Phosphorous is an essential plant nutrient and is the second most common fertilizer nutrient applied in crop production. The role of mycorrhizal fungi in P nutrition of corn (Zea mays L.) in high fertility soils in unclear. A study was conducted to determine the effect of extractable P on mycorrhizal biomass and to evaluate the temporal dynamics of mycorrhizal fungi during the growing season in two irrigated corn fields in Nebraska. The objectives were assessed by the installation of soil-containing chambers prior to tasseling, and sequential removal of the chambers during the reproductive period. These chambers were assembled with and without P amendment and soil enclosed with mesh that allowed or excluded root penetration. Mycorrhizal biomass was measured using the biomarker fatty acid C16:1cis11. Root length increased from VT to R4 at one site, and in the other from VT to R2. In both corn fields the mycorrhizal biomarkers inside the chambers increased 7 to 24% throughout the reproductive stages of the crop tasseling to maturity, confirming translocation of C from the plant to the mycorrhizal symbiont. This increase in mycorrhizal biomass was greatest in chambers where the bioavailability of P was low and roots were present, suggesting a possible role in P acquisition. Further work is needed to quantify the mycorrhizal contribution to P uptake during the reproductive stages of corn as this will have significant impact on P fertilizer recommendations and the hybrid corn industry which has largely ignored the mycorrhizal symbiont.