This article describes a novel, hands-on method to qualitatively determine the extent of microbial activity in topsoil using ordinary blank paper. Appropriate and scalable for the high school and college level, these experiments expose students to some of the challenges facing environmental researchers and also contribute to curriculum development of soil topics for environmental education. Through experimentation, students discover that paper containing high amounts of starch can be used to determine the degree of microbial activity in topsoil. After the application of soil solution eluent to paper, the paper is allowed to dry. Students react the paper with a KI + I2 solution, and a deep blue coloration results that diminishes over time. Using the principles of complementary color combinations and a simple, handmade, cadmium sulfide–light emitting diode (CdS–LED) reflection photometer, the color can be measured and the extent of microbial activity established.
Supplement
A number of materials related to this paper are available. They include: a longer version of the paper with additional figures, a table, and directions for constructing the reflection photometer; notes for the instructor; and instructions for students.
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