1. Ap Environmental Science
Unit 4: Effects of Agriculture on the Environment (Ch. 10)

2. How Agriculture Changes the Environment
Agriculture is one of our greatest successes and while also a major source of environmental damage.
Major environmental problems associated with agriculture:
Soil erosion
Sediment transport and deposition downstream
On-site pollution from overuse and secondary effects of fertilizers and pesticides
Off-site pollution of other ecosystems, of soil, water and air
Deforestation
Desertification
Degradation of aquifers
Salinization of soil (“Salting”)
Accumulation of toxic organic compounds
Loss of biodiversity

3. The Plow Puzzle
Land left undeveloped in natural forests develops high levels of organic matter in definite layers of soil
Land that has been plowed for agriculture is turned over, loosening soil and removing organic matter through erosion and removing natural layering of the soil

4. Depth of disturbance for most equipment is at least 14”
The Plow Puzzle
Plows – the physical disturbance of soil using large farm “implements” that are dragged through the soil either by “work animals” or machines
They shape the land for efficient planting, but they destroy the soil structure thus making it more prone to erosion and loss of fertility.
Depth of disturbance for most equipment is at least 14”
What is the energy cost?

5. Our Eroding Soils
When land has been cleared of its natural vegetation, the soil begins to lose its fertility
Erosion is tied to the loss of particles that help maintain presence of plant nutrients
Became a national issue in the US in the 1930s
Intense plowing + drought
Loosened soil blew away during the
“Dust Bowl” years

6. Our Eroding Soils The land that became the Dust Bowl had been prairie
Deep rooted grasses had held soil in place
After plowing soil becomes exposed to rain and wind effects
When original vegetation (“canopy cover”) is cleared soil changes
Soil exposed to sunlight speeds the rate of decomposition

8. Our Eroding Soils
Traditionally declines in soil fertility were treated using organic fertilizers
Animal manures, worm castings
In the 20th century crop production increased
Chemical fertilizers
Adding nitrogen and phosphorous to the soil was easily achieved

9. Our Eroding Soils
Since WWII mechanized farming has seriously damaged land
More than 1 billion hectares of land affected
In the US 1/3 of topsoil has been lost (washed to sea)
This is the result of massive disturbances to the soil by plowing and use of heavy farm equipment in concert with natural weathering

10. Where does eroded soil go?
A lot of it travels down streams and rivers
Deposited at their mouths
Fills in water ways
Damages fisheries and coral reefs
Sedimentation has chemical effects
Enrichment of waters, eutrophication
Transport of toxic chemical pesticides

12. Making Soils Sustainable
Soil forms continuously
But very slowly
1mm of soil formation takes years
To be truly sustainable soil lost should equal
amount of new soil produced

13. Contour Plowing
Land is plowed perpendicular to the slopes and as horizontally as possible to the “contour” of the land horizontally.
Benefits:
One of the most effective ways to
reduce soil erosion
Also uses less fuel and time

14. No Till Farming
Land is not plowed, but herbicides and integrated pest management controls weeds
The goal is to suppress and control weeds, but not eliminate them at the expense of soil conservation
Stems and roots not a part of the harvest remain in the soil and are allowed to decompose in place
Additional benefit is that it reduces the release of CO2 accelerated soil decomposition
In the U.S. 18% of farming practices employ no-till farming well behind averages in other countries of 25-55%

15. Grazing on Rangelands
Almost half of the Earth's land area is used as rangeland
30% of Earth’s land area is arid rangeland
Arid rangeland easily damaged especially in time of drought
Streams and rivers also damaged
Trampling banks and depositing fecal matter into water systems

17. Traditional vs. Industrial Agriculture
In modern industrialized agriculture
Cattle initially raised on open range
Transported to feed lots
Major impact is local pollution from manure
Traditional herding practices
Damage land through overgrazing
Impact varies depending on density
relative to rainfall and soil fertility
Concentrated Animal Feeding Operation
- Also centers for spread of disease and pollution in modern agriculture

18. Biogeography of Agriculture Animals
Everyplace people have dispersed they have bought animals with them
Pre-industrial and throughout western civilization
Environmental effects of introductions
Native vegetation may be greatly reduced and threatened with extinction
Introduced animals may compete with native herbivores, threatening them with extinction as well

19. Carrying Capacity on Grazing Lands
the maximum number of species per unit area that can persist w/o decreasing the ability of that population or its ecosystem to maintain that density in the future.
When the carrying capacity is exceeded, the land is overgrazed. (sometimes poor grazing practices can lead to problems even though the number of animals may have been small).

