Water quality impairment related to N loss from crop production fields continues to be a concern in Iowa, including meeting the USEPA nitrate-N drinking water standard and reducing N export to the Gulf of Mexico. Therefore, in-field production practices would be helpful to aid in reduction of nitrate leaching and movement to water systems. One practice identified in the science assessment for the Iowa Nutrient Reduction Strategy is use of a winter cereal rye (Secale cereal L.) cover crop, where a mean 31% (29% standard deviation) nitrate-N reduction would be expected, but with a 6% (22% standard deviation) corn yield decrease (SP 435). Due to cost, planting flexibility, success in establishment, and winter hardiness, winter rye has been a common cover crop choice. However, the impacts of winter rye on crop productivity differ among geographic areas and production systems, including the influence on N recycling and corn N fertilization requirement. With N returned to the soil as cover crop biomass degrades, is it immobilized by microbial processing of the cover crop biomass, or is it added to plant-available N during annual crop N uptake? The objectives of the research were to determine the impact of a winter cereal rye cover crop on corn N fertilization requirement and corn and soybean crop productivity.