer O and A missing. Why?

8) Short Answer: What determines how quickly Horizon O and A form?

Some estimates predict that 50 million people could be displaced in the next 10 years due to desertification, a form of soil degradation.

Some estimates predict that 50 million people could be displaced in the next 10 years due to desertification, a form of soil degradation.

Section 2 Soil Degradation and Conservation

• What causes soil erosion?• How serious of a problem is it?• What are ways that farmers,

ranchers and forestry lead to soil erosion?

Causes of Soil Erosion

Wind

Water #1

People

Soil Erosion

• Often occurs faster than soil is formed, depleting fertile topsoil

• Crops, trees, and other plant communities protect soil from erosion.

Did You Know? More than 19 billion hectares (47 billion acres) of the world’s croplands suffer from erosion and other forms of soil degradation resulting from human activities.

Did You Know? More than 19 billion hectares (47 billion acres) of the world’s croplands suffer from erosion and other forms of soil degradation resulting from human activities.

Impacts of Soil Erosion• Loss of soil fertility• Sediment runoff causes

problems in surface water (pollution, clog ditches, boat channels, reservoirs)

• #1 source of U.S. water pollution

• Renewable only on LONG timeframes (200-1,000yrs. for 1 inch)

What time of year do you think most farm fields in U.S. are vulnerable to erosion?

On Ag. land in U.S. today, soil is eroding 16 times faster than it is created

Areas of serious concern

Areas of some concern

Stable or nonvegetative areas

Farming Practices That Reduce Erosion

• Intercropping: Different crops mixed together

• Crop rotation: Crops are alternated.

• Shelterbelts: Tall plants block wind.

• Conservation tillage: Soil turnover is reduced.

• Terracing: Steep slopes turned into “steps”

Tillage vs. Conservation Tillage

Contour and Strip Cropping

Ranching Practices• Ranching is the raising and

grazing of livestock.

• Overgrazing causes and worsens many soil problems.

• Range managers encourage grazing limits and enforce them on publicly owned land.

Forestry Practices• Forestry practices,

such as clear-cutting, can increase erosion.

• Today, practices that reduce soil erosion, such as selective logging, are increasingly common.

Soil Pollution• Too much, or carelessly

timed irrigation can waterlog crops and lead to salinization—a buildup of salts in upper soil horizons.

• Toxic pesticides can remain in soil for a long time, eventually filtering to groundwater.

Desertification

Soil Salinization

Soil Pollution

Section 2 Review

• What causes soil erosion?• How serious of a problem is it?• What are ways that farmers,

ranchers and forestry lead to soil erosion?

Humans have been practicing agriculture for about 10,000 years.

Humans have been practicing agriculture for about 10,000 years.

What is that?

Aldo Leopold

There are two spiritual dangers in not owning a farm. One is the danger of supposing that breakfast comes from the grocery store, and the other that heat from the furnace.

Section 3 Agriculture

• Describe the history of farming.• Analyze the costs and benefits of the “Green

Revolution”• What are some ways farmers control weeds

and pests?• Why are pollinators important to farmers?

The Beginnings of Agriculture

People were hunter-gatherers through most of human history, until agriculture developed about 10,000 years ago.

Why 10,000 years ago?

Agriculture History• In early agriculture,

people began planting seeds from plants they liked most

• Agriculture and livestock provided a stable food supply, which allowed the development of modern civilization.

Types of Agriculture

• Traditional Agriculture

Industrial Agriculture

The Green Revolution• Introduced new technology, crop

varieties, and farming practices to the developing world in the mid- to late 1900s

Benefits:

• Increased crop yields and saved millions of people from starvation in India and Pakistan

• Prevented some deforestation and habitat loss by increasing yields on cultivated land

Green RevolutionCosts:• Led to a 7000% increase in energy used by

agriculture

• Worsened erosion, salinization, desertification, eutrophication, and pollution

Pests and Weed Control (Farmers Enemies)

• Chemical pesticides: Effective and cheap, but can lead to resistance

•Biological pest control: Permanent solution, but can harm nontarget organisms

•Integrated pest management: Increasingly popular solution, combines chemical and biological pest-control methods

Pests and Weed Control

Cactus moth larvae are used to control prickly pear cactus, but also threaten many rare, native cacti around the world.

Pollinators• Agriculture relies on

pollinators, such as insects.

• Native and domesticated pollinator populations have declined due to pesticide use, parasites, and other as-of-yet unknown causes

Section 3 Review

• Describe the history of farming.• Analyze the costs and benefits of the

“Green Revolution”• What are some ways farmers control

weeds and pests?• Why are pollinators important to

farmers?