Estimating Corn Yield Before Harvest

By Grant Mehring, Assistant Professor, Research and Joel Ransom, Extension Agronomist for Cereal Crops
The process for estimating yield that we describe here is widely used and is proposed due to its simplicity.
The general equation is: ears per acre x kernels per ear divided by a divisor = bushels per acre

Duaine Marxen
Hettinger County Extension
1. Ears per acre: The first step is to determine the number of ears per acre. To do this, count the number of ears that will likely produce an ear at harvest within the length of a row that represents one thousandth of an acre (17.4 feet for 30 inch rows or 23.75 feet for 22 inch rows). Only count the ears that will likely contribute to yield at harvest. Late silking ears on runted plants and ears on tillers should not be counted. In situations where there are multiple ears on a single plant, avoid including the second and third ears unless you feel comfortable in estimating their potential contribution to overall yield.
2. Kernels per ear – to get a good estimate of the number of kernels per ear, count the number of rows and the number of kernels per row from about every five ears in the row that you count to determine ear numbers. Multiply the number of rows by the number of kernels in a row omitting the bottom most kernels and any kernels that did not get fertilized in the tip of the ear. As grain filling progresses, kernels that obviously are not filling did not get fertilized or may have aborted due to stress after fertilization. The kernels on the uppermost portion of the ear in the photo below have not yet been fertilized (silks still attached) and at this point should not be included in the kernel count. Take an average of the kernel numbers per ear for all of the ears that were counted.
3. Kernel weight divisor – The final factor, which is the least known at this point in the development of the crop, is a factor that estimates seed size. From trials we conducted last year, we propose a kernel weight divisor of 90 (about 280 gms per 1000 kernels). Smaller divisors can be used if you expect kernel size to be larger (using a hybrid that produces large kernels and/or to estimate conditions of exceptionally good grain fill).
4. An example – if within a 17.4 ft length (assuming a 30-inch spacing) you count an average of 30 ears and the five ears which were counted for kernels numbers had 400, 350, 375, 290, and 380 kernels (average = 359 kernels) then the estimated yield would be (30 x 359)/90 = 120 bu per acre.
This form of yield estimation is just an estimate. Check it with your yield monitor and grain cart scales at the end of a field to confirm its usefulness in the future. It is naturally very hard to capture whole field variability with an estimation using only a small part of a given field.
Dates to Remember:
Oct. 7 – 4-H Youth Pheasant Hunt

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