Abstract

Objective

In this experiment you will test if soil color can be used to evaluate the moisture content of the soil.

Introduction

The amount of water present in the soil is called the moisture content. Moisture is very important and the amount of moisture needs to be in a careful balance, not too dry and not too wet. The moisture content of the soil also needs to match the plants and animals living in the habitat. Some organisms need a lot of moisture, like ferns and salamanders. Others, like cacti and snakes, are adapted to desert habitats and need very little water. Most often, evenly moist soil is a haven for plants and small, soil-dwelling animals.

Moisture conditions affect the soil structure in many ways. Soil that is too wet or does not drain properly can suffer from erosion. Soil that is too dry can become hard and compacted. Also, different types of soil respond to moisture differently. A sandy soil will drain water quickly, but a clay soil will absorb water and become soggy.

Since the moisture content of the soil is so important, how can it be measured? In this experiment you will learn how to use color scales to indicate the moisture content of your soil. By adding increasing amounts of water to dry soil and taking a photo you can develop a standard assay for soil moisture. Where will your soil be on the moisture scale?

Terms, Concepts, and Questions to Start Background Research

To do this type of experiment you should know what the following terms mean. Have an adult help you search the internet, or take you to your local library to find out more!

• soil
• moisture
• color scale
• Grayscale Color

• How does the color of soil change when moist or dry?
• How is a color scale developed?
• Do different soil types have different colors when moist or dry?

Bibliography

• RVDE, 2004. "Activities: Soil Moisture and Evaporation Modeling" U.S. Geological Survey (USGS), Recovery and Vulnerability of Desert Ecosystems (RVDE) Program. [accessed: 4/28/06]
  http://mojave.usgs.gov/rvde/activ_soil.html
• SREL. 2004. "Kids DO Science, Comparing Earth & Mars; Classifying Soils." University of Georgia, Savannah River Ecology Laboratory (SREL). [accessed: 4/28/06]
  http://www.uga.edu/srel/kidsdoscience/kidsdoscience-soils.htm
• Brynie, F.H., 2005. Parent's Crash Course: Elementary School Science Fair Projects, Hoboken, NJ: Wiley Publishing Inc. pp 162-164.

Materials and Equipment

• soil samples
• Zip-lock baggies
• small shovel or spoon
• markers
• small baking dish
• water
• small Dixie cups for mixing
• measuring spoons and cups
• cookie sheet
• oven
• paper
• digital camera
• computer
• printer

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Experimental Procedure

1. Collect a sample of soil from your backyard with a spoon or small shovel and put the sample in a Zip-lock baggie. Label the baggie with the date and the location you collected the sample from.
2. Remove the soil from the Zip-lock baggie and put it into a small baking dish. Place the dish in the oven on a cookie sheet.
3. Bake the sample at low heat (200^oF) for 2-3 hours to evaporate all of the water from your sample.
4. Remove the soil from the oven and allow to cool completely.
5. Using a measuring spoon, place 2 Tablespoons of dry soil into each Dixie cup, making 7 samples total.
6. Add different amounts of water to each sample and stir thoroughly. Here is a data table to help you know how much water to add:

   Sample	Soil (Tbs)	Water (tsp)
   1	2 Tbs	1 tsp
   2	2 Tbs	1 1/2 tsp
   3	2 Tbs	2 tsp
   4	2 Tbs	2 1/2 tsp

7. On the sheet of paper, use a marker to write the number of teaspoons of water added to each sample on the sheet of paper. Leave enough room for a spoonful of each sample to be placed above each number. Arrange the numbers to fit on one sheet of paper so that you can take a photo of the paper later.
8. Place one spoonful of each soil sample above the matching number.
9. Take a photo of your sheet of paper from above with a digital camera. Be sure to fit all of your samples in the photo. You will use this photo to make your scale.
10. Download the photo to your computer, and print out the photo in black and white.
11. Go to http://www.kumagera.ne.jp/kkudo/grayscale.jpg and download the grayscale image. Print out a copy of this scale in black and white.
12. Compare the colors of your soil samples with the different grayscale colors. Assign each sample a number (from zero to 100%) from the grayscale by matching up the colors of the scale with those of your photo.
13. Make a graph of your data by hand or you can try using the Create a Graph web site for kids from the National Center for Education Statistics.
14. Is there a difference between dry samples and wet samples? What happens to the color as more water was added? How can this scale be used for practical purposes?

Variations

• In this experiment, you only tested soil from one sample to make a scale. Sample different areas of your yard and compare to your scale. Can you use your scale to estimate the moisture content of soil from different places in your backyard? Is there a difference in soil moisture in sunny or shady locations?
• Try testing your soil moisture from the same location on different days. Does soil moisture change with the weather? Don't just compare the obvious rainy and dry days. Compare hot and cool days or cloudy and sunny days. Sample soil each day after a rain shower. How much does the moisture decrease each day?
• Will your color chart work for different types of soil? Repeat the experiment using soil collected from different locations that have different types of soil. Also try using store bought potting soils or compost. How does moisture effect the colors of each type of soil?

• For more science project ideas in this area of science, see Geology Project Ideas.

Credits

Sara Agee, Ph.D., Science Buddies

Brynie, F.H., 2005. Parent's Crash Course: Elementary School Science Fair Projects, Hoboken, NJ: Wiley Publishing Inc. pp 162-164.

Last edit date: 2006-08-15 17:10:26