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4 si t 50-minutese o O R Y 0- 1-2 10 o n s Organic Matter Test s ACTIVITY OVERVIEW LAB O R AT Students conduct a laboratory experiment to test the garden soil for organic matter. Students use an experimental control as a basis of comparison. The results help determine whether the garden soil contained sufficient nutrients. Students are then prepared to decide how to solve the garden problem. KEY CONCEPTS AND PROCESS SKILLS (with correlation to NSE 5-8 Content Standards) 1. Scientists use common units of measurement to collect data. This system is known as the metric or international system (SI). (Inquiry: 1) 2. Soil consists of weathered rocks and decomposed organic material from dead plants, animals, and bacteria. (Earth Science: 1) 3. Soils vary in composition, such as in the amount of organic matter that they contain. (Earth Science: 1) 4. Scientists conduct experiments, make accurate measurements, and compare results to construct scientific knowledge. (Inquiry: 1) 5. Scientists set up controls in an experiment as a basis of comparison. (Inquiry: 1) KEY VOCABULARY control milliliters (mL) organic matter A-91 Activity 10 • Organic Matter Test MATERIALS AND ADVANCE PREPARATION For the teacher * 2-3 large containers or tubs transparency of Scoring Guide: GROUP INTERACTION * 1 overhead projector Transparency 10.1, "OM Testing Procedure" (optional) For each group of four students * 2 SEPUP trays 1 sample of Soil A 1 sample of Soil B 1 sample of local soil (optional) 1 cup of water 2-3 plastic tubes 2-3 tube caps 1 30-mL graduated cup 1 50-mL graduated cylinder 1 bottle of Organic Matter testing solution (0.2 M KMnO4 [potassium permanganate] solution) 1 pipette 1 Organic Matter Color Chart * clock with second hand * piece of white paper * masking tape * paper towels For each student * 1 pair of safety goggles * 1 lab apron 1 Student Sheet 2.1, "KWL: Analyzing the Garden Problem" copy of GROUP INTERACTION Scoring Guide (optional) *Not supplied in kit A-92 Organic Matter Test • Activity 10 Once again, a local soil can be added to the activity as a third soil for student investigation. Gather large containers or tubs for soil set up and clean up. Provide them in a common area where students can collect and return the soil easily. To clean up after the activity, decant the permanganate solution off the top of the tub. The remaining soils can be thrown out. Provide access to water for cleaning out the soil tubes. Masters for Scoring Guides can be found in Teacher Resources III: Assessment. SAFETY NOTE Students must wear safety eyewear and a lab apron during this investigation. Do not allow students to touch the chemicals. The OM testing solution may stain clothes and skin, so students should rinse off any solution that touches their skin or clothes with plenty of water. Have all students wash their hands when finished with the investigation. The concentration of the KMnO4 solution in this activity is dilute enough that it can be safely poured down the drain and flushed with running water. If a more concentrated permanganate solution develops due to evaporation, it should be treated before disposal. Either calcium (powder), calcium carbonate (crushed antacids), or magnesium sulfate (Epsom salt) can be used to precipitate the permanganate from solution. Dissolve one of the three substances in the potassium permanganate solution and mix until the solution becomes clear. Then the precipitate can be thrown with solid wastes in the trash and the liquids can be poured down the drain and flushed with running water. TEACHING SUMMARY Getting Started 1. Students review the function of organic matter in a garden. Doing the Activity 2. (GI ASSESSMENT) Introduce the GROUP INTERACTION (GI) Scoring Guide. 3. Students test the organic matter content of the soils. 4. Discuss the use of a control experiment in the investigation. Follow-Up 5. (LITERACY) Students determine whether the school garden soil contained adequate organic matter. A-93 Activity 10 • Organic Matter Test BACKGROUND INFORMATION Field Tests for Organic Matter Soil organic matter (SOM) and related soil properties are probably the most widely acknowledged indicators of soil quality. Since SOM has no definite chemical composition, soil organic carbon (SOC) is more commonly measured and reported in scientific literature. Soil organic carbon is naturally variable across soil types and climates. Scientists and farmers are increasingly interested in making simple field assessments of soil quality. The USDA Natural Resources Conservation Services has developed several tools for field tests. The test used in this activity is based on this test. Potassium Permanganate (KMnO4) The OM testing solution is 0.2 M of a neutral to slightly alkaline solution. It is stable and is appropriate to handle in concentrations of 0.0006 to 0.4 M. It is used in human and veterinary medicine as an antiseptic treatment for skin infections and wounds. Potassium permanganate is an oxidizing agent. In the activity, portions of the soil organic carbon react with the KMnO 4 and bleach the solution to a light pink or clear color. This is a result of the hydrolyzing and oxidizing effects of the KMnO4 on the carbon compounds in the soil. REFERENCES Weil, R., Islam, K., Stine, M., Gruver, J., & Samson-Liebig, S. (2003). Estimating active carbon for soil quality assessment: A simplified method for laboratory and field use. American Journal of Alternative Agriculture, 18, 3-17. A-94 Activity 10 • Organic Matter Test FOLLOW-UP 5. too-long reaction time may create a lighter color result. If a local soil is tested, it is not uncommon to get a clear color result, indicating a large amount of organic matter. Sample student results are shown in the table below: Sample Laboratory Results Soil Sample Color After Reaction Result Interpretation Soil A magenta some organic matter Soil B pink a lot of organic matter Control Tube C dark purple no organic matter This activity, like Activity 4, "Soil Columns," instructs students to measure the soil in milliliters instead of grams, as most scientists would do. You may wish to review why the experiment uses a measure of volume (mL) instead of mass (g) for measuring the amount of soil (see Teaching Suggestion 3 of Activity 4). 