Determining the proper nitrogen (N) fertilization rate is important for the economic viability of corn production. A desire for high yields, fueled by low fertilizer N costs, led producers to apply rates that ensured adequate N rather than risk costly yield losses due to a shortage of N. Due to water quality concerns and recently high N fertilizer prices, management strategies are needed that can improve the efficiency and profitability of N use. With N application rates based on economic return instead of maximizing productivity, producers want to confirm that rate decisions are working adequately. Also, if unexpected N losses occur, help is needed with decisions for rescue N applications.