Soil Erosion and Degradation

Soil Erosion and Degradation PA Standards

4.2.12.C: Renewable and Nonrenewable Resources

4.4.10.B: Agriculture and Society

“The nation that destroys its soil destroys itself.”- Franklin D. Roosevelt (1937)

Analyze factors that influence the availability of natural resources.

Assess the influence of agriculture science on farming practices (plowing).

Key Questions How are soils being degraded and eroded? What can be done to reduce these losses?

Consider this…

Human activity accelerates natural soil erosion.

One-third to one-half of world’s croplands are losing topsoil faster than it is being renewed by natural processes .

HOW MUCH OF THE EARTH IS AVAILABLE FOR FARMING? Question: How much of the Earth is available

for farming?

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How are soils being degraded and eroded?

SOIL EROSION AND DEGRADATION Soil erosion lowers soil fertility and can

overload nearby bodies of water with eroded sediment. Sheet erosion: surface water or wind peel off thin

layers of soil. Rill erosion: fast-flowing little rivulets of surface

water make small channels. Gully erosion: fast-flowing water join together to

cut wider and deeper ditches or gullies.

SOIL EROSION AND DEGRADATION

Soil erosion is the movement of soil components, especially surface litter and topsoil, by wind or water.

Soil erosion increases through activities such as farming, logging, construction, overgrazing, and off-road vehicles.

Global Outlook: Soil Erosion

Soil is eroding faster than it is forming on more than one-third of the world’s cropland.

What can be done to reduce these losses?

SUSTAINABLE AGRICULTURE THROUGH SOIL CONSERVATION

Modern farm machinery can plant crops without disturbing soil (no-till and minimum tillage. Conservation-tillage farming:

Increases crop yield. Raises soil carbon content. Lowers water use. Lowers pesticides. Uses less tractor fuel.

SUSTAINABLE AGRICULTURE THROUGH SOIL CONSERVATION

Terracing, contour planting, strip cropping, alley cropping, and windbreaks can reduce soil erosion.

Biodiversity Loss Soil Water Air Pollution Human Health Loss and degradation of grasslands, forests, and wetlands

Erosion Water waste Greenhouse gas emissions from fossil fuel use

Nitrates in drinking water

Loss of fertility Aquifer depletionPesticide residues in drinking water, food, and air

Salinization Increased runoff and flooding from cleared land

Other air pollutants from fossil fuel use

Fish kills from pesticide runoff

WaterloggingSediment pollution from erosion Greenhouse gas

emissions of nitrous oxide from use of inorganic fertilizers

Contamination of drinking and swimming water with disease organisms from livestock wastes

Desertification

Killing wild predators to protect livestock

Fish kills from pesticide runoff

Surface and groundwater pollution from pesticides and fertilizers Belching of the

greenhouse gas methane by cattle

Loss of genetic diversity of wild crop strains replaced by monoculture strains

Bacterial contamination of meat

Overfertilization of lakes and rivers from runoff of fertilizers, livestock wastes, and food processing wastes Pollution from

pesticide sprays

Review Key Questions How are soils being degraded and eroded? What can be done to reduce these losses?

Thought Problems How does deforestation, over farming, and over grazing contribute to erosion or

arable land?

If we exhaust the food-producing resources we have now, won’t science devise new ways to increase food production as it has been done in the past?

What conclusions can we draw about the relationship between a growing population and a shrinking amount of land capable of growing food for those people?

How can we preserve farmland?

Thought Problems - Answers How does deforestation, over farming, and over grazing contribute to erosion or

arable land? 1/32 of land is suitable for agriculture; deforestation increases erosion, over farming

decreases land nutrients, and over grazing increases erosion and decreases nutrients

If we exhaust the food-producing resources we have now, won’t science devise new ways to increase food production as it has been done in the past? Hydroponics; genetics; decrease nutrients, decrease health in livestock; increase in

antibiotics

What conclusions can we draw about the relationship between a growing population and a shrinking amount of land capable of growing food for those people? Famine; decreased nutrients; different types of food

How can we preserve farmland? No plow farming; stop wasting, rotate crops; conservation tillage, best management

practices; limit development; buy local; eat lower on the food chain

Case Study: Soil Erosion in the U.S. – Some Hopeful Signs

Soil erodes faster than it forms on most U.S. cropland, but since 1985, has been cut by about 40%. 1985 Food Security Act (Farm Act): farmers

receive a subsidy for taking highly erodible land out of production and replanting it with soil saving plants for 10-15 years.

Desertification: Degrading Drylands

About one-third of the world’s land has lost some of its productivity because of drought and human activities that reduce or degrade topsoil.

Very severeSevereModerate

Salinization and Waterlogging

Repeated irrigation can reduce crop yields by causing salt buildup in the soil and waterlogging of crop plants.

CleanupPrevention

Soil Salinization

Solutions

Reduce irrigation

Switch to salt-tolerant crops (such as barley, cotton, sugarbeet)

Flush soil (expensive and wastes water)

Stop growing crops for 2–5 years

Install underground drainage systems (expensive)

Salinization and Waterlogging of Soils: A Downside of Irrigation

Example of high evaporation, poor drainage, and severe salinization.

White alkaline salts have displaced cops.

SUSTAINABLE AGRICULTURE THROUGH SOIL CONSERVATION

Fertilizers can help restore soil nutrients, but runoff of inorganic fertilizers can cause water pollution. Organic fertilizers: from plant and animal (fresh,

manure, or compost) materials. Commercial inorganic fertilizers: Active

ingredients contain nitrogen, phosphorous, and potassium and other trace nutrients.

THE GREEN REVOLUTION AND ITS ENVIRONMENTAL IMPACT

Since 1950, high-input agriculture has produced more crops per unit of land.

In 1967, fast growing dwarf varieties of rice and wheat were developed for tropics and subtropics.

THE GREEN REVOLUTION AND ITS ENVIRONMENTAL IMPACT Lack of water, high costs for small farmers, and

physical limits to increasing crop yields hinder expansion of the green revolution.

Since 1978 the amount of irrigated land per person has declined due to: Depletion of underground water supplies. Inefficient irrigation methods. Salt build-up. Cost of irrigating crops.

THE GREEN REVOLUTION AND ITS ENVIRONMENTAL IMPACT Modern agriculture has a greater harmful

environmental impact than any human activity. Loss of a variety of genetically different crop and

livestock strains might limit raw material needed for future green and gene revolutions. In the U.S., 97% of the food plant varieties available

in the 1940 no longer exist in large quantities.