The article focuses on an experiment for the analysis of microbial activity in topsoil. It is stated that topsoil is the topmost layer of soil, which contains large amounts of bacteria and other microorganisms, that make the soil rich in nutrients to be used by plants. The microorganisms include bacteria, viruses, fungi, algae, and protozoa. In the experiment, qualitative analysis of microbial activities in topsoil is done by using white copy paper and a handmade cadmium sulfide-light emitting diode (CdS-LED) reflection photometer. White paper sheets are dipped in a soil solution, and treated with iodine, which results in a blue color. The depth of the blue color is measured by using the handmade reflection photometer.