Corn Harvest Measurements

Asked August 6, 2014, 7:17 AM EDT

I work for a small NGO in Mali, West Africa and we work with rainfed corn and peanuts producer. We have been tasked with conducting harvest measurements to determine if our technical methods increase yields. I was wondering if anyone could tell me the advantages and disadvantages of using the corn slide rule (Yield Component Model) to estimate corn harvests? We have very limited access to resources and have relatively unskilled workers who will be measuring the harvests. Thank you in advance!

Outside United States

1 Response

The corn slide rule is the one I use. I actually have a old corn sheller that I use when moisture drops below 30%, but weighing 25-30% corn will over estimate yields also

Disvadntage. Tends to over estimate because we count more kernels than we will harvest. If you have a lot of people doing the counting, you will get different results. The less people, the more reliable.

Advantage -it can be used as early as the milk stage of kernel development

The yield component method involves use of 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 a "fudge‑factor" since it is based on a predetermined average kernel weight. Since weight per kernel will vary depending on hybrid and environment, the yield component method should be used only to estimate relative grain yields, i.e. "ballpark" grain yields.

In the past, the YIELD COMPONENT METHOD equation used a "fudge factor" of 90 (as the average value for kernel weight, expressed as 90,000 kernels per 56 lb bushel), but kernel size has increased as hybrids have improved over the years. Dr. Bob Nielsen at Purdue University suggests that a "fudge factor" of 80 to 85 (85,000 kernels per 56 lb bushel) is a more realistic value to use in the yield estimation equation today. Moreover, given the exceptionally favorable growing conditions we have experienced in 2014, a fudge factor of 75 (75,000 kernels per 56 lb bushel) may be appropriate for some fields . For more on this check

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.

The more variable crop development is across a field, the greater the number of samples that should be taken to estimate yield for the field.

Example: You are evaluating a field with 30‑inch rows. You counted 29 ears (per 17' 5" = row section). Sampling every fifth ear resulted in an average row number of 16 and an average number of kernels per row of 33. The estimated yield for that site in the field would be (29 x 16 x 33) divided by 85, which equals 180 bu/acre.