20. Carrying Capacity on Grazing Lands
Overgrazing
Slows the growth of vegetation
Reduces the diversity of plant species
Leads to dominance by plant species that are relatively undesirable to the cattle
Hastens loss of soil by erosion
Subject the land to further damage from trampling

21. Desertification
Deserts occur naturally where there is too little water for substantial plant growth.
The warmer the climate the greater the rainfall needed to convert an area from desert to non-desert
The crucial factor is available water in the soil for plant use
Factors that destroy the ability of a soil to store water can create a desert

22. Desertification Earth has five natural warm desert regions
Primarily between 15o and 30o north and south of the equator
Based on climate 1/3 of Earth’s land area should be desert
43% of land is desert
Additional area due to human activities

23. Desertification
Desertification – the deterioration of land in arid, semiarid, and dry sub humid areas due to changes in climate and human activities.
Serious problem that affects 1/6 of world population (1 billion people)
The leading cause of desertification are bad farming practices.
Failure to use contour plowing
To much farming
Overgrazing
Conversion of rangelands to croplands in marginal areas
Poor forestry practices

24. Desertification
Desert like areas can be created anywhere by poisoning of the soil
World wide chemicals account for 12% of soil degradation
Irrigation in arid lands can cause salts to build up to toxic levels

25. Desertification
First step is detection of symptoms (achieved by monitoring)
Lowering of water table
Increase in the salt content of soil
Reduced surface water
Increased soil erosion
Loss of native vegetation
Next step is proper methods of soil conservation, forest management and irrigation
Good soil conservation includes: use of wind breaks, reforestation

26. 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
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

27. Sustainable Organic Agriculture
More
Less
High-yield polyculture
Soil erosion
Soil salinization
Organic fertilizers
Aquifer depletion
Biological pest control
Overgrazing
Integrated pest management
Overfishing
Loss of biodiversity
Efficient irrigation
Loss of prime cropland
Perennial crops
Crop rotation
Food waste
Water-efficient crops
Subsidies for unsustainable farming and fishing
Soil conservation
Subsidies for sustainable farming and fishing
Population growth
Poverty

28. Controlling Pests In agriculture pests are undesirable:
Competitors, parasites, and predators
In agriculture pests are mainly
Insects, nematodes, bacterial and viral diseases, weeds and vertebrates.
Loss can be large
Estimated at 1/3 of potential harvest and 1/10 of the harvested crop

29. Controlling Pests Weeds are a natural pest to crop production
Because a farm is maintained in a very early stage of ecological succession and enriched by fertilizers and water
It is a good place for crops
AND early-successional plants (weeds)
Weeds compete for all resources
Light, water, nutrients, and space to grow.
Weeds are a natural pest to crop production

30. Controlling Pests
Organisms found in nature (such as ladybugs) control populations of most pest species as part of the earth’s free ecological services.
We use chemicals to repel or kill pest organisms as plants have done for millions of years.
Chemists have developed hundreds of chemicals (pesticides) that can kill or repel pests.
Pesticides vary in their persistence.
Each year > 250,000 people in the U.S. become ill from household pesticides.

31. History of Pesticides Pre- Industrial Revolution methods
Slash and burn agriculture
Planting aromatic herbs that repel insects
Modern science-based agriculture
Search for chemicals that would reduce abundance of pests
The first, like arsenic, were toxic to all life
Killed both pests and beneficial organisms

32. History of Pesticides Second stage began in the 1930’s
Petroleum based sprays and natural plant chemicals
(e.g., nicotine)
Third stage was the development of artificial organic
compounds
DDT, broad-spectrum
Aldrin and dieldrin used to control termites
Toxic to humans and has been found in breast milk

