Lab: Soil Testing

Background: Our entire food supply is dependent on soils, whether it be for plants to grow (nutrients, water supply) or animals need to eat plants that grow in good soils. Some indicators of soil quality are texture, pH, buffering capability, color, and nutrient content. In this laboratory you will be performing tests to determine the quality of soils.

Pre-lab: Answer these questions in your lab notebook in complete sentences

  1. What are the three major categories of soils (according to texture)?
  2. What are some indicators of soil quality?
  3. What might a low pH in soil indicate?
  4. What is 'leaching'?
  5. What physical, chemical and biological processes lead to soil formation?

Equipment:

NOVA 5000

pH sensor and electrode

soil from three locations: meadow, forest garden

water pH 7

coffee filters (3)

Styrofoam cups (3)

Test tubes (3)

Funnel

Spoons (3)

Stirring rod

Simulated acid rain

Graduated cylinder

Copy this Data Chart into your Lab notebook

Location of Sample Soil / Color / Texture/
Feel / pH
of
soil
sample / Phosphorus
Present
(high, medium, low) / Nitrogen
Present
(high, medium, low) / Potassium
(high, medium, low) / pH of
acid
raid / pH of acid rain after filtered through soil sample / Change
In pH due to buffering
In soil
Forest / 4
Meadow / 4
Garden / 4

Part 1: Color, texture and pH

  1. Measure 3 teaspoons of soil from your bag into a Styrofoam cup.
  2. Break up any lumps and remove vegetation
  3. Record all colors that you see in the soil onto your chart.
  4. Rub the soil between your thumb and forefinger. How does it feel? Record this in your chart.
  5. Add 120 ml of distilled pH 7 water to the cup. Stir with the stirring rod carefully stir the soil and water mixture for about one minute.
  6. Allow the soil to settle in the bottom of the cup.
  7. Measure the pH in the WATER ABOVE THE SOIL. Record the pH in your chart.
  8. DO NOT DISPOSE OF THE WATER!!! YOU WILL NEED IT
  9. Repeat this steps for the other two samples.

Part 2: Nutrient Testing

In this part, you will test the soil for the following nutrients: potassium, phosphorus, and nitrogen

Phoshporus test:Phosphorus is important because1. Vital for root formation 2.Essential for development of cell tissue 3. Vital for development of healthy seeds and fruits

  1. Pour some of the water from your soil sample into a test tube
  2. Add 6 drops of phosphorus indicator (get from the teacher)
  3. Place a WHITE phosphorus tablet in the bottom of the test tube.
  4. Give tube about 5 minutes to dissolve. Tap the test tube a few times. Tablet may not dissolve completely.
  5. A deep blue color indicates Phosphorus. Deep blue (high phosphorus) medium blue( med. Phosphorus) and light blue/no color (low phosphorus). Record your results in your data table.

Potassium test Potassium is important because it 1. Promotes photosynthesis and efficient use of water 2. Strengthens natural mechanisms for disease resistance, drought tolerance, transplanting shock

  1. Pour some of the water from your soil sample into a test tube.
  2. Add a blue potassium tablet. As it dissolves, water will turn light purple. Add drops, one at a time and shake tube gently until water turns bluish.
  3. Count the number of drops it took for solution to turn blue (stop at 20).

Number of drops

0-8—Very High

10-high

12-16-medium

18-low

20 very low

  1. Record results and number of drops in your data table. Use the color chart from your teacher.

Nitrogen test Nitrogen is important in soils because: 1. Part of every living cell (proteins) 2. Directly involved in photosynthesis 3. Stimulates above-ground growth

  1. Pour some of the water from your soil sample into a test tube
  2. Add 20 drops of nitrogen extract solution
  3. Using the .5 g measuring spoon from your teacher to put one measure of nitrogen indicating powder into the test tube.
  4. Shake gently.
  5. Pink indicates the presence of nitrogen. The brighter pink, the more nitrogen. Use the color chart from your teacher.

REPEAT THE STEPS WITH EACH SAMPLE, WASH THE TEST TUBES THOUROUGHLY BETWEEN EACH STEP!

Part 3: Buffering Effect of Soil on acid rain.

Background: The ability to neutralize acid is know as buffering capacity. Soils that contain a lot of limestone (calcium carbonate) or any source of calcium are excellent at neutralizing acids. Since calcium carbonate is basic, it reacts with strong acids to produce a weaker acid, therefore maintain the pH of the soil at a habitable level. If acid rain or snow falls for several decades, the acid water will exhaust the soil's buffering capacity, resulting in a lower soil pH. You will be investigating the soils of your community to see how well it neutralizes or buffers the acid that falls to the ground. Optimum pH for nutrient intake is 6.5. In highly acidic soils, few plants grow. There might be some weeds which are hardier. Few soils are basic with a pH greater than 7.

  1. Empty your soil from your cup into the trash and obtain a new sample.
  2. Place a coffee filter in the funnel.
  3. Add the new soil sample into the funnel on top of the coffee filter.
  4. Place the cup under the filter
  5. Measure out 50 ml of simulated acid rain (pH 4) into your graduated cylinder.
  6. Slowly pour the simulated acid rain intot he soil sample, allowing the cup to collect the filtered water.
  7. If you have a lot of clay, you may have to squeeze the filter.
  8. Measure the pH of the water collected in the cup and record in your data table,
  9. Repeat for the other two smples.
  10. Calculate the change in pH. And Record in your data table.
  11. Clean up your area.
  12. Wash your hands thoroughly with soap and warm water.

Post lab questions:

  1. What were the differences n soil pH testings among the soils
  2. Which samples were acidic? Which were basic?
  3. Why is nitrogen vital to soils? Which sample had the most? Which had the least?
  4. Why is potassium vital to soils? Which sample had the most? Which had the least?
  5. Why is phosphorus vital to soils? Which sample had the most? Which had the least?
  6. Why did the garden soil appear to have consistently high levels of each nutrient?
  7. How would leaching affect the results of the soils?
  8. In part 3 you added simulated acid rain the soil samples and collected the simulated rainwater as it filtered through the soil in which soil sample(s) did the pH of the filtered water remain unchanged (as compared to pH in part 1)?
  9. Which, if any. Of the samples tested had an increase in pH after adding simulated acid rain?
  10. Which, if any, had a decrease in pH after added simulated acid rain?
  11. Which soil had the best buffering effect? (pH stayed almost the same)
  12. What might be added to the soil that is too acidic to increase pH?
  13. Why should farmers have their soils tested for pH and nutrient content?