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Soils

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Soils

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  1. Soils

  2. What is soil? • Thin layer on the earth’s surface that is made by the interaction of five factors: rocks, sunlight, water, air, and living organisms

  3. Soil Composition The average soil is mainly composed of mineral particles that come from rocks. Below is the composition of an average soil. Taken from http://www.physicalgeography.net/fundamentals/10t.html

  4. Soil Formation/Composition • The formation of 1 meter of soil can take from 100 – 100,000 years to form (depending on the conditions present) • Climate affects rate • Higher temp. and more rain = faster soil formation • Rain provides water for chemical reactions to occur and warmer temp. increases speed of reactions

  5. Soil formation/Composition • Rocks are the “parents” of the soil • Parent material affects the kind of soil that is formed • Different rocks contain different minerals • Color of soils is partially dependent on the minerals the soils contain

  6. Soil formation/Composition • Weathering – the process of breaking rocks apart or removing minerals from them. • Weathering agents can be physical and chemical • Weathering agents include water, ice, wind, temperature changes, sand, glaciers, and plant roots

  7. Soil formation/CompositionWeathering • Temp. changes cause rocks to expand and contract cracking rocks and releasing minerals • Water in cracks can turn to ice further splitting rocks • Roots can act as physical wedges. They can also produce chemicals that dissolve minerals from the rocks • Sand and rocks carried by moving water scour the soil and rocks beneath • Glaciers that carry much bigger rocks can file and scrape rocks below • Wind-blown sand acts like a sandblaster on the surfaces of rocks

  8. Soil formation/CompositionChemical Changes in Rocks • Equation for ferric oxide reaction (rust) Significance of reaction:

  9. Soil formation/CompositionChemical Changes in Rocks • Equations for Carbonic acid formation and calcium and bicarbonate ion formation: • Significance of reactions:

  10. Soil Composition • The average soil consists of 25% air and 25% water. • Water and air are extremely important -for plant roots -for many of the bacteria, protists, fungi, and animals that live in the soil -All of the organisms that live in the soil interact together to form the soil ecosystem

  11. Soil CompositionOrganic Matter • An average soil contains 5% of organic matter • Although organic matter is only a small percentage of the overall soil it is extremely important • In an average soil, 80% of the organic matter is humus, 10 % is roots, and 10% is organisms

  12. Humus • Humus-partly decomposed organic matter that was once living or was produced by a living thing. • Provides nutrients to many organisms • Increases water-holding capacity of soil • Provides nutrients to plants

  13. Image taken fromhttp://urbanext.illinois.edu/soil/SoilBiology/soil_food_web.htm

  14. Taken from http://permaculturenews.org

  15. Soil texture • Mineral particles in soil are classified by size • Size of particles determines soil texture • See soil texture chart on page 213

  16. Soil Texture

  17. Soil Triangle

  18. Spaces in soil • Normally 40-60% of volume of soil is pore space • Important for water and air to travel through soil • Determine infiltration and percolation rates • Size of spaces is dependent on texture • Smaller particles=smaller spaces • Larger particles=larger spaces

  19. Key terms • Soil texture – size of mineral particles • Infiltration – the ability of water to soak into the soil • Water holding capacity – the ability of soil to store water • Aeration – the ability of air to move through the soil

  20. Soil Comparison *Loam is considered an ideal soil for many crops due to its mix of different soil particles (sand, silt, and clay)

  21. Soil Structure • Structure-when individual particles are “glued” together to form larger pieces • The “glue” is produced by organisms in the soil • Granular structure-rounded clumps with a diameter of less than 1.5 cm • Crumb structure-irregular shaped clumps • Platy structure-soil particles glued together into thin horizontal plates

  22. Soil Profile (in descending order) • Topsoil-top layer of humus rich soil • Subsoil-layer of soil beneath the topsoil (does not contain humus) • Parent material –the pieces of rock that lie on top of solid rock • Bedrock-solid rock

  23. Soil Conservation • Erosion-the process in which wind or water move soil to new locations • Erosion occurs naturally but can also be caused by human activities • To much erosion is bad for farming • Displaced soil can also be a major pollutant of aquatic ecosystems

  24. Some causes of erosion • Overgrazing by livestock • Repeated years of monocultures • Plowing land • Construction • Surface mining • logging

  25. Preventing erosion • Contour planting-planting across a slope (rather than up and down it) • Strip cropping-strips of close growing plants are planted next to crops that are planted in rows • Diversion terraces-ridges of soil that are constructed along the contours • Waterways-wide ditches that are planted with a permanent grass cover

  26. Contour planting http://www.extension.iastate.edu/agdm/crops/html/images/a1-41/image5.jpeg

  27. Strip Cropping http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1088801071&topicorder=12&maxto=16

  28. Diversion Terraces http://www.wi.nrcs.usda.gov/programs/solutions/diversion.html

  29. Waterways http://milford.nserl.purdue.edu/weppdocs/overview/practices.html

  30. Preventing erosion • Crop rotation • Windbreaks • Conservation tillage-methods to reducing the amount of tilling and avoid the use of the moldboard plow • Cover crops-grasses or legumes planted to hold soil in place

  31. Crop Rotation http://www.marionswcd.net/crop-rotation/

  32. Windbreaks http://www.mda.state.mn.us/protecting/conservation/practices/fieldwindbreak.aspx

  33. Conservation Tillage http://nfrec.ifas.ufl.edu/programs/impacts_conservation_tillage.shtml

  34. Cover Crops http://biocontrol.ucr.edu/irvin/research/wsare.html

  35. The dust bowl • Dust bowl- Area in the southern part of the great plains which experienced massive amounts of soil erosion during the 1930s • Caused by poor farming practices combined with drought and winds • As a response the federal government created several agencies and policies to prevent soil erosion