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Estimating Corn Grain Yields before Harvest

Corn growers in Minnesota may want to predict grain yields prior to harvest in order to help develop grain marketing, harvest and storage plans. One option is to use a yield component method originally developed by the Agricultural Engineering Department at the University of Illinois. These yield components include number of ears per acre, number of kernel rows per ear, number of kernels per row, and weight per kernel. It can be used as early as the “roasting ear” or milk (R3) stage of kernel development.

Crop uniformity greatly influences the accuracy of this yield estimation technique. The less uniform the field, the greater the number of samples that should be taken to estimate yield for the field. Calculate estimated grain yield using the Yield Component Method as follows:

  • Count the number of harvestable ears in a length of row equivalent to 1/1000th acre. For 30-inch (2.5 feet) rows, this equals 17.4 feet. For other row spacings, divide 43,560 by the row spacing (in feet) and then divide that result by 1000.
  • On every fifth ear, count the number of kernel rows per ear and determine the average number of kernels per row. Try to use a system such as the 5th, 9th, and 13th ears from one end of the row.
  • Then multiply each ear’s row number by its number of kernels per row to calculate the total number of kernels for each ear. (Do not count kernels on either the butt or tip of the ear that are less than half the size of normal size kernels.)
  • Yield (bushels per acre) equals (ear number) x (average row number) x (average kernel number)  divided by 80* = bushels per acre
  • *Range in kernel number per bushel based on growing conditions: Excellent = less than 75, Average = 75 to 85 and Poor growing conditions = greater than 85
  • Repeat the procedure for at least four additional sites across the field. Calculate the average yield for all the sites to estimate the yield for the field.

For example, you are evaluating a field with 30-inch rows and counted 30 ears (per 17’ 5” row section). Calculate that the average number of kernels per ear, based on sampling the average of the 5th, 9th, and 13th ears in the sampling row, was 511. The estimated yield for that site would (30 x 511) divided by 80, which equals 192 bu/ac.

Final weight per kernel obviously cannot be measured until the grain is mature (kernel black layer) and, realistically, at harvest moisture. Consequently, an average value for kernel weight, expressed as 80,000 kernels per 56 lb bushel, is used as a proverbial “fudge factor” in the yield estimation equation. The equation originally used a “fudge factor” of 90, but kernel size has increased as hybrids have improved over the years. Consequently, a “fudge factor“ of 75 to 85 is a more realistic value to use today.

Sources: Nelsen, Bob 2013. Estimating Corn Grain Yield Prior to Harvest. Department of Agronomy, Purdue University.


David Nicolai
Extension Educator, Crops & Institute for Ag Prof Coord
(651) 480-7706
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