Investigating the pH of Soils

Lesson Content

• Lesson Plan Template:

  Guided or Open Inquiry

• Learning Objectives: What will students know and be able to do as a result of this lesson?

  
  

  Students will learn about soil pH, what factors affect the pH of soil and how important it is to the growth of plants. Students will learn to use reputable resources to support their findings. Students will be expected to write a detailed lab report that thoroughly explores the concept while integrating the data from their investigation.

• Prior Knowledge: What prior knowledge should students have for this lesson?

  
  

  SC.5.L.17.1 Compare and contrast adaptations displayed by animals and plants that enable them to survive in different environments such as life cycles, variations, animal behaviors and physical characteristics.

  SC.8.P.8.8 Identify basic examples of and compare and classify the properties of compounds, including acids, bases, and salts.

• Guiding Questions: What are the guiding questions for this lesson?

  
  
  1. What is pH a measure of?
  2. How do we measure the pH of soil?
  3. What range of pH in soil is optimum for specific plants?
  4. How does adding fertilizer and lawn lime affect the pH of soil?
  5. What factors contribute to changing pH levels in soil?
  6. What are some environmental issues related to soil pH?
  7. Can you identify reputable resources that develop your understanding of a topic?
  8. What elements are important in a thorough lab report?

• Introduction: How will the teacher inform students of the intent of the lesson? How will students understand or develop an investigable question?

  
  
  • Problem: Soil pH is vital to the healthy growth and yield of plants and crops. Numerous factors affect the pH of soil. There are ways we can change the pH of soil to reach optimum pH for the type of plant/crop we need.
  • For this investigation we are going to find out how we can alter the pH of soil.
  • Follow up will include the how and the why this happens. Students will test different soil enhancements farmers and gardeners use to adjust the pH: calcitized limestone (lawn lime) and fertilizer (with more than 20% of sulfur).
  • Students will gain experience using a pH Sensor and learn soil pH measuring technique as you determine the pH of a soil sample.

• Investigate: What will the teacher do to give students an opportunity to develop, try, revise, and implement their own methods to gather data?

  
  

  Students will conduct preliminary research on soil pH; what factors affect the pH of soil, what are optimum pH levels for specific plants and crops and what can be done to prepare and adjust soil pH to get the composition you need.

  Students will test pH of three different types of soil as a preliminary activity. For follow up extension, students will then design their experiment based on their questioning.

  Materials Needed:

  • Vernier pH probes with Go Link interface (or use pH strips)
  • Computers with Vernier Logger Lite installed (if using Vernier probes)
  • Create the soil samples (make sure to test ahead of time to know what type of range your students will find):
  • You will need at least 40 mL per sample per group for this preliminary test. Keep an extra bin for each type for clean up. You will be able to use these later when students conduct follow up activities)
  • Lawn Lime (calcitized limestone)
  • Fertilizer (Miracle Gro or similar with at least 20% sulfur)
  • Soil sample A (Lawn Fertilizer such asMiracleGro (with at least 20% Sulfur) added to potting soil--make sure to double or triple the recommended amount on the package to get an exaggerated reading), B (Lawn Lime added to potting soil, again add double or triple the amount recommended to get an exaggerated reading), and C (Control -General potting soil)
    • C:
    • A:
    • B:
  • Distilled water
  • Paper towels
  • Spoons
  • Graduated Cylinders (for water)
  • Measuring cups

  Procedure:

  Students will conduct research on the computer all about the pH of soil; what factors affect the pH, what is added to soil to adjust the pH and what causes plants to need pH at a certain level. Students will use only reputable sources to find their information (you should review this with your students--have students help you define what reputable means in this case). They will need to cite their sources later on in their final lab report.

  After the initial research students will summarize their findings. Next up is a lab to test or confirm their preliminary research:

  Students can record their preliminary data onto a lab sheet created by the teacher with similar questions used on the pH_of_Soil_Student_Data_Sheet.docx. 

