Irrigation water often contains a significant amount of nitrate- N that is readily available to corn. When the season total amount of N supplied in irrigation water exceeds 15 lb N per acre it should be deducted from the recommended N. For each foot of effective irrigation water applied, one ppm nitrate- N in water is equal to 2.7 lb N per acre. Irrigation amounts vary from year to year, and the N credit for irrigation should be based on the three- year average irrigation amount up to the corn R3 (milk) stage. Overall, in Nebraska 65 percent of the total irrigation amount is applied by August 1. Long term, average amounts of irrigation are estimated to be 8 in/yr in eastern Nebraska, 9 in/yr in central Nebraska, 12 in/yr in west central Nebraska, and 20 in/yr at the western Nebraska border with Wyoming (simplified from Sharma and Irmak, 2012)