Are you studying soil science, gardening, or agriculture with your students? If so, there is nothing quite like a soil textures jar lab to learn about sand, silt, and clay in soils! In this lab activity, students observe the distribution of grain sizes in soil samples, then classify the soils using the soil textures triangle.

If a scientist wants to know a soil’s texture, then they need to figure out the proportion of sand, silt, and clay in the sediment part of the soil. But this can be a challenge. How do you separate and measure all those tiny grains? Soil scientists use a few different methods for doing this.

This most basic method, the “jar test”, is easy to do in a classroom setting. Shake up soil and water in a jar. Then, watch the grains settle over time. Larger grains settle faster than smaller ones.

In this post, you will learn how to set up a soil textures jar test lab in your classroom. You can also get print-formatted versions of these directions, worksheets, handouts, and classroom posters to use during this lab in my Soil Textures Mini Study!

Gather Your Materials

Gather the following materials for the lab. Each lab group will need:

• 2 or 3 soil samples: collect different soils from 2 or 3 places. Avoid soils with a very high organic matter content, such as compost. Bring at least 300 mL of each soil per lab group so that you have some extra in case mistakes are made.
• Sieve
• Tray
• 2 or 3 straight-sided, tall bottles (~ 500 mL)
• Water
• Dispersing agent: borax or dish detergent (optional)
• Teaspoon
• Permanent marker
• Time keeping device (e.g., smartphone)
• Ruler
• 2 or 3 sticky notes
• Student lab handouts (1 set per student)

Set-Up

1. This lab involves lots of waiting. You must collect certain measurements hours and days apart – make sure to plan accordingly.
2. Before starting, it may help to sieve your soil samples to remove any large gravel, cobbles and roots. To do this, place the soil into a sieve. Select a sieve with openings no smaller than 2 mm. Gently shake the sieve over the tray. The soil will fall through while the larger gravel, cobbles, and roots will remain in the sieve. If you do not have a sieve, you can also spread the soil out on a tray and pick out any especially large gravel, cobbles, and roots by hand.
3. Borax will help the clay settle. If you do not have any, dish detergent can be used as a substitute.
4. Once students begin the procedure, the bottles should not be moved. Select an area for this lab where the bottles can sit undisturbed for a few days.

Directions

1. Pass out the materials.
2. Demonstrate the method with the first soil. Fill a bottle about one third of the way with a soil sample.
3. Gently tap or shake the bottle until the surface of the soil is flat. Then, use a permanent marker to mark the level of the soil on the outside of the bottle. Label the mark “initial”.
4. Fill the rest of the bottle with water.
5. Optional: add 1 tsp (5 mL) of the dispersing agent.
6. Tightly cap the bottle.
7. Shake the bottle vigorously for 5 minutes.
8. The instant you stop shaking the bottle, set it on the counter and start a stopwatch. Do not move or disturb the bottle once the stopwatch starts.
9. Sand takes about 1 minute to settle. After 1 minute, mark the top of the sand layer on the bottle with a marker. Label this mark “sand”. Measure the thickness of the sand layer with the ruler and record it on the student handout.
10. Silt takes 2 hours to settle and clay takes at least 48 hours to settle. Students should write the times these measurements should be taken on a sticky note and place it on the bottle. Depending on the length of your class period, you may need to measure and record the thickness of the silt layer for your students in 2 hours.
11. Students should then set up their second (and third) bottle(s) with the other soil sample(s) by repeating all the above steps.
12. Students will measure and record the thickness of the clay layer at least 48 hours later. The water may still look murky above the settled sediment. This is because a small amount of very fine clay is still in suspension. The final soil level may be somewhat less than the initial soil level. This is because shaking and settling changes a soil’s structure and amount of pore space.
13. Once students collect all  of the measurements, show the students how to calculate the percentages of sand, silt, and clay in each soil sample. For example:

Reflection Questions

1. Find each of your soil samples on the soil textures triangle (external link). What is the name of each of your soils?
2. In your own words, define soil texture.
3. A soil is made of 35% clay, 40% silt, an 25% sand. What type of soil is it?
4. A soil is made of 10% clay, 5% silt, and 85% sand. What type of soil is it?
5. You are selecting a soil to plant a cactus in. The cactus needs a fast-draining soil, so you are looking for a soil with plenty of coarse sediments. Which soil is a better choice: a sandy loam or a silt loam? Why? (See the soil texture triangle).
6. You are choosing a place to dig a hole in your yard to build a fish pond. You do not want the water to drain out of the pond into the soil, so you are looking for a soil with plenty of fine sediments. The left side of your yard is a silty clay and the right side of your yard is a loamy sand. Where would you build the pond? Why? (See the soil texture triangle).

This lab comes from my Soil Science Unit!

Your students will love the illustrated learning materials, plus you’ll support Wild Earth Lab with your curriculum purchase!

Explore more curriculum from Wild Earth Lab:

If you enjoyed this post, I know you will love using my environmental science materials in your classroom!

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