Module 1:  Testing the field capacity of soil.  Back to the top.    

     Introduction:  In this experiment the ability of soil to hold or retain water will be tested.  Since nitrogenous nutrients are water soluble, the ability of the soil to retain water would theoretically be related to the amount of nutrients the soil can hold.  This theory will be tested in Module 2.  It may be useful to know that water has a density of one gram(g) per liter(l).  This means that one gram of water has a volume of one milliliter(ml).  Therefore, one liter of water, which contains 1000 ml of water, has a mass of 1000 g or 1 Kg.  Data may be placed in Data Table 1 or Data Table 2.

Materials:  For a class of 30, groups of three.  Please adjust according to class size.

1.      20 Plastic planter containers, large cups, or similar container with holes in

      the bottom for drainage.

2.      Soil.  Have available at least two samples per group.  Examples include

      sand, peat moss, topsoil, clay, potting soil, compost, or mixtures of the

      above.

3.      Water.

4.      Containers to hold the water.

5.      Scale.

Questions to ask, discuss, and record before beginning: 

1. What is field capacity?
2. What are the properties of the soils to be tested?  Describe the density, mass, and color of the soil samples.
3. Based on the observations conducted, which soil sample do you think will have the greatest field capacity?  Record the answer as your hypothesis.

Procedure: 

1. Mass the containers that will be used for holding the soil samples.
2. Fill each container with the same volume of soil. Mass the containers with the soil samples.  This is the total mass of cup and soil.
3. Subtract the mass of the cup from the total mass of the cup with soil and record result.  This is the mass of the soil.
4. Slowly add water to the soil sample until water begins to flow from the holes in the bottom of the container.  When water begins to flow stop adding water. 
5. After water stops flowing obtain the new mass of the cup and soil.  Record result.
6. Subtract the dry mass of the cup and soil from the new total mass.  Record result.  This is the total mass of water the soil holds.

Questions to ask, discuss, and record after experiment:

1. Discuss what was learned from the experiment.  Did everyone have the same results/ observations?  How did you hypothesis compare with the actually result?
2. What were the characteristics of the soil type that retained the most water?  What volume of water was retained by the soil?
3. Prepare a bar graph comparing the type of soil with the mass of water retained.
4. Discuss some ways the experiment could be carried out differently.  For example, how could adding water more quickly or slowly affect the results?  How would mixing various soils, such as sand and peat, affect the field capacity of each?

Data Table for Module 1: 

Data Table 2 for Module 1: