Materials Included In Kit

Additional Materials Required

Safety Precautions

Although this activity is considered nonhazardous, follow all laboratory safety guidelines. Wash hands after handling the materials in this kit. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. All materials may be dried and saved for future investigations. If disposal of the materials is needed, follow Flinn Suggested Disposal Method #26a.

Teacher Tips

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. Both parts of this laboratory activity can reasonably be completed in one 50-minute class period.
• Four square yards of cheesecloth are included in this kit. Cheesecloth squares may be cut ahead of time before class. 1" x 1" pieces of cheesecloth work well for Activity 1.
• Sand and gravel samples may be dried and saved for additional tests.
• Have students perform the experiments again using their own soil samples or soil that has been obtained from the school grounds.
• Additional topics such as soil profiles, soil analysis, soil conservation and erosion may be discussed with the students at this time. Flinn Scientific has many other kits that cover a wide range of soil topics.

Sample Data

Data Table 1. Dry Soil Drainage

Data Table 2. Wet Soil Drainage

Data Table 3. Permeability and Porosity

Answers to Questions

Activity One and Two

1. How did the drainage rate of the loosely packed soil compare with that of the tightly packed soil?

   The drainage rate of the loose soil was faster than the packed soil both when the soil was dry and wet.

2. What happened to the drainage rate when the soils were already moist (Activity 2)?

   The drainage rate slowed when the soil was already moist.

3. Given your results, would water-soaked soil be able to hold more or less water if a rainstorm occurred? Would the water seep into the soil rapidly?

   Water-soaked soil would be able to hold less water in a rainstorm. The water would seep into the soil very slowly.

4. What other types of factors could affect the drainage rate of soil?

   Type of soil, amount of water added to soil, etc.

5. List some possible sources of error in Activity 1.

   Errors in calculation, how tightly the soil was packed, the amount of soil and water added, etc.

Activity Three

6. Define porosity and permeability. How do they compare?

   Porosity is the total volume of air and water soil can hold. Permeability is the ease in which water and air can move through soil. In general, the higher the porosity the faster the permeability will be.

7. Use Equation 1 from the Background section to calculate the porosity of each of the soil samples.

   Percent porosity = pore space volume/total volume of soil x 100

   (i.e., for sand 29.8 mL/100 mL x 100 = 41.2%)

   Sand___29.8%___
   Fine Gravel___38.6%___
   Coarse Gravel___43.8%___

8. What is the relationship between the porosity and the grain (particle) size of each soil sample?

   Porosity increases when the size of the particles increases.

9. What type of soil retained the most water? Why?

   The sand retained the most amount of water. The smaller the particle size, the higher the water retention.

10. Calculate the permeability of each soil type using the following equation:

    Permeability = 1/Initial time for water to reach bottom of tube

    Sand___0.04___
    Fine Gravel___0.25___
    Coarse Gravel___0.50___

11. What is the relationship between the permeability and the grain (particle) size of each soil sample?

    Permeability increases when the size of the particles increases.

12. Which soil type tested in this activity would cause the most water runoff? The least?

    The sand would promote the highest amount of runoff because of the small particle size. The gravel would cause the least amount of runoff.

References

Plaster, E. J. Soil Science and Management; Delmar; Albany, New York, 1992; Chapter 3.

Introduction

Do all types of soils hold the same amount of water? How much water can different types of soil hold? In this activity, the porosity, permeability and drainage rate of various soils will be tested and discussed.

Concepts

• Soil
• Runoff
• Compaction
• Porosity
• Permeability

Background

Soils are composed of different physical combinations of mineral particles and organic matter in many different sizes. One of the most important physical properties of soil is known as soil texture. Soil texture, by definition, is the size of mineral particles in the soil. Mineral particle size is a major factor that influences both the amount of air in soil (aeration) and the capacity of soil to retain water. The volume of air and water that soil can hold is known as the soil pore size or porosity. The larger the soil particles, the larger the soil pore size will be; and the smaller the soil particle size, the smaller the pore size (see Figure 1).

The percent porosity of soil is measured using the following equation.

Water tends to drain more rapidly through larger soil pore size than small pores. As water runs through any type of soil, it pulls small amounts of air along with it. When water enters soil that has a small pore size, the air fills the pores or voids in the soil. As the small pore spaces are filled, the soil holds or retains a greater amount of water. This is why it is important to have a good mixture of different types of soil for plant growth. A combination of large and small pores provides both better aeration and water retention in soil.

