Estimating corn yield potential can help with harvest decision-making. The corn yield component method can be used as early as the R3 (milk stage) growth stage.
Estimating corn grain yield prior to harvest may produce yield estimates that are within 20 to 30 bu/acre of actual yield.2,3 Crop uniformity has a large influence on the accuracy of any estimation method. Samples should be taken randomly throughout a field to provide the best yield estimate. Yield should be determined in five to 10 locations per field unless conditions are variable, requiring a higher number of samples.4 More samples will be needed to represent a non-uniform field and improve the accuracy of the estimate.
Corn Yield Component Method
This method is used widely and can be used as early as the R3 (milk) stage of corn growth. It’s risky to make estimates prior to R3 because stresses can affect kernel development and cause kernel abortion.3 This method is based on the assumption 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. The first three components can be measured from field samples but kernel weight is unknown until physiological maturity and must be represented by a calculated factor. The average value for kernel weight (90) is derived using 85,000 kernels per 56 pound bushel. Some agronomists think that 80 to 85 is a more appropriate factor for current use because kernel size has increased since this formula was first developed many years ago.3
At each sample site:
Measure 1/1000th of an acre (17 feet, 5 inches for 30-inch rows or 23 feet,10 inches for 22-inch rows);
Count the number of harvestable ears in that area; and then,
Collect every fifth ear within that area and proceed through the following steps and record your measurements. Don’t sample nubbins, abnormal ears, aborted kernels or count 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.3
Step A. The number of harvestable ears in 1/1000th of an acre = _________ (A).
Step B. The average number of kernels per ear on every fifth ear = _________ (B).
Step C. Estimate of yield potential per acre by multiplying A x B ÷ 90 (or the factor from Table 1 that best represents growing conditions) = _________ (C).
Step D. Repeat steps A-C at a representative number of sample sites in the field. The estimated yield potential per acre of the entire field = the average C.
Table 1. Average Kernel number/bu based on growing conditions during grain filling.3
Kernel Factor for Equation
Range in Kernel Number per Bushel
75 (or less)
Less than 75,000
Greater than 85,000
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 times 511) divided by 85, or a 180 bu/acre estimate of yield potential.3
Poor conditions during grain filling 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.2 Kernel size and weight can vary by corn product and environmental conditions, which can compromise the accuracy of the estimate.
1 Nielsen, R.L. 2011. Effects of stress during grain filling in corn. Corny News Network, Purdue University.
2 Thomison, P. 2010. “Predicting” corn yields prior to harvest. C.O.R.N. newsletter. The Ohio State University.
3 Nielsen, R.L. 2011. Estimating corn grain yield prior to harvest. Corny News Network, Purdue University.
4 Lauer, J. 2002. Methods for calculating corn yield. University of Wisconsin. Field Crops 28.47-33.