Chapter 15, Section 2: Crops & Soil Standards: SEV4a, b, c Food & Agriculture
What is arable land? Land that can be used to grow crops Only 10% of land on earth is arable. Urban areas occupy 3% and are currently invading arable land.
What is the history of agriculture? Traditional Agriculture Plows pulled by animals to turn & loosen soil. Organic fertilizer (animal manure) used to enrich soil for plant growth. Drainage ditches were dug to bring water to plants for irrigation. Weeds pulled by hand.
What is the history of agriculture? Modern Agriculture Large machines plow land and harvest crops. Synthetic chemical fertilizers used instead of manure Overhead sprinklers & drip systems irrigate crops Synthetic chemical pesticides are used to kill pests The chemical fertilizer & pesticides are often oil based.
How does soil form? Rock breaks down into fine particles and mix with decomposing matter to make topsoil. Chemical Weathering Rock is broken down by chemical rxn btwn water & a substance in rock that can be dissolved EX: Lichen secrete acids that break rock down Physical Weathering Water Wind Bacteria, fungi, earthworms all break down dead matter & recycle nutrients back to soil. Earthworm burrows allow air to circulate in soil
What are the layers of soil? Surface litter/Organic layer- leaf litter, partially decomposed organic matter Topsoil- organic matter, living organisms, fine rock particles; also water & air Subsoil- larger rock particles, some organic matter, mostly inorganic compounds Parent Rock- bedrock that has been weathered Bedrock- solid rock layer
What problems are associated with our use of soil? Erosion Movement of rock & soil by wind or water ½ of topsoil in US has eroded- affects ability to grow crops Farming increases rate of erosion through plowing & irrigation Desertification Land in arid/semi-arid areas becomes more desert-like Due to overgrazing & planting too many crops Salinization Soil too salty to grow plants in. Becomes salty from Over-irrigation Low rainfall Flooding field with freshwater can remove excess salt White salt deposits on cropland
What steps are taken to conserve soil? Terracing- cutting levels into steep hillside to slow water erosion Contour plowing- plowing across hill on gentle slope to slow water erosion Strip plowing- leaving strips of vegetation in every other row so roots hold soil in place
What steps are taken to conserve soil? Drip irrigation- using series of hoses to drip water around plant roots; expensive but very effective No-till harvesting- harvesting crop without turning soil. Roots hold soil to prevent erosion Cons- old crop might crowd out new crop and decrease crop yields
What steps are taken to conserve soil? Crop Rotation- Rotating crops to replenish nutrients in soil. Corn crops remove nutrients from soil so planting a crop of soybean the next year will replenish those nutrients back to the soil. Compost Partly decomposed organic matter from yard waste, home food waste, or crop waste Added with chemical fertilizers to enrich soil.
You should be able to… Explain the difference between traditional and modern farming methods. Describe the structure and composition of fertile soil. Explain why the presence of plants helps prevent soil erosion. Explain why soil conservation is an important agricultural practice.