We continue to search for methods and products that will increase nitrogen (N) use efficiency in corn production. Several years ago a controlled release N fertilizer was developed. The fertilizer is urea coated with a substance that controls the rate of N release based on the temperature and amount of soil water. It is currently sold in Iowa as ESN. The objective of this study was to compare the response of corn to addition of fall and spring-applied ESN and aqua ammonia (AA) at different N rates.