Maize-N model is a computer program that estimates field-specific, economically optimal N rate (EONR) for corn crop based on mechanistic and quantitative understandings of corn cropping system. It achieves the goal systematically: (1) simulate maize yield potential and year to year variation using historical weather data and user-proposed management including hybrid maturity, planting date and plant population, (2) assess attainable yield either based on field-specific, past yield record or using generic estimation, (3) estimate N uptake requirement for the attainable yield, (4) simulate mineral N release from soil organic matter, crop residues (including roots) and manures, (5) estimate recovery efficiency of applied N fertilizers, and (6) assess EONR of fertilizer maize based on pricing info of grain and fertilizer. It has been tested and validated in US Corn Belt and is being tested globally.