  1. Fill out preliminary questions from online data collection form or on their data sheet.
  2. Label 3 cups: A, B and C.
  3. Keep a 4th cup about half full of distilled water. You will use this to rinse your pH meter after each test.
  4. Place about 40 mL of sample soil into cup--normally you would measure soil on a balance, but for the sake of this experiment you want to find a 1:1 solution of soil to water in volume (make sure they match your labels!)
  5. Pour about 40 mL of distilled water into cup. (you want a 1:1 solution)
  6. Stir each sample.
  7. Plug pH meter into Go Link interface. Plug the USB end into the computer.
  8. Open the Logger Lite software (green icon on desktop)
  9. The sensor should automatically be detected and should be showing pH.
  10. Gently remove pH sensor from buffer solution bottle.
  11. Rinse pH meter in distilled water. Keep in water until ready to test.
  12. Place pH meter into sample to be tested, Click the green 'Collect' button on the program. Continue taking the reading for about 30 seconds or until the pH stays constant. Click red 'Stop' when finished.
  13. Click 'Store' on the software. This will save your current reading and allow you to continue with the next.

   

  1. Repeat steps 11-14 for next sample.
  2. Repeat steps 11-14 for next sample. (Students would then save their Logger lite file)
  3. Complete lab data on form: http://goo.gl/DfDRb
  4. Clean up by pouring wet soil into appropriate bin. Rinse cups for next group.
  5. Pour out distilled water, rinse out pH sensor, replace into buffer solution container.

  Write up recommendations based on your findings. (on electronic form)
  
  As a class we review data together to draw conclusions. Relate to possible causes. Ask students to reflect back on what they have learned in history classes about the great Dust Bowl, the cotton plantations pre-Civil war and how this might relate to our investigation.
  
  Continue this problem investigation with improving soil quality for poor soils in areas where this is a major issue. How often does soil pH need to be tested? What are the causes and effects of acidic or basic soil?
  
  After completing this lab, students will first use reference sources to find out more about soil pH before they choose and investigate a researchable question dealing with soil pH.
  
  Some topics to consider in reference search are:

  • soil pH
  • soil acidity
  • soil nutrients
  • soil components
  • soil horizons
  • soil types
  • buffers
  • effects of acid deposition on soil

  Biology: As part of the unit on studying pH and the activation energy required for biological processes. Plants need the right conditions and elements in order to conduct the chemical reactions needed to process elements for food and energy. In this case plants need the soil to contain a certain amount of elements that are available for reactions. However, if the pH of the soil is not ideal, the plants won't have elements necessary for processing. Not all plants need the same soil conditions. Determine the type of soil optimum for maximum growth.
  
  Chemistry: How the delicate balance of elements are available to activate based on the pH. The availability of iron, copper, phosphorus, zinc, and other nutrients, as well as the negative effects of various substances, are controlled in large part by soil pH. Some potentially toxic substances in soils, such as aluminum (Al3+) and lead (Pb2+), have little effect on plant growth under alkaline or basic conditions, but are a serious concern when the same concentrations occur in acid soils. Many nutrients, especially phosphorus, show their greatest availability in slightly acid to neutral soils, with distinct lower accessibility with increases or decreases in soil pH.
  
  Environmental Science: The balance of using the earth wisely, by not wasting fertilizer and lime if not needed, by rotating crops to restore the required nutrients to the soil, how education is needed to plant smart. The minimal amount of chemicals necessary to produce healthy crops. Soil pH is an indicator of soil weathering. Soil pH values reflect the mineral content of the parent material, the length of time and severity of weathering, and especially the leaching of basic materials from the soil profile. Factors such as the type of vegetation, annual rainfall, and drainage as well as the activities of man also influence soil pH.

• Analyze: How will the teacher help students determine a way to represent, analyze, and interpret the data they collect?

  
  

  The teacher should encourage collaboration and discussion among groups. Check to see what other groups are finding in their tests. Are students receiving the same results? What would account for the variation?

