This project is designed to study the N fertilization needs as influenced by location and climate in continuous corn and corn rotated with soybean. Multiple rates of fertilizer N are spring applied, with the intent to measure yield response to 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 each rotation practice, differences that exist between the two rotations, responses to applied N across different soils and climatic conditions, and evaluation of tools used to adjust N application.