Nitrogen Timing in Wheat

By Tracy Sayler

These graphical summaries of wheat research in North Dakota and Minnesota, help illustrate the following general guidelines, observations, and recommendations for nitrogen application and timing for spring wheat production in the Northern Plains.

• It’s recommended that wheat growers apply enough preplant N to meet historical yield goals.
• Pre-plant N usually results in optimum yield and protein.
• The wheat plant will respond to post N if there’s insufficient soil N and/or pre-plant - N. Therefore, it’s OK to supplement with post applied N to meet environmental conditions favorable for higher than historical yield goals.
• With adequate soil N, application of additional N after tillering
  (5 leaf) generally affects % protein, not yield.
• Rainfall is needed to move N to the root system with post emergence application. Timely rainfall is often not reliable, so post emergence application/rainfall timing is critical.
• Post application needs to be made before nitrogen deficiency symptoms occur – applying N after yellowing may not be able to help a crop fully recover from N deficiency stress, let alone boost yield.
• If using split N applications, realize the risk that delayed post emerge N (because of weather or other factors) can have on crop development.
• Top-dressing N may have little or no effect on grain yield if pre-plant N rates are sufficient.
• Grain protein can be increased by use of top-dressed N, but there may be a diminishing return as the amount of pre-plant N increases.
• Slow-release N can improve grain protein.
• To save yield potential, supplemental N (when needed) should be applied before 5 leaf stage and needs to be incorporated someway into the soil and root zone.
• Excess N will result in lodging and can be problematic with sugarbeets in rotation.
• Spring wheat varieties all seem to respond to foliar N in the same way, with no significant differences in yield or protein by variety. However, research has demonstrated differences among how varieties are affected by UAN – some are more sensitive to leaf burn than others.  Use early morning or evening applications to minimize leaf burn.
• Innovations such as liquid N stream bars, specialized streamer nozzles, and air spreaders can be essential tools to  maximize the potential of foliar N while minimizing leaf burn.
• Lodging potential increases at high N rates, variable of course depending upon variety, growing conditions and soil mineralization rate.

Research information, data, and summaries from Terry Gregoire and David Franzen, North Dakota State University; and Jochum Wiersma, George Rehm, John Lamb, Albert Sims, University of Minnesota.

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Figure 1.  Effects of post applied dry ammonium nitrate to 4-5 leaf wheat in western and northwest Minnesota. (Early 1990’s Lamb and Rehm).  Hard red spring wheat grain yield response to various rates of top dressed N at different levels of pre-plant soil N. Values shown are averaged across 21 sites.

Figure 2.  Effects of post applied dry ammonium nitrate to 4-5 leaf wheat in western and northwest Minnesota. (Early 1990s Lamb and Rehm). Hard red spring wheat grain protein response to various rates of top dressed N at different levels of pre-plant soil N. Values shown are averaged across 21 sites.

Effect of Total Nitrogen Available on Wheat Yield
(bu/a, Langdon 2003-04. Soil N = 35 lbs/a. 10 lbs N as a starter. Rest was urea supplied ppi.  No lodging in 2003. Lodging did occur at maturity in 2004.)

Effect of Fertilizer Timing on Wheat % Protein
(Langdon 2003-04. Soil N = 35 lbs/a. 10 lbs N as a starter. SB (stream bar) application with 28-0-0 in 2003. Total N for all treatments = 180 lbs/a in 2003, 170 lbs in 2004)

Effect of Total Nitrogen Available on Wheat % Protein
(Langdon 2003-04.  Soil N = 35 lbs/a. 10 lbs N as a starter. Rest was urea applied ppi).

Effect of Fertilizer Timing on Wheat Yield
(Langdon, 2003-04. Soil N = 35 lbs/a. 10 lbs N as a starter. SB (stream bar) application with 28-0-0. Total N for all treatments = 180 lbs/a. in 2003. 170 lbs in 2004. No lodging on trial in 2003).

Effect of Fertilizer Timing on Wheat % Protein
(Dryland Carrington 2003. Soil N = 44 lbs/a. Additional 40 lbs. N as soybean credit.  SB (stream bar) application with 28-0-0. total N for all treatments = 180 lbs/a). LSD = 1.2

Effect of Fertilizer Timing on Wheat Yield
(Dryland Carrington 2003. Soil N = 44 lbs/a. Additional 40 lbs N as soybean credit. SB (stream bar) application with 28-0-0. Total N for all treatments = 180 lbs/a). LSD = 8.6

Effect of Fertilizer Timing on Wheat Lodging
(0 = no lodging, 9 = flat). Carrington 2003. Soil N = 44 lbs/a. Additional 40 lbs N as soybean credit. SB (stream bar) application with 28-0-0. Total N for all treatments = 180 lbs/a.

Dryland

Irrigated

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