Wheat and N: What to do?

Published: March 12, 2020

It's been another tough year for wheat so far.

A lot of planned wheat acres did not get planted last fall due to the wet fall and slow harvest over much of the state. Much of the wheat that did go in was planted late.
For late-planted wheat, formation of fall tillers will be less than for wheat planted on time. And tillers are a crucial component of wheat's potential yield, determining total heads that form. The best growers know to plant more seeds when planting late, in order to emerge from winter with enough tillers (or close to it). More plants help to compensate for fewer tillers per plant.

Early spring N can also stimulate formation of additional tillers. Now on March 11, some of the window in which additional tillers can form has passed, but some of that window is still left.

My research has showed that, in most years, wheat yield is higher when all or most N is applied just before jointing.

The exception to that rule comes when tiller count at green-up is low. There will be more fields in that situation this year than in most years, and thus more need for early N this year.

The most accurate method is by counting tillers; 60 per square foot or less means that you desperately need N soon to maintain yield potential; 90 or more per square foot means that you should probably wait until just before jointing to apply N. Between 60 and 90, some N now would be good but not crucial. If you're not willing to count tillers, the eye test works reasonably well. If the wheat looks thin, applying some or all N as soon as possible will probably pay. If it looks thick, wait. In between, probably apply some or all N soon, but it's not as critical.

Last year was similar to this year—wet fall, slow harvest, late wheat planting, cool and wet winter. Early N was probably critical in many fields last year.

This was proven in one farm field where "early" N out-yielded late N by 10 bushels even though more N was applied later. A split N application was planned, but the first application (about 55 lb N/acre) was stopped about 1/3 of the way through the field due to rutting. This was already well after green-up due to wet conditions. It took 12 more days for the farmer to get back in; by that time tillering had ended. He decided not to make a second application where he had already applied, but applied 75 lb N/acre to the rest of the field. Because his tiller count was low (I think about 40-45 per square foot), the earlier N timing really paid off. The extra yield from applying early would have easily paid for a plane to apply the N.

Take-home

• If your wheat looks thin or has less than 60 good tillers/square foot, apply N as soon as possible. If the field is too wet to drive, seriously consider getting a plane to do the job. If you can't get N on soon, monitor the field closely as it may be a candidate for planting another crop.
• If your wheat looks just okay, you should probably get some N on soon, but it's not as critical as in fields that look thin. You could consider splitting the N into two applications, or just apply all now.
• If your wheat looks good, especially if it has more than 90 good tillers/square foot, wait until just before jointing to apply N.