HUTCHINSON, Minn. — The USDA Minnesota Crop Progress Report issued September 3rd estimates that eighty-four percent of the corn crop has reached the dough stage, falling to 11 days behind last year and 9 days behind the 5-year average. Corn dented was 25 percent, nearly 2 weeks behind last year and 10 days behind normal. The Minnesota corn growing season has been one of extreme variability.
Corn which is at least dented is at a stage where the growers may more accurately use the Yield Component Method for estimating corn grain yield. Use the yield component method estimation obtained by this method for general planning purposes since kernel size and weight is probably only accurate within plus or minus 20 bushels of the actual yield. Obviously, the more ears you sample within a field, the more accurately you will “capture” the variability of yield throughout 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 22-inch row this equals 23.75 feet. The more ear counts you make (assuming they accurately represent the field or zone of interest), the more confidence you have in the yield estimate.
- 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, count only kernels that are in complete rings around the ear.)
- 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 for this article included:
Nelsen, Bob 2018. Estimating Corn Grain Yield Prior to Harvest. Department of Agronomy, Purdue University.
https://www.agry.purdue.edu/ext/corn/news/timeless/YldEstMethod.html
— Dave Nicolai, Extension Educator, Crops, UMN Extension
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