Quick, Easy Method to Show Living Soil Organisms to High School or Beginning‐Level College Students

Abstract

The living component of soil is difficult for students to learn about and understand because students have difficulty relating to things they cannot see (beyond sight, beyond mind). Line drawings from textbooks help explain conceptual relationships but do little to stimulate an active interest in the living component of soil. Alternatively, movies, videotapes, or more recently web-based videos show motion of the organisms but the environment is artificial compared with direct observations on a soil the student has collected. Inexpensive, easy-to-prepare media dishes can be used for growing organisms from soil brought into the classroom by the student. The techniques described in this article are relatively simple and require little expertise to grow the organisms. An inexpensive microscope (ideally up to 500× magnification but acceptable to 100× magnification) and light source are needed but an autoclave and aseptic conditions are not required. The organisms are grown in mixed culture in petri dishes on lowenergy medium. Although bacteria grow prolifically on the dishes, their small size makes individual organisms hard to see at 500× but they serve as a major food source for larger organisms that can be observed. Different organisms will develop based on dish moisture. Wetter conditions encourage protozoa and rotifer growth, whereas drier soil conditions favor fungi, nematodes, and springtails. With several dishes at different moistures, fungi, protozoa, mites, springtails, nematodes, rotifers, potworms, and perhaps a nematode-trapping fungus or tardigrada can be commonly observed. Web resources should be used to provide beginning students with high quality images and video to confirm observations from the culture dishes.