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Soil Texture

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Author: Janice VanCleave

Effects of Regolith Size

A great part of the Earth's crust is covered with plant growth. The survival of theses 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 relationship 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) plastic transparent jars
  • 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. 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 37.1).
  7. Put the particles left in the colander into jar 1.
  8. Pour the particles on the newspaper into the fine-mesh strainer. Shake the strainer over the newspaper until no particles fall through.
  9. Put the particles in the strainer into jar 2 and the particles on the newspaper into jar 3.
  10. Compare the amount of material in each jar.

Effects of Regolith Size

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 (loose particles including soil, that cover Earth's surface) that supports plant growth. Soil composition includes small rock particles, humus (decayed animal and plant matter), air, and water. Soil provides support as well as nutrients for plants.

Not all soils are alike. Soil composition can vary by the type of rock and the amount and composition of humus it contains. Most soil contains particles of varying size. In this experiment, you separate 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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