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

2. Many environmental problems result from agriculture:
Soil erosion
Sediment transport and deposition downstream
On-site pollution from fertilizers and pesticides
Deforestation
Desertification
Degradation of water aquifers
Salinization
Accumulation of toxic metals and organic compounds
Loss of biodiversity

3. Loss of Nutrients Soil is KEY to sustainable farming, but…
Organic matter is not cycled back into the soil.
Soil is exposed to sunlight (This speeds up decomposition of organic matter)

4. Loss of soil fertility
The rate of loss of fertility is : measured as the time required for the soil to lose ½ of its original store of chemical elements necessary for crop growth.
Depends mostly on climate : warmer and wetter climates accelerate this process

5. How do we combat this? Organic fertilizers – Cow manure
Don’t provide enough of the chemical elements lost
Industrial Produced Fertilizers –
Major increase in crop production in 20th century
Nitrogen – nitrogen gas is converted to nitrate
Phosphorus – bird guano, mined

7. Where Eroded Soil Goes: Sediments Also Cause Environmental Problems
-Downstream
-Into lakes and ponds – brings fertilizer with it – **Eutrophication**

8. Ways to slow erosion Making Soil Sustainable Contour Plowing
Fall plowing, multiculture, terracing, crop rotation
Contour Plowing
No-Till Agriculture
Combination of farming practices that include not plowing the land and using herbicides to keep down weeds.

10. Controlling Pests
Pests = undesirable competitors, parasites or predators
Insects
Nematods (worms)
Bacterial & viral diseases
Weeds
rodents

11. Crop Loss Pests account for an estimates loss of:
1/3 potential harvest (weeds)
1/10 harvested crops (herbivores)
Weeds – Early successional plant
Fast growing
Seeds spread easily
Successful in harsh environments

13. History of Pesticides Pre-Industrial Revolution Little could be done
Slash and Burn agriculture – decreased density of pests
Aromatic herbs – repel insects – citronella
Search for “narrow spectrum pesticide” – single target
Earliest pesticides – inorganic compounds - arsenic

14. History Cont’d
1930’s
Petroleum based sprays and natural plant chemicals.
Many plants naturally produce chemicals to protect against disease and pests
Ex/ Nicotine – primary agent in pesticides today
Not as effective as desired

15. History Cont’d Artificial Organic Compounds DDT
Aldrin all have side effects that affect
Dieldrin living organisms
These pesticides were prone to Bioaccumulation!!!

16. History Biological Control
Use biological predators and parasites to control pests
Bacterium – Bacillus Thuringiensis
Disease that affects caterpillars
Spores of BT sold commercially
Important in controlling Gypsy Moths
Harmless to mammals
Wasps – parasites to caterpillars
Ladybugs
Sex pheromones – bait in insect traps

17. End of History Integrated Pest Management Goals:
Control of agricultural pests using several methods together, including biological and chemical agents
Goals:
To minimize the use of artificial chemicals
To prevent or slow the buildup of resistance by pests to chemical pesticides

18. Genetically Modified Crops
Development of hybrids for small grains has increased productivity in 20th century
Worry !!! production of “super hybrid” – would be overly productive and grow everywhere OR ----
Could interbreed with weeds – creating a “superweed”. Resistant to pesticides --- OR—
“super hybrid” may require more fertilizer, pesticide and/or water.

20. The Terminator Gene
A genetically modified crop which has a gene to cause the plant to become sterile after the first year
Prevents GMC from spreading
Farmers MUST purchase seed each year
WORRY --- crop growth could be controlled by whoever has the seeds.

21. Grazing on Rangelands
Overgrazing occurs when the carrying capacity is exceeded. It can cause severe damage to lands
It is important to properly manage livestock, including using appropriate lands for gazing and keeping livestock at a sustainable density

22. Desertification
Desertification is the deterioration of land in arid, semi- arid and dry sub humid areas due to changes in climate and human activities
Can be caused by
Poor farming practices
Conversion of marginal grazing lands to croplands