Increasing corn populations to 28,000-30,000 plants per acre usually bumps up yield. But if you do it with the wrong hybrid, you might be wasting money.

University of Illinois 1997 research on six 108- to 112-day hybrids revealed an average 8-bu-per-acre yield increase by boosting corn populations to raise harvest stands from 24,000 to 28,000 plants/acre.

However, optimum population can vary considerably from hybrid to hybrid, seed company tests show. And with seed-corn prices rising - due to the costs of new technology - growers will be wise to plant each hybrid at its optimum rate. At $90-125 per bag for 80,000 kernels, seed costs $1.12-1.55 per thousand seeds.

So what's a prudent 1998 seeding-rate strategy?

"Overall, in the past few years, most hybrids have shown a maximum dollar return per acre at a harvest population near 30,000 plants per acre," says Brian Meese, Concept Farms coordinator for Asgrow Seed Co., Ames, IA. "But with the wide range of hybrids we offer today, there are differences in how individual hybrids respond to population."

The differences, says Meese, usually relate to the degree of a hybrid's ear-flex and stalk quality.

Hybrids with moderate-to-good ear flex tend to lengthen their ears under lower plant populations and thus compensatefor fewer plants per acre. They don't usually benefit as much from higher populations. And hybrids with moderate stalk strength can have standability concerns at excessively high populations.

"To determine your optimum population for a given hybrid, ask a seed company representative for advice based on your specific area, growing conditions and agronomic practices," Meese recommends.

Dave Henderson, Pioneer field sales agronomy manager at Alexandria, IN, agrees with Meese.

"For the majority of our lineup, we suggest a harvest stand of 28,000-30,000," Henderson notes.

"As a general rule, the earlier the hybrid's maturity, the greater the benefit from high population. This has been proved in many population tests and may be due to the shorter plant stature and fixed-ear type of the early season hybrids."

Nevertheless, he adds, "There are hybrids in all maturities that we can push too high, and we want growers to know which are which."

Regardless of hybrid or maturity, farmers generally sacrifice yield potential with harvest stands below 26,000, Henderson says.

Pioneer 1997 population studies in Illinois, Indiana, Ohio and Michigan back up the hybrid-specific concern. Based on the results of 17 hybrids tested, company agronomists recommend that three have a harvest stand of at least 30,000; four near 30,000; seven near or above 26,000; and three near 22,000.

Asgrow uses a 1-9 rating system for plant population and other agronomic characteristics of its hybrids. Scores of 1-3 indicate above average; 4-6, average. Of six of Asgrow's premier 105- to 114-day hybrids, two are rated 2 on response to high population; one is rated 3; two are rated 4; and one is rated 5.

In trials at the University of Illinois' Dekalb Research Center, five of six hybrids yielded best at about a 28,000 harvest population. But the sixth hybrid posted its top yield at a 36,000 stand in both 20" and 30" rows.