Learn About Different Types of Soil (page 2)
Design Your Own Experiment
- Porosity is the percentage of a material's volume that is pore space (small, narrow spaces between particles in materials). How does the shape of soil particles affect porosity? Compare rounded and angular-shaped objects of comparable size. For example, compare smooth rocks or beads with aquarium gravel. Fill a measuring cup with the round objects. Note the visible spaces between the objects. Measure the volume of the spaces by filling the cup to the 1-cup (250 ml) mark with a measured amount of water. Repeat, replacing the rounded objects with the angular-shaped objects. Repeat again, using a mixture of equal parts of the rounded and angular objects.
- Permeability is the measure of how easily water flows through a material. If water flows quickly through soil, the soil is said to have high permeability. How does texture relate to the permeability of soil? Use the point of a pencil to make six equal-size holes in the bottom of three 9-ounce (270 ml) paper cups. Cut circles from coffee filters to fit in the bottom of each cup. Label the cups "coarse," "medium," and "fine." Mark a line 2 inches (5 cm) from the bottom of each cup. Fill to this line with samples of the three soil textures corresponding to the labels on the cups. Lay two pencils parallel to each other across a plate, then set the cup of coarse sand on the pencils, making sure that the pencils do not cover the holes in the cup (see Figure 16.2). Ask a helper to time you as you pour 100 ml of tap water into the cup. Stop timing when no more water drains from the cup. Record the draining time in a chart like Table 16.1. Measure the amount of water that drained from the cup by pouring the water from the plate into a measuring cup. Record the amount of water in milliliters. Calculate the drainage rate by dividing the amount of water drained by the time it took to drain. Record this answer. Repeat the procedure with the other soil samples. The most permeable soil is the one with the highest drainage rate.
Get the Facts
- A cutaway section of the Earth would reveal a soil profile made up of layers called horizons. Mature soils have three basic horizons. What is the composition of each horizon? For information about horizons, see David Lambert and the Diagram Group, The Field Guide to Geology (New York: Facts on File, 1988), p. 106.
- Pedologists (soil scientists) divide soil into different types. Six basic types are tundra, desert, chernozem, ferralsol, brown forest, and red-yellow podzol. What types of plants grow in each soil type? How does climate affect soil types? What is the composition of the different soil types? For information about soil types, see The Field Guide to Geology, pp. 108–109.
- Soils differ in the size of the particles they contain. Soil types in order of decreasing particle size are sand, silt, and clay. Most soils are not pure sand, silt, or clay, but mixtures of all the types. Such mixtures are called loam. How much sand is needed for the soil to be called sandy loam? What is a heavy soil? a light soil? See "soil" in various encyclopedias for information about soil.
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