In this article we describe a multi-week investigative laboratory in microbial ecology/diversity and nitrogen cycling that we have used in our introductory biology course. This module encourages active student involvement in experimental design, using the scientific literature and quantitative analysis of large data sets. Students analyze soil microbial community diversity using EcoPlates (sole source carbon utilization patterns). Also, functional analysis of these communities includes assays for nitrate, nitrite and ammonium to determine experimental effects on the nitrogen cycle. Students are continually assessed by various strategies throughout the module. (Contains 4 tables and 2 figures.)