Much of the primary fertilizer nitrogen (N) for corn is applied in the spring as pre-plant or sidedress, where efficiency of N use should be greatest. Fall N fertilizer application success can be enhanced by following several suggestions: only use anhydrous ammonia; apply in late fall after soils cool to 50 degrees F (4-inch depth) and are trending cooler (the colder the better, and most years in Iowa this is sometime in November); consider a nitrification inhibitor to further slow nitrification to nitrate; and avoid fall application to soils that are more prone to wetness or leaching (poorly or excessively drained soils).