4. Discuss the use of a control in the investigation. Use Analysis Question 1 to lead a discussion about the use of Tube C in the experiment. Ask, Why are we testing a tube without any soil in it? Explain that there is no organic matter in Tube C because there is no soil in it. Because this is known, this provides a basis of color comparison for the other tubes, confirming that the test worked as intended. Review the term control. Explain that this is part of an experiment wherein a procedure is performed with the purpose of establishing a basis for comparison. Discuss an example of another experiment that includes a control. For example, if investigating Substance X to learn whether it causes bread to rise, a good experiment would use two loaves of bread. Both loaves would be mixed, kneaded, and baked in an identical manner, but one would contain Substance X and the other, the control, would not. The control is necessary to show that Substance X made the bread rise. A-96 (LITERACY) Students determine whether the school garden soil had adequate organic matter. Student results should indicate that Soil B has more organic matter than Soil A, the garden soil. Soil B should have a lighter color than Soil A and both soil solutions should be lighter than the control tube C. Help students put these results in context by going back to Student Sheet 2.1, "KWL: Analyzing the Garden Problem," and answering the outstanding questions. An example is shown on the next page, with the latest additions shown in bold italics. Recall that when Ms. Clayson brought in the other bag of soil, she mentioned that it was from a garden where plants were growing well. Use Analysis Question 3 to discuss what students think the problem is with the garden and possible solutions to it. They will explore recommendations for the garden further in the next activity, but start them thinking about it by asking them to sum up their thoughts based on the evidence presented so far. Give students an opportunity to articulate their individual ideas based on the evidence and group discussion. Write the following statements on the board and have students complete them individually in their science notebooks: I think the problem with the school garden is ____________________________________________. My evidence for this is ___________________. Although the students have evidence that the primary problem of the garden is a lack of nutrients, the evidence does not give the full story. Point out that this could result from the history of farming on the land, the naturally sandy soil, or both. The lack of nutrients is related to its composition, but its cause is not exactly known. Organic Matter Test • Activity 10 Student Sheet 2.1 "KWL: Analyzing the Garden Problem" BEFORE the Reading AFTER the Reading What I know about the garden What I want to know about the garden What I learned about the garden There is a garden on the school Why did the plants die? Could be The school and the garden are on property. poor soil composition, lack of land that was once farmland. water, or lack of light. There is a problem with this The farmer once grew lettuce on garden. Did they get enough water? Yes. the farm. New plants died after they were Does the garden get enough Many of plants have been planted planted. sunlight? Yes. in the garden and died. The science class is going to study Is the soil "good?" Better The garden gets lots of sunlight the garden. question: Does the soil have and is hot, with an average noon- time enough nutrients (or organic temperature of 21°C (70°F). matter) for growing plants? Likely not, since it has less than Soil B, The soil is dry and sandy. which is good for growing plants. One neighbor is growing healthy Where exactly is the school garden? Alongside the classrooms. What can be planted in the garden: flowers or vegetables? plants in a soil of a different color. This soil has been watered (at least once). Plants need water, air, sunlight, and soil. Possibly both. The soil could be a problem. What kind of plants were planted The garden gets enough sunlight, water, and air. there already? Both. Did the farming history affect the garden? Yes, it is likely that it used The topsoil could be missing silt, clay, or nutrients (probably not up a lot of the natural nutrients missing sand). found in the soil. How can we test if the soil in the garden is good for growing The soil has less organic matter than Soil B, which is good for growing plants. plants? Using an organic matter test. A-97 OM Testing Procedure Soil Water OM Testing Solution A 10 mL of Soil A 30 mL 5 mL B 10 mL of Soil B 30 mL 5 mL C None 30 mL 5 mL ©2006 The Regents of the University of California Tube in Cup Issues and Earth Science • Transparency 10.1 A-99