Through thorough, random sampling and applying knowledge of your crop,you can produce a reasonable yield estimate.
By Erik Larson, Mississippi State University Extension
There is a method you can use to estimate corn yield by thoroughly sampling random ears in a field.
The first thing you need to do is to count the total number of ears in one thousandth of an acre. The length of row to count depends upon your row width, as noted below.
Row length which equals 1/1000 acre:
- 17’5″ in 30″ rows
- 13’9″ in 38″ rows
- 13’1″ in 40″ rows
The next step is to calculate the average number of kernels per ear. You do this by counting the number of kernel rows around the ear, as well as the number of kernels in the length of row. The key to obtaining accurate estimates of kernel number is to truly collect random samples and collect enough ears to generate a good estimate. Try closing your eyes while grabbing ears, so you don’t bias your sample. These values are multiplied to generate an estimate of number of kernels per acre and should be relatively accurate, if you do your part.
However, in order to calculate yield, you must also integrate kernel weight into the calculation. There are numerous factors that can influence kernel weight, with the most important likely being the overall stress level endured during late grain fill, and hybrid genetics. Therefore, try using your knowledge of the crop to characterize a reasonable value for kernel weight. The value normally used for estimating kernel weight is 0.01116. However, corn kernel weight can vary by 40% or more, so you might produce a much better estimate by picking a value between 0.009 for stressed, dryland corn and 0.013 for a crop produced under optimal growing conditions.
The old saying "garbage in = garbage out" is certainly pertinent to this procedure, but if you are willing to methodically collect representative data and apply your knowledge of crop conditions and hybrid characteristics, to assess kernel weight, you can produce a reasonable estimate of corn yield.
The formula for estimating corn yield is:
Yield (bu/a) = (# of ears in 1/1000 acre)(avg. # of kernel rows/ear)(avg. # of kernels/row)(value for seed wt.)
(30.4 ears in 1/1000 acre)(15.0 kernel rows/ear)(39.5 kernels/row)(0.01116 value for seed wt.) = 201 bu/a.