The time of year is approaching where yield estimates can be done on grain corn. Remember that grain corn yield is a function of the number of ears per acre, number of kernels per ear, and the weight per kernel. Using the yield component method that was developed at the University of Illinois, yields can be estimated as early as the milk stage of development.
Calculating Estimated Grain Corn Yield:
Step 1. Ear Number – Using a row length equal to 1/1000th acre (row width 30 ” = 17′ 4″; row width 36 ” = 14′ 6”), count and record the number of ears in the length of row that are harvestable.
Step 2. Average Number of Kernels per Ear – Pick 3 representative ears and record the number of complete kernel rows per ear and average number of kernels per row. Multiply each ear’s row number by its number of kernels per row to determine total number of kernels for each ear. Calculate the average number of kernels per ear by summing the values for all the sampled ears and dividing by the number of ears.
Note – Don’t count the extreme butt or tip kernels, but rather begin and end where you perceive there are complete “rings” of kernels around the cob. Do not count aborted kernels.
Step 3. Estimate yield by multiplying the ear number by the average number of kernels per ear, then dividing the result by 90: Yield (bu/ac) = (ear number) x (average # of kernels per ear) / 90.
Note: The value of 90 is a “fudge factor” for kernel weight and it represents the average number of kernels (90,000) in a bushel of corn at 15.5% grain moisture. If grain fill conditions have been excellent (larger kernels, fewer per bushel), use a lower value (80). If grain fill conditions have been stressful (smaller kernels, more per bushel), use a larger value (100).
Here’s an example: Field has 30” rows. You counted 24 ears (per 17’ 5” length of row). Sampling three ears resulted in 480, 500 and 450 kernels per each ear, where the average number of kernels per ear would be (480 + 500 + 450) divided by 3 = 477. The estimated yield for that location in the field would be (24 x 477) / 90, which equals 127 bu/ac.
Remember that yield estimates are only as accurate as the number of samples taken so repeating this exercise in several areas of a field will improve accuracy. Since corn is in the early grain filling stages, water availability, insects, weeds, diseases, and other factors can still affect seed fill and therefore final yields. However, as the plant approaches maturity, environmental stresses have less impact on final yield so yield estimates made that are closer to maturity should be more accurate.
Submitted by: Pam de Rocquigny, Provincial Cereal Crops Specialist, Manitoba Agriculture