Materials Included In Kit

Additional Materials Required

Safety Precautions

Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. 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 disposed of in the trash according to Flinn Suggested Disposal Method #26a.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. This laboratory activity can reasonably be completed in two 50-minute class periods.
• Soil samples should be obtained locally. It is best to collect soil samples by digging a hole at least 12 inches deep. All large stones, roots or thatch should be removed from the sample before placing the soil in a large plastic sealable bag. Use the soil samples as soon as possible to obtain the most accurate results.
• Encourage students to obtain soil samples from various locations to increase the diversity of classroom results.|Four square yards of cheesecloth are included in this kit. Cheesecloth squares may be cut before class. 1" x 1" pieces of cheesecloth work the best for Part 3.
• A drying oven will be needed for the Soil Moisture Experiment.
• The percent of organic matter in the soil may be determined using the following procedure:
  1. Measure and record the mass of an aluminum weighing dish or a glass Petri dish.
  2. Add about 10 g of air-dried soil to the weighing dish and record the precise combined mass of the dish and the soil.
  3. Place the weighing dish in an oven at 110 °C and allow the soil to dry for 2 hours.
  4. Remove the weighing dish from the oven and place it in a desiccator to cool.
  5. Measure and record the combined mass of the dry soil and the weighing dish.
  6. Measure and record the mass of an empty 30-mL crucible and lid.
  7. Add the dry soil to the crucible. Cover the crucible with the lid and measure the combined mass of the crucible, soil and lid.
  8. Set up a Bunsen burner on a ring stand beneath a ring clamp holding a clay, pipe-stem triangle. Do NOT light the Bunsen burner at this time.
  9. Place the covered crucible at an angle on the clay triangle. Adjust the height of the ring clamp so that the bottom of the crucible is about 2 cm above the burner.
  10. Light the Bunsen burner and brush the bottom of the crucible with the flame for 2–3 minutes to slowly heat the crucible and its contents.
  11. Place the burner on the ring stand and heat the crucible in the hottest part of the flame for 15 minutes.
  12. Turn off the gas source and remove the burner. Allow the crucible to cool for a few minutes, then place it in a desiccator to cool to room temperature.
  13. Measure and record the mass of the crucible, lid and its contents.
  14. Repeat steps 9 and 10 and re-heat the crucible and its contents for 5 minutes. Allow to cool and measure and record the mass.
  15. Repeat as necessary until constant mass is achieved—the mass should not change by more than 0.02 g between readings. See the following chart of sample data.
      {10848_Hints_Table_1}

Sample Data

Part 1. General Observations and Sketches

Soil is very dark and dense; it is also moist. There are some large rocks and roots present as well as several ants. The soil has a relatively small particle size.

Part 2. Soil Moisture

Mass of empty aluminum dish ___1.10___g
Mass of dish plus soil sample before heating ___15.25___g
Mass of dish and soil sample after heating ___11.42___g
Mass loss due to heating ___3.83___g
Percent mass loss ___27.1___%

Part 3. Permeability

Dry Soil Drainage

Wet Soil Drainage

Part 4. Porosity

Answers to Questions

1. Describe, in detail, the composition of the local soil sample using the observations from Part 1. Classify the materials found as abiotic or biotic. What size particles are most prevalent in your sample?

   Answers will vary depending on composition of local soil sample.

2. Why is it important to have organic material in soil?

   Organic matter serves as a reservoir of nutrients and water in the soil, aids in reducing compaction of soil and increases water infiltration into the soil.

3. Compare the soil moisture results obtained by other students in the class. Is there a correlation between the soil texture and/or particle size of the soil and the amount of moisture it retains? Explain.

   In general, the larger the soil particle size, the better the drainage will be. This is why golf greens and sports fields are designed with sand-based soils. Very fine particles such as sand tend to drain poorly but retain more water in the soil system.

4. What is the benefit of soil with high moisture levels? What about possible drawbacks?

   Soils with high moisture content may promote higher amounts of plant growth. Soils with excess moisture, however, may cause excess runoff which will lead to soil degradation or flooding. Excess soil moisture may also stunt plant growth due to decreased oxygen levels in the soil.

5. Using the results from Part 3, compare and contrast the drainage rate of dry versus wet soils.

   In general, the drainage rate of wet soil is slower than that of dry soil.

6. How would the drainage rate of the soil change if the given soil were more compacted?

   The drainage rate of the soil would be slower with a more compacted soil sample.

7. What other factors may affect the drainage rate of soil?

   The type and composition of soil, slope angle, plant and animal activity, climate, etc.

8. Compare the contrast the drainage rates for the local soil sample and the given sand sample. Given the results, would areas composed of your local soil sample or sandy areas be more prone to flooding?

   In general, the drainage rate of the sand will be higher than soil.

9. Calculate the permeability of your local soil sample and the given sand sample using the following equation: Permeability = 1/Initial time for water to reach the bottom of tube.

   The results obtained using the sample data are as follows:

   {10848_Answers_Equation_1}
10. What is the relationship between the permeability and the particle size of each soil sample?

    Permeability increases when the size of the particles increase.

11. Using the results from Part 4 and Equation 1 from the Background section, calculate the percent porosity of your local soil sample and the given sand sample.

    The results obtained using the sample data are as follows:

    {10848_Answers_Equation_2}
12. What is the relationship between soil particle size and porosity?

    Porosity increases when the size of the particles increase.

Introduction

In this activity, the amount of moisture, permeability and porosity of local soil samples will be explored and tested.

