Materials Included In Kit

Additional Materials Required

Safety Precautions

The phenolic rose bengal solution is moderately toxic by ingestion, inhalation and skin absorption; avoid skin contact. TesTabs contain chemicals that may irritate skin or be harmful if swallowed. The single-use TesTabs in this kit were designed with safety in mind. A single tablet, either alone or reacted with a sample, is a very low health hazard. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. 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 solid materials in this kit may be placed in the trash according to Flinn Suggested Disposal Method #26a. All solutions may be rinsed down the drain with excess water according to Flinn Suggested Disposal Method #26b.

Teacher Tips

• Enough materials are provided in this kit for 30 students working in pairs, or for 15 groups of students. The pH, nitrates and phosphates portions of this laboratory activity can reasonably be completed in one 50-minute class period. The soil microbes test requires a one-week incubation time and then one class period to stain and view the microbes.
• The phenolic rose bengal solution should be shaken before use.
• The nitrate and phosphate tests often need to settle for 5–10 minutes before the color of the liquid in the tubes becomes unmasked by the dirt. Be sure students let the tubes sit undisturbed while waiting. If no color change occurs, allow the test tubes to settle for a longer time period.
• The instructor may provide the soil samples or students may be allowed to obtain soil samples on their own. The choice is up to the discretion of the instructor.
• Have students do further research and use the results found in this activity to determine the quality of the soil sampled. The Internet and local university libraries will be a great place to start.

Sample Data

Soil Analysis

Soil Microbe
Use the space to draw and identify soil microbes.

Introduction

Soil is literally teeming with life. What exactly is in soil and how is the quality of soil measured? Perform the following activities and find out.

Concepts

• pH
• Nitrates
• Soil analysis
• Phosphates
• Bacteria

Background

In this activity, four different soil tests will be performed: pH, soil nitrogen, soil phosphorous and soil microbes. pH is a measure of how acidic or basic materials are. Recall that the pH scale runs from 0 to 14, with pH 7 being neutral, greater than pH 7 are basic, and values less than pH 7 are acidic. When we measure the pH of soil, we actually measure the pH of the soil in solution. pH refers to the relative abundance of hydrogen ions in solution.

As water becomes more acidic, the pH value decreases from 7 to 6 to 5 to 4 and so on. As the solution becomes more basic, the pH value increases from 7 to 8 to 9, etc. (see Figure 1). A normal pH scale has a range of 0 to 14. Most aquatic organisms require a pH range between 6.5 and 8.2. At pH levels below 5, larval stages of insects and other small aquatic organisms may die off rapidly. Water with abundant algae and vegetation growth usually has a significantly high pH. This is due to the fact that rapidly growing algae and vegetation remove carbon dioxide from the water during photosynthesis. At pH levels above 9, fish may have a difficult time excreting ammonia from their bodies.

The pH of the soil solution affects how much soil nutrients are available to plants. When soil is too acidic or too basic, important soil nutrients, like nitrogen and phosphorus, are not available to plants. The pH of soil can be altered by adding chemicals, such as limestone (to make it more basic) or alum (to make it more acidic).

Nitrates accumulate in soil from decaying vegetation, the atmosphere, fertilizer used in agriculture, animal excrement and sewage. Unpolluted water generally has an overall nitrate level less than 4 parts per million. If the concentration of nitrates reaches more than 10 parts per million, water may be unfit to drink. Surface water high in nitrates causes the overgrowth of algae and other organisms which will foul the water found in our water sources. This overgrowth of algae is known as an algae bloom. Algae blooms deplete the water of oxygen and may even create dead zones where fish will no longer live.

Nitrogen concentration in soil is important to plant growth. Plants use nitrogen to make chlorophyll, the green pigment so important to plants. Nitrogen is key for rapid plant growth and healthy green leaves. Sufficient nitrogen is especially important for lawns and healthy green leaves in green, leafy vegetables.

Phosphorus is a vital element of life and is usually found naturally in water in the form of phosphate ions. Phosphate originates from fertilizers, wastewater of domestic origin, such as human, animal and plant residue, and from wastewater of industrial origin. Phosphates are also added to farm and city water systems to control water hardness. Phosphates from detergents can result in overgrowth of algae (also know as algae blooms), which in turn will cause the algae to die at a high rate and undergo decomposition. This decomposition process depletes oxygen from the water and results in increased fish kill.

Phosphorus is necessary in plants for root growth and development. It helps plants grow strong and helps in the production of flowers and fruit. Phosphorus is especially important in food crops with edible roots (e.g., beets, potatoes, carrots and radishes). Testing for phosphorus usually requires dilution since the phosphorus test is very sensitive.

There are several different groups and sizes of microorganisms in soil. Organisms, such as bacteria, fungi, actinomycetes, protozoa and nematodes, are all found in soil. These organisms live in the films of water surrounding soil particles and compose less than 2 percent of dry soil’s overall mass.

