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.
- 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)
- Distilled water
- Paper towels
- Graduated Cylinders (for water)
- Measuring cups
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.
- Fill out preliminary questions from online data collection form or on their data sheet.
- Label 3 cups: A, B and C.
- Keep a 4th cup about half full of distilled water. You will use this to rinse your pH meter after each test.
- 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!)
- Pour about 40 mL of distilled water into cup. (you want a 1:1 solution)
- Stir each sample.
- Plug pH meter into Go Link interface. Plug the USB end into the computer.
- Open the Logger Lite software (green icon on desktop)
- The sensor should automatically be detected and should be showing pH.
- Gently remove pH sensor from buffer solution bottle.
- Rinse pH meter in distilled water. Keep in water until ready to test.
- 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.
- Click 'Store' on the software. This will save your current reading and allow you to continue with the next.
- Repeat steps 11-14 for next sample.
- Repeat steps 11-14 for next sample. (Students would then save their Logger lite file)
- Complete lab data on form: http://goo.gl/DfDRb
- Clean up by pouring wet soil into appropriate bin. Rinse cups for next group.
- 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
- 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.
- From this test, what crops would grow best in soil sample A?
- From this test, what crops would grow best in soil sample B? From this test, what crops would grow best in soil sample C?
- From this test, what does sulfur seem to do to the pH of the soil?
- From this test, what does limestone seem to do to the pH of the soil?
- How does pH relate to aluminum toxicity in the soil?
- What is the main chemical in limestone? How does limestone change the pH of the soil?
- Summarize your findings in written form. Make sure to include excerpts from your research to support your findings.