Consider these variables when determining how many seeds to plant per acre:

  • Yield potential of the field. Invest in seed for good ground. On fields with long-term yield averages of 190 bushels per acre or better, aim for 33,000 ppa or more, suggests Thomison. For 150-bushel fields, 30,000 ppa may do the trick, and if 120 bushels or less is all you can expect on a field, back off to 20,000 to 22,000 ppa, he advises.
  • Seed germination. Check each bag’s seed tag for germination percentage of that lot, suggest breeders at Dekalb. Most seed has a germination percentage greater than 95%, but some can be as low as 85%.
  • Historic attrition rate. A certain percentage of seeds won’t germinate due to a wide variety of challenges in a field. Normal attrition rates in Iowa State University studies range from 3% to 7%, notes Roger Elmore, Iowa State University Extension corn specialist. Figure out what your attrition rate typically is — and if it’s much greater than local averages, find out why.
  • Planting conditions. The cool soils of no-till fields in early to mid-April can stress seedlings and limit populations, Thomison points out. He suggests increasing seeding rates 10% to 15% higher than your desired population in those circumstances. On the flip side, if conditions are dry at planting and show no signs of improving, be conservative with your populations, advises Elmore.
  • Maturity. Early-maturing hybrids typically require higher populations than later-maturing ones, according to Dekalb.

30-inch corn rules

Of course, hitting your target population requires fewer seeds per foot in narrower rows. In corn, the question of optimum row spacing seems to be mostly a matter of your equipment and your comfort level.

In Iowa, modern hybrids in 30-inch rows intercept 95% of the available sunlight at silking — the prime target for corn, says Elmore. That’s what it takes to produce optimum yields, he notes, so rows any tighter than 30 inches rarely improve Iowa harvests unless early-season stress, like drought, slows canopy closure in the middles.

As with most seed-related issues, your seed dealer will be an invaluable source of information
on optimum populations in your conditions. Ask.