Soil Composition Lab
Abstract:
(you don’t have to do a full write up for this)
Introduction:
Answer the following questions in paragraph form.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
What 3 things determine the characteristics of soil?
What are the layers of soil?
Which layers/horizons contain humus (the dead organic material)? How does it get there?
What are some chemical soil tests? Which chemical tests will you be doing?
What elements are you testing for? Are they macronutrients or micronutrients?
What do some physical tests? Which physical tests are you doing?
What is soil texture?
What are 4 soil types are you using?
What is porosity?
What is permeability?
What is percolation?
Procedure and materials:
You will be given composted soil from the garden, topsoil, sand (fine and medium) and gravel. For the
chemical tests, test 1 soil (garden or topsoil) and 1 sand or gravel.
1. You will do the following chemical tests: N, P, K, pH
Write a summarized procedure for the N, P, K test below:
Write a summarized procedure for the pH test below:
2. You will need to use physical tests to determine the following characteristics of soil: Texture, Porosity,
and Permeability. Use the materials on your desk sparingly, since there is another class that must also
do the lab.
Texture
1. Place 25 mL of soil mixture in a 100mL graduated cylinder.
2. Add water until there is 75 mL of water in the cylinder.
3. Cover the cylinder with plastic wrap and secure with a rubber band.
4. Invert several times with your hand over the mouth of the graduated cylinder.
5. Let sit for about 30 minutes or until soils have settled into layers.
6. Measure the volume of the layers of sand, silt and clay.
7. Measure the total volume of the sample.
8. Calculate the percentage of each type of soil.
9. Identify the type of soil in your sample by using the Soil Texture Triangle.
Porosity Test
1. Put the top on the empty Gatorade bottle with the bottom cut off.
2. Add your soil type (gravel, coarse sand, fine sand) to the Gatorade bottle neck (about 7 cm from
the bottom).
3. Fill up your graduated cylinder with tap water to 100 mL. Begin pouring the water into the
Gatorade bottle until the soil is saturated (cannot hold any more water).
4. Measure and record the amount of water that you poured into the Gatorade bottle, by
determining the water missing from the graduated cylinder. (You started with 100mL).
5. Then, carefully dump the mixture of soil and water into the beaker. If you need to use a popsicle
stick to scrape out all the soil, you can. Record the total volume of the substance by observing
measuring the total volume in the beaker.
6. The volume of the pore space is the volume of water added to saturate the soil without going
over the top of the soil. Therefore, the volume of water you added is the volume of your pore
space.
7. Determine the total porosity, by using the following equation:
Porosity = Volume of pore space x 100 = %
Total volume of sample
8. Record your answer in the data table.
9. Do a control; where only pour 100 mL of water into the Gatorade bottle to the neck. Record in
row 1 of your porosity table.
10. Dump waste materials into the appropriate waste bins. Please do not mix the soil types. I will
use them again.
Permeability Test
1. Fasten the filter paper over the end of the Gatorade bottle where the cap is with a rubber band.
2. Fill the Gatorade bottle to the neck (7 cm from bottom) with a soil type (fine sand, coarse sand,
gravel).
3. Tap gently to compact soil in Gatorade bottle.
4. Have someone get ready to time the drainage time.
5. Fill a graduated cylinder with 50 mL of water.
6. Hold Gatorade bottle over a plastic cup, so that you can see the bottom end which the water
will come out of.
7. Pour the 50mL into the top of the Gatorade bottle.
8. Record the time it takes for the water to drain through (stops dripping) from the bottom of the
Gatorade bottle.
9. Measure the amount of water collected in the plastic cup using the graduate cylinder, and
record your measurement.
10. Calculate the percentage of water retained by the soil particle type by subtracting amount of
water drained into the cup from the 50mL amount and then multiplying by 100 to arrive at the
percentage.
11. Now calculate the rate of drainage for each soil particle type by dividing the amount of water
drained into the cup by the amount of time it took the water to drain.
12. Return the Return used soil sample containers to marked containers. Please do NOT mix the soil
types.
Data:
Figure 1. This table shows the chemical composition of N, P, K and pH
Sample (soil or
Nitrogen (N)
Phosphorus (P)
Potassium (K)
sand/gravel)
pH
Figure 2. This Table shows the Porosity of the various substances and measurements taken to calculate
the porosity, using the formula Porosity = Volume of pore space x 100 = %
Total volume of sample
Sample
Volume of
water added
Total volume of
Sample (H2O +
soil)
Volume of Pore space
Porosity
(calculated as a
%)
Control=no
soil/sediments, just
water
Fine Sand
Coarse Sand
gravel
Figure 3. This table shows the measured amount of water drained and retained in three different soil
types, and the rate of drainage.
Sample
Time that it
mL of water
mL of water
Percentage Rate of
took to
that drained
retained in
of water
drainage
drain (in
through the
the soil
retained
(mL/s)
seconds)
soil
by soil
Fine sand
Coarse sand
Gravel
Figure 4. This table shows the measured volumes of sand, silt and clay which make up the texture.
Soil Type
Sand
Silt
Clay
Volume
Results
Graph your results in accordance to the captions given.
Percent
Figure 5. This graph shows the amount of N, P, and K.
Figure 6. This graph shows the pH of the soil tested.
Figure 7. This graph shows the porosity of fine sand, coarse sand, and gravel.
Figure 8. This shows the drainage rate/permeability of fine sand, coarse sand and gravel.
Figure 9. This shows the percent of soil types: sand, silt and clay in the soil.
Discussion:
Answer the following in paragraph form.
1. What were your results?
2. How could these results be used to identify the best soil for your crops?
3. What would happen if you removed all the topsoil by tilling the ground or using industrialized
farming methods? What does this do to the nutrient content and the composition of the soil?
4. Why is decomposition important to the soil? How can decomposition be used to create naturally
produced, organic fertilizer?
5. What are some advantages and disadvantages of inorganic fertilizer? How do you think that
adding an inorganic fertilizer to your soil would have affected it?
6. Was your testable question answered? Why or Why not?
7. What other factors could have affected your results?
8. If you were to do this experiment again, what would you do differently?