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OSU Extension

College of Food, Agricultural, and Environmental Sciences

August 7, 2018 - 8:14am -- Anonymous

There are a number of cornfields in the Wayne County area that are at the milk and dough stage of kernel development.  Some of these fields look very good and others are showing symptoms of nitrogen deficiency as indicated by a lighter green plant color and/or firing and senescence of lower plant leaves as the plant mobilizes nitrogen for use in grain fill.  Growers may want to know what kind of yield to expect at harvest and there are a couple of methods typically used to estimate yield in the field pre-harvest.  The two most common are the yield component method and the ear weight method.  The ear weight method requires that the corn grain be at physiological maturity with a moisture content of 30 to 35%.  We are not at that stage of grain development yet, so in this column the focus will be on the yield component method, because it can estimate yield as early as the milk stage of grain development.  Peter Thomison, OSU Extension corn production specialist, provides the following explanation and procedure regarding the yield component method.

“THE YIELD COMPONENT METHOD was developed by the Agricultural Engineering Department at the University of Illinois. The principle advantage to this method is that it can be used as early as the milk stage of kernel development.  The yield component method involves use of a numerical constant for kernel weight that is figured into an equation in order to calculate grain yield. This numerical constant is a "fudge‑factor" based on a predetermined average kernel weight. Since weight per kernel will vary depending on hybrid and environment, the yield component method will only estimate "ballpark" grain yields. When below normal rainfall occurs during grain fill (resulting in low kernel weights), the yield component method will overestimate yields. In a year with good grain fill conditions (resulting in high kernel weights); the method will underestimate grain yields.

In the past, the yield component method equation used a "fudge factor" of 90 (as the average value for kernel weight, expressed as 90,000 kernels per 56 lb. bushel), but kernel size has increased as hybrids have improved over the years. Dr. Bob Nielsen at Purdue University suggests that a "fudge factor" of 80 to 85 (85,000 kernels per 56 lb. bushel) is a more realistic value to use in the yield estimation equation today.

Calculate estimated grain yield as follows:

Step 1. Count the number of harvestable ears in a length of row equivalent to 1/1000th acre. For 30‑inch rows, this would be 17 ft. 5 in.

Step 2. On every fifth ear, count the number of kernel rows per ear and determine the average.

Step 3. On each of these ears count the number of kernels per row and determine the average. (Do not count kernels on either the butt or tip of the ear that are less than half the size of normal size kernels.)

Step 4. Yield (bushels per acre) equals (ear #) x (avg. row #) x (avg. kernel #) divided by 90.

Step 5. Repeat the procedure for at least four additional sites across the field. Given the highly variable conditions present in many stressed fields, repeat the procedure throughout field as many times as you think appropriate, then calculate the average yield for all the sites to make a yield assessment of the entire field.

NOTE: If there is extensive leaf firing and senescence and little green tissue evident, and kernels appear to be shrinking, using 120 or even 140 as the “fudge-factor” might be more appropriate. Making some assessments using both 90 and 120 can provide an idea of the range in yield possible.”