The Nitrogen Rule of Thumb? There Isn't One.

04:22PM Apr 06, 2015
( Ben Potter )

Add a pound of nitrogen, grow a bushel of corn. That simple rule of thumb that has governed thousands of fertility decisions over the years. But that equation might not be entirely accurate, according to Harry Stine, CEO of Stine Seed Company.

“People put on 200 lbs. of nitrogen and expect to get 200 bu. of corn,” he says. 

But many, many factors are at play that often renders that rule of thumb inaccurate, Stine adds. For example, a farmer who applies zero nitrogen to a given field still might reap 70 or 80 bu. of corn.

Thomas Morris, professor of plant science at the University of Connecticut, says the "1 pound / 1 bushel" rule of thumb should not be a part of today's crop management equation.

"Making the best decision about the rate of N to apply to an individual corn field cannot be boiled down to a rule of thumb," he says. "Using rules of thumb for a complex decision, like how much N to apply to individual corn fields, only results in over- and under-application of N, which is not good for the farmer or the environment."

Morris, who also consults for the Environmental Defense Fund, says there are several good online tools to help with making smart fertility decisions, including the Iowa Soybean Association's On-Farm Network, the Indiana On-Farm Network, the Adapt Network and the Kansas Ag Research & Technology Association. Further, thousands of strip-trial research  plots completed by these networks has been compiled in the "Maximum Return to N" database.

"The MRTN database provides the N recommendation for seven land grant universities in the Corn Belt, and it is the best place to obtain a baseline recommendation for farmers in those states," Morris says.

Stine notes that a smart fertility program should also incorporate spreading out nutrients through the course of the season. The soil can only hold so much, and the probability of leeching goes up if you put on high amounts early. Stretching a fertility program so some goes on pre-plant, some goes on at-plant, and applying a significant part while the crop is growing in the summer is often a good bet, he says.