Concepts

• Permeability
• Porosity
• Moisture

Background

Soil is an important natural resource. By providing both structure and nutrients for plant growth, healthy soil ensures a bountiful and healthy food supply for life on Earth. Soil is also a vital component of the hydrologic (water) cycle. Soil acts as a natural filter, adsorbing chemicals that may be applied to the soil or incorporated into the soil from other sources. “Chemical waste” that may be processed by the soil includes fertilizers, herbicides and pesticides, biological and agricultural waste products and industrial waste chemicals. The ability of soil to protect against runoff and groundwater contamination depends on the mixture of particles in the soil, its pH and oxygen content, the amount of organic matter and on the presence of microorganisms.

Often thought of as “just dirt,” soil is actually a complex mixture of inorganic minerals and organic matter as well as air, water and even biological organisms. As a rough estimate, only about 50% of soil consists of “solids” (inorganic and organic substances)— the rest is air and water.

The size of the particles in the soil is a major factor that influences both the amount of air in the 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 (see Figure 1). The reverse is also true—the smaller the soil particle size, the smaller the pore size (Figure 1).

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

Percent Porosity = (Pore Space Volume/Total Volume of Soil) x 100

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.

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.

Experiment Overview

The purpose of this experiment is to investigate the moisture, permeability and porosity of a local soil sample. General observations about the soil will be made and recorded and the soil sample will be dried for 24 hours to determine its moisture content (Parts 1 and 2). In Parts 3 and 4, the permeability and porosity of the soil will be investigated by measuring the amount of time it takes water to drain through the soil and the volume of water retained by the soil.

Materials

Safety Precautions

Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Follow all laboratory safety guidelines.

Procedure

Part 1. General Observations

1. Obtain a local soil sample.
2. Place the soil sample on a tray or large piece of white paper.
3. Use a magnifying glass and carefully observe the soil sample (e.g., color, particle size, presence of insects, other plant materials) and record the observations on the Soil Analysis Worksheet.
4. Sketch everything that is seen on the Soil Analysis Worksheet as well.

Part 2. Soil Moisture

1. Using a balance, measure the mass of an aluminum dish and record the value on the Soil Analysis Worksheet.
2. Using a teaspoon, place several spoonfuls of soil in the aluminum dish.
3. Measure the combined mass of the aluminum dish and the soil sample. Record this “before heating” mass on the Soil Analysis Worksheet.
4. Place the aluminum dish and soil sample in a drying oven at a temperature of 90–95 °C for 24 hours.
5. After 24 hours the soil should be heated to dryness. Carefully remove the aluminum tray and soil from the drying oven with a hot pad.
6. Measure the combined mass of the aluminum dish and soil sample after heating and record the result on the Soil Analysis Worksheet.
7. Determine the loss in mass and calculate the mass loss of the soil due to heating on the Soil Analysis Worksheet.

Part 3. Permeability

Permeability of Dry Soil

1. Obtain a clear tube with two open ends.
2. Rubber-band two pieces of cheesecloth to one end of the tube (see Figure 2).
   {10848_Procedure_Figure_2}
3. Place the tube upright, with cheesecloth end down, in a plastic cup (see Figure 3).
   {10848_Procedure_Figure_3}
4. Using a graduated cylinder, measure and place 40 mL of dry soil into the tube.
5. Hold the tube 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.
6. Stop timing when the water stops dripping from the bottom of the tube. Record the elapsed time as the Drainage Time on the Soil Analysis Worksheet.
7. Divide the amount of water placed into the tube by the time required for drainage, determine the drainage rate (also known as percolation rate) of the soil in mL per second. Record this value on the Soil Analysis Worksheet.
8. Pour the water from the cup into a sink. Save the tubes with the soil and the cups for the Permeability of Wet Soil activity.

Permeability of Wet Soil

9. Place the tube with the wet soil in the cup once again.
10. Holding the tube above the cup, fill the tube again with 20 mL of water. Start timing as soon as all of the water has been poured into the tube.
11. Stop timing when the water stops dripping from the tube. Record drainage time for the first tube in seconds under Drainage Time on the Soil Analysis Worksheet.
12. Calculate and record the drainage rate for the wet soil on the Soil Analysis Worksheet.
13. Repeat steps 1–12 of Part 3 using sand in place of the local soil sample. Record all data in the Soil Analysis Worksheet.

Part 4. Porosity

1. Obtain a tube with one end closed.
2. Using a graduated cylinder, measure out 100 mL of dry soil and place it in the tube.
3. Measure 100 mL of water into a graduated cylinder. This will be the initial amount of water.
4. 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 soil is saturated (water reaches the bottom of the soil). See Figure 4.
   {10848_Procedure_Figure_4}
5. Record the amount of time it takes the water to reach the bottom of the tube on the Soil Analysis Worksheet under Initial Time.
6. Record the Amount of Water Remaining in the Graduated Cylinder on the Soil Analysis Worksheet.
7. Subtract the amount of water remaining in the graduated cylinder from the initial volume of water (100 mL). The difference is equal to the volume of the pore spaces in the soil. Record the pore space volume on the Soil Analysis Worksheet.
8. Empty the graduated cylinder.
9. Pinch the tube and pour the water retained in the soil from the tube into the empty graduated cylinder. Be sure not to pour any of the soil into the graduated cylinder. Record this amount of water as Water Drained from the Tube on the Soil Analysis Worksheet.
10. 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 on the Soil Analysis Worksheet.
11. Repeat steps 1–10 of Part 4 using sand in place of the local soil sample. Record all data in the Soil Analysis Worksheet.
12. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

10848_Student.pdf