What are nitrogen application options for corn?
For example, risk increases if application is made when soils are wet and then dry (ammonia moving up the injection track); with higher application rates; when soils with high clay content are wet (sidewall smearing of the injection track and ammonia moving toward the soil surface during application); and when soils are very dry and coarse textured (larger ammonia band).
A few things can reduce the risk of ammonia damage: wait and apply when soil conditions are good; have a deep injection depth (6 to 7 inches or more); wait several days until planting; if the injection placement relative to future corn rows can’t be controlled, apply at an angle; if the injection track can be controlled with GPS guidance positioning technology, then split future corn rows – with this guided system no waiting period is needed. Anhydrous ammonia nitrifies more slowly than products like urea or UAN solution, so is a preferable N fertilizer for soils with greater potential for losses in wet conditions.
If decisions are made to plant corn and then apply N sidedress, be certain to check that needed fertilizer products and application equipment will be available. Best options for sidedressing, in order from most to least preferable, are:
injected anhydrous ammonia, UAN, or urea
broadcast dry ammonium nitrate, ammonium sulfate, or urease inhibitor treated urea
surface dribbling UAN solution
Sidedress injection can begin immediately after planting if corn rows are visible or GPS guidance positioning equipment is used. Be careful so that soil moved during injection does not cover seeded rows or small corn plants. It is easiest to inject in the row middle and there is no advantage in attempting to place the band close to the row. Corn roots will reach the row middle at a small growth stage. Injected N can also be applied between every-other-row. That technique will provide equivalent response as when placed between every row.
For many soils, when planting corn after soybean there can be adequate N in the root zone to meet the needs of small corn plants. For corn after corn, there is a greater chance that additional N is needed for early growth. Preplant or starter N can help meet those needs, and is especially important if sidedressing is delayed significantly or there will be a planned mid-to-late vegetative stage application in either rotation.
Broadcasting urea, ammonium sulfate, or ammonium nitrate across growing corn might cause some leaf spotting or edge browning where fertilizer granules fall into the corn whorl. The chancesof this happening increases with larger corn and higher application rate. As long as the fertilizer distribution is good and not concentrated over plants, the leaf damage should only be cosmetic.