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).
Iowa State University
Sawyer, John E., "Fertilizer Nitrogen Application This Fall" (2015). Integrated Crop Management News. 1781.
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