One of the most common ways to estimate corn grain yield is to first count the number of harvestable ears per 1/1000th of an acre. Next, count the number of kernel rows per ear on every fifth ear and figure the average. Then, count the number of kernels per row on these ears, and figure the average. Finally, figure yield in bushels per acre as (ear#) x (average row #) x (average kernel #) / 90.
If the year has been unusually dry and the kernels are small, then use 110 instead of 90 in the equation.
Row length needed to equal 1/1000th of an acre in 30-inch rows is 17 feet 5 inches. For 20-inch rows, the row length is 26 feet 2 inches. For 36-inch rows, the row length needed is 14 feet 6 inches.
For a lengthier discussion on estimating corn grain yields prior to harvest, see the following Web-based article from Purdue University. http://www.kingcorn.org/news/timeless/YldEstMethod.html. Corn grain yield involves the continuous interaction of genetic, climatic, soil, plant pest, and nutrient factors present for a specific growing season. However, from a crop management standpoint, it is helpful to characterize the most critical stages of development in the life of a corn plant with respect to determining final grain yield. Following are four critical stages in the development of a corn plant that are fundamental to determining corn grain yield.
The first of these critical stages is emergence. Corn does not have the ability to compensate for poor stands as well as other crops such as soybean. Establishing a uniform, optimum population stand is the first step in developing corn grain yield potential. Studies on the genetic evolution of corn indicate that modern hybrids tolerate field stress associated with higher plant populations better than their earlier genetic predecessors. Growers should continually evaluate the carrying capacity of their fields by putting in a few strip trials to determine the optimum plant population for each field. Keep in mind that as corn genetics continue to evolve, you will likely need to continually adjust your planting population upward to find that optimum plant population for each field. The 2006 planting season will be remembered for highly variable stand establishment. Areas with good drainage generally came through with good stand emergence. Conversely, areas with poor drainage suffered significant stand loss.
The second critical growth stage is when the plant determines the number of kernel rows and the number of potential kernels (ovules) per row. This is primarily determined during the rapid phase of corn vegetative growth, which generally occurs in early to mid July in Michigan. The number of kernel rows per ear is heavily influenced by genetics and is generally determined by growth stage V12, which corresponds to the 12 leaf collar stage. The number of potential kernels per row is being determined at V12 and is usually completed a week to 10 days prior to silking (V17). The number of potential kernels per row is strongly influenced by field conditions. Managing corn to reduce environmental, pest, moisture and nutrient stress during this time will maximize the potential number of harvestable kernels. Follow a plan to ensure adequate nutrient levels and minimize stress from pests such as weeds and insects during this critical period to establish the potential for high yield. Most of the state came through this stage of development in great shape. Adequate soil moisture during the vegetative growth stages across much of the state has set the stage for good corn grain yields this fall.
The third critical stage is pollination. Successful pollination is required to convert potential kernel numbers to actual developing kernels. Pollination occurs when a pollen grain is shed from the tassel, lands on an emerged silk, grows down the length of the silk, and successfully fertilizes the ovule. It generally takes 2 to 3 days for all the silks on an ear to be exposed and pollinated. Pollen shed generally occurs in the late mornings and early evenings and the pollen shed period typically lasts from 1 to 2 weeks. From a management perspective, there is not a lot that can be done to ensure good pollination since it is highly dependent upon the weather. Droughty conditions can de-synchronize pollen shed and silk emergence and also can desiccate silks and pollen grains. This results in barren ears or in short ears with barren tips. Insect pests such as adult corn rootworm beetles can feed on emerging silks and reduce pollination and therefore should be scouted during silk emergence. Finally, because the tassel and all leaves are completely exposed, the plant is especially vulnerable to hail damage at this stage. We are currently in the midst of the pollination stage of corn in much of the state. At this point, it appears that we should be in great shape for maximizing corn grain pollination.
The final critical growth stage for determining corn yield is the grain fill or kernel development period. The grain fill period which begins at pollination and ends at kernel black-layer formation generally takes from 60 to 70 days (855 to 1200 GDD) for Michigan conditions depending upon climate, planting date, and hybrid relative maturity. The size and weight of harvested kernels are determined at this time and under adverse conditions kernel number can also be reduced. Stress on the corn plant during the grain fill period can affect final yield by reducing either of these factors. Although field and machinery conditions can still influence final harvestable yield, the corn plant photosynthetic factory has completed its work at the kernel black-layer formation stage of development.
For more information on this or other topics related to corn production, contact your state extension corn specialist or your local extension educator/agent.
The following is the link to the corn extension specialists: state extension corn specialist