How To Estimate Corn Yield Prior To Harvest

DR. ERICK LARSON 

MISSISSIPPI STATE, MISSISSIPPI

There is a method you can estimate corn yield by thoroughly sampling random ears in a field. It will take some effort, knowledge and luck to represent a field, but it can satisfy your desire regarding the upcoming harvest. The issue with any estimate is kernel weight cannot be measured prior to physiological maturity, because grain fill is still occurring. Thus, this procedure is often more of a learning exercise than anything else.

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 the ear or kernels per 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. I strongly suggest closing your eyes while sampling ears, so you don’t bias your sample, because invariably you will pick large ears. Alternatively, you can pick 10 or 20 consecutive ears to measure. These values are multiplied to generate an estimate of number of kernels per acre and should be relatively accurate, if you do your part.

 In order to estimate yield, you must also integrate kernel weight into the calculation. The problem with this method or any other variant for estimating corn yield prior to harvest, is that you aren’t collecting any physical data which measures kernel weight – limiting the accuracy. Accordingly, this method of yield estimation may get you in the ballpark, but leaves considerable opportunity for error which is not accounted for.

There are numerous factors that can influence corn grain fill and kernel weight, including any type of stress during late grain fill and hybrid genetics. Thus, you can expect considerable variation from year to year, particularly since we have had substantially more heat and drought stress this year, than we have had for several years. Thus, it is best to use your judgement to characterize a reasonable value for kernel weight.  The standard value historically used for estimating kernel weight is 0.01116.  However, corn kernel weight can vary by 40% or more depending upon environmental conditions and hybrid characteristics. Thus, I suggest selecting a seed weight value between 0.0095 for stressed, dryland corn and 0.0135 for a healthy crop grown with irrigation or otherwise optimal growing conditions. These values are based upon seed weights measured from corn grown in Mississippi and correspond with 241g per 1000 kernels for 0.0095 and 343g per 1000 kernels for 0.0135. This value will have a dramatic effect on the accuracy of the estimate, so adjust your calculations accordingly.

 The old saying “garbage in equals garbage out” is certainly appropriate for this yield estimation procedure. You must be willing to methodically collect representative data and apply your knowledge of crop conditions and hybrid characteristics to appraise kernel weight, in order to produce a reasonable estimate of corn yield. This means taking multiple measurements of plant population and sampling ten or preferably more ears for kernel number.

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.)

Example:

(34 ears in 1/1000 acre)(15.5 kernel rows/ear)(38.0 kernels/row)(0.012 value for seed wt.) = 240 bu/a ∆

DR. ERICK LARSON: MISSISSIPPI STATE UNIVERSITY