The corn yield equation described by University of Illinois crop physiologist Fred Below sounds simple: More plants per acre, more kernels per plant and heavier kernel weights equals higher yield. But when several uncontrollable factors come into play, like weather, nutrients, soil types and hybrids, the yield equation becomes a challenge that’s impossible to control.

There’s one yield factor farmers can control: planting populations.

That’s easy. Push planting populations for higher yields. It’s not that simple, however, Below explains. To push populations, you need the right row spacing. Planting populations reach a point of diminishing returns in 30-inch rows, and yields decline above 38,000 plants per acre. Below believes narrow rows are the only way to push planting populations and avoid yield penalties.

What happens to corn plants when you push populations in 30-inch rows? “The plants know who is next to them,” he explains. “They know they compete with their neighbor.”

Overcrowded plants battle for nutrients and light, the root systems shrink, and yields decline. Below’s research team pulled roots from six different combinations of row spacing and plant population, ranging from 32,000 plants per acre in 30-inch rows to 50,000 plants per acre in 20-inch rows. The difference in root mass was visually obvious (see below), and yields were consistently higher in narrow rows.

POPULATION PROBLEM: What happens when you plant too many corn plants in 30-inch rows? The root system shrinks and yield declines, says Fred Below, University of Illinois crop physiologist.

With 38,000 plants per acre, 20-inch rows outperformed 30-inch rows by roughly 5 bushels per acre.  At 44,000 plants per acre, the yield advantage jumped to 16 bushels per acre.

It’s all about light interception, Below says. Narrow-row plants get more light from better plant-to-plant spacing, and they have more robust root systems.

Below understands the challenges that come with narrow-row operations, like equipment resale and residue management. But if planting population is the only controllable factor in the yield equation, narrow rows may be the only answer for higher yields. “We look at the factors that have the biggest effect on yield,” he explains. “In our last five years of research, it’s more plants, narrow rows and better fertility.”

Feeding plants from the start
In any row width and planting population configuration, Below recommends using starter fertilizer or banding nutrients like nitrogen, phosphorus, sulfur and zinc.

“We’ve seen a striking improvement when we have banded or used starter nutrients,” he says. “Adequate fertilizer sets the plant’s trajectory.”

The V4 growth stage is a critical stage as a plant comes off the seed’s nutrient reserves. “Somehow, the plant knows that conditions are good and all systems are a go,” Below says.