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Decision Support for a Foliar Application of Nitrogen (06/28/18)

In last week’s Crop and Pest Report, Franzen and Endres published the recipe for a foliar application of N that can increase grain protein by 0.5 to 1.0% in spring wheat.

Decision Support for a Foliar Application of Nitrogen

In last week’s Crop and Pest Report, Franzen and Endres published the recipe for a foliar application of N that can increase grain protein by 0.5 to 1.0% in spring wheat. The cost of this treatment can vary from $20 to $30 per acre depending on the price of the fertilizer used and its application cost. The profitability of this treatment is dependent on the actual increase in protein achieved, the protein premium in the market and the yield of the treated crop. Predicting what the market premium (or discount) for protein will be at harvest is not easy but is influenced by the quality of other wheat classes both in the USA and elsewhere. Additionally, and sometimes most importantly, the premium is influenced by the quality of the spring wheat crop produced in North Dakota. It is, therefore, not uncommon for the premium to be high in years when yields are high and protein is low. Conversely, when the state’s average yield is low due to drought or higher than average temperatures, protein will tend to be high and the protein premium will decline or disappear. Last year the premium was relatively low most of the year since there was enough good quality wheat around.

As mentioned above another factor that impacts the profitability of the application of this N treatment is the crop’s yield. For wheat that is fully headed, it is now possible to estimate yield based on the visible components of yield. The following is a method used by the Wheat Quality Council’s spring wheat tours. The three components that contribute to yield are the number of spikes per area, the number of kernels per spike and the kernel weight. Kernel weight can vary by variety and the environment, and cannot be precisely determined until maturity. This is one of the reasons that estimating yield is just that, an estimate with some level of variance from the actual. The formula described below uses a historic average for kernel weight to allow for an estimation prior to maturity and harvest. That value and other conversion factors are incorporated into the value “0.142” included in the numerator. Since small differences in the numbers used in this formula can results in large differences in the estimated yield, multiple samples taken from representative areas of the field will help improve the accuracy of the estimate.

 

Bushels/acre = (spikes per 3 ft of row X spikelets per spike X kernels per spikelet X 0.142

Row spacing in inches

 

Directions for obtaining the values for this formula:

  1. Count the number of spikes in a three-foot length of row (taking an average of several counts improves the estimate). Do not count small heads that will not significantly contribute to yield. If the crop was planted with an air seeder in bands or as paired rows, count the spikes from the entire width of the band or both rows in the pair.
  2. Count the number of spikelets in six or more randomly selected spikes. Omit the top and bottom spikelets as they contribute little to the overall yield.
  3. For the number of kernels per spikelet use 2.3 unless the crop has been stressed, then 2.1 kernels per spikelet.
  4. If not known, determine the row spacing by measuring the distance between several rows or bands of wheat. Most double disc drills are set at 6, 7, or 8 inch row spacings. The width of air seeded bands can vary. To determine the row spacing of the bands, measure the distance between the edge of one band to the same edge of the adjacent band.                                                          (Continued on next page)

Examples from research plots in Prosper this year (both spike numbers and spikelets per spike are lower this year than for those reported last year):

 

Winter wheat

(95 spikes in three foot row X 15.2 spikelets per spike X 2.3 kernels per spike X 0.142)/(7 inch row spacing) = 67 bu/acre

 

Spring wheat

(85 spikes in three foot row X 12.8 spikelets per spike X 2.3 kernels per spike X 0.142)/(7 inch row spacing) = 50 bu/acre

 

Durum wheat

(85 spikes in three foot row X 14.2 spikelets per spike X 2.3 kernels per spike X 0.142)/(7 inch row spacing) = 56 bu/acre

 

Assuming that the above estimate for spring wheat is accurate, and that the protein premium will be similar to current levels of about $0.25 per point (5 cents per fifth), and that we are able to increase the protein contain of the grain by 1% with the foliar N treatment, the foliar N treatment would result in an increased return of $12.5 per acre (50 bu per acre x 0.25 extra income per bushel). In this scenario, the increase in grain value would not cover the cost of the application. At the premium assumed in this example a yield of 120 bu per acre would be required to produce the extra income needed to pay for the treatment cost if assumed to be $30 (80 bu per acre if the treatment cost was $20 per acre).

Joel Ransom

Extension Agronomist for Cereal Crops

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