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?.
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 rxnbtwn 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.