1. Effects of Agriculture on the Environment
Chapter 12
Effects of Agriculture on the Environment

2. Case Study – Clean-Water Farms
Concern: erosion and water quality
How concern was addressed: convert some areas to grass and rotate animals through newly created paddocks
Results: evenly distributed wastes, prevented overgrazing, able to increase size of herd
Intensive Rotational Grazing/Management Intensive Grazing – addresses which theme?

3. 12.1 – How Agriculture Changes the Environment
Soil erosion
Sediment transport/deposition down stream
On-site pollution
Off-site pollution
Deforestation
Desertification
Degradation of aquifers
Salinization
Accumulation of toxic metals
Accumulation of toxic organic compounds
Loss of biodiversity

4. 12.2 – The Plow Puzzle Fig. 12.2 – Only ants eat bread crumbs
….“man is everywhere a disturbing agent. Wherever he plants his foot the harmonies of nature are turned to discords.”
“The equation of animal and vegetable life is too complicated a problem for human intelligence to solve, and we can never know how wide a circle of disturbance we produce in the harmonies of nature when we throw the smallest pebble into the ocean of organic life.”
Fig – Only ants eat bread crumbs
George Perkins Marsh

5. 12.3 – Our Eroding Soils
American Dust Bowl of the 1930’s
-soil erosion rates in the U.S. have decreased but regeneration is slow
Decline in organic matter due to: a)vegetation is cleared/crops planted and harvested
b) less input of dead organic matter
c) soil is exposed to sun speeding rate of decomposition

6. 12.3 continued
What factors increase the rate at which soil fertility is lost?
Organic vs synthetic? Paper or plastic?
Conversion of nitrogen gas to nitrates and phosphorus from guano and marine fossils

7. 12.4 – Where Eroded Soil Goes
Physical effects: sediments fill in productive waters and can destroy coral reefs
Chemical effects:

8. 12.4 continued
Making soils sustainable – amount lost = amount produced
- 1mm can take from 10 to 40 years to form
- options include: a) fall plowing, b) multiculture, c) terracing, d) crop rotation, e) contour plowing, and f) no-till agriculture

9. 12.4 continued
Contour plowing – land is plowed ┴ to the slopes and as horizontally as possible
Single most effective in decreasing erosion

10. 12.4 continued No-till – uses herbicides and IPM to control weeds
- decreases release of CO2
- leave unused portions of plants to decay
- 17.5% of farms in U.S.

11. 12.5 – Controlling Pests Define pest Insects Nematodes
Bacterial/viral diseases
Weeds
Vertebrates
Account for a loss of 1/3 potential and 1/10 of harvested crops(in U.S.)

12. 12.6 History of Pesticides Remove weeds by hand/planted aromatic herbs
Search for “magic bullet”/early pesticides were highly toxic Ex) arsenic
1930’s – petroleum-based sprays/natural plant chemical Ex) nicotine
- safe, but not as effective

13. 12.6 continued Artificial organic compounds Ex) DDT(broad-spectrum)
Biological control – a) Bt, b) wasps, c) ladybugs, d) pheromones

14. 12.7 – Integrated Pest Management
Biological Control, use of some chemical pesticides, some methods of planting crops
Key: control vs elimination of pests
Monitoring of pesticides: a)breakdown may be slow, b) intermediate may be toxic, c) many unanswered questions

16. 12.8 Genetically Modified Crops
Positive
Negative
Natural
“superhybrid”
“superweed”
Growth on marginal lands
3 methods faster/more efficient development of new hybrids
Ex) symbiotic relationship w/bacteria

18. 2. Introduction of the terminator gene
Positive
Negative
Prevents gm crop from spreading
Not for economically disadvantaged

19. 3. Transfer of genes Positive Negative Improved nutritional value
Novel effect
Ex) rice w/beta-carotene
Non-target organisms affected

20. 12.9 Grazing on Rangelands
~ ½ of Earth’s land area is used as rangeland
I – Traditional and Industrialized Use – overgrazing vs feedlots are source of local pollution
II – Biogeography of Agricultural Animals-
2 major environmental affects – 1. native vegetation may be greatly reduced and threatened with extinction

21. 12.9 continued Introduced animals may compete with native herbivores
Ex) Brazilian Amazon Basin – burn forest
- plant crops(~4yrs)
- convert to rangeland(~4yrs)
- move on

22. 12.9 continued
III – Carrying capacity- varies with rainfall, topography, soil type, soil fertility
- exceed carrying capacity overgrazing decrease plant diversity/increase soil erosion/leads to dominance by plant species undesirable to cattle

23. 12.10 – Desertification – Regional Effects and Global Impact
Expanding due to: changes in climate
human activities  destroy a soil’s ability to store water
The geographic location of deserts is controlled by descending air masses.
They occur on the leeward side (rain shadow) of a mountain range.
They also occur at latitudes 30 degrees N and 30 degrees S as a
result of global air circulation
Rising air masses expand, cool, and precipitate moisture.
Descending air masses compress, warm, dry, and evaporate moisture
I – What causes deserts?
a) poor forestry and farming practices
b) overgrazing
c) conversion of rangelands to croplands
d) irrigation

24. 12.10 continued II – Preventing desertification
Step 1 – detect symptoms such as: lowering of water table, increase in salt concentration in soil, decrease in surface water, loss of native vegetation, and increase in soil erosion
Step 2 – attempt to control activities listed above

25. 12.11 – Does Farming Change the Biosphere?
Affects species diversity
Increases CO2 in atmosphere
Changes in biogeochemical cycles
Change in land cover
a) change in reflection of light by surface
b) changes in rate of evaporation of water
c) change in rate of exchange of chemical compounds produced/removed by living things