This project aims to 1) test APSIM's ability in simulating long term corn yield response to nitrogen and crop rotation using data from 14 locations (each with 10 to 20 years of data) in Iowa and Illinois, 2) use the model to better understand the yield response to N relationship, and 3) explore predictability of economic optimum N rate. This is a collaborative project with John Sawyer and Emerson Nafziger.