The Enid News and Eagle, Enid, OK

January 18, 2014

It’s time to top dress area wheat crop

By Rick Nelson, Extended Forecast
Enid News and Eagle

ENID, Okla. — There are few crop inputs that deliver as much return on investment as nitrogen fertilizer.

It takes approximately two pounds of nitrogen, costing approximately $1, to produce one bushel of grain worth about $6. Of course, nitrogen is not the only yield determining factor in a wheat crop.

Top dress nitrogen fertilizer is especially important because it is applied and utilized at a time when the plant is transitioning from vegetative to reproductive growth. Several things, including the number of potential grain sites, are determined just prior to jointing and it is imperative that the plant has the fuel it needs to complete these tasks.

Jointing also marks the beginning of rapid nitrogen uptake by the plant which is used to build new leaves, stem, and the developing grain head. The nitrogen stored in these plant parts will be used to fill the grain later in the season, and the plant is dependent on this stored nitrogen to complete grain fill.

When to apply

• In order to have full benefit, nitrogen must be in the rooting zone by the time wheat is jointing. Jointing occurs around the second week of March in northern Oklahoma.

• Moisture is required to move nitrogen into the rooting zone.

Since precipitation is usually limited in January and February in Oklahoma we need the nitrogen out on the field prior to precipitation arriving. Do not apply nitrogen to frozen ground.

Nitrogen will move with water. If melting snow or frozen rain is moving to the ditch, so will nitrogen applied to the soil surface.

• Consider splitting or delaying top dress nitrogen applications to sandy soils until closer to jointing, as leaching can occur.

How much

to apply

• On average it takes about 2 pounds per acre of nitrogen for every bushel of wheat yield.

In addition, dual-purpose wheat requires 30 pounds per acre of nitrogen for every 100 pounds per acre of beef removed. You can subtract your soil test NO3-N from these total requirements.

• It is OK to adjust top dress nitrogen plans based on your current yield potential.

When you submitted your soil test, you might have stated a 50 bushels per acre yield goal which would require 100 pounds per acre of nitrogen; however, it is important to take a hard look and determine if this yield goal is still realistic based on your current crop status.

It is not suggested to adjust based on what one thinks the weather might do, but be realistic and adjust your top dress nitrogen up or down based on current field conditions.

What source to use

• The plant does not care about nitrogen source. A pound of nitrogen is a pound of nitrogen. Focus on getting the correct amount applied at the correct time, and choose your product based on price and application uniformity.

• Streamer nozzles almost eliminate leaf burn from UAN; however, leaf burn is generally not an issue until temperatures warm and/or you are applying fairly large amounts of UAN. Stream nozzles are also not affected much by wind and deliver a uniform pattern in a variety of conditions.

There also are some studies that indicate banding of UAN through the use of stream nozzles will reduce nitrogen immobilization on crop residue.

• One cannot, however, tank mix herbicides when using streamer nozzles.

Nelson is Oklahoma Cooperative Extension Service educator for Garfield County.