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1. Soil Erosion and
Degradation

2. 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).

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

4. 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 .

5. HOW MUCH OF THE EARTH IS
AVAILABLE FOR FARMING?
 Question: How much of the Earth is available
for farming?
 http://www.agclassroom.org/teacher/screensavers

6. How are soils being
degraded and eroded?

7. 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.

8. 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.

9. Global Outlook: Soil Erosion
 Soil is eroding faster than it is forming on more
than one-third of the world’s cropland.

10. What can be done to
reduce these losses?

11. 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.

12. SUSTAINABLE AGRICULTURE
THROUGH SOIL CONSERVATION
 Terracing, contour
planting, strip
cropping, alley
cropping, and
windbreaks can
reduce soil erosion.

13. 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 depletion
Pesticide
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
Waterlogging
Sediment 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

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

15. 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?

16. 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

18. 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.

19. 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.

20. Very severeSevereModerate

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

22. 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)

23. Salinization and Waterlogging of
Soils: A Downside of Irrigation
 Example of high
evaporation,
poor drainage,
and severe
salinization.
 White alkaline
salts have
displaced cops.

24. 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.

25. 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.

26. 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.

27. 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.