Understanding N Utilization, Minimizing Loss

With a balmy winter already under our belts and the prospect of an even dryer summer than 2011 looming, the recent CropLife Media Group Webinar, “Understanding Nitrogen Utilization And Minimizing Loss,” tackled a rather timely topic for growers and ag retailers. Speakers during the presentation were Dr. Barney Gor­­don, agronomic consultant/professor emeritus, Kansas State University, and Dave Schwartz, vice president of sales and business development, Specialty Fer­tilizer Products (SFP).

Gordon started the discussion by examining how crucial proper nitrogen (N) management is to crop yield. For example, in order for a grower to produce an average yield of 250 bushels of corn per acre, one would need to supply that crop with 188 pounds of N per acre.

Sounds easy. Not so fast, said Gordon.

“We all know that nitrogen can be pretty tricky,” he said. “It’s an unusual element and it can be lost in many different ways.”

There are four distinct mechanisms of nitrogen loss in the field:

  • Immobilization. Especially a problem in no-till operations with heavy surface residue, N is being utilized by microbes that live in the soil rather than the crop it is intended for. Placing fertilizer away from carbon can reduce the risk of this occurring.
  • Denitrification. When applying nitrate on heavier, clay-based soils, involves the gaseous loss of N. Warm temperatures greatly increase the risk of occurrence.
  • Ammonia Volatilization. More of a problem with urea and urea-containing products, this is the gaseous loss of ammonia from surface-applied urea. Generally worse in no-till conditions, the evaporation of drying water is the driving force. Gordon cited several factors that affect this process, among them: pH level, temperature, ammonia concentration, soil texture characteristics and moisture, wind speed and concentration of the urease enzyme.
  • Leaching. The downward movement of N molecules in the nitrate form, this is more of a problem on sandier soils with large pore spaces. The longer the time between fertilization and uptake, the more risk incurred.“Losses with volatilization can be significant, up to around 10% to 20% of the applied N, and they can happen quite rapidly when conditions are ideal,” said Gordon.

UAN Factors

Gordon then presented a study concerning UAN (urea + N) application methods. Observing corn fields in Scandia, KS, between 2008-09, Gordon found that of the three most common application methods (broadcast, dribbled and knifed), knifed produced the highest average yield at 188 bushels per acre. Comparably, broadcasting the UAN mixture brought an average yield of 168 bushels per acre.

“Knifing that nitrogen in under the residue takes care of a lot of those volatilization problems,” said Gordon. “It does not do anything to denitrification, it doesn’t solve the leaching problem, but it does take care of that volatilization problem that we had with urea and urea-containing fertilizers.”

However, for those growers that use the broadcast method, Gordon offers the following options to slow N loss:

  • Urease Inhibitors. These are used to control volatilization. Agrotain (nBTPT) is an example of a urease inhibitor as it deactivates the urease enzyme, thus preventing the hydrolysis of urea.
  • Controlled release N. Urea granule is coated but allows water to diffuse across the membrane. N release is then temperature controlled. ESN from Agrium is an example.
  • Long-chain liquid polymer coating of urea. UAN — Nutri­sphere-N from SFP, is an example. Nutrisphere-N sequesters nickel (Ni) ions in urease and bio available Ni ions in the soil. The result is a slowed hydrolosis of urea. It also acts as a nitrification inhibitor by sequestering iron and copper out of the soil with the result being slower nitrification.

In summary, subsurface application of N is the most efficient application method, but if surface applying, banding is more efficient than broadcasting. If broadcasting, there are products available that can minimize N losses and improve efficiency, said Gordon.

Schwartz agreed. “In 184 total corn trials that we’ve run with Nutrisphere-N treated urea, there’s an average bushel per acre yield increase of 14.9, which is a 7.7% increase overall,” he said. “The beauty of this product is the longevity with which it performs. It has that length of control that can get you through lots of different types of loss activities, and the multitudes of losses that it covers makes it a very broad spectrum product for a retailer.”

Additionally, in 15 wheat trials with Nutrisphere-N treated urea, a 7.3 bushel per acre yield increase (11%) was observed.

“You have to find something that really fits all the different methods of application and gives you a wide spectrum of use options to keep your customers happy,” said Schwartz. “I really see this being a good product for the custom applicator.”

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