Among essential crop nutrients, nitrogen is the greatest management challenge due to highly dynamic transformations and losses. Applied N rates may be insufficient for optimum yields, or substantially exceed crop needs. The latter results in water, climate, energy and air pollution concerns, especially with maize (Zea mays L.) production. The economic optimum N rate is impacted by several features of a production environment, including inherent soil and climate characteristics, weather, agronomic management, and economic/risk factors. Conventional N calculators for maize are static, generalized and inherently imprecise. Adaptive maize N management in the 4R context can be supported by dynamic simulation models that incorporate the complexities of production environments and weather. As a case study, the Adapt-N technology is discussed with features on critical factors affecting N dynamics and the estimation of an EONR for maize production environments.