With the end of August in sight, now is a good time to get out and estimate your corn yields. Done properly, yield estimates can be useful to help with grain marketing and to prevent any surprises at harvest. Done incorrectly, yield estimates can lead to wild coffee shop stories and disappointment at harvest!
Most yield estimates in corn are based off of the yield component method which was originally developed by the University of Illinois. The yield components that are taken into account are the number of ears per acre, number of kernel rows per ear, number of kernels per row, and weight per kernel. The first three factors can be evaluated at this time, while the last one is a bit of a guess.
To get the first three factors, pick multiple locations in the field and do the following steps; count the number of harvestable ears in 1/1000th of an acre, and count the rows around and number of kernels per row on every 5th ear. Personally when I count ears I like to mark off the distance with a tape measure and then count the number of ears on two rows on each side of the tape measure. I then average the ear count for those four rows to give me better data to help account for the variability across the field.
When counting kernels, don’t count the first few kernels on the butt of the ear or the last few tip kernels. By pulling every 5th ear, we are trying to avoid skewing the data by only picking the largest ears. However, if one of the ears you pull is a nubbin or odd ear which doesn’t represent the rest of the field, reselect with the next ear. Average all of your kernel counts so you have one number for rows around and kernels per row.
Once you have the numbers, multiply the number of ears by the number of rows around by the number of kernels per row. Next we need to divide by the number of kernels that we expect per bushel. The number can range from 60,000 to 100,000 kernels per bushel, so this is where a lot of variability is introduced into yield estimates. If you are in an irrigated field, I would probably go on the lower end like 70 or 75,000, while dryland is likely to be higher at 80 or 85,000. You can check with your seed supplier to see if they have an average kernel count for your hybrid.
So for example, let say I checked an irrigated field and got a total of 28 ears in 1/1000 of an acre, average rows around of 17, and a kernel number of 34 per row. I would take 28 x 17 x 34 = 16,184 then divide by 75 gives me 215.8 bushels. Do this multiple times in each field to get an idea of what to expect when you start combining.
Even if you aren’t going to do a yield estimate, I would still strongly recommend getting out and walking through your fields, as there are some surprises out there. One dryland field I looked at this week in northern Colfax County had a high percentage of ears with very poor pollination, with less than half of the potential kernels pollinated. In this field it was easy to see that pollination was going on when we had the hot July weather as the lower kernels didn’t develop, but the last 1/3 to half of the ear did pollinate, probably during the cool period during the first week of August.