Recent work concluded that during water limited periods the evaporative fraction (EF), a measure of plant transpiration and consequently latent heat flux as well as photosynthesis, declines with both surface (≈5-10 cm) and root-zone limited soil moisture. Thus, surface soil moisture alone, which can be observed via satellite, could describe EF during water limited periods. The benefit is that satellites can retrieve the top ≈5 cm soil moisture. However, this hydraulic link between the surface and the root-zone soil moisture may not hold in the U.S. Corn Belt. Tile drainage below much of the Corn Belt prevents shallow water tables (≤ 2 m) from rising above the depth at which the tiles are buried (≈1-2 m). Shallow water tables can act as a water source for crops during the growing season because roots reach as deep as 1.5 m. We hypothesized that EF would remain high in the Corn Belt during limited surface soil moisture if crop roots have access to soil water via capillary rise from the water table. Therefore, if satellite-observed surface soil moisture is low, we could not assume a low EF. To test our hypothesis we analyzed latent and sensible heat flux, surface soil moisture, and meteorological variables at several AmeriFlux sites and three Iowa State University eddy covariance sites. EF for corn and soybean declined when surface soil moisture became limited for a sandy loam soil with a 20 m water table (Rosemount, MN). On the other hand, EF for corn did not decline with limited surface soil moisture for the clay loam soils with a shallow water table (Ames, IA). Limited soil water content occurs at higher values of soil moisture for clay soils than sandy loam soils. We do not have direct measurements of root-zone soil moisture and hence cannot yet determine whether sufficient root-zone soil moisture above the water table or the water table itself contributes to the lack of EF decline. However, Agro-IBIS VSF, an agro-ecosystem model that accounts for variably-saturated soil water movement, can vary the depth to water table with all other variables remaining constant. The model results show that the groundwater depth impacts the surface soil moisture to latent heat flux relationship. At present we can conclude that satellite observations of the top 5 cm soil moisture (e.g., from NASA's SMAP and ESA's SMOS) cannot determine EF in shallow water table portions of the Corn Belt, contrary to previous work.