LON-CAPA How many ears does a corn plant produce?

The Maize Page

I have a friendly "bar bet" with a co-worker about how many ears of corn grow per stalk. He said it was one and only one. I disagreed so we drove to a near by corn field and looked at some of the stalks along the road side. It appeared that he was correct, each stalk we saw only had one ear of corn. I told some members of my family, and they think I'm crazy. Either they picked some of the ears off the stalk already, or I counted wrong.

The answer depends on the population density of the corn field. Briefly, the ear of a corn plant is a branch. If you think about what happens to stands of other more familiar plants (think, for instance, of a christmas tree farm), you know that the more space an individual plant has for growth the more it will branch (the "bushier" it will be). This is an interaction of the plant's genes with its environment; specifically a response to how much light, water and nutrients there are for each individual plant. As you crowd a plant there are fewer growth resources (light, water, nutrients) per individual and as a result there is less branching.
In commercial stands of corn, it is not unusual for farmers these days to be planting in the range of 30 to 35 thousand plants per acre. Although most such corn would be planted in 30-inch row spacing, there is great interest in planting in narrower rows (such as 15 and even 10 inches) and perhaps even solid-seeding the plant (i.e., without rows at all). Whatever the planting arrangement, a stand of corn with 35,000 individuals per acre is one that is so thick that you cannot walk through it, meaning that there is extremely high competition between individual plants for their growth resources. You would therefore expect that there would be less branching (i.e., fewer ears) per plant. In fact, a ratio of about 0.9 ears per plant over a whole acre would not be unusual. The 0.1 loss of ears/plant is referred to as "barrenness," and it is a measure of how tolerant a given variety of corn is to high density environments. The greater the barrenness the less tolerant to high density a cultivar would be. Today's cultivars of corn are highly tolerant of high densities, meaning that they will give at least 0.9 (very near 1.0) ears per plant when planted in high populations. They have been selected to do this.
However, ANY cultivar of corn when planted in environments with low competition (e.g., the border rows of a corn field or in a low population field) will respond by branching more, in other words by producing more ears per plant. It is true that there has been breeding effort devoted toward the development of what are termed "strongly single-eared" varieties, but what this means is that these varieties tend to branch less in low population conditions than other varieties, not that they are genetically incapable of responding in the way that is normal for a corn plant, to branch more when given more resources per individual plant. There was great interest for a time in breeding strongly single-eared types with uniform ear height, and this had to do with earlier harvesting practices (both by means of hand labor as well as with early mechanical pickers). These days corn harvesters (called "combines") will harvest ears from any height, and in whatever number they are produced on single stalks, so it is not as important an issue as it once was. However, as explained above, modern cultivars of corn are selected to perform at their peak under highly competitive conditions, and for all intents and purposes this means that they will only produce one ear under commercial production conditions. You might be interested to know that you can plant corn at higher populations than recommended for grain production. When you do this, you intentionally increase barrenness (decrease the number of ears/stalk) and produce greater amounts of stover (stem and leaf material). This is what is done when a producer is interested in silage rather than grain.
Those are the facts. I'll leave it to you to settle your bet.

Ricardo J. Salvador

An addendum from Dr. Irvin C. Anderson:

The number of ears per plant varies as a function of genotype and plant density and other factors as you know. There is and old hybrid, WF9*C103, that even at 5000 plants per acre only shoots one ear, but its optimum plant density is 10 -13 thousand plants/acre. One of the first studies that showed the nature of tolerance to high plant density was done in the 1950s by Forest Troyer with DeKalb. He grew a population at very high densities and only selfed plants that had receptive silks at anthesis of that plant. Those plants were the first to silk, most were delayed or did not produce plants with silks. From this program he got inbreeds that were prolific and withstood high plant densities. I expect that the plants he selected had small tassel size genes since small tassel or low IAA concentration in tassels gives tolerance to plant density. Present day hybrids have smaller tassels than old hybrids. One reason commercial hybrid companies have trouble developing hybrids with small tassels is that in hybrid production they have trouble with the male inbred producing adequate pollen because plants are small and the pollen needs to disperse some distance, and large tassel size is a dominant characteristic.