Source: South Dakota State University
By Mark Rosenberg
July 19, 2012 — Estimating corn yields, especially under stressed conditions such as drought, is never absolute or easy. As the dry weather continues the challenge of whether to leave fields or utilize them for feed becomes more pressing.
Yields are an accumulation of all the growing conditions the corn experiences during the summer. However, at various stages stress is worse than at others. Soil types and pH levels may also aggravate the situation.
Crop stages that are critical to achieving the best potential yields are the first 45 days after planting and the 2 weeks before and after tasseling. The potential size and length of the ear is determined at V6-V8 and V10-V12 respectively. However that doesn’t answer the initial question.
If an estimate is wanted or needed, here is one formula that may help answer the question.
Estimating begins with determining the length of row needed to equal 1/1000 of an acre. You can accomplish this by dividing 43,560 square feet by the row spacing (in feet) and divide that 1000. For example on 30 inch rows figure (30/12=2.5), then plug in the numbers to formula. (43,560 /2.5 feet)/1000 = 17.42 feet.
Using the above example you need to measure 17.4 feet at several locations in the field. Count the numbers of ears developing in the row in the designated area. Record this information and average the number of ears after scouting the field.
Pick a couple of ears randomly from the survey area. Count the number of rows per ear and the number of kernels in a selected row. Average the number of both counts and multiply them to determine the average for the number of kernels per ear. The kernels per ear are then multiplied by the average ears per acre giving the kernels per acre.
There around 90,000 kernels per bushel in normal corn. Droughty corn typically runs between 100,000 to 110,000 kernels per bushel, depending on the severity of the stress. To determine the estimated yield divide the kernels per acre by the estimated kernels per bushels.
For example, a field has 16,000 ears per acre, an average of 14.3 rows of kernels per ear and 24 kernels per row. The producer would figure 16,000 ears/acre x 14.3 rows of kernels per ear x 24 kernels per row/110,000 kernels per bushel totaling 49.9 bushels per acre.
Research estimates that drought stressed corn will yield one ton of silage for every five bushels of grain harvested. This would mean the example above would potentially yield 10 tons of silage at 30% dry matter.
For further reading on yield estimations and utilizing drought stressed corn, please visit: