Thinking About a Sidedress Nitrogen Application? Here's How It Could Help Your Crop

The conditions many farmers experienced since this past fall have changed many planned nitrogen applications for this year’s corn crop. Because of the rainfall events across much of the Corn Belt, lots of preplant nitrogen plans were abandoned. In many cases, the corn was planted first and is now being fertilized with nitrogen as a sidedress application.

First, let’s look at the three most common nitrogen sources used to sidedress corn:

Anhydrous Ammonia (NH3) (82-0-0)

Generally, NH3 is the least expensive form of agricultural use nitrogen. NH3 goes through a nitrification process, converting to NH4 and then to NO3 (nitrate)—the form the plant prefers. Time to complete this process varies with soil and air temperature.

NH3 is also the most difficult and dangerous form of nitrogen to handle. It is a compressed gas in liquid form. It does not contain any water, and when injected into the soil, NH3 has a strong attraction to the water present. That’s why soil conditions are important to consider with any anhydrous application. The closing of the knife tracks is critical to hold the NH3 in the soil, or it can be lost into the atmosphere. The escaping NH3 gas may also cause the delicate tissues of corn leaves to burn.  

Urea (46-0-0)

This is the dry granular form of nitrogen produced from anhydrous ammonia. It is usually sold at a reasonable cost for the return to farmers. It has the ease of handling and spreading, but does have some nitrogen loss risk involved. When applied to the soil, urea quickly changes to ammonium bicarbonate and nitrate (NO3). If granular urea is spread over growing corn, some granules may be captured in the whorls of the corn and can cause minor leaf burn. If left on the soil surface, urea may convert to ammonia gas causing nitrogen loss, which is why some form of incorporating it into the soil is suggested.

UAN (28% and 32%)

UAN is produced by combining urea and ammonium nitrate. Approximately 25% of UAN is immediately available to the plant, making it a great source of nitrogen where plants are deficient. Ease of application methods, such as surface dribble, Y-drops, knifing into soil, mixing with irrigation water, or mixing with pesticides and other fertilizers, make it a desirable form of nitrogen to use. However, if not incorporated, some nitrogen loss as ammonia gas can be expected.

PRO TIP: There are many nitrogen stabilizers that can be applied with each of these sources to slow the process of nitrogen converting to nitrate (NO3) for the plants use. This may not be needed on your farm, if the nitrogen is being applied to rescue or provide immediate nitrogen to plants. Check your local regulations regarding the use of stabilizers in your area.

Four Tips to Get the Most Out of a Sidedress Application
  • Typically, all nitrogen planned for the corn crop should be applied by early tassel or R1 stage of growth, so timing is key.

  • Sidedress applications are the most efficient use of nitrogen, but split applications can be useful in some situations.

  • Nitrogen should be placed close to roots for quick uptake. (If you’re knifing in nitrogen post-emergence, be careful to prevent corn root pruning.)

  • A pivot irrigation system is also a valuable tool to apply nitrogen as the plants require it; protecting against some nitrogen loss in case you experience a severe hail or other event.

But What N Does Your Crop Already Have Available?

Those that did get nitrogen applied last fall need to determine the amount of nitrogen remaining, if any, after leaching and washing from rainfall events.

A simple soil test for nitrate may be a good investment to find the level available to seedlings in the top 8 inches of soil. If the seedlings appear light green, or show some yellowing, this could indicate a nitrogen deficiency. These symptoms can also be caused by lack of warm weather, lack of sunshine, or herbicide interaction caused by saturated soils and weather conditions.

Besides an early soil test, tissue tests can be good for determining the amount of nitrogen present in the plants. Tissue tests can be done weekly, but nothing beats diligent scouting to observe the corn’s visual attributes. Paying attention to field details will pay off dividends in yield in the fall.

Read this next: The Pros and Cons of Spring and Fall Soil Tests(2 min)

Tune in to the latest episode on The FBN podcast with FBN's Head of Agronomy Dr. Darin Lickfeldt and Senior Staff Agronomist Doyle Oerter. Together, they address nitrogen fertility and what growers should know about sidedress and lay-by applications of nitrogen on corn. 

Listen and subscribe onApple Podcast,Spotify,Google Play Music,Google Podcasts and Stitcher.

ALWAYS READ AND FOLLOW LABEL DIRECTIONS. It is a violation of federal and state/provincial law to use any crop chemical product other than in accordance with its label. The distribution, sale and use of an unregistered pesticide is a violation of federal and/or state law and is strictly prohibited. It is your responsibility to confirm prior to purchase and use that a product is labeled for your specific purposes, including, but not limited to, your target crop or pest or weed, and its compatibility with other products in a tank mix.