1. Review: Effects of Agriculture on the Environment

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 Ag
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

3. How Agriculture Changes the Environment
Major environmental problems cont.
Deforestation
Desertification
Degradation of aquifers
Salinization of soil (“Salting”)
Accumulation of toxic organic compounds
Loss of biodiversity

4. 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.

5. Our Eroding Soil
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. You can see that erosion has decreased since 1982 by a huge percentage, but erosion continues to claim a lot of our cropland.

7. Our Eroding Soil 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 is cleared soil changes
Soil exposed to sunlight speeds the rate of decomposition
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

8. Where Does Eroded Soil Go?
Since WWII mechanized farming has seriously damaged land: > 1 billion hectares, in US 1/3 of topsoil has been lost (washed to sea)
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

9. 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

10. Contour planted slopes

11. No-Till Agriculture
Land is not plowed, but using 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
Additional benefit is that it reduces the release of CO2 accelerated soil decomposition

12. Fertilizers, Pesticides & IPM

13. Fertilizers
Organic: Organic matter from plants and animals. Typically made from animal manure that has been allowed to decompose.
Inorganic: (synthetic) Produced commercially. Usually done by combusting natural gas, which allows nitrogen from the atmosphere to be fixed and captured in fertilizer.

14. Controlling Pests 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

15. Controlling Pests
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. Weed are also early successional plants as well!

16. Pesticides
Pesticide – a substance that kills/controls organisms that people consider pests
Insecticides targets insects & Herbicides target plants
1st generation: natural chemicals from plants, 2nd generation: synthetic, created specifically
Broad-spectrum pesticides: Designed to kill many different types of pests
Selective pesticides: Designed to kill a narrower range of organisms
Persistence: Length of time they remain deadly in the environment for years, magnified in food webs

17. The 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

18. Bioaccumulation – some pesticides are found to build up over time in the fatty tissues of predators
Example: DDT
When an organism containing the pesticide is eaten, the chemical is transferred to the consumer
Eventually leads to very high pesticide concentrations at high trophic levels

19. The History of Pesticides
Second stage began in the 1930
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

20. Resistance
Resistance – pest populations may evolve resistance to a pesticide over time. These are said to be resistant.
Pesticide treadmill – the cycle of pesticide development followed by pest resistance, followed by development of pesticide
Positive Feedback Loop

21. The History of Pesticides
Forth 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 ladybugs, or parasitic wasps
Proven safe and effective

22. Integrated Pest Management (IPM)
Fifth stage
IPM uses a variety of methods
Biological control
Chemical pesticides
Methods of planting crops (crop rotation, intercropping, planting pest resistant crop varieties, creating habitats for predators, limited use of pesticides)
Goal can be control, but never complete elimination of pests
Economically makes sense
Does less damage to ecosystem, soil, water and air

23. Integrated Pest Management
No-till or low-till agriculture another feature of IPM
Helps build levels of natural enemies of pests

24. Monitoring Pesticides in the Environment
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

25. What does the slide tell us about the overall usage in the US compared to the entire world?

26. 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 fecal matter

27. Peruvian grazing happens at high altitudes where soils are thin and susceptible to erosion damage

28. Traditional and Industrial Use of Grazing and Rangelands
In modern industrialized agriculture
Cattle initially raised on open range
Then transport 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

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

30. Carrying Capacity of 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).

31. Carrying Capacity of 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

32. 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

33. 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

34. 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)

35. What Causes Deserts
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

37. What Causes Deserts
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

38. Preventing Desertification
First step is detection of symptoms
Lowering of water table
Increase in the salt content of soil
Reduced surface water
Increased soil erosion
Loss of native vegetation
Achieved by monitoring

39. Preventing Desertification
Next step
Proper methods of soil conservation, forest management and irrigation
Good soil conservation includes
Use of wind breaks
Reforestation

40. Does Farming Change the Biosphere?
1st Agriculture changes land cover
Resulting in changes in reflected light
The evaporation of water
The roughness of the surface
Rate of exchange of chemical compounds
2nd Modern ag increases carbon dioxide
Major user of fossil fuels
Clearing land speeds decomposition

41. Does Farming Change the Biosphere?
3rd Affect climate through fires
Associated w/ clearing land
Add small particulates to the atmosphere
4th Artificial production of nitrogen
Alters biogeochemical cycle
5th Affects species diversity
Reduces diversity and increases # of endangered species