This project is designed to study the N fertilization needs in continuous corn and corn rotated with soybean as influenced by location and climate. Multiple rates of fertilizer N are spring applied, with the intent to measure yield response to this N within each rotation on a yearly basis for multiple years at multiple sites across Iowa. This will allow the determination of N requirements for continuous corn and rotated corn, differences that exist between the two rotations, responses to applied N across different soils and climatic trends, and evaluation of tools for site adjustment of N application.