Mississippi’s warm, wet climate can pose considerable issues with nitrogen fertilization, particularly for crops which are known to be responsive and demand high amounts for optimal productivity, such as corn. Nitrogen, unlike some other nutrients, is very subject to change forms in the soil, which can substantially affect its availability to plants. The South’s warm, high rainfall climate greatly increases potential nitrogen loss through denitrification and leaching, compared to drier and colder climates. Therefore, optimizing your fertilizer dollars can involve considerable more planning than simply applying a given fertilizer rate.

The primary methods we suggest to improve corn nitrogen utilization are:

1. Use split application timing to limit nitrogen fertilizer exposure and losses when crop demand is low.

2. Take measures to minimize volatility potential of urea-based nitrogen sources.

  • Inject liquid UAN-solution in the soil.
  • Apply urea during the “first split,” rather than later when temperatures are higher.
  • Limit the amount of urea-based fertilizers you broadcast of your total N program.
  • Apply urease inhibitors to urea-based sources when you broadcast them on corn.

Nitrogen sources and application

Using the right nitrogen source and application method may be more important to corn grain yield, than how much you apply. It is becoming more popular to aerially apply urea to corn fields, but while this method is quick and convenient compared to injecting liquid nitrogen, there is risk associated with its use on corn that requires more management. Urea (46-0-0 or 41-0-0-5) or urea-containing nitrogen sources, including UAN-solution (N-sol, 32%, or 28-0-0-5), are subject to volatilization loss when applied to the soil surface (either broadcast or dribbled in a band). This risk may offset convenience or other savings. In fact, no-tillage research studies in Missouri and Tennessee show UAN-solution and urea broadcast on the soil surface reduced corn yield potential 9 to 23 percent compared to ammonium nitrate broadcast, UAN-solution injected, or anhydrous ammonia injected. Thus, we strongly suggest using methods to minimize urea volatility potential. Of course, injecting UAN-solution in the soil solves this issue, and is why this practice is standard.  roadcasting urea-containing sources during the “first” split application period should reduce risk, because temperatures are generally cooler and likelihood of rainfall capable of incorporating nitrogen is greater.

These environmental conditions reduce the potential for volatility losses. On the other hand, hotter temperatures and more infrequent showers later in the summer, promote high potential nitrogen loss.  You can reduce volatility by adding proven urease inhibitors, such as Agrotain, to granular urea or UAN-solution. Urease inhibitors temporarily slow the activity of the urease enzyme. But you’ll still need timely rainfall or overhead irrigation to get urea-based N into the soil to reduce loss and make it available so the plants can use it. Tillage can also incorporate urea, but may not be practical, and should be assessed relative to savings.  Sole reliance on granular urea to supply nitrogen for corn also exposes plants to leaf burn from broadcast application, if you use the preferred split application strategy. Thus, this strategy requires strict management, multiple applications, and a little help from Mother Nature in order to be successful for corn production.