Permeability is another key characteristic of soil. Permeability is the relative ease in which water and air can move through soil. Water flows through soils with high permeability very easily. Soils with low permeability allow much less water flow or drainage. Soils that have high permeability can be pictured as being loose and soils with low permeability can be thought of as being tight or compacted.

Compaction of soil also plays a major role in the amount of water that is drained through soil. Compaction occurs when pressure is applied to a soil surface. As soil becomes compacted, the pores in the soil become smaller. The number of large pores decreases, which, in turn, lowers the aeration level of soil. Compacted soil also leads to a decrease in permeability.

Permeability also decreases when soil becomes saturated with water. Saturation of soil and high levels of introduced water (rainfall for example) lead to runoff of water. Runoff is water that is not absorbed by the soil and flows to lower ground, eventually draining into streams, lakes, rivers, and other bodies of water. Excessive amounts of water runoff can cause severe flooding, which can lead to extensive property damage.

Materials

Safety Precautions

Although this activity is considered nonhazardous, follow all laboratory safety guidelines. Wash hand thoroughly with soap and water before leaving the laboratory.

Procedure

Activity One—Drainage Rate of Dry Soil

1. Obtain two clear tubes with open ends.
2. Rubber-band two pieces of cheesecloth to one end of each tube (see Figure 2).
   {11840_Procedure_Figure_2}
3. Place each tube upright, with cheesecloth end down, in a plastic cup (see Figure 3).
   {11840_Procedure_Figure_3}
4. Measure 40 mL of soil using a graduated cylinder.
5. Place the 40 mL of loosely packed soil in tube 1.
6. Place the same amount of soil (40 mL) in tube 2. Tightly pack the soil down, using a wooden dowel or the eraser end of a pencil.
7. Hold tube 1 above the plastic cup and pour 20 mL of water into the tube. Use a stopwatch or a watch with a second hand to time the drainage of the water. Start timing as soon as all of the water has been poured into the tube.
8. Stop timing when the water stops dripping from the bottom of tube 1. Record time under Time of Drainage for the Loose Soil in Data Table 1.
9. Repeat steps 7 and 8 for tube 2. Record the time for drainage of the water for tube 2 in seconds under Time of Drainage for Packed Soil in Data Table 1.
10. Using the amount of water placed into each tube and the time required for drainage, determine the drainage rate of the loosely- and tightly-packed soil in mL per second. Record these values in Data Table 1.
11. Pour the water from each cup into a sink. Save the tubes with the soil and the cups for Activity 2.

Activity Two—Drainage Rate of Wet Soil

12. Place each of the tubes with the wet soil in the cups once again.
13. Hold tube 1 above the cup and once again fill the tube with 20 mL of water. Start timing as soon as all of the water has been poured into the tube.
14. Stop timing when the water stops dripping from the tube. Record drainage time for the first tube in seconds under Time of Drainage of Wet Soil in Data Table 2.
15. Repeat steps 12 and 13 for tube 2. Record the time for the second tube under Wet Soil in the data table.
16. Calculate the drainage rate for tubes 1 and 2 using the procedure described in step 10.
17. Dispose of the soil and clean the tubes according to the instructor.

Activity Three—Permeability and Porosity of Varied Soil Types

18. Obtain a tube with one end closed.
19. Using a graduated cylinder, measure out 100 mL of sand in the tube.
20. Measure 100.0 mL of water into a graduated cylinder. This will be the initial amount of water.
21. Start a timer (use a stopwatch or watch with a second hand) and slowly pour water from the graduated cylinder into the tube until the sand is saturated (water reaches the top of the soil). Figure 4. Record the amount of time it takes the water to reach the bottom of the tube in Data Table 3 under Initial Time.
    {11840_Procedure_Figure_4}
22. Set the graduated cylinder containing the remaining water to the side for step 25.
23. Obtain the graduated cylinder. Record the Amount of Water Remaining in the Graduated Cylinder in Data Table 3.
24. Subtract the amount of water remaining in the graduated cylinder from the initial volume of water, 100 mL. This will give the volume of the pore spaces in the sand. Record this value in Data Table 3.
25. Empty the graduated cylinder.
26. Pinch the tube and pour the water retained in the sand from the tube into the empty graduated cylinder. Be sure not to pour any of the sand in the graduated cylinder. Record this amount of water as Water Drained from the Tube in Data Table 3.
27. Subtract the Water Drained from the Tube from the Pore Space Volume of the sand. This value will be the Volume of Water Retained. Record this value in Data Table 3.
28. Dispose of the sand sample according to your instructor and repeat steps 20–28 for the fine and coarse gravel samples.
29. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

11840_Student1.pdf