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Supplemental Nitrogen Applications
Supplemental N can be applied to wheat after emergence to correct deficiency symptoms, boost protein or maintain yield potential.
Top-dressing N before the first joint extends will not leave wheel tracks in fields. Traffic across fields later breaks the stem below the joint and will leave tracks visible through harvest.
Both dry and liquid N products can be used for top-dressing grain crops. Application prior to rainfall improves update efficiency as nutrients are moved into the root zone. The most common products available are urea (46-0-0) and urea-ammonium nitrate solutions (UAN, 28-0-0). In addition, a limited number of fertilizer dealers maintain inventories of ammonium nitrate (33-0-0) and urea solution, usually (20-0-0) or the same product with added sulfur and an analysis of (20-0-0-3).
The dry products frequently are less expensive and are surface applied as a broadcast application. The liquid products offer the advantage of being used as a herbicide carrier. Urea solutions offer an added advantage of reduced leaf burn.
Dry granular products can be applied at any rate. The amount of liquid N that can be applied without leaf burn diminishes as temperatures rise and crop growth accelerates. Forty lb N/acre as liquid N is a relatively safe rate when temperatures are cool and small plants provide 40-60 percent ground cover. With high temperatures and a ground covering crop canopy safe rates drop to 10-25 lb N/acre with increased margins of safety for urea solutions.
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