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The Basics of Soil Science

The Basics of Soil Science

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The Basics of Soil Science

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  1. The Basics of Soil Science

  2. What is soil? • It is composed of minerals, organic material, and living forms. • Functions: • Medium for plant growth • Recycler of raw materials/environmental filter • Regulator of water supplies • Habitat for soil organisms

  3. Components of Soil: Minerals • Minerals are particles formed by the weathering of rocks. • Rocks are weathered when exposed to water, air, and organisms (microbes, plants, and animals).

  4. Components of Soil: Organic Matter • Consists of organic substances, including living organisms, carbonaceous remains of organisms, and organic compounds produced by decomposition. • Some of the living organisms found in soil: • Plants, fungi, bacteria, algae, protozoa, worms, insects, and mammals.

  5. Soil Texture

  6. Soil Texture Video Clip •

  7. Soil Particles • The minerals that make up soils are made of different sized particles. • This amount of these particles determines the texture of the soil.

  8. Soil Particles • There are three particles of soil: • Sand: can be seen by the naked eye and feel gritty; these particles don’t stick together • Silt: are too small to see without a microscope, feel smooth but not sticky when wet. • Clay: the smallest sized particles; are sticky when wet and form hard clods when dry.

  9. Soil Texture • There are 12 textural classes for soil. • All of which are based on the percentage of sand, silt, and clay particles. • The easiest way to determine texture of a soil is by feeling the soil when wet.

  10. Soil Texture • Three broad groups of textural classes: • Sandy Soils: contains at least 70% sand particles of the soil by weight • Loamy Soils: An ideal loam would exhibit properties of sand, silt, and clay in equal proportions. • Clayey Soils: class names in this group are the amount of clay particles required to be in each of the classes: • Clay-at least 40% clay • Sandy Clay-at least 35% clay • Silty Clay-at least 40% clay

  11. Soil Structure • Granular and crumb: rounded aggregates usually lying loosely and are separated from each other. Common in surface A horizons. • Platy: relatively thin horizontal plates. Often found in compacted horizons and E horizons. • Prismatic and columnar are characterized by vertically oriented aggregates or pillars. • Prismatic: aggregates are longer than wide; have angular edges and tops. • Columnar: aggregates are longer than wide; top and sides are more rounded.

  12. Soil Structure • Structureless • Massive: all of the particles are stuck together in one giant mass. • Single-grained: sand dune or beach sand • Block-like: angular blocky and subangular blocky subtypes where the aggregates have been reduced to blocks, irregularly six-faced, with their three dimensions more or less equal. • Subangular blocky: rounded corners • Angular blocky: corners not rounded

  13. Soil Profile

  14. Soil Profile • Soil consists of many layers called horizons. • The soil profile is a 2D section of soil showing each of the horizons. • Horizons are influenced by soil-formingprocesses.

  15. Soil Horizons: • O-made up of organic horizons that form above the mineral soil. Usually occur in forested areas and are generally absent in grassland areas. • A-humus accumulates at this layer to darken the soil. This layer has high biological activity, including rooting. • E- Large amounts of clay and iron have been removed from this layer. It is a zone of maximum leaching (eluviation or removal).

  16. Soil Horizons • B-known as the zone of illuviation (I=input). Illuviation is the process of deposition in lower soil horizons of material eluviated from upper horizons. • C- Layer of unconsolidated (loose) soil parent material. • R- Consolidated hard rock (i.e. bedrock).

  17. Soil Color

  18. Soil Color • Soil color is the soil characteristic that is easiest to determine and identify. • It is used to distinguish and identify soil horizons. • The color of the soil tells us about the components of the soil. • It is classified according to: • Hue-the dominant spectral color (i.e. red or yellow) • Value-the amount of light reflected (0-black to 10-white or very light) • Chroma-the purity of the color (0-grayed to 10-pure color)

  19. Soil Color: Descriptions • Yellow-Red: presence of iron-oxides • Dark Brown/Black: high organic matter content • Black: Manganese mineral deposits • Gray: low oxygen level (wet soil) • White: calcium carbonates Soil Color Chart

  20. Soil Water

  21. Facts about Water • It takes 17,000 gallons of water to produce one meal for the average human adult. • Amount of Water on Earth: • Oceans 97.25% • Ice 2% • Ground Water 0.7% • All other Water (<.05%) • Lakes 60% • Soil Water 33% • Atmosphere 6% • Rivers 1%

  22. Facts about Water • Water has a high surface tension • Water is able to dissolve salts • It has strong cohesive and adhesive properties=capillary forces

  23. Soil Water • Saturation: when all of the soil’s pores are filled with water • Field Capacity: the maximum amount of water a soil can hold against the force of gravity. • Permanent Wilting Point: where the plant can no longer maintain its turgor pressure and stays permanently wilted. • Hygroscopic: absorbed water • Plant Available Water = Field Capacity + Permanent Wilting Point • Capillary Water = Field Capacity + Permanent Wilting Point + Hygroscopic

  24. Soil pH

  25. Soil pH • Measures the acidity (low #), neutral (7) or the alkaline (high #) of the soil. • It is important to understand when determining what crops/plants can grow in a particular soil. • Alkaline soils are very sodic (salty) which makes it harder for plants to absorb nutrients.

  26. Soil Fertility • Out of the 17 Essential plant nutrients, 14 of them come from the soil

  27. Soil Fertility • Nutrients are available at different pH levels

  28. Soil Degradation

  29. What is soil degradation? • It is the destruction of the soil structure. • It begins with erosion then moves on to desertification and ends with a loss of soil and plant nutrients. • The primary causes are: • deforestation • overexploitation for fuel wood • overgrazing • industrialization

  30. Soil Degradation • The Dust Bowl of the 1930’s was a result of soil degradation. • Many environmentalists blame agriculturists and agricultural practices for soil degradation. • Do you think they are right? • What is evidence that supports this statement? • What is some evidence that disproves this statement?

  31. Soil Erosion • Erosion is the term given to soil loss due to the mobilization of topsoil by the forces of water and wind. • Wind and water move the eroded particles to another location, where it is deposited as sediment. • Soil erosion is a natural process that removes soil from the land.

  32. Soil Erosion Management Practices: • The principles of controlling erosion are to: • use land in accordance with its capability • protect the soil surface with some form of cover • control runoff before it develops into an erosive force. • Examples: • Strip Cropping • Cover Crops • Windbreaks • Contour Farming • Terrace Farming

  33. Careers in Soil Science • Wetland specialist • Watershed technician • Hydrologist with Board of Health • Environmental technician • State soil and water quality specialist • Soil Conservationist • County Agricultural Agent • Landscaping business • Farming

  34. Careers in Soil Science • On-site evaluation • Crop consultant • Soil scientist, mapping and interpretation, U.S. Department of Agriculture • Research technician • Conservation planner • District marketing manager for an agricultural firm • County conservationist • Crop production specialist • Research scientist