Harmful Impact of Agriculture on the Environment

1. Chapter 12 Effects of Agriculture on the Environment

2. 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 Modern agriculture has a greater harmful impact on environment than any human activity.

4. Soil Composition • 3 main components - Sand, silt, clay • Sand is the largest particle (of the 3) with the smallest surface area, rock and gravel even smaller surface area • Clay is the smallest particle with the largest surface area

5. Porosity and Permeabilty • Clay is the most porous and retains the most water – has the most pore spaces. • Of these 3 soil components, Sand is the most permeable and lets the most water drain through. Rock and larger gravels are even more permeable • Oil and gas extraction related to porosity and permeability

6. Soil Erosion • 3 kinds: sheet, rill, or gully • Lowers soil fertility by depleting plant nutrients in topsoil • Pollutes nearby bodies of water by overloading them with eroded sediment, which can kill fish and shellfish and clog irrigation ditches, boat channels, reservoirs, and lakes

7. Economics of Soil Erosion: Soil is eroding faster than it is forming on about 38% (over 1/3rd) of the world’s cropland • Can increase a country’s need to import food • May intensify competition among nations for food • Causes damages to agricultural land and indirect damage to waterways, infrastructure and human health – estimated to cost around $375 billion per year worldwide ($45 billion per year in US alone) • Good news: Since 1985’s Food Security Act, US has cut soil losses on croplands by 40% because farmers receive a subsidy for replanting highly erodible land with soil saving trees for 10-15 years.

8. Ways to slow erosion: • Conservation-tillage farming – uses special tillers and planting machines that disturbs soil minimally • Low-till or no-till agriculture • Benefits: Increases crop yields, raises soil carbon content, lowers use of water, pesticides, and tractor fuel. Drawbacks: Machinery is costly; more effective in some areas and with certain crops than with others

9. Other ways to reduce soil erosion: • Terrace farming – converts steeply sloped land into broad terraces that run across land contours; retains water and reduces soil erosion by controlling run-off • Contour farming – works with the natural contours of the land; plant and plow in rows across slope of land; holds soil and slows water run-off

10. Other Ways to Reduce erosion (cont.) • Strip cropping – planting alternating strips of a row crop with another crop that completely covers soil; traps soil and reduces water run-off • Alley cropping or agroforestry – crops planted in alleys between trees or shrubs; reduces water evaporation and retains soil moisture • Windbreaks or shelterbelts of trees to reduce wind erosion and retain soil moisture

12. Restoring soil fertility: • Organic fertilizers improve soil structure, add organic nitrogen, stimulate beneficial soil bacteria and fungi. 3 types: animal manure, green manure, compost • Crop rotation • Many farmers use inorganic fertilizers which contain nitrogen, phosphorus, and potassium. Can run off into waterways and pollute them. Does not replace organic matter in soil, so should be used with organic fertilizers for healthiest soil.

13. Green Revolutions – between 1950 and 1970 and again since 1967 • Increased yields per unit area in global food production using these three steps: • 1st step: Develop and plant monocultures of selectively bred or genetically engineered high yield varieties of key crops like rice, wheat, corn • 2nd step: produce high yields by using large amounts of fertilizer, pesticides, and water • 3rd step: Increase the number of crops grown per year through multiple cropping • Problem: lack of water, high costs for small farmers, physical limits (such as poor soils) to increasing crop yields

15. 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

16. IPM Method Examples • Prevention: barriers (Ex: fences, nets) to keep out animals; planting herbs that deter pests; removing pests’ sources of food, water and shelter • Physical or mechanical controls: traps; spraying water or vacuuming to remove pests off crops • Biological: use natural predators like ladybugs, spiders, parasitic wasp to control a target pest; plant nectar producers to encourage natural bird and insect predators • Cultural: proper sanitation and debris removal • Pesticides: as last resort but utilizes ones that are least toxic but effective to target specific pests; combined with other methods above

17. Genetically Modified Crops

19. The Terminator Gene • A genetically modified crop which has a gene to cause the plant to become sterile after the first year • Keeps farmers from saving GMO seeds • Farmers must buy patented GMO seeds annually from corporations

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 grazing and keeping livestock at a sustainable density

21. Desertification: • Desertification: the deterioration of land in arid, semi- arid and dry sub humid areas due to changes in climate and human activities • Dryland productivity drops by 10% or greater, has occurred on about 1/3rd of world’s land due to drought and human activity • Can be caused by • Poor farming practices such as overgrazing • Deforestation • Mining • Conversion of marginal grazing lands to croplands

22. Causes and Consequences of Desertification: • Causes: • Overgrazing • Deforestation • Erosion • Salinization • Soil compaction • Natural climate change • Consequences: • Worsening drought • Famine • Economic losses • Lower living standards • Environmental refugees

23. Carrying capacity of US pasture and rangeland in average number of cows per square km