What Factors are Impacted by Increasing Plant Populations in Corn?

Advances in hybrid corn genetics combined with changes in agronomic practices have resulted in substantial increases in corn yields over the past century. Corn yields have increased more than a five-fold from what they averaged in the 1930s at 30 bu/acre (Figure 1).^1,2,3 Corn breeders have selected for higher yielding corn products under increased seeding densities, resulting in increased “crowding stress” tolerance.⁴ These yield gains have been attributed primarily to increased plant density rather than increased per-plant yield. Subsequently, optimal plant populations have increased strikingly in recent years. Along with corn hybrid selection, corn growers can make decisions on maximizing plant populations for yield and profit by understanding how plant density affects yield potential.

Figure 1. Historical corn yield in the United States from 1996 to 2024. Image courtesy of USDA National Agricultural Statistics Service, https://www.nass.usda.gov/Charts_and_Maps/Field_Crops/cornyld.php.

Modifications to Yield Components of Corn

Yield components of corn, including ears per acre, kernel rows per ear, kernels per row, and kernel size, directly impact yield. All are influenced by environment, genetics, and agronomic practices. These yield advances are attributed to the ability of corn plants to sustain a high harvest index at increased plant populations.^1,5 Harvest index (HI) is the ratio of grain relative to overall plant biomass. A high HI is the result of partitioning more plant resources into grain rather than overall plant biomass, resulting in enhanced grain yield.⁶ Plant breeders select for corn products that can partition dry matter to the ear and enhance photosynthesis during grain fill.

Modern corn products have been bred to tolerate higher population densities, producing consistently greater yields with less lodging at increased plant populations. General seeding rate recommendations typically fall between 35,000 to 45,000 seeds per acre to maximize yield potential (Table 1). It is important to consider which corn products are best suited for soil conditions, water availability, and nutrient resources as these factors can influence optimal seeding rate.

Table 1. Effect of corn seeding rate on grain yield, kernel number, and kernel weight (Champaign, Illinois 2011).

Benefits of Ear Flex at Lower Corn Plant Densities

Ear flex refers to a corn plant’s ability to adjust the size of the ear in terms of length, girth or kernel depth in response to management practices, including plant population, or the growing environment. Corn products are typically classified as flex-ear, semi-flex-ear, or fixed-ear, based on how much they change ear size in response to population or environmental conditions. Corn products with a greater degree of ear flex can increase ear size in response to lower plant densities (Figure 2). Determinate or 'fixed' ear type corn products typically have greater yields at high plant densities. Contrasting yield components can be observed when flex and fixed ear types are evaluated. For instance, a flex ear corn product can have a greater number of kernels per area, while a fixed ear corn product can have heavier individual kernels under similar conditions.⁷ Understanding the ear flex capability of a specific corn products can influence planting density decisions.⁸

For more information on specific corn products and ear flex, please refer to your seed guide and talk to your local Bayer representative for recommendations.

Enhanced Photosynthesis in Increased Corn Plant Populations

Plant populations near 45,000 plants per acre may be required to consistently achieve 300 bushels per acre yield goals of the future.⁷ Photosynthesis is one plant process that remains a target for genetic improvement to potentially increase crop yield.^1,9,10 Currently, photosynthetic activity is being increased by using leaf angle to maximize sunlight capture and increasing stay-green characteristics for prolonging the duration of photosynthesis during grain fill. Leaves angled 75 degrees from horizontal have enough sunlight to increase photosynthesis, while the remaining direct light penetrates lower canopy leaves.⁹ There is evidence that such upward angled leaves were introduced to modern corn products through a mutation of an auxin binding protein.¹¹ Auxin distribution and sensitivity is affected by red to infrared (R:FR) changes. Plants can detect neighboring plants by changes in R:FR light in the canopy. Close plant spacing can result in elongated growth, less branching, and redistribution of leaves to the upper canopy to avoid lower shaded leaves.

Delayed leaf senescence, or stay-green characteristics, allow plants to continue photosynthesis during grain fill. Maintaining photosynthesis during grain fill helps increase kernel weight by providing more energy for the plant to convert sunlight into stored energy. Additionally, corn products with greater tolerance to disease can maintain leaf health and photosynthesize late into grain fill stages and potentially result in a moderate increase in kernel weight.⁶

Improved Drought Tolerance and Nitrogen Utilization

Corn hybrids bred for higher planting densities have also been selected for improved drought tolerance. Drought tolerance is a quantitative measurement that is influenced by the expression of multiple genes and the environment. Products that can withstand drought-associated risks can help stabilize yield potential under less-than-ideal growing conditions.

Modern corn hybrids have also been selected for improved nitrogen (N) use efficiency. A study of corn N use and efficiency from four decades (1970s, 1980s, 1990s, and 2000s) demonstrated that modern corn products utilize N more efficiently. When planted under low N conditions (approximately 63 lb/acre), corn products released in the early 1970s had 17 percent barrenness compared to 5.8 percent for hybrids released in the 2000s.⁶ The newer corn products distributed carbon and N more efficiently to the shoot and ear, despite N being limited. It is thought that corn product selection has led to plants with traits for enhanced metabolic pathways to the ear. High density corn plants tend to develop smaller root systems; however, nutrient uptake efficiency and partitioning have increased over time as new corn hybrids are introduced.

Summary

Corn plant architecture and metabolic processes have been altered over time, resulting in improvements to the harvest index and increasing corn yield potential. This can be attributed to genetic improvement from directed plant breeding as well as improvements in agronomic practices. Genetic modifications to N uptake and use efficiency, enhanced photosynthesis, as well as improvements to harvest index and canopy architecture have been key to increasing plant density and corn yield potential.

Sources

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⁸ Fromme, D.D., Spivey, T.A., Grichar, W.J. 2019. Agronomic response of corn (Zea mays L.) hybrids to plant populations. International Journal of Agronomy vol 2019:1-8. https://www.hindawi.com/journals/ija/2019/3589768/
⁹ Long, S.P., Zhu, X-G., Naidu, S.L., and Ort, D.R. 2006. Can improvement in photosynthesis increase crop yields? Plant, Cell & Environment vol 29:315-330. https://doi.org/10.1111/j.1365-3040.2005.01493.x
¹⁰ Ren, B., Liu, W., Zhang, J., Dong, S., Liu, P, and Zhao, B. 2017. Effects of plant density on the photosynthetic and chloroplast characteristics of maize under high-yielding conditions. Naturwissenschaften vol 104:12. https://pubmed.ncbi.nlm.nih.gov/28246890/
¹¹ Fellner, M., Ford, E.D., and Van Volkenburgh, E. 2006. Development of erect leaves in a modern maize hybrid is associated with reduced responsiveness to auxin and light of young seedlings in vitro. Plant Signal Behavior. Vol.1:201-11. https://doi.org/10.4161/psb.1.4.3106
Web sources verified 02/05/2026. 1214_111227