Garden Science: Soil pH Lab

Summary

In this 8th grade science lesson, students test the pH levels of soil from three different sites in the garden to determine the level of acidity in the garden soil.

Objectives

After this lesson, students will be able to:

• Use scientific tools to determine whether the soil is acidic, basic, or neutral

Assessments

During this lesson, students will:

• Accurately test and record the pH of the soil using a pH strip and probe.

Materials

• Watering cans
• Trowels for stirring
• pH strips
• pH color key
• pH probe
• Signs for sample areas
• Clipboards
• Pencils
• Soil pH Lab worksheets
• Visual aid

Before You Begin

• Copy the Soil pH Lab worksheet to hand out
• Create the visual aid
• Label the sites where samples will be collected.
• Collect all the materials, then set them up to make a pH lab

Procedures

At the Opening Circle

1. Welcome students and introduce the Soil pH lesson as an extension of what they learned about pH in the Kitchen.
2. Ask students explain what pH measures.
3. Explain that pH is relevant to the garden because it indicates nutrient availability.
4.  Explain that the ideal acidity level for soil is between 6 and 7. 
5. Explain that micro-organisms, like bacteria are most prevalent in slightly acidic soil (6-7) and that micro-organisms are responsible for making nutrients available to plants.
6. Explain that students will use two scientific methods- the probe and pH strips- to test the pH of three different areas in the garden: annual bed, perennial bed, and mulch pile
7. Prompt students to think about scientific procedures and why it is necessary to test three different areas of the garden
8. Ask students to predict which site will be the most acidic and why
9. Divide students into working groups for garden jobs, and lead one of the groups to the pH lab for the first rotation.

At the pH Lab

1. Gather students around the pH lab table, and divide the group into three smaller groups. Each group should have a watering can and a kit including a bucket with a shovel, clipboard with a worksheet, pH strips, and pencil. 
2. Each group of 2-3 students will test a sample from the site.
3. Bring students to their test site and demonstrate how to make a soil solution, dip the pH strip, and read the probe.
4. Have each group take a reading from the strip and probe, record their data on the worksheet and return to the station to derive a mean average.
5. Ask students to identify their samples as acidic or basic.
6. Ask students what abiotic factors might alter the pH of the soil: Rain, sun, and temperature.
7. Prompt students to think about methods that can be used for maintaining the soil pH between 6 and 7: compost, amendments etc.
8. Have students prepare the pH lab for the next group and return to garden work.

At the Closing Circle

1. Using the white board at the front of the Ramada, collect data from each group.
2. Ask students what they notice about the pH of each site.
3. Tasting

Vocabulary

pH

Basic or alkaline

Acidic

Neutral

Micro-organisms