Do you really need all that nitrogen?

URBANA, Ill. – Researchers at the University of Illinois are finding that many Illinois farmers tend to err toward excess applications of fertilizer nitrogen. The most commonly cited reasons for the overapplication are the desire to produce higher yields, uncertainty about the true nitrogen requirements of corn, and a lack of research.

Cheap insurance. “Nitrogen fertilizer overapplication has been viewed by many as a cheap form of insurance to assure against nitrogen losses and to make certain that enough nitrogen is available in case conditions are right for high yields,” said Fred Below, plant physiologist.

“However, skyrocketing costs for nitrogen fertilizer and increasing concerns about water quality are compelling reasons for farmers to improve their management of nitrogen.”

Current research. To help answer lingering questions, research is under way at the University of Illinois to verify how well the current recommended fertilizer rate in Illinois of 1.2 pounds of nitrogen per bushel of grain produced – minus any applicable credits – applies to modern, high-yielding hybrids.

“Documentation that this recommendation is adequate, or even too high, for modern hybrids would serve as justification against overapplication of fertilizer, which would save farmers money and help improve the quality of Illinois waters.” Below said.

A series of on-farm and experiment-station trials have been conducted over a wide range of production practices and conditions to better evaluate nitrogen needs.

“In addition to testing unfertilized plots to assess the soil’s capacity to supply the crop with nitrogen, we varied the rate of nitrogen fertilizer applied at six to seven different rates in 30- to 40-pound increments,” Below said. “All other management practices at the individual locations remained in line with local recommendations considered conducive to high yields.”

What trials found. Of the more than 40 trials conducted over the past three years, no more than 1.2 pounds of nitrogen per bushel of grain was needed to optimize productivity. In most cases, considerably less was required.

Averaged over all locations and years, the economically optimum rate came in at slightly less than 1.0 pounds per bushel.

“Especially surprising were the relatively high yields of more than 100 bushels per acre produced without any supplemental nitrogen and the fact that highest nitrogen requirements were typically associated with the lowest-yielding plots,” Below said. “Locations with the highest yields tended to have lower nitrogen requirements, presumably because the soil supplied the needed nitrogen.”