• Plant Health
  • Oct 23, 2020

Nitrogen Management Essentials for an Effective Postharvest Application

A corn plant uses approximately 75% of its nitrogen between the V5 and tasseling growth stages (from approximately June 1 to July 15). The closer to that time period you apply nitrogen the better, because it will be less exposed to elements such as rainfall or temperatures that can leach it out or volatilize it.

However, it’s typically not logistically possible for farmers to apply all of their nitrogen in the spring or in-season. Fall applications may be necessary, and there are ways to make them successful. Here are some tips to ensure postharvest nitrogen applications are as effective as possible.


1. Wait until soils are 50 degrees or cooler and always use a stabilizer.

At temperatures of 50 degrees or lower, the activity of the bacteria that convert nitrogen from its fertilizer form to its leachable form (nitrate) decreases dramatically. These bacteria don’t completely stop working, but below 50 degrees they’re inactive to the point that the amount of nitrogen that does convert to nitrate is minuscule.


In addition, be sure to keep an eye on shifting soil temperatures. In some areas of the Corn Belt, soils can be 50 degrees or cooler the first part of October, then increase in temperature if the weather gets unseasonably warm at the end of the month or even into November. Since we can’t predict these weather patterns, you should always include a stabilizer with any fall nitrogen applications.


2. Think ahead about nitrogen needs.

Over an extended period, you’ll probably have a somewhat higher nitrogen retention rate if you keep more of it in the field and plant-available with spring or in-season applications. However, applying nitrogen preplanting or at planting generally delays your planting date, which could potentially result in a yield loss.


Applying half your total nitrogen in the fall as a baseline can be a good idea so you won’t have to apply it right away in the spring. Then, a good strategy is to apply the other half at preemergence or in-season as a side-dress or top-dress to help spread out risk.


3. Apply the right kind of nitrogen.

Throughout much of the Corn Belt, the most common fall nitrogen application is anhydrous ammonia, which is somewhat of a nitrogen stabilizer itself because it will temporarily reduce the number of bacteria that transform ammonium into nitrate. This can buy you a couple of weeks of stabilization-like activity before the bacteria return and convert the fertilizer to nitrate, but you should still use a nitrogen stabilizer with anhydrous ammonia to achieve the longer control that’s required to prevent nitrate leaching.


Dry urea is becoming more popular as a nitrogen fertilizer source because in some states the handling and transport of anhydrous ammonia is highly regulated. Although urea is easier to spread, it does convert to nitrate more quickly than anhydrous ammonia does. A fair amount of urea gets applied in the fall; however, you should absolutely not apply it without a stabilizer.


So although it’s optimal to apply nitrogen in the spring closer to when corn plants need it, logistics make applying some nitrogen in the fall necessary. If you’re going to apply fall nitrogen, ensure you’re familiar with the properties of the form of nitrogen you’re applying, include a stabilizer and apply it when soil temperatures are 50 degrees or cooler. If you have any questions about fall nitrogen applications, be sure to talk with your local trusted advisor.


All photos are either the property of WinField United or used with permission.
Important: Before use always read and follow label instructions. Crop performance is dependent on several factors many of which are beyond the control of WinField United, including without limitation, soil type, pest pressures, agronomic practices, and weather conditions. Growers are encouraged to consider data from multiple locations, over multiple years, and be mindful of how such agronomic conditions could impact results.
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