AGRISCIENCE EXERCISE

University of Arkansas - AgriScience Project

AGRISCIENCE EXERCISE

PHYSICAL SCIENCES IN AGRICULTURE/ENVIRONMENTAL RESOURCE SYSTEMS

Key Concept: The Physical Environment / Soil & Land Resources

Sub-Concept: Understanding Soil & Water / Basic Soil Properties

Agricultural Context: Soil Particle Types

Exercise: Separate Soil Particle Types

Applied Principle: There are three soil particle types, found in various combinations in different soils. The combination of particles in a particular soil affects its productivity and possible uses.

Goals:

Identify the three major soil particle types.
Describe why particle size is an important consideration in determining the use of a certain soil.

Materials: (per group)

Soil samples
Glass jar with tight-fitting lid
Small amount of liquid fabric softener
Medicine droppers

References: Iowa 4-H and Youth Programs Staff. (1983). "Dirt is a four-letter word." 4-H Ding Darling Soil Water Wildlife Project. Ames, IA: Cooperative Extension Service, Iowa State University.

Klumpp, M. and Ruby, S. (undated). "Sand, Silt and Clay." Oklahoma Aqua Times Teacher's Guide. Stillwater, OK: Cooperative Extension Service, Division of Agricultural Sciences and Natural Resources.

USDA - Soil Conservation Service. (1986). "Are all soil particles the same size?" Soil and Water Conservation Activities for Youth. Washington, D.C.: USDA.

Teacher Preparation Notes:

Soil particles vary considerably in size and weight because some rocks and minerals are harder than others and on not break apart as easily as do the softer rocks or minerals. The largest (heaviest) pieces of soil in the glass jars will settle to the bottom first. These may be identified as "sand". The smaller pieces settle very slowly and may be identified as "silt". Some particles never settle but stay suspended in the water and are "clay". Clay will eventually settle but rarely in the time period allotted. You may wish to have the students observe the jars over a longer period of time and graph the buildup of the clay layer to see just how slowly it forms.

Procedures for Conducting the Activity:

1. Before conducting this activity in class, the instructor should obtain at least three soil samples which are very different in composition. Try to find an eroded/cut place (back-hoe hole, utility line ditch, etc.) at least four feet deep, where different layers of soil are visible, and take samples from each layer, as well. In addition to the soil which will be collected by the students, these should become a part of the activity.

2. Divide the class into small groups of 3 or 4 students each.

3. As a class, lead the students to determine a location on the school grounds from which each group is to collect a small sample of soil. These locations should be as diverse as possible, such as a flowerbed, near a sandbox, etc.

4. Allow the groups to collect their respective samples, instructing them to fill their jars only about 1/4 full.

5. The jars should now be filled to 2/3 full with water, a dropper full of water softener added, the lids placed on tightly, then shaken vigorously for two minutes.

6. Allow the contents of the jars to settle out for the next 20 to 30 minutes.

[In the mean time, the class may explore another aspect of soil properties, as determined by the instructor. If the previous 5 steps have not left enough time to allow the soil to settle out, or to move on to another activity, this activity may be completed the next day. Be sure the jars are labeled and set in a place where they may remain undisturbed until the activity may be finished.]

7. Have students hold a piece of paper against the side of each jar; draw a diagram showing the different layers; label each layer based on its particle size.

8. Discussion Questions:

a. What are the three types of soil particles?

b. Which settled first? Second? What was left suspended? Why?

c. What effect do you think soil particle size has on how land is used?

d. What type of soil would be best for a garden? Why?

e. What are some properties you think soil should have to be most productive?

f. What is the typical composition of soils in your community?

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