Name:________________________________________ Date:_________________________ Period:_______
Soil Texture Lab
APES – Mrs. Irwin
From Friedland & Relyea Environmental Science for AP* © BFW Publishers
Objective:
Correctly use the soil texture pyramid to identify unknown samples of soil and to determine how soil texture
relates to soil permeability.
Part 1
Materials:
• 100 ml graduated cylinder
Alum
• 3 soil samples
• Water
• 2 rulers
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.
Add one scoop of alum.
4. Place the cylinder on the table and let it settle for approximately 20 minutes.
5. Once the soil has settled, there should be three distinct layers. 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 ÷ Total volume of soil) = 100% of sand, silt, or clay
7. Use the following Soil Texture Pyramid 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%.
8. Repeat the above procedure for the other soil samples.
Soil Sample
1
% Sand
% Silt
% Clay
Soil Texture
2
3
9. While you are waiting for the soil to settle and separate, follow the instructions in the Soil Texture By
Feel chart that follows.
10. Fill out the following chart with the results of the soil texture by feel test. Did you get the same
answers?
Soil Sample
Soil Texture by Feel
Analysis
1
2
3
Analysis:
1. Explain the relationship between soil texture and water?
2. Which types of soil can be mixed together to form the best loam?
3. What are the causes of erosion?
4. What can be done about erosion problems?
5. Which soil sample would be more subject to erosion? Explain why this is so.
Part 2
Materials:
• 2 plastic cups
• 3 soil samples
• 50 ml beaker
• 50 ml graduated cylinder
Background Information:
A soil's permeability is a measure of the ability of air and water to move through it. Permeability is influenced
by the size, shape, and continuity of the pore spaces, which in turn are dependent on the soil bulk density,
structure, and texture. Most soil series are assigned to a single permeability class based on the most restrictive
layer in the upper five feet of the soil profile (Table 1). However, soil series with contrasting textures in the soil
profile are assigned to more than one permeability class. In most cases, soils with a slow, very slow, rapid, or
very rapid permeability classification are considered poor for irrigation.
Infiltration is the downward flow of water from the surface through the soil. The infiltration rate (sometimes
called intake rate) of a soil is a measure of its ability to absorb an amount of rain or irrigation water over a
given time period. It is commonly expressed in inches per hour. The infiltration rate is dependent on the
permeability of the surface soil, moisture content of the soil, and surface conditions such as roughness (tillage
and plant residue), slope, and plant cover.
Coarse textured soils such as sands and gravel usually have high infiltration rates. The infiltration rates of
medium and fine textured soils such as loams, silts, and clays are lower than those of coarse textured soils and
more dependent on the stability of the soil aggregates. Water and plant nutrient losses may be greater in
coarse textured soils, so the timing and quantity of chemical and water applications is particularly critical on
these soils.
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 ml 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:
Volume of
Water (ml)
Soil Sample 1
Soil Sample 2
Soil Sample 3
Analysis:
1. Which soil sample contains the most clay? Sand?
2. Why would a farmer need to know the soil permeability of his land?
3. Which of the soil samples held more water and why?
4. Which sample has the greatest infiltration rate?