  The reason to use an electronic spreadsheet like Google Docs is so students can see what all others in the class are finding instantly to compare their results. It is important for teachers to make students feel comfortable enough with their data to not change their data to more closely match others in the class, but if they are finding something different to figure out or ask for assistance to see what the difference might be caused by.

  Students will be answering the following post lab questions:

  For the following questions conduct research to check for crops in your region that would grow best in these pH levels. Make sure you find two reputable sources - government or university sites.

  1. From this test, what crops would grow best in soil sample A?
  2. From this test, what crops would grow best in soil sample B? From this test, what crops would grow best in soil sample C?
  3. From this test, what does sulfur seem to do to the pH of the soil?
  4. From this test, what does limestone seem to do to the pH of the soil?
  5. How does pH relate to aluminum toxicity in the soil?
  6. What is the main chemical in limestone? How does limestone change the pH of the soil?
  7. Summarize your findings in written form. Make sure to include excerpts from your research to support your findings.

• Closure: What will the teacher do to bring the lesson to a close? How will the students make sense of the investigation?

  
  
  1. Ask students to share their findings with the class. Discuss and find a consensus. Have students identify their sources. Did any students find sources that were contradictory? What should we do when we find this? How can you guarantee the information you find is accurate? --Students should conclude that the source should be from a research site if at all possible, if not look to see if a site at least sites their source such as Wikipedia.
  2. This lesson might lead to further study depending on your class. Students might begin a series of plant growing experiments, or soil chemistry experiments examining the effectiveness of plant enzymes in different pH levels. Students might start a school garden, hydroponics, or other type of exploration with plants.

• Summative Assessment

  
  
  1. Students will be able to explain what adding fertilizer or lawn lime to soil will do to the soil, what this means for plants, and how adding these chemically affects the pH of the soil. Students will explain how the science of soil is an important issue in agriculture, environmental science, and/or the possibility and issues involved in growing plants on other planets or moons such as Mars.
  2. Student IMRAD formatted lab reports will include explanations of what this all means.
  3. Student IMRAD lab reports will include research articles that support their findings. They will printout their research findings, highlight where in the article it reinforces their results and supports their explanation.

  IMRAD Lab Report Template.docx

• Formative Assessment

  
  
  1. Review understanding of pH. At this point most students will recall that items with a pH of less than 7 are an acid and those above 7 are a base. As we get into the more scientific understanding: the number of hydronium ions in solution, regular questioning of the students will help the teacher see if students are processing the information.
  2. Read a research article together relating to pH of soil, asking students to share what they understand from the reading. Students will discuss what this might mean and how it relates to our problem that we will be investigating.
  3. As students are working on their investigation/lab experiments, ask students to explain:
     • pH and how does it relate to the health of the soil or the growth of plants in the soil.
     • how pH affects the ability of plants to take in other minerals
     • how pH of the soil allows some chemicals such as aluminum to become toxic to plants
     If they aren't able to answer these questions, guide them by questioning, reminding them of what had been previously discussed in class or lead them to articles on these topics. Review with students the importance of reliable research.
  4. Give students examples of articles (news sources, government sites and others) and ask students whether these resources are reputable.
  5. Get the students to decide/agree together what types of research are to be used in this project.
  6. Review the IMRAD Lab report format for this project (attached). Go over each section with students if this is the first time using this type of format and ask students to clarify how they could complete each section or what it might look like.
  7. Review the IMRAD Rubric with students asking for students to describe what each criteria might include.

• Feedback to Students

  
  
  1. The teacher should rotate through each group questioning students about what they are finding, and asking them to explain what is causing their readings. If students are confused the teacher should guide their understanding through questioning to lead them back to an understanding.
  2. While students are reading and discussing the research articles, the teacher will question students on how this relates to their experiment. If students are having trouble making connections the teacher will ask students questions to direct them to the connections.