How to Teach About Soil-Testing Methods

Select three outdoor areas with distinctive soil conditions for the soil-testing procedures. For example, choose areas with high, medium and low vegetation or areas with high, medium and low levels of human traffic.

Divide students into groups. Guide students to each of the soil-study areas. For each area, first ask groups to write down and draw their observations of the site. Ask them to note the presence of plants, mosses, trees and other wildlife and the presence of man-made structures and human traffic.

Provide each group with a tin can, with the top and bottom removed, 1/2 liter of water and a stopwatch. Instruct students to insert the tin can approximately 2 inches into the soil. One student pours 1/4 liter into the can while another student starts the stopwatch. Ask students to record how long it takes for the soil to completely absorb the water. Groups perform this test a second time with the remaining amount of water. This test to measure the infiltration rate should be performed at all three sites.

Instruct groups to spoon out a sample of soil at each site. Students should touch the soil and record the visual and textural observations and if they think the soil is clay, sand or loam. Clay is light brown, has no grit and is easily rolled into a ball. Sandy soil is gritty and does not stick together at all; it may contain several colors of particles. Loam is a combination of the two, gritty and sticky, and usually has a darker color.

Give each group a nail, a yardstick and a smaller ruler. Ask one group member to swiftly drop a nail from 3 feet high into the soil at each site. Another group member will measure the portion of the nail that was inserted into the ground. Ask groups to repeat this process three times for each site to measure average soil compaction.

Give each group a garden trowel and ask them to dig a hole at the site approximately 6 inches deep. At this depth, students should take a soil sample of at least 4 tbsp., but advise them to take more just in case. Groups place samples in an adhesive plastic bag or a jar and label the sample denoting the site from where it came.

Demonstrate to students, when in a laboratory environment, how to test the soil for pH, nitrogen, phosphorus and potassium. Soil-testing kits usually come with instructions, but generally you would add a tbsp. of soil to a paper cup, add distilled water and stir. Then a testing strip is inserted into the cup and the strip changes color to represent a measurement.

Discuss with students their findings for each site involving plant and human observations, water absorption, compaction, soil texture and chemistry. Ask students to prepare a lab report that explains the relationship between the presence of plant life and soil conditions for each site.