Advanced-Level Science Projects

Can Healthy Plants Be Grown in Soil Containing No Microorganisms?

Soil is home to a great number and wide range of microorganisms, among them algae, fungi, bacteria, and viruses.

Although the number of microorganisms found in soil can sound alarming, it's important to know that these tiny organisms need nutrients in order to grow and be active in the soil. If the soil lacks the necessary nutrients, the majority of microorganisms may be physiologically inactive.

Microorganisms can be both good news and bad news for plants and those who grow them. Some help to decompose roots, stems, and leaves of plants that die, helping to recycle nutrients in the soil. Others increase nutrients in the soil and make it more fertile. Some even act as natural fertilizers.

Scientific Surprise

There normally are between one and 10 million microorganisms present in one gram of soil—which is only 1/28 ounce—a tiny, tiny amount. There are more bacteria and fungi than any other type of microorganisms.


Not all microorganisms are helpful, however. Some can infect plants through their roots and cause considerable damage.

In this suggested science fair project, you would investigate whether plants grow better in soil containing microorganisms than in soil that has none. To do so, you'd take a sample of fertile soil from your garden or a field, and divide it into two parts. Bake one part in the oven at 350 degrees for one hour to destroy all the microorganisms, and leave the other batch alone.

Plant the same number of the same type of seeds in each of the different batches of soil, and provide the same environment and care to each group. Record your results carefully.

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Excerpted from The Complete Idiot's Guide to Science Fair Projects © 2003 by Nancy K. O'Leary and Susan Shelly. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.

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