Assessing Winter Wheat Stands and Estimating Yield Potential - UNL CropWatch, Sept. 28, 2012

Assessing Winter Wheat Stands and Estimating Yield Potential - UNL CropWatch, Sept. 28, 2012

September 28, 2012

With the lack of precipitation this summer and fall, winter wheat stands in fields that were seeded or will be seeded may be less than desired. Dry soil results in poor germination and hard, dry soil makes it difficult to achieve proper seeding depth, particularly in no-till fields. Loose seedbeds are a problem in tilled fields as the soil will dry out quickly after seeding.

Dry soil conditions contribute to crown and root diseases since dry soil warms up and cools down six times faster than moist soil. This alternating freezing and thawing will diminish the health of the wheat plant, damaging stands and decreasing yield potential. Loose seedbeds and shallow seeding depth can cause these same problems, especially with winter kill.

Estimating Wheat Yield Potential

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Determining a reasonable estimate of wheat yield allows growers to predict if it is in their best interest to reseed the field if soil conditions improve.

To estimate winter wheat yield potential, the assumptions are that

  • plants are healthy,
  • soil moisture and nutrients are adequate, and
  • weeds, insects, and disease are not affecting yield.

Added to the uncertainty of yield estimates is wheat's natural ability to compensate for changes in the environment.

Table 1 is an easy tool to estimate wheat yield potential; however, it relies on several assumptions to make a yield estimate in the fall.

  1. Wheat plants, on average, develop about five heads.
  2. Each head, on average, develops about 22 kernels.
  3. There is an average of 16,000 kernels per pound.

Late-planted wheat and wheat seeds that do not germinate until later because of dry conditions will tiller less and have fewer heads.

To use Table 1, count the number of plants per foot of row. It is best to use at least five feet of row in at least five sites within the field and calculate the average number of plants per foot of row. If the stands are uneven, for example the stand is better or worse in the wheel tracks, make sure your percentage of samples in these areas accurately represents the proportion of these areas in the whole field. Locate the column in the table that corresponds to your average number of plants per foot of row and then move down that column until it intersects with the row corresponding to your row spacing. This is your estimated yield under good growing conditions.


Table 1. Estimated wheat yield potential.
  Number of plants/foot row
Row spacing 1 2 3 4 5 6 7 8 9 10 11 12
---inches--- ---------------------------------------------bushels/acre----------------------------------------
6.0  10  20  30 40 50 60
7.5  8  16  24  32  40  48  56  64
9.0  7  13  20  27  33  40  47  54  60
 10.0  6  12  18  24  30  36  42  48  54  60
 12.0  5  10  15  20  25  30  35  40  45  50  55 60
 14.0  4  9  13  17  21  26  30  34  39  43  47 52


Recommendations for Reseeding in the Fall to Thicken up Stands

  • Wheat can be seeded directly into thin areas of existing stands. Reseed at a slight angle to initial seeding and, if possible, use a disk drill rather than a hoe drill as it causes less damage to existing wheat plants.
     
  • The general recommendation is to increase the seeding rate by 10 to 15 lb per acre per week after the suggested seeding date for your area. (This represents an additional 150,000-225,000 seeds based on 15,000 seeds/lb.) The maximum seeding rate for rainfed wheat is 120 lb (1,800,000 seeds) per acre or up to twice the seeding rate at the suggested date for your area.
     
  • Subtract the present stand in the field if it is fairly uniform. For example, if you have a 50% stand, reduce the reseeding rate by 50%. If many areas of the field only have a 20% stand, you would only reduce the reseeding rate by 20%. Also, if viable seed is still present in the soil and at the proper depth in firm soil, reduce the seeding rate by the appropriate amount as this seed will probably grow.
     
  • If some plants lack vigor or the crowns are shallow, do not reduce the seeding rate for these plants as they may not survive.
     
  • To compensate for the reduced fall rooting of the late seeding, apply phosphorus with the seed.

Robert Klein, Extension Western Nebraska Crops Specialist
Paul Jasa, Extension Engineer
Jennifer Rees, Extension Educator