Ch12 Farming and the Environment SH.pdf
Transcript
Chapter 12 Farming and the Environment How Agriculture Changes the Environment Agriculture is one of our greatest sources of environmental damage. Major environmental problems – – – – Soil erosion Sediment transport and deposition downstream On-site pollution from overuse and secondary effects of fe...
Chapter 12 Farming and the Environment How Agriculture Changes the Environment Agriculture is one of our greatest sources of environmental damage. Major environmental problems – – – – 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 0 0 000 s How Agriculture Changes the Environment (2) Major environmental problems are: – – – – – – Deforestation Desertification Degradation of aquifers Salinization Accumulation of toxic organic compounds Loss of biodiversity Soil and Soil Profile Plowing: Boone or Bane? There is nothing in nature like the plow 031 - Big difference between soils of an unplowed forest and soils of previously forested land that has been plowed and used for agriculture The more altered the soil the greater the amount of material must be added each year - Fertilizers, pesticides, water gradually wear off Our Eroding Soil me 0 When land is cleared off its natural vegetation, the soil begins to lose its fertility by: - Physical erosion Became a national issue in the US in the 1930s - 0 Intense plowing and drought (The Dust Bowl of the 1930s) Soil loosened by years of plowing was blown away by string winds Plowing: Old and Modern Rill Erosion Rill erosion is the removal of soil by concentrated water running through little streamlets Tillage (plowing) loosens the soil making it more susceptible to rill erosion. Dust Bowl of the U.S. Midwest Poor agricultural practices and a major drought created the Dust Bowl in he 1930s that lasted about 10 years. Our Eroding Soil (2) so The land that became the Dust Bowl had been prairie - Deep rooted grasses that held soil in place - After plowing soil exposed to elements When original vegetation is cleared soil changes - Crops harvested and removed, less organic matter returning to soil - Soil exposed to sunlight which speeds rate of decomposition Our Eroding Soil (3) 0 Traditionally decline in soil fertility combated using organic fertilizers - Animal manure In the 20th century crop production increased - Chemical or artificial fertilizers add nitrogen and phosphorous to the soil Since WWII mechanized farming has seriously damaged land - > 1 billion hectares - In US 1/3 of topsoil has been lost Boobies on a guano island. Birds stand on phosphate deposits formed of bird droppings that forms a major source of phosphorous for agriculture for centuries. Where Eroded Soil Goes 6 A lot of it travels down streams and rivers - Deposited at their mouths fill in water ways - Damage fisheries and coral reefs Sedimentation has chemical effects - Enrichment of waters, eutrophication Transport of toxic chemical pesticides Making Soils Sustainable Soil forms continuously - But very slowly 1 mm of soil formation takes 10-40 years 90 To be truly sustainable soil lost should equal amount of new soil produced. One way to sustain soil is: Contour Plowing: Land is plowed perpendicular to the slopes and as horizontally as possible. O Os - One of the most effective ways is to reduce soil erosion - Also uses less fuel and time 0 Contour plowing minimizes erosion on sloping ground Grazing on Rangelands (land used for grazing) Almost half of the Earth's land area is used as rangeland 0 - 30% of Earth’s land area is arid rangeland Arid rangeland easily damaged especially in time of drought Streams and rivers also damage - Trampling banks and fecal matter Carrying Capacity of Grazing Lands 0 Carrying capacity - The maximum number of species per unit area that can persist without 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. Carrying Capacity of Grazing Lands (2) 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 Increases loss of soil by erosion Subjects the land to further damage from trampling Desertification Desertification is 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) 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 Desertification (2) Earth has five natural warm desert regions Primarily between 15o and 30o north and south of the equator Based on climate only ~30-33% of earth’s land area should be desert, but - 43% of land is desert - Addition area due to human activities Causes of Desertification In general, desert like areas can be created anywhere by poisoning the soil - World wide chemicals account for 12% of soil degradation - Irrigation in arid lands can cause salts to build up to toxic levels Causes of Desertification (2) The leading cause of desertification are bad farming practices. Failure to use contour plowing Too much farming Overgrazing Conversion of rangelands to croplands in marginal areas Poor forestry practices Effects of Desertification Lowering of water table Increase in the salt content of soil Reduced surface water Increased soil erosion Loss of native vegetation Preventing Desertification First step is detection of symptoms―awareness - Achieved by monitoring groundwater, soil depth, fertility, agricultural practice, chemical degradation, etc. Next step - Proper methods of soil conservation, forest management and irrigation Good soil conservation includes - Use of wind breaks Reforestation
