Research Update: Fertilizer Rates and Timing for Irrigated Wheat

Research Update: Fertilizer Rates and Timing for Irrigated Wheat

July 11, 2008

Winter wheat, long a mainstay of dryland agriculture in the Panhandle, is being grown on an increasing number of irrigated fields, according to Dr. Gary Hergert, soils and fertility specialist at the University of Nebraska Panhandle Research and Extension Center at Scottsbluff.

Irrigated wheat is gaining popularity for several reasons:

  • It will grow under limited irrigation, a situation many farmers are facing.
  • Wheat prices have risen enough to cover the higher input costs associated with irrigation.

But while there's a large database about dryland wheat production, there's not much data on producing the crop under irrigation. Hergert hopes to remedy that.

At the recent field day at the High Plains Ag Lab near Sidney, Hergert reported on three years of research into improved nitrogen management for white wheat. The research is funded by the Nebraska Wheat Board. Test plots are located at Sidney, Alliance and Scottsbluff. The study will run for two more years.

Although the focus is white wheat, Hergert said the recommendations should apply to hard red wheat as well. Also driving the need for research is the fact that farmers need to sharpen management skills. They face not only limited water supplies, but also rapidly increasing fertilizer prices. Hergert said the price of nitrogen has more than doubled in the past two years and phosphorus has nearly quadrupled.

One lesson that growers should take from these conditions is the importance of doing a good job of soil testing, according to Hergert. That means collecting samples down to a depth of 3 to 4 feet. Many growers collect only shallower samples, he said.

The UNL study compared several fertilizer application timings:

  • All preplant
  • One-third preplant and two-thirds at the joint stage of plant development
  • One-fourth preplant, one-half at joint stage, and one-fourth at boot stage

In addition to nitrogen timing, the study also compares different nitrogen rates. Full irrigation is applied at the High Plains Ag Lab and the Alliance site, and three different rates (4, 8 and 12 inches) are used at the Scottsbluff site.

Three years of research have resulted in some preliminary data about irrigated wheat's response to different nitrogen timing and rates.

As far as timing, the top yields have come from the second option - one third of the fertilizer applied in the fall and two-thirds at boot stage, Hergert said.

As far as nitrogen rates, Hergert said maximum yields have been produced when the amount of residual nitrogen in the top 4 feet of soil, along with the applied fertilizer, totals 200 to 210 pounds of nitrogen per acre. Top nitrogen rates to maximize yield have not been higher than 100 pounds per acre, Hergert said. This is not as high as has been commonly assumed to produce high yields, he said.

David Ostdiek
Extension Communications Specialist
Panhandle REC, Scottsbluff