Spore numbers and species diversity of vesicular-arbuscular mycorrhizal (VAM) fungi from agricultural soils may be significantly lower than those observed in native soils (Hetrick and Bloom, 1983). In a survey of corn fields from four locations throughout a growing season, one soil (Scandia, Kansas) contained primarily Gigaspora spp. at all sample dates (G. rosea was present on two of the sample dates) while the others contained primarily or exclusively Glomus spp., including G. etunicatum (Hetrick et al., 1984). The present study was initiated to determine whether the Scandia soil favored sporulation of Gifasopra spp. and conversely whether a soil containing predominantly Glomus spp. would preferentially stimulate Glomus spp. sporulation. Because nonsterile soil has been shown to suppress mycorrhizal growth response and root colonization (Hetrick et al., 1986), the effect of nonsterile versus sterilized soil and interspecific competition on sporulation was also studied to determine whether these factors influenced species dominance and might also explain the low spore numbers observed in agricultural soils