Three nitrogen response studies were conducted in Iowa to compare the effect of a controlled release fertilizer, ESN, to urea and aqua ammonia (AA), on corn grain yields, biomass yields, and soil nitrate (NO3 --N) and ammonium (NH4+-N) concentrations. Experiments were conducted at two sites from 2003 through 2007 for the spring-applied ESN/urea study, two sites from 2006 through 2007 for the fall and spring-applied ESN/AA study, and one site from 2006 through 2007 for the spring applied ESN/AA study. N rates in the studies were 0-202 kg ha-1 in 34 kg N ha-1 increments in the ESN/urea study and 0-202 kg N ha-1 in 67 kg N ha-1 increments in the fall and spring-applied ESN/AA studies. Four of nine site-years in the ESN/urea study had significantly higher corn grain yields due to ESN. One of four site-years in the fall and spring-applied study had higher grain yields to either fall or spring application of ESN. Neither year of the spring-applied ESN/AA study had significantly higher grain yields due to ESN. Biomass yields, the above ground portion of the plant minus the ear, were also collected at physiological maturity. None of the nine site-years in the ESN/urea study had a positive response to ESN. One of the four site-years in the fall and spring-applied ESN/AA study had a positive response to spring-applied ESN. Neither year of the spring-applied ESN/AA study had a positive response to ESN. Soil samples were taken to measure NH4+-N and NO3--N concentrations at the V-6, V-15 growth stages, and also post-harvest at a depth of 0-30 cm. A 31-60 cm soil sample was also taken at post harvest. Throughout all of the studies, ESN treatments usually had higher concentrations of soil NH4+-N and NO3--N. Higher concentrations of residual N left in the soil after harvest can be subject to loss overwinter.