I’ve heard a lot of talk this year that looking at corn from the cab of the truck is lot different than what is being seen out in many fields. With such variability, it will be interesting to see how close early yield estimates come to matching what is actually harvested from the field. Of course, some are saying the crop is worse when you actually get out of the truck and get in the field, but surprisingly, I’ve heard many this year say the crop is actually better once they get out in the field… so who knows?
I’ve been asked many times throughout the years about different procedures that can give a fairly simple and accurate estimate of yield before the crop is fully grown. I’m sure everyone has their own process and procedure. In fact, many of you have probably forgotten more than I actually know about walking in the field and forecasting an accurate yield. But one method I like to use is called the “yield component method” which is often referred to as the “slide rule” or corn yield calculator. The yield component method was developed by the Agricultural Engineering Department at the University of Illinois and said to produce yield estimates that are extremely close to that of the actual final yield. We all know that an estimate with good accuracy can be helpful for general planning purposes.
The principle advantage of this method is that it can be used as early as the milk stage of kernel development. The yield component method involves using 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 the “fudge factor” since it is based on a predetermined average kernel weight.
Remember, with weight per kernel varying depending on hybrid and environment, the yield component method should be used only to estimate relative grain yields. When below normal rainfall occurs during grain fill (resulting in low kernel weights), the yield component method has been known to slightly overestimate yields. In a year with good grain fill conditions, the method could perhaps underestimate grain yields. In the past, the yield component method equation used a “fudge factor” of 90, but since kernel size has increased over the years. Bob Nielsen at Purdue University suggests an updated number of 80-85. (Source: Perdue University; University of Illinois, University of Nebraska, Kansas State University)
To use the Yield Component Method to estimate your corn yield, use the following steps. Of course, if you see variable crop development across a certain field you are measuring, the greater the number of samples should be taken to estimate yield for that field. For more information on the yield component method, check out Bob Nielsen’s write-up on the method from Perdu University HERE. You can also check out the article called Estimating Corn Yields, by Peter Thomison at Ohio State University Extension.
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 85.
Step 5. Repeat the procedure for at least four additional sites across the field. Keep in mind that uniformity of plant development affects the accuracy of the estimation technique.
