APES - Soil Texture Lab

Objective: To learn how to use the soil texture pyramid to identify unknown samples of soil and to discover how soil texture relates to soil permeability

Part 1

Procedure:

  1. Fill the graduated cylinder with 25 ml of your soil sample.
  2. Add 75 ml of water to the graduated cylinder.
  3. Cover the graduated cylinder with your hand and invert several times until the soil is thoroughly mixed.
  4. Place the cylinder on the table and let it settle overnight. Repeat steps 1-3 with the remaining two soil samples. Make sure to clearly label each cylinder as soil sample 1, 2, and 3.
  5. Once the soil has settled, there should be three distinct layers. Take soil sample 1 and measure the volume of each layer and the total volume of the sample.
  6. Calculate the percentage of each layer and enter your results in the chart that follows. (Do this calculation 3 times- once for each layer.)

Volume of layer 1 + 2 + 3

Total volume of soil = 100% of sand, silt, or clay

  1. Use the soil texture pyramid in Figure 25.8, page 280 of the textbook to identify the type of soil in your sample.

Directions for using a soil texture pyramid:

•Using a ruler, find the point along the base of the triangle that represents the percent of sand in your sample. Position the ruler on the line that slants in the direction that the numbers are facing for percent sand.

•Place the edge of a second ruler at the point along the right side of the pyramid so that the ruler slants in the direction that the numbers are facing for percent silt.

•Using a pencil, put a dot where the two rulers intersect. The place where they intersect is the type of soil texture you have. You can check for accuracy by drawing a straight line to the right; that number should be the amount of silt that you have. The three percentages should add up to 100%

  1. Repeat steps 5 through 7 with the remaining two soil samples.

Soil Sample / % Sand / % Silt / % Clap / Soil Texture
1
2
3
  1. Now that you have determined the type of soil samples that you have, follow the instructions in the chart “Guide to Texture by Feel”. You can find this chart at the following link to the USDA Natural Resources Conservation Service website:
  2. Fill out the following table with the results of the soil texture by feel test.

Soil Sample / Soil Texture by Feel Analysis
1
2
3

Analysis Questions:

  1. What is the relationship between soil texture and water?
  1. Which types of soil can be mixed together to form loam?
  1. What are the causes of erosion?
  1. What can be done about erosion problems?
  1. Which soil sample would be most subject to erosion?

Part 2

Background Information: Be sure to review the chemical and physical properties of soil on pages 280-281 in the text.

Procedure:

  1. Take one of the plastic cups and poke three holes in the bottom.
  2. Fill that cup halfway with one of the soil samples. Pack it down lightly to avoid having large air spaces.
  3. Have one of the lab partners hold the cup with the soil above an empty cup with no holes so that they can catch the water as it drips through the soil.
  4. The other lab partner should measure out 50 mls of water and slowly pour it on top of the soil.
  5. Time for 1 minute and then set the cup with the soil aside. (Be careful where you place the cup. It will continue to drip water, so put it in a sink or over a cup or beaker.)
  6. Pour the water from the second cup into the graduated cylinder to see how much of the 50 mls came through.
  7. Record the amount in the following chart; repeat the procedure for the remaining two soil samples.

Data:

Soil Sample 1 / Soil Sample 2 / Soil Sample 3
Volume of Water (mls)

Analysis Questions:

  1. Which soil sample contains the most clay? Sand?
  1. Why would a farmer need to know the soil permeability of his land?
  1. Which of the soil samples held more water and why?