Water quality impairment related to nitrogen (N) continues to be a concern in Iowa, including the nitrate drinking water standard, USEPA proposed surface water quality nutrient criteria, and Gulf of Mexico hypoxia. Addressing these issues could include strict guidance for N input to corn and resultant N use practices that require very high level of management and risk, with unknown economic consequences. Rate of N application is an important management factor in corn production related to nitrate reaching surface water systems. Rate is also important in regard to economic return. While applying only the needed fertilizer N rate in a given year will not stop nitrate from leaving corn fields, nor necessarily achieve proposed water quality goals, it can result in reduced residual soil nitrate and help lessen corn production's impact on water quality Therefore, it is possible that being able to assess corn N fertilization need differentially each season would improve corn N use efficiency and reduce nitrate susceptible to loss compared to application of an "average" agronomic rate each year.