Recent research suggests that N recommendations developed using the linear plateau model have a poor relationship with the economic optimum N rates. These results have been attributed to inaccurate assessment of N mineralization. The objective of this study was to determine the influence of soil moisture regime on yield, N responses, and mineralization because not only do environmental conditions vary from year to year but yield also varies from location to location. Field experiments were conducted in Aurora, South Dakota, 2002, 2003 and 2004. Treatments were natural rainfall, natural rainfall + irrigation, and four N rates (0, 56, 112, 168 kg N/ha). Plant samples were analyzed for ¹³C discrimination (Δ), ¹⁵N, and total N. An interaction between soil moisture regimes and N rates was not observed. Increasing N rates increased corn grain yields and applying supplemental irrigation increased corn grain yield and N mineralization. The optimum N rate was similar in both soil moisture regimes. This work suggests that the linear plateau model is not accurate because it does not account for increased N mineralization effect of soil moisture regimes.