A field survey evaluated the population composition of AM fungal species in Clarion (a well drained fine-loamy, mixed, mesic Typic Hapludoll) and Webster (a poorly drained fine-loamy, mixed, mesic Typic Endoaquoll) soils of four soybean (<i>Glycine max</i>, L.) fields. Soil tests for available P in the Clarion soil ranged from 14 to 143 mg P kg^-1 soil and those from Webster soil ranged from 38 to 203 mg P kg^-1 soil. Spores from six species of <i>Glomus</i> and species from the genera <i>Acaulospora</i>, <i>Gigaspora</i>, and <i>Paraglomus</i> were found in the original field soils. <i>G. claroideum</i>, <i>G. etunicatum</i>, <i>G. mosseae</i>, <i>G. viscosum</i>, and <i>Paraglomus occultum</i>-like spores were prevalent in both Clarion and Webster soils of all four fields. Trap cultures on different soybean cultivars, BSR201, Iowa2052, Mandarin, and Peking grown in pots inoculated with field soil samples from Clarion or Webster in the greenhouse, led to detection of several additional AM fungal species, including <i>G. clarum</i>, <i>G. coronatum</i>, <i>G. fasciculatum</i>, <i>G. vesiforme</i>, <i>Acaulospora calossica</i>, and <i>Entrophospora infrequens</i>. The variability of AM fungal species distribution was larger among the fields than within the fields. The richness of <i>Glomus</i> AM fungal species varied from 8 species in the Webster soil of a field with very high available P to 12 species in Clarion soil of one field where the available P was not as high. Spores of <i>G. mosseae</i> constituted 90% of the spore population in Webster soil with a very high level of P. Spore morphology-based identification of <i>Glomus</i> species, <i>G. claroideum</i>, <i>G. etunicatum</i>, <i>G. intraradices</i>, and <i>G. mosseae</i>, and of spores in the <i>Gigaspora</i> genus found in our soil and root samples was confirmed using polymerase chain reaction (PCR)-based rDNA fingerprinting protocols.