Chapter 12

1. Chapter 12 Effects of Agriculture on the Environment

2. Case Study: Clean-Water Farms • Farmers concerned about erosion, pesticides, fertilizers, and livestock waste (impact on environment). Started clean water project. • Convert some crops to grass to lessen erosion. • Rotate animals in areas of land to reduce concentrated wastes and overgrazing. • Benefits farms and environment.

3. 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

4. The Plow Puzzle • Plowed soil is different than natural soil. • Natural soil has distinct layers and is rich in organic matter. • Plowed soil churns all layers together and is poor in organic matter. • How is it possible that farmers have been growing crops in plowed soil for thousands of years?

5. Layers of Soil

6. Our Eroding Soils • Soil is lost to erosion. • Plowed soils erode more quickly. • Ex: American Midwest circa 1930’s: The Dust Bowl. • Topsoil was blown away when drought occurred.

7. Fertilizers • Fertilizers are used to replace provide nitrates to plants. • Traditional fertilizers were organic such as cow manure. • Artificial fertilizers are converted atmospheric nitrogen into nitrates, mined phosphorus, and other additives. • Erosion has slowed in the US, but not in many other countries.

8. Where Eroded Soil Goes: Sediments Also Cause Environmental Problems • Ways to slow erosion: • Making Soil Sustainable • Contour Plowing • No-Till Agriculture • Combination of farming practices that include not plowing the land and using herbicides to keep down weeds.

9. Conservation Tilling

10. Controlling Pests • Pests are any organism that lessens agricultural production. • Controlling pests is the attempt to stop succession. • Pesticides are any chemical used to reduce pests.

11. History of Pesticides • Prehistoric farmers planted herbs (to repel insects) near crops. • Early chemical pesticides included arsenic, which is poisonous to most living things. • 1930’s farmers used petroleum and plant-based chemicals like nicotine. Safe, but not effective. • Later, scientist began developing chemicals like DDT. Effective, but not safe.

12. Pesticides, cont. • Scientists search for a “narrow-spectrum pesticide” to kill pests, but not desired plants. • An alternate to chemical control is to use biological control. • Biological controls are natural predators. • Though safer than chemicals, biological controls may have undesirable side-effects.

13. Integrated Pest Management • 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

14. Integrated Pest Management

15. Genetically Modified Organisms • Gene for desired trait is removed from donor organism and inserted into bacteria plasmid DNA. • Bacteria infects target plant and inserts gene into target plant DNA. • Target plant (GMO) expresses gene for new trait.

16. Spread of GMO

17. The Terminator Gene • A genetically modified crop which has a gene to cause the plant to become sterile after the first year. • Used to prevent the spread of GMO’s. • Drawback is that farmers must purchase their seeds every year.

18. GMO Downfalls • GMO’s can have unexpected effects on the ecosystem. • Ex: Bacteria gene inserted into a potato caused ALL of the potato cells to produce a toxin, thus endangering other organisms.

19. Traditional vs. Industrial Grazing • In traditional grazing, herds of animals are led from one area to another and allowed to graze on existing plants. • In industrialized grazing, plants are grown specifically for grazing, and animals are contained in small, fenced-in areas, thus upsetting the environment.

20. 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

21. Carrying Capacity of Pasture and Rangeland (Cows per square kilomenter)

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

23. Symptoms of Desertification • Lowering of water table • Increased salt content of soil • Reduced surface water • Increased erosion • Loss of native vegetation

24. How Agriculture Changes the Biosphere • Land cover changes result in changes to sunlight reflection, evaporation, and chemical cycles. • Increase in CO2 by use of fossil fuels and clearing of land. • Species diversity reduced.

25. Summary • Industrial Revolution and rise in agricultural sciences have led to a revolution in agriculture. • Modern fertilizers have led to an increase in crop yields per unit area. • 20th Century agriculture has relied on machinery and the use of abundant energy. • Little attention paid to erosion, loss of groundwater, effects of pesticides. • Overgrazing damages land. • Desertification is caused by poor farming practices. • Currently, both ecological and genetic revolutions are happening.