A field experiment was conducted to monitor decomposition of corn stalk residue and the concomitant development of the microbial population inhabiting the residue. The quantitative and qualitative involvement of bacteria, actinomycetes, and fungi were examined during the course of decay. The soil in which the study was conducted had a mean annual microbial biomass of 71 g*m−2to a depth of 10 cm. The maximum biomass associated with the corn residues was 14 g*m−2of which 85% was fungal. During the active period of the first year, approximately 70% of the residue was lost. By relating residue (substrate) utilization to population estimates over time, the mean first year generation time for microbial biomass was calculated as 10 days, with the peak activity demonstrating a generation time <1 day. The peak fungal growth rate was 0.008 g biomass (dry)*g−1of residue*day−1. The initial predominant invading fungal genus wasMyrothecium.