Nitrogen (N) efficiency is a fairly easy number to calculate. You take pounds of N applied per acre divided by the bushels raised. You can do this by zone or field or even on a per-farm operation.
“Farmers brag about this efficiency number like it’s a credit score,” notes Ken Ferrie, Farm Journal Field Agronomist. “I think it's a carry-over from the days when we used to say, ‘1.2 pounds of N per bushel on our yield goal minus our credits.’”
But that N efficiency number is only a positive when you’re confident your rate of N is not the limiting yield factor in a field, or when you’re comparing the efficiency between two different hybrids.
As a case in point, Ferrie relates a recent farmer discussion.
“I was working with a grower the other day who said he was proud of the fact that he had a nitrogen efficiency factor of .7 across his whole farm operation. The problem is we had identified at least six different fields where we were sure nitrogen was a limiting factor,” Ferrie recalls.
Ferrie showed the grower a series of results from field test plots that Ferrie’s agronomic team had conducted. In one nitrogen-friendly field, Ferrie’s team harvested 225 bushels per acre with only 110 pounds per acre of N and got an efficiency factor of .5.
That looked good to the grower until Ferrie showed him another plot result where he had applied 130 pounds of N and produced 247 bushels per acre. So, he still had a nitrogen efficiency of .5, but the yield was 22 bushels per acre higher.
“Now, even at 50-cent N, this field produced an additional $70 an acre profit,” Ferrie reports.
The issue is N efficiency is a positive, but it’s not a positive when you don’t supply the amount your corn needs to deliver optimum yields. You have to figure out how to strike a balance between N efficiency and yield results.
In the following Boots In The Field Report podcast, Ferrie talks further about how you can accomplish that in 2019. Listen here for more information: