Thicker Corn Populations Don't Always Need More Nitrogen

CORN ILLUSTRATED: Seed company tests show no advantage to higher N rates on thicker populations

Published on: Feb 4, 2014

Planting seeding rates for corn have marched upwards steadily since the 1970s. It has gone from not far over 20,000 seeds per acre to more than 30,000 seeds per acre. When Joseph Petrosino shows a chart of planting rates for the Midwest, it's pretty a much a straight line going up across the decades.

But a nitrogen chart is a different story. Petrosino, an agronomist for Stewart Seeds and part of the AIM program, working in Indiana but primarily in Ohio, says the N rate starts out at 80 pounds per acre not long after nitrogen was first introduced for corn production, then goes to 160 to 180 and levels out. It's still fairly flat for the rate of N farmers apply today.

"Many people ask us if they should boost their nitrogen rate if they are planting thicker," he says. "From our own data and what we've seen elsewhere, we don't see an advantage for increasing nitrogen rate about the level that worked for you at somewhat lower seeding rates."

Plant more seeds, same N rate: Test results from Stewart Seeds team of AIM agronomists so far indicate that even at 37,000 seeds per acre, fixed-ear hybrids dont need more commercial N that if planted at lower rates.
Plant more seeds, same N rate: Test results from Stewart Seeds' team of AIM agronomists so far indicate that even at 37,000 seeds per acre, fixed-ear hybrids don't need more commercial N that if planted at lower rates.

Related: Trend Toward Higher Corn Population Will Continue

Last year the AIM team of agronomists conducted tests with populations. Flex ear hybrids that respond more to environment topped out at about 34,000 seeds per acre. That's where the maximum yield came from. Nitrogen rate didn't seem to matter once it got to the top rate.

Fixed ear hybrids that usually have the same size ear regardless of conditions, were still putting out more bushels at 37,000 seeds per acre compared to 31,000 seeds per acre. Petrosino says they will probably up the seeding rate to 40,000 or even higher this year to try to find where the stopping point on population is for some of the racehorse, fixed-ear hybrids that can withstand the stress of thicker planting.

Customers who have attended Stewart Seeds meetings by and large say they're going to apply about the same amount of nitrogen this year as they have in the past. The results reported by Petrosino wouldn't indicate the need for more N on thicker stands if you're already applying economic rates of N.


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