MANHATTAN, Kan. -- Time is running out for topdressing the 2006 winter wheat crop, said Kansas State University agronomist Dale Leikam.

The nitrogen (N) in topdress applications must be moved into the root zone with precipitation in order to be efficiently used by wheat, said Leikam, who is a nutrient management specialist with K-State Research and Extension.

"If we don't get enough precipitation to move the applied N into the root zone, wheat plants may be unable to utilize it when they need it most," he said. "Since about one-third of total N utilized by wheat is in the plant by jointing, it is best to apply topdressed N early -- preferably December through February -- in order to try to make sure we get enough moisture to move the N into the root zone."

In some areas, there has been no significant moisture since early last fall. Where nitrogen was topdressed on wheat this winter in those areas, there has not been enough moisture to move it into the root zone. While some may worry about N volatilization loss or immobilization, the bigger concerns are the effect of dry soils on wheat growth and the fact that the applied N has not yet reached the root zone, Leikam said.

Typically, the biggest yield response to nitrogen with wheat is where the N is in the root zone before jointing, he explained. In the dry areas of the state this year, wheat may begin jointing before a rain occurs to move the topdressed N into the soil.

If rains do not come until after the wheat has jointed, will the topdressed N still have any impact on yields?

"In most cases, yes," the agronomist said. "Even though we would prefer to have the N in the root zone before jointing, N can still increase yields on N-deficient wheat if it is taken up as late as the boot stage."

About one-half of the total N utilized by wheat is in the plant by early boot stage. Nitrogen taken up at this time will not increase tiller numbers or maximum potential head size, but it can increase kernel weight and help maintain potential kernel numbers per spikelet.

"In this way, N taken up at a later growth stage by wheat that is deficient in N can increase, or at least help protect, yields," Leikam said.

SOURCE: K-State news release.