Bacteria has three general shapes—cocci (spherical), bacilli (rod-shaped) and spirillum (spiral-shaped) (see Figure 2). The two most common forms found in soil are cocci and bacilli. Cocci generally range in size from 0.0005 mm to 0.0025 mm in diameter. Bacilli vary from 0.0002 mm to 0.002 mm in width to 0.001 to 2.015 mm in length. Actinomycetes are branched filamentous unicellular organisms (see Figure 3). They are similar to fungi in appearance but contain no cell cross walls and are similar in size to bacteria. The population of actinomycetes is very high in soils of neutral pH, especially where a high amount of grass is present. Fungi are large microorganisms that vary greatly in structure (see Figure 4). Most fungi are filamentous organisms that are distinguished from actinomyctes by their large diameter filaments and by the presence of cell divisions within these filaments. Many fungi may be seen by the naked eye. Plant roots may also be seen in this activity. They may be distinguished from fungi and actinomycetes because they become progressively smaller or larger from one end to the other. Fungi and actinomycetes are generally not tapered at their ends.

Materials

Prelab Questions

1. Obtain a soil sample from your area. It is best to collect the soil sample at a depth of approximately six inches deep. Note: A soil sampling tube or small garden trowel may be used to obtain the sample.
2. Place the soil sample in a plastic soil-sampling cup. Fill the plastic soil sample cup ¾ full.
3. Label the outside of the plastic soil-sampling cup with your name and location where the sample was taken.

Safety Precautions

The phenolic rose bengal solution is moderately toxic by ingestion, inhalation and skin absorption; avoid skin contact. TesTabs contain chemicals that may irritate skin or be harmful if swallowed. The single-use TesTabs^® in this kit were designed with safety in mind. A single tablet, either alone or reacted with a sample, is a very low health hazard. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Procedure

pH

1. Label a plastic soil sample tube pH.
2. Use a plastic spoon to transfer a small amount of the soil from the plastic soil sampling container to a soil sample tube.Add soil up to the 1-mL mark on the tube.
3. Add distilled water to the soil sample tube up to the 10-mL mark.
4. Add a pH TesTab tablet to the soil sample tube.
5. Screw the top onto the soil sample tube and shake vigorously for 30 seconds.
6. Let the tube sit undisturbed in a test tube rack for one minute.
7. Observe the color of the liquid in the tube. Compare the color to the Color Comparison Chart for pH. Record the pH in the Soil Analysis Worksheet.

Nitrates

1. Obtain a clean soil sample tube and label it Nitrate.
2. Using a plastic spoon, add the soil sample up to the 1-mL mark on the soil sample tube.
3. Using a Beral pipet, add vinegar up to the 2-mL mark.
4. Add distilled water to bring the level up to the 10-mL mark the soil sampling tube.
5. Cap the tube and shake for 1 minute.
6. Let the tube sit for at least 5 minutes to let the soil particles settle.
7. Decant 5 mL of the solution into a clean soil sampling tube.
8. Add one Nitrate Wide Range TesTab tablet to the tube.
9. Screw the top onto the soil sample tube and shake vigorously for at least one minute. If any part of the TesTab is still visible, shake until it all dissolves.
10. Stand the tube in a rack and let it sit undisturbed for 3–5 minutes.
11. Observe the color of the liquid in the tube. Compare the color to the Color Comparison Chart for nitrate and record the concentration in the Soil Analysis Worksheet.

Phosphates

1. Obtain a clean soil sample tube and label it Phosphate.
2. Using a plastic spoon, add the soil sample up to the 1-mL mark on the soil sample tube.
3. Using a Beral pipet, add vinegar up to the 2-mL mark.
4. Add distilled water bring the level up to the 10-mL mark on the tube.
5. Cap the tube and shake for 1 minute.
6. Let the tube sit for at least 5 minutes to let the soil particles settle.
7. Decant 5 mL of the solution into a clean soil sampling tube.
8. Add one Phosphate TesTab tablet to the tube.
9. Screw the top onto the soil sample tube and shake vigorously for at least one minute or until the TesTab dissolves.
10. Stand the tube in a rack and let it sit undisturbed for at least 5–10 minutes.
11. Observe the color of the liquid in the tube and compare the color to the Color Comparison Chart for phosphate.
12. Record the phosphorus concentration in the Soil Analysis Worksheet.

Soil Microbes

1. Moisten the remaining soil in the plastic soil-sampling cup with distilled water. Do not totally saturate the soil.
2. Insert a glass microscope slide vertically into the soil. Press the soil firmly against the slide.
3. Label the exposed portion of the slide above the soil line with your group’s initials.
4. Place the cap on the plastic soil-sampling cup to avoid excessive evaporation.
5. Leave the container at room temperature for one week.
6. After a week, remove the slide from the soil-sampling cup so that one side of the slide is left undisturbed. Wipe the other side clean with a paper towel.
7. Hold the slide with tongs. Using a Bunsen or alcohol burner, fixate the slide, undisturbed side-up, by passing it gently over a low flame several times.
8. Using a beaker and a hot plate or burner, set up a boiling water bath.
9. Hold the slide over the boiling water bath.
10. Cover the area of the slide to be stained with a small piece of paper towel.
11. Flood the paper towel with drops of phenolic rose bengal solution. Continue heating the slide for 10 minutes—keep adding the phenolic rose bengal solution as needed to prevent the paper towel from drying out.
12. Remove the paper towel from the slide and gently wash the slide with distilled water.
13. Air-dry the slide and examine with a microscope under low and medium power. Record drawings of soil microbes seen on the slide in the Soil Analysis worksheet.

Student Worksheet PDF

10539_Student1.pdf