Corn Plant Population

Actual planting rates should exceed expected final stand by 5 to 15 percent to allow for germination failure and seedling mortality. Stand establishment is generally more difficult in cool soils. Thus, increase planting rates to allow for more stand failure in early plantings.

Hybrids often respond differently to varying plant populations, depending on the environment and their genetic backgrounds. Therefore, picking an optimum plant population may seem to be a somewhat arbitrary task. However, suitable plant populations can be selected by following the seed company's recommendations and monitoring corn physiological indicators for several years or locations with different environments.

Research indicates corn yields are maximized when one ear per plant is produced. This is important because plant population affects the number of ears per plant. Low plant population causes corn to become prolific (produce more than one ear per plant). Ear barrenness (the failure of a plant to produce a seed bearing ear) and ear tip kernel abortion occur when high plant population causes intense interplant competition and is accentuated by high environmental stress. Therefore, monitoring the number of prolific or barren stalks and extent of ear tip kernel abortion can indicate a suitable plant population.

A population should be high enough so limited sunlight penetrates through the fully developed crop canopy at silking. Incomplete light interception limits yield because all available energy is not being used. Light interception varies with plant population, hybrid, row width, and growth conditions. Late maturing hybrids normally intercept more light than do the early maturing hybrids because late maturing hybrids have more and larger leaves. Thus, early maturing hybrids should generally be planted thicker than the late maturing hybrids to compensate for their sparser leaf canopies.

Numerous studies show increased corn yields resulting from narrow row widths. This has led to around 80 percent or more of corn producers in the United States using 30-inch or narrower planting equipment. Corn producers in Mississippi use a greater percentage of wide-row equipment (greater than 30-inch row spacing) than the national average because, until recently, narrow-row cotton pickers were not available. Increased yields are obtained in narrow rows primarily because of more efficient light interception and utilization resulting from improved plant spacing. Improved plant spacing from narrow rows has allowed increased hybrid selection for more upright leaf orientation, which allows a thicker plant population and greater photosynthetic efficiency. However, this advantage is squandered in wide rows because hybrids with upright leaf orientation can not intercept light in the wide row middles. Thick-canopied, late-maturing hybrids planted at low to moderate plant population are generally still recommended for wide rows.

Table 1. Corn plant spacing (inches) at four different plant populations and row widths

By Dr. Erick J. Larson, Extension Agronomist

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Information Sheet 1548
Extension Service of Mississippi State University, cooperating with U.S. Department of Agriculture. Published in furtherance of Acts of Congress, May 8 and June 30, 1914. RONALD A. BROWN, Director

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