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CropTalk: Yield Components of Corn

August 2020

Published on Monday, August 3, 2020

Corn grain yield, typically measured in bushels per acre, can be broken down into distinct components that each contribute to the weight of harvested grain. While genetics govern some yield components, much of the harvested yield is directly affected by environmental conditions and management practices. Yield components include number of plants per acre, number of ears per plant, the number of kernels per ear, and the weight of each kernel.

Yield potential begins with the number of plants per acre. Planting population varies based on the yield potential of the soil and the hybrid, as hybrids differ in their response to plant density. Weather conditions, seedling diseases, and insects can all reduce the number of plants per acre compared with the seeding rate. Narrower rows tend to support higher plant populations by reducing competition among plants as they spread out down the row. Plant architecture, driven by genetics, often dictates whether a hybrid is suitable for narrow row and high population situations.

Control This Component:
Seeding Rates: Typically range from 28,000 to 40,000 seeds/A. pending the soil productivity level and hybrid recommendations.
Planting Conditions: Soil temperatures of 50° F or higher is the traditional recommendation. Planting prior to a warming trend is important. Do not plant 24 hours prior to a cold rain in order to avoid chilling injury.
Seeding Depth: The PFR Proven™ corn planting depth is 2 in., but ideal planting depth may vary slightly from 1.5 in. to 2 in. based on specifi c soil types. Shallow planting can lead to standability issues later in the season, while deep planting can reduce emergence.
Seed Treatments: Use a comprehensive seed treatment, like Escalate® yield enhancement system, to protect the seed and young plant from pathogens and insect damage.
Closing Wheels: Beck’s Practical Farm Research (PFR)® has repeatedly shown that after-market spiked closing wheels improve emergence and yield compared to the standard two solid rubber closing wheels.

Modern corn plants typically produce only one ear. Some hybrids may produce two ears, and two ears are more common where populations are thin and resources are abundant. Additional ears are not drivers of yield due to a low number of kernels per ear and the small kernel size on the non-dominant ear.
Control This Component: In modern corn hybrids, more than one ear per plant is typically a signal of low population, and is common on end rows and near areas of reduced plant stands.



The number of kernels per ear is determined by both the number of rows around the ear (in multiples of two) and the number of kernels per row. Both numbers are primarily controlled by genetics, but are also affected by the environment. Hybrids differ in how many rows around the cob they typically produce; the average is 16 but the number of rows ranges from 14 to 20. Determination of rows around the ear begins at the early growth stages and is complete by V8. Early-season stress during the V4 to V8 growth stages can reduce the number of rows around. Nutrient defi ciencies — particularly nitrogen (N), drought, cold or freezing temperatures during early development, or herbicide injuries are examples of common stressors that would reduce or limit the number of rows around.

The number of kernels per row is determined in the plant between the V6 to VT growth stages. An ear starts with approximately 1,000 embryos (potential kernels), but the fi nal number of kernels can vary greatly. Embryos that produce a silk during the pollination stage have the potential to produce a mature kernel, but stress during pollination, such as heat, drought, nutrient defi ciencies, and physical damage can adversely affect the number of kernels that are pollinated. After pollination, kernels can be aborted due to plant stress, resulting in reduced yield.

Control This Component:
Crop Nutrition: Ensuring adequate nutrition throughout the season by splitting N applications between preplant/ planting and sidedress can increase kernel number.
Biotic Stress: Select hybrids with good disease ratings; use a comprehensive seed treatment, Bt traits, fungicides, and insecticides to limit pest pressure.

Kernel weight is determined by kernel size and kernel density, or test weight. The resources available to the plant during the grain fi ll period prior to black layer control kernel weight. Test weight tends to be controlled by genetics, but is also infl uenced by late-season stresses such as drought or disease. Anything that reduces the optimal productivity of the plant during this period can result in reduced grain fi ll or kernel weight. Stress can be induced by drought, excessive heat (including excessive nighttime heat resulting in increased respiration), nutrient defi ciencies, foliar diseases, and defoliation due to hail or a killing freeze.

Control This Component:
Fungicides: Fungicide applications protect from disease and can improve overall plant health. Applications prior to the VT or R1 growth stage are usually not economical.
Nitrogen: Split N applications can increase kernel weight.
Moisture Stress: Irrigation and tile drainage can help maintain plant health.

You can estimate your yield based upon the components described above as early as the R4 growth stage (dough stage). Be cautious if the plants are entering a stressful period, as some kernels may abort or not reach their full potential after your estimate.

In the formula below, the number 90 represents 90,000 kernels/Bu. This is a function of test weight and kernel size. The number could be as low as 65 or 80 (under excellent growing conditions), and as large as 100 (under stressful conditions during grain fi ll). Smaller kernels due to late-season stress mean a larger number of kernels per bushel.

To estimate yield, count the number of plants in 1/1000th of an acre, which is 17.5 ft. in 30-in. row corn. Then, choose three random and representative ears to count rows and kernels. Use the average number of kernels per ear in your calculation. This estimate needs to be completed several times throughout a fi eld to get a more accurate representation of yield. Field variability can greatly influence yield from point to point.

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Aaron Brooker

Aaron Brooker

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