Ag Tips from JJ: August 15

Brought to you by: Jonah T. Johnson, MS, CPAg, CCA - Sales Agronomist, PCT | Sunrise

August 15, 2019: Curious what your corn will yield? Time to check your ears!

Okay, so I will back-up a step. Not everyone’s corn in Ohio is through the reproductive stages yet, but for those of you that have pollinated ears of corn, now may be the time to estimate what to expect as far as production.

Several nuances exist this year due to the environmental extremes we have experienced. The biggest factors were the early abundance and now the absence of water coupled with extreme heat, both daytime and nighttime over the last several weeks. Drought stressed corn coupled with high temperatures can challenge corn during pollination and early grain fill.

The biggest variable in estimating yield in stressed corn fields will be the “fudge factor.” The common “fudge factor” used by most is the 90,000 kernels per 56-pound bushel. Research from Purdue University suggest that 80-85,000 kernels per bushel may be more realistic in a normalized year.

According to Dr. Emerson Nafziger at the University of Illinois under current drought stress “…. If there's a fair amount of green leaf area and kernels have already reached dough stage, using 90 as the “fudge-factor “ might be reasonable. It typically doesn't help much to try to estimate depth of kernels at dough stage, when kernel depth is typically rather shallow anyway, especially if there are 16 or more kernel rows on the ear.”

“If green leaf area is mostly gone, however, and kernels look like they may be starting to shrink a little, kernels may end up very light, and using 120 or even 140 as the “fudge-factor” might be more accurate.” Learn more here.

The following excerpt is from a recent OSU’s C.O.R.N newsletter by State Extension Corn Specialist Dr. Peter Thomison on how to estimate corn yield prior to harvest:

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, a stage many Ohio corn fields have probably achieved. The yield component method involves use of a numerical constant for kernel weight which is figured into an equation in order to calculate grain yield.

This numerical constant is sometimes referred to as a "fudge‑factor" since it is based on a predetermined average kernel weight. Since weight per kernel will vary depending on hybrid and environment, the yield component method should be used only to estimate relative grain yields, i.e. "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.

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 late planted and 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.


Example: You are evaluating a field with 30‑inch rows. You counted 24 ears (per 17' 5" = row section). Sampling every fifth ear resulted in an average row number of 16 and an average number of kernels per row of 30. The estimated yield for that site in the field would be (24 x 16 x 30) divided by 90, which equals 128 bu/acre.


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.


Happy Estimating!