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Learn About Different Types of Soil

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Author: Janice VanCleave

A great part of the Earth's crust is covered with plant growth. The survival of these plants depends on the physical and nutritional support they receive from a mixture of particles of weathered rock and humus called soil.

In this project, you will learn the differences between coarse-, medium-, and fine-textured soils. How the texture of soil and the shape of its particles affects a soil's porosity will be determined. You will also examine the relation between soil texture and permeability. Soil profile and types will be studied.

Getting Started

Purpose:   To determine the texture of soil.

Materials

  • garden trowel
  • 1-quart (1-liter) bowl
  • marker
  • masking tape
  • three identical 1-pint (500-ml) transparent jars
  • 1 quart (1 liter) of soil
  • newspaper
  • colander with large holes
  • large fine-mesh strainer

Procedure

  1. Select a spot with soil, such as near a tree or where plants are growing. A bare soil area in a garden is also acceptable. Ask for permission to remove about 1 quart (1 liter) of soil.
  2. Use the trowel to fill the bowl with soil.
  3. Use the marker and tape to number the jars 1, 2, and 3.
  4. Lay the newspaper on a table.
  5. Spread the soil on the newspaper and pick out any live animals and parts of dead animals and plants, and return them to where the soil was collected.
  6. Soil Texture: Effects of Regolith Size

  7. Pour the soil into the colander, and shake the colander over the newspaper until no more particles fall through the holes in the colander (see Figure 16.1).
  8. Put the particles left in the colander into jar 1.
  9. Pour the particles on the newspaper into the fine-mesh strainer. Shake the strainer over the paper until no particles fall through.
  10. Put the particles in the strainer into jar 2 and the particles on the newspaper into jar 3.
  11. Compare the amount of material in each jar.

Results

The soil is separated into three sizes of particles—large, medium, and small. The amount of material in each jar will vary with different soil samples.

Why?

Soil is the top layer of the regolith that supports plant growth. Soil is composed of particles from weathered rock, humus (decayed animal and plant matter), air, and water. Soil is necessary for life of both plants and animals. It provides the building blocks of materials that most plants need to make food. And animals, either directly or indirectly, depend on plants for food.

All soils are not alike. The weathered rock samples come from different kinds of rocks, and the amount and composition of humus vary. Most soil contains particles of varying size. In this experiment, you separated the particles. Coarse-grained particles, as in jar 1, are larger than medium-grained particles, as in jar 2. Fine-grained particles, as in jar 3, are smaller than the other two particle types. The texture of soil depends on which type of particles predominates in the soil. For example, if there are more particles in jar 3, then your soil sample would be considered fine-textured.

Try New Approaches

  1.  
    1. Soil texture can be estimated by rubbing it between your fingers. Determine the feel of different textures, then collect a variety of soil samples from very coarse to very fine.
    2. Compare the amount of the different-size particles in each sample collected in the previous experiment by repeating the original experiment. Science Fair Hint: Use photographs or diagrams of the jars of particles to represent the comparison of particles in different soil textures.
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