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Soils. Mr. Gust. Soil Definition. A layer of natural materials on the earth’s surface containing both organic and inorganic materials and capable of supporting plant life. Why is Soil Important?. Gives plants something to grow in Holds nutrients Home to microorganisms Holds water

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  1. Soils Mr. Gust

  2. Soil Definition • A layer of natural materials on the earth’s surface containing both organic and inorganic materials and capable of supporting plant life.

  3. Why is Soil Important? • Gives plants something to grow in • Holds nutrients • Home to microorganisms • Holds water • Provide us with a food source

  4. Soil Formation Factors Five factors control soil formation: • Parent material-Source of mineral matter • Limestone, sandstone, shale, basalt • Time-longer forming, thicker soil • Climate-greatest effect on rate. Hot wet climate goes fastest • Vegetation- More vegetation, increased soil forming • Topography-slope. Erosion elevated, less soil formed

  5. Physical properties of soil: • Soils are made up of four substances: • Small mineral particles – from the breakdown of rocks – about 45% • Organic matter – plant and animal material, both dead and living, microbes – about 5% • Water • Air • Percentages of water and air can vary greatly

  6. Ideal soil growing media: Air 25% Solid 50% Water 25%

  7. Soil textures: • Large particles: stones, cobbles, gravel • Mineral particles in soil: • Sand (largest particles) • Silt (smaller) • Clay (smallest) • Soil texture refers to the amount of sand, silt and clay in the soil.

  8. Soil Particle Sizes

  9. Particle sizes: (diagram) Texture Sand Silt Clay Sand compares to barrel Silt compares to a plate Clay compares to a coin

  10. How can you tell what soil texture you have? • Sand can be seen with the naked eye. Feels gritty. • Silt is intermediate in size. Visible under microscope. Feels like talcum powder. • Clay is smallest particle. Feels slick and sticky when wet, firm when moist and hard when dry. Size of particles affects moisture-holding ability, plowing, which crops can be grown.

  11. Hydrometer Method • Largest particles fall out first • Measure amount (mm) of each particle size • Use chart to determine soil type

  12. Pores • Spaces in soil between the mineral material (sand, silt, clay), organic matter • Micro Pores • Water filled at field capacity • Macro Pores • Air filled at field capacity • Field capacity=amount of moisture in soil after excess water has drained away

  13. Pores

  14. Soil/water relationships: • Water drainage depends on soil pore size • Large pores in the soil can take in water more rapidly than fine pores. • Sandy soils drain fastest • Clay soils retain water longer

  15. Soil/Water Relationships • Saturation • Can take no more water, water starts to puddle on top • Field Capacity • Moist • Wilting Point • Plant can not uptake any more water, starts to wilt

  16. Soil profile (horizon) is … • The arrangement and properties of the various soil layers • Topsoil (A Horizon) • Organic material, dead plant/animals, roots, humus • Subsoil (B Horizon) • Clay that has moved (leached) down over time • Parent material (C Horizon) • Rock

  17. More about topsoil: • Surface, top layer of soil • From a few inches to several feet thick • Darker, contains organic material • Softer, more easily worked than underlying areas. • Also called the A horizon • Farmland

  18. More about subsoil: • Layer just under topsoil • Lighter in color – may be red, brown, yellow or gray in color • Little or no organic material • Usually higher in clay content than topsoil • Firmer, more difficult to penetrate • Also called the B horizon

  19. More about parent material: • Lower soil layer • Material from which topsoil and subsoil developed • Very firm and difficult for roots to penetrate • Also called the C horizon

  20. What does soil color indicate? • Drainage • Brown or dark brown surface soil layers indicate the presence of organic matter. • Subsoils are often reddish brown, red, yellowish brown, yellow or gray, indicating how wet the soil is at certain times. • Gray means poorly drained and clay • Red, brown or yellow colors means well drained • Light/dark color can affect heat too

  21. Soil depth is: • The total depth of topsoil, subsoil and parent material for plants to grow. • Can cause the yield of a crop to be high or low. Deep rooted plants, such as alfalfa, will not grow well when planted on a shallow soil. • Deep soil= 35 inches plus • Moderately deep soil=20 to 34 inches deep • Shallow soil= 10 to 20 inches deep. • Very shallow soil is 10 inches or less.

  22. Soil pH: • Water in soil contains dissolved mineral salts – the “soil solution.” • Numbers from 1 to 14 measured with a pH meter • Some materials added to soil change the pH (peat moss is acidic, limestone is alkaline) Alkaline Acidic Neutral 5 7 1 2 3 4 6 8 9 10 11 12 13 14

  23. Cation exchange capacity (CEC): • The total number of exchangeable cations a soil can hold (the amount of its negative charge) is called its cation exchange capacity or CEC. • The higher a soil's CEC, the more cations it can retain. • Cations include Phosphorus, Potassium • CEC increases as organic matter/clay increases.

  24. Organic matter improves the soil: • Soil organic matter consists of plant and animal residues in various stages of decay. • The 4 benefits of organic matter: • Improves physical condition and structure • Increases water infiltration • Decreases erosion losses • Supplies plant nutrients (increased CEC)

  25. Soil Erosion • Erosion is the process of wearing away or removing • Water • Splash • Sheet • Rill • Gully • Stream bank • Wind • Surface creep • Saltation • Suspension

  26. 1965 soil taxonomy system for the United States: • Gelisols - soils with permafrost within 6 feetof thesurface • Histosols - organic soils NRCS photos

  27. 1965 soil taxonomy system for the United States: • Spodosols - acid soils with a subsurface accumulationof metal-humuscomplexes • Andisols - soils formed in volcanic ash NRCS photos

  28. 1965 soil taxonomy system for the United States: • Oxisols - intensely weathered soils of tropical and subtropicalenviron-ments • Vertisols - clayey soils NRCS photos

  29. 1965 soil taxonomy system for the United States: • Aridisols - calcium carbonate-containing soilsin aridenviron-ments • Ultisols - soils with a subsurface zone of silicate clay accumu-lation NRCS photos

  30. 1965 soil taxonomy system for the United States: • Mollisols - grassland soils • Alfisols - another type of soil with a subsurfacezone ofsilicateclayaccumu-lation NRCS photos

  31. 1965 soil taxonomy system for the United States: • Inceptisols - soils with weakly developed subsurfacehorizons • Entisols - soils with little or no morphological develop-ment NRCS photos

  32. Wrapping it all up: • Soil is the soft outer covering of the earth. • One of our most importantnatural resources • Necessary for plants to grow • Provides food for plants, which in turn furnish food for humans and animals • Stores much of the water that plants use

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