Assessing Corn Yield Potential

• Estimating corn yield potential is helpful for harvest planning at separate times during the growing season.
• Crop uniformity has a large influence on the accuracy of any estimation method and samples should be taken randomly throughout a field to provide the best yield estimate.
• The corn yield component method and the corn ear weight method are two ways to estimate corn yield potential prior to harvest and each method can produce yield estimates that are within 20 bushels per acre of harvested yield.¹

Corn Yield Component Method

This method assumes that grain yield can be estimated using the number of ears per acre, number of kernel rows per ear, number of kernels per row, and kernel weight. This method can be used as early as the milk growth stage (R3).² Estimating the yield prior to R3 can result in inaccurate estimates because stresses can affect kernel development and result in kernel abortion.³ The first three components can be measured from field samples, but kernel weight is unknown until physiological maturity (black layer) and must be estimated by using a calculated factor. The average value for kernel weight (90) is derived using 85,000 kernels per 56-pound bushel (Table 1).⁴ A more modern estimate of kernel weight is 80 to 85, because kernel size has increased since this formula was first developed many years ago.³

• Step 1: At each sample site, measure 1/1000th of an acre (Table 2). Do not sample abnormal ears, nubbins, or aborted kernels, and avoid dropped ears or ears on severely-lodged plants. Count kernels where there are complete rings of kernels around the cob, and avoid counting kernels on the extreme ends of the ear (Figure 1).¹
• Step 2: Count the number of kernel rows per ear on every fifth ear and determine the average.
• Step 3: On the same fifth ears, count the number kernels per row and determine the average.
• Step 4: Determine an estimate of yield potential per acre at each sample site by multiplying the number of ears by the average number of rows and the average number of kernels and dividing by 90 or the factor that best represents growing conditions (Table 1).

Estimated Yield (bu/acre) = (ear #) × (average row #) × (average kernel #)/90

• Step 5: Repeat this procedure at a representative number of sample sites in the field. Calculate the average yield potential of all the sites to get an estimate of the yield potential of the entire field.

Example: Harvestable ear count is 30. The average number of kernels per ear from every fifth ear is 511. Growing conditions were average (85). The estimated yield potential for that site would be 30 multiplied by 511 and divided by 85, or a 180 bu/acre estimate for yield potential. Poor conditions during grain fill can cause lower kernel weights, resulting in an underestimation of yield potential with the yield component method. Conversely, it can overestimate yield potential if kernel weight is higher than normal, during superior growing conditions.³

Kernel size and weight can vary by corn product and environmental conditions, which can compromise the accuracy of the estimate.

Table 1. Kernel number per bushel based on growing conditions during grain filling.¹

Corn Ear Weight Method

This method should only be used after corn has reached physiological maturity or black layer (R6). This method may be more accurate than the corn yield component method because it is based on actual kernel weight. However, it is not entirely accurate as it includes average shell out percentage.⁵

• Step 1: Sample several representative sites in a field. Count the number of harvestable ears in 1/1000th of an acre at each site (Table 2) at several random sites throughout the field. At each site:
  • a. Weigh every fifth ear and calculate the average ear weight per site.
  • b. Hand shell kernels from those ears.
  • c. Determine the average grain moisture with a moisture tester.
• Step 2: Calculate the average yield potential at each site:
  • a. Multiply the number of ears by the average ear weight.
  • b. Multiply average grain moisture by the factor 1.411.
  • c. Add 46.2 to the value calculated in (b.). average grain moisture and multiply by 1.411 (b).
  • d. Divide result from (a) by the result from (c).
  • e. Multiply result from (d) by 1,000.

Example: The number of harvestable ears is 24. Average ear weight of every fifth ear is 0.5 lb. The average grain moisture is 30%. The estimated yield potential is [(24 × 0.5)/ (1.411 × 30) + 46.2)] x 1,000 = 135 bu/acre.^2,5

Table 2. Measurements to calculate number of plants in 1/1000th acre based on row width.²

Sources

¹Nafziger, E. D. 2002. Illinois agronomy handbook, 24th edition. Chapter 2. University of Illinois Printing Services. Urbana, IL. 23-25. http://extension.cropsciences.illinois.edu/

²Lauer, J. L. 2002. Methods for calculating corn yield. Agronomy Advice. Corn Agronomy. University of Wisconsin. https://corn.agronomy.wisc.edu/WCM/W095.aspx

³Thomison, P. 2015. Estimating corn yields. C. O. R. N. Newsletter. Agronomic Crops Network. Ohio State University Extension. https://u.osu.edu/knoxcountyag/2023/09/07/estimating-corn-yields/

⁴Nielsen, R. L. 2018. Effects of stress during grain filling in corn. Corny News Network, Purdue University. https://www.agry.purdue.edu/ext/corn/news/timeless/GrainFillStress.html

⁵Birkey, N. 2009. Estimating grain yields in corn. Michigan State University Extension. https://www.canr.msu.edu/news/estimating_grain_yields_in_corn

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