Maize grown under continuous cultivation often yields less than maize rotated with soybean, which many agronomists attribute to N availability. Our objective was to evaluate the role of N supply on the yield penalty of continuous maize, with particular emphasis on root development. Two commercial hybrids were grown in 2005 on plots where soybean or maize was the previous crop (main plots), and fertilized with six rates of N (0, 35, 70, 135, 200, 270 kg N/ha). Each main plot was also subdivided into Fall and Spring tillage of the previous crop residue in order to further alter N availability. Differences in aboveground plant growth attributed to previous crop were evident by V8, while N-induced growth differences were not seen until V12. At both stages, continuous maize plants had smaller shoots (average of 20%), but more roots (both volume and surface area) than those rotated with soybean. Neither of these growth differences was altered by N level, and spring tillage generally exacerbated the growth effects of continuous maize, while having no effect on rotated maize. While both previous crop and N supply altered grain yield (average of 1.4 Mg/ha for both parameters), the yield penalty associated with continuous maize could not be overcome with additional N. Our data suggests that maize residue, more than N availability, is the cause of the yield penalty associated with continuous maize.