Soil Stories

Adapted from "Profiles of Soil," Walnut Creek National Wildlife Refuge Prairie Learning Center.

Lesson Introduction

In this study, students will be asked to describe the physical characteristics of soil, which depend on both texture and structure. Properties such as aeration (the ability of air to flow through the spaces in the soil), water infiltration, and heat transfer are influenced by soil texture and structure. These properties greatly influence the kinds of plants that grow in a place.

How the soil feels and the size of individual soil particles is defined as texture. Texture is determined by feeling moistened soil samples from each soil horizon and can be classified in the following way:

Sandy - feels gritty, particles are as large as grains of sand
Silty - feels smooth, slick and not very sticky, particles are small, hard to see
Clay - feels smooth, plastic, and very sticky, particles are so small and packed, cannot be seen

Structure is a description of how groups of soil particles, called "peds", are shaped when they are cemented together by the organic material, colloidal clay, iron oxides, and aluminum oxides present in the soil. The following are some of the categories:

Granular - loosely packed peds
Platy - horizontal peds (like a stack of plates)
Subangular blocky - round-cornered peds that fit together
Angular blocky - sharp-cornered peds that fit together
Columnar - tall peds with rounded tops
Prismatic columnar - tall peds with sharp corners

The color of a soil layer indicates the amount of organic material content or mineral content. For example, the black soil of a prairie is also called 'humus', rich decomposed material.

Soil horizons, or layers, are the recognizable changes in color and appearance in the soil. Their normal arrangement is as follows:

1. topsoil - darkest color, highest in organic material content.
2. subsoil - lighter in color, area of deposition of leached materials.
3. parent material - rock material that is the basis of the soil, but which has little interaction with the surface layers.

Plant growth is influenced by the temperature above and below the soil surface during the growing season. Temperatures recorded in this study will vary accordingly.

Plants need soil nutrients. The pH (the acidity or alkalinity) of the soil influences the rate of nutrient absorption of various plants.

Illinois State Goal	Standard	Learning Benchmarks
12	B	4a. Understand the fundamental concepts, principles and interconnections of the life, physical and earth/space sciences. Know and apply concepts that describe how living things interact with each other and with their environment. Compare the physical, ecological, and behavioral factors that influence the interactions and interdependence of organisms.

Advanced Preparation

Lesson Objectives

The students will:

• compare various soil sites, based on differences in color, texture, temperature, and structure.
• determine the history of the soil site in terms of its plant and mineral development.

Time Allotment

60 to 75 minutes

Materials

• 1 soil pH kit
• 3 hand lenses
• 1 soil thermometer
• 1 soil probe or trowel
• 1 yardstick
• 3' x 3' sheet of cloth
• 1 micromonolith card
• pencils
• 3 clear baby food jars with lids

PROCEDURE

Tap Prior Knowledge

1. Discuss the following with your students: Why do plants need soil? Are there different types of soil? Where does soil come from?

Share with Neighbor

2. Have students work in pairs to consider the plants that grow in the study site and compare them to the plants that may grow in a healthy tallgrass prairie. How are they different? How are they the same?

Hands-on Activity

3. Take temperature readings at three levels: Air temperature (3 feet above the soil surface), Ground temperature (3 inches above soil surface), and Soil temperature (3 to 6 inches below surface). Record all data on micromonolith sheet.
4. Write a description of the materials on the soil surface. Measure the depth of these loose materials on the soil's surface.
5. Using the probe or trowel, take individual soil samples in the baby food jars and place them on sheet of cloth for comparisons.
6. Examine the first layer, the topsoil. You can work on them in the field or transport them to the classroom in the baby food jars in order to describe the soil's color, texture, and structure.
7. Measure the depth of the topsoil, its pH level, and its temperature.
8. Examine the second layer, the subsoil. Describe its color, texture, and structure. Measure the depth, pH, and temperature of the subsoil.
9. Examine the parent material. Describe the color and type of rock materials found in this layer. Draw a profile of the soil sample with its layers.

Introduce Scientific Principle/Environmental Issue

10. See Ken Robertson's description of different types of prairie soils: The Tallgrass Prairie in Illinois

Learning Outcomes

Upon completing the lesson, students will be able to:

• Collect and describe the physical characteristics of a soil sample.


• Measure the temperature and pH of a soil sample
• Relate the soil characteristics to the growth of different kinds of plants

Internet Resources

Soil

The Tallgrass Prairie in Illinois
PEERS Make and Takes: Soil Classification Information
Soil Investigation: Table of Contents
Effects of Corn Monoculture on Soils
Soil Image Library

Prairie Plants

Prairie Phlox (Phlox pilosa)
Kansas Prairie Wildflowers
UW-Madison Botanical Garden
Kenneth R. Robertson