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  • Soil is actually very difficult to define. Organic material

  • Inorganic material: The size of the pieces varies. It may appear as pebbles, gravel, or as small as particles of sand or clay.

  • Introsoil

    1. 1. The “Dirt” on Dirt Biology 20 : Soil
    2. 2. What is soil?  Soil is the top layer of the earth’s surface, composed of rocky material and also mineral particles mixed with organic matter.  Mineral particles come from weathered “parent material” (rock material)  Organic matter is decayed plant and animal material  Soil is formed over a long period of time  Soil Formation takes place when many things interact, such as oxygen (air), water, plant life, animal life, rocks, and chemicals.
    3. 3. Soil Profil e
    4. 4. Soil Formation  Soil is formed from the weathering of rocks and minerals.  The surface rocks break down into smaller pieces through a process of weathering and is then mixed with moss and organic matter.  Over time this creates a thin layer of soil.  Weathering – is the process of breaking down rocks
    5. 5. Soil Formation & Plants  Plants help the development of the soil.  How?  The plants attract animals, and when the animals die, their bodies decay.  Decaying matter makes the soil thick and rich.  This process continues until the soil is fully formed.
    6. 6. Soil Types  Sand, silt, and clay are the basic types of soil.  Most soils are made up of a combination of the three.  The type of soil varies from place to place on our planet and can even vary from one place to another in your own backyard.
    7. 7. Soil Composition  Soils are a mixture of different things; rocks, minerals, and dead, decaying plants and animals.  Soil can be very different from one location to another.  The inorganic materials are the rocks that have been broken down into smaller pieces.  The organic material is decaying living matter. This could be plants or animals that have died and decay until they become part of the soil.
    8. 8. Soil Composition & H2O  The amount of water in the soil is closely linked with the climate and other characteristics of the region.  The amount of water in the soil changes its composition  The amount of water in the soil also changes the amount of oxygen in the soil  Example:  Very wet soil like you would find in a wetland probably has very little oxygen.
    9. 9. Soil Horizons (layers)  Soil is made up of distinct horizontal layers; these layers are called horizons.  They range from rich, organic upper layers (humus and topsoil) to underlying rocky layers ( subsoil, regolith and bedrock).
    10. 10. Soil Horizons  O Horizon - The top, organic layer of soil, made up mostly of leaf litter and humus (decomposed organic matter).  A Horizon - The layer called topsoil; it is found below the O horizon and above the E horizon. Seeds germinate and plant roots grow in this dark-colored layer. It is made up of humus (decomposed organic matter) mixed with mineral particles.  E Horizon - This eluviation (leaching) layer is light in color; this layer is beneath the A Horizon and above the B Horizon. It is made up
    11. 11. Soil Horizons  B Horizon - Also called the subsoil - this layer is beneath the E Horizon and above the C Horizon. It contains clay and mineral deposits (like iron, aluminum oxides, and calcium carbonate) that it receives from layers above it when mineralized water drips from the soil above.  C Horizon - Also called regolith: the layer beneath the B Horizon and above the R Horizon. It consists of slightly broken-up bedrock. Plant roots do not penetrate into this layer; very little organic material is found in this layer.  R Horizon - The unweathered rock (bedrock) layer that is beneath all the other layers.