Update from the Field: Count on Corn
Posted by Dave Dyson, Agronomist on August 28, 2019
Several times this past week, I have been asked two big questions: “How is the corn crop progressing?” and “What is your best guess at yield for the 2019 corn crop?” Scouting the corn field at 55 MPH will not tell you much. The only way to get an accurate sense of the 2019 crop is to stop and walk into the field.
The first thing I always do when walking into a field of corn is to push on the stalks. You don’t have to put all your might into the “push”, just give it a little shove and see if it snaps over. This little stalk strength test will tell you if disease or insects have weakened the corn plant. If the stalk is weak, you will need to put this field on the priority harvest list. Weakened corn stalks will be the first to fall over, once the corn matures. If you can’t pick the crop up off the ground it really doesn’t matter how big the yield will be.
Next, you will want to walk past the “end rows” and into the main part of the field. If you’re coming into the field from the side, walk about 60 feet. This ensures you start estimating yield past any compaction issues related to turning equipment around. If the corn rows are 30 inches apart, which is standard, mark off 17 feet 5 inches. This represents 1/1000 of an acre. If the corn rows are not 30 inches apart, you need to figure out what 1/1000 of an acre is and measure off that distance. Using 1/1000 of an acre makes calculations easier. Count the corn plants that will bear an ear between your marks, as this will be your population in 1/1000 of an acre. Write that number down for later use. You will want to shuck back the 5th, 15th, and 25th ear. Using the same ear number will ensure the randomness of your sample. Write down the average number of rows around each of the three ears. As an example, Figure 1 shows 18 rows.
Figure 1: This picture shows the number of rows around an ear of corn to be 18. All ears will have an even number of rows around the cob. This picture was taken at the Walton Farm Center Crop Plot in 2018.
Write down the average number of kernels per row on each of the three ears. As an example, Figure 2 shows 36 kernels per row. Stop counting a few kernels from the tip. You will now multiply the (number of ears in 1/1000 of an acre) x (average number of rows around the ears) x (average number of kernels per row). Then, divide that result by a numerical factor that represents kernel weight; I like to use 90. You will need to repeat this process every 10 acres to get an accurate yield estimate of the field.
Figure 2: This picture shows the number of kernels in a row to be 36. Do not count all the way to the tip or the base when counting kernels in the row. This picture was taken at the Walton Farm Center Crop Plot in 2018.
The kernel weight number is the amount of kernels per bushel. Depending on weather, soil, and hybrid genetics, the kernel weight can vary from 65,000 kernels/bu for heavy corn to 100,000 kernels/bu for light corn. I like to use 90,000 (or 90 because we are only looking at 1/1000 of an acre) for the numerical factor. This will give a lower estimate, but I feel it’s always better to be pleasantly surprised than disappointed.
In conclusion, get out and scout your field right now! Preparing for a potential crisis or success will prepare you for harvest. If you are not comfortable or don’t understand the formula, contact your sales representative or a member of The Andersons agronomy team.
Dave Dyson is a regional agronomist for The Andersons’ Farm Centers which are located throughout Ohio, Michigan, and Indiana. He is an Indiana native and grew up on a dairy farm in Miami County. A graduate of Purdue University with a degree in Crop & Soil Science, Dave has a deep knowledge of various agronomic topics and is committed to helping growers improve their crops. If you have any questions, Dave can be reached at firstname.lastname@example.org.