Determining Wheat Plant Populations

November 15, 2011 in Uncategorized

After wheat emerges, it is a good idea to go back to the field and perform a stand evaluation.  In the fall, count the number of plants per square foot to determine if the field is still at 100% yield potential.  Below are a couple methods to taking stand counts on wheat and what to look for:

After the wheat has emerged, make a stand count to determine if your target population was achieved and if the final stand is acceptable for maximum yield potential. Make fall stand counts one to two weeks after emergence. Make spring stand counts before greenup of the plants occurs to determine if winter damage has reduced the initial plant population obtained in the fall. Count only whole plants, not tillers. Fields with stand counts below 15 plants per square foot have less than 75 percent yield potential (Table 3-4) and probably should not be kept but used instead for planting corn or soybeans. If stand counts are adequate to keep but somewhat reduced from optimum, consider an early nitrogen application.
To determine the number of plants per square foot:

1. Use a yardstick, or cut a dowel rod to a 3-foot length.
2. Place the measuring stick next to an average-looking row, and count all plants in the 3-foot length of the row. Record the number.
3. Repeat the counting process in at least five other locations well spaced around the field. Record all numbers.
4. Average all of the stand counts from the field.
5. Calculate plants per square foot with the following equation: plant number = (average plant count * 4) / row width in inches

Table 3-4. Wheat yield potential based on plants per square foot.
Final Stand (%) Plants/sq ft Plants/sq yard Potential yield* (%).
100 30-35 270-315 100
80 24-28 216-252 100
60 18-21 162-189 90-95
50 15-18 135-162 75-80
40 12-14 108-126 60-70
20 6-7 54-63 40-50
*This provides an estimate of the relationship of wheat stand to yield potential and is only a guide. Many factors (plant vigor, weather, disease, fertility management, planting date, and variety) influence how a wheat stand ultimately responds to achieve its final yield potential.

A second method to counting stands is to determine the length of row needed to equal one square foot (Table 3-5). Mark the needed length on a dowel rod or stick and then count the plants in a row.

Table 3-5. Length of row needed for 1 square foot.
Row Width (in) Row Length for 1 sq ft
(ft) (in)
6 2.0 24.0
7 1.7 20.6
7.5 1.6 19.2
8 1.5 18.0
10 1.2 14.4

Tiller and Head Counts:

Taking a tiller count which includes main shoot and tillers at Feekes 3 (roughly Zadoks 22 through 26) is the first step in all fields for determining nitrogen needs in late winter or early spring. To determine tiller numbers, count all stems with three or more leaves. Tiller counts below 70 per square foot indicate the need for nitrogen at Feekes 3. At recommended populations, many plants will have only three to four stems (main shoot plus two to three tillers, Zadoks 22 or 23). Thus, 70 to 100-plus tillers (stems) per square foot at Feekes 3 are considered adequate.
Head counts can be taken late in the season after heads have fully emerged (Feekes 10.5, Zadoks 58 or later) to help estimate yield potential. An ideal count for maximum yields is 60 to 70 heads per square foot (540 to 630 per square yard) with 35 kernels per head and 16 to 18 spikelets per head. For adequate yields, 55 heads per square foot (500 per square yard) are needed. If the number of heads per square foot is too high (90 to 100), severe lodging can occur and seeding rates were probably too high. Use the same procedure to count tillers or heads as outlined above for plant populations.

Source:
Lee, Chad, James Herbek, David Van Sanford, and William Bruening.  2009.  A Comprehensive Guide to Wheat Management in Kentucky.  Kentucky Cooperative Extension Pub ID-125. Online. http://www.uky.edu/Ag/GrainCrops/ID125Section3.html#3