33. History of Pesticides
In1962 Rachel Carson wrote Silent Spring which introduced the U.S. to the dangers of the pesticide DDT and related compounds to the environment.
She was inspired to write her book after studying the profligate use of synthetic chemicals in agriculture following WWII
Silent Spring began an environmental movement to question how we treat the environment in our attempts to make nature work for us

34. History of Pesticides
Fourth stage is a return to biological and ecological knowledge.
Biological control - the use of predators and parasites to control pests
The use of Bacillus thuringiensis (BT) is the most widely used BioInsecticide
Predatory insects such as spiders, ladybugs, or parasitic wasps
Other biological control agents
Sex pheromones (chemicals released to attract opposite sex) used as bait in traps to interrupt reproductive cycle

36. Integrated Pest Management
Fifth stage
IPM uses a combination of methods
Biological control
Chemical pesticides
Methods of planting crops (mixed fields)
Goal can be control, but never complete elimination of pests
Economically makes sense
Does less damage to ecosystem, soil, water and air

37. Integrated Pest Management
Many scientists urge the USDA to use three strategies to promote IPM in the U.S.:
Add a 2% sales tax on pesticides.
Establish federally supported IPM demonstration project for farmers.
Train USDA personnel and county farm agents in IPM.
The pesticide industry opposes such measures.

38. Pest Management Concerns
Continued use of pesticides and genetically modified organisms has led to generations of pests that develop resistance to pest control methods
Superpests are populations of pests that have become resistant to pesticides.
Superpests challenge farmers as they cause more than $200 million per year in U.S. crop losses.
These pests have caused an increased use of pesticides and herbicides by 25% in the last 10 years

39. Worldwide Pesticide Use
World pesticide use exceeds 2.5 billion kg
US use exceeds 680 million kg
$32 billion worldwide, $11 billion in US
Once applied may decompose
in place or be carried by wind
and water
Breakdown products can also be toxic
Eventually fully decompose but can take a long time

40. Pest Management Concerns
Government regulation has banned a number of harmful pesticides but some scientists call for strengthening pesticide laws.
The Environmental Protection Agency (EPA), the Department of Agriculture (USDA), and the Food and Drug Administration (FDA) regulate the sales of pesticides under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA).
The EPA has only evaluated the health effects of 10% of the active ingredients of all pesticides

41. Ideal Pest Management
The ideal pest-killing chemical has these qualities:
Kills only the target pest.
Does not cause genetic resistance in the target organism.
Disappears or breaks down into harmless chemicals after doing its job.
Is more cost-effective than doing nothing.

42. Genetically Modified Crops
Three methods:
1. Faster and more efficient development of new hybrids
2. Introduction of the “terminator gene”
3. Transfer of genetic properties from widely divergent kinds of life (fish genes to Strawberries or tomatoes)

43. Genetically Modified Crops
To increase crop yields, we can mix the genes of similar types of organisms and mix the genes of different organisms.
Artificial selection has been used for centuries to develop genetically improved varieties of crops.
Genetic engineering develops improved strains at an exponential pace compared to artificial selection.

44. New Hybrids
Accelerated production of hybrids since the Green Revolution
Probably as harmless as the development of agricultural hybrids has been with conventional methods but there are concerns about problems that could be caused when they are quickly introduced in new environments
Concern that genetic modification may produce
“superhybrids”
Could become pest or transfer genes to closely related weeds

45. Terminator Gene
A genetically modified crop that has a gene which makes the organism sterile after the first year
Purposeful sterility
Prevents a genetically modified organisms from uncontrolled spreading
Protects the market for the corporation that developed it
Criticism
Farmer’s in poor nations must be able to grow next years crops from their own seeds
Gives an advantage to developed countries

46. Gene Transfer Genes transfer from one major life form to another
Most likely to have negative and undesirable impacts than the previous two methods
E.g. Bacillus thuringiensis
Produces toxin that kills caterpillars
Gene identified and transferred to corn
Engineered corn now produces its own pesticide

47. Gene Transfer Pro: Bt plants thought to be a constructive
step in pest control
No longer need to spray pesticide
Con: Bt plants produce toxin in all cells
Even in pollen that can spread
Monarch butterflies that eat pollen may die
Concerns about the effects of humans
consuming genetically modified foods