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Know the Difference Between Seeding Rate and Final Harvest Population

Know the Difference Between Seeding Rate and Final Harvest Population
Corn Illustrated: Specialist stresses it's the final population that counts.

Most farmers talk in terms of seeds dropped per acre for corn. Most seed companies talk about seeding rates, even when referring to plots or test trials. Bob Nielsen, Purdue University Extension corn specialist, says that's the wrong way to be looking at corn populations.

"What really matters is the final stand at harvest," he says. "What you want to know is how many ears you're going to harvest, not how many seeds you dropped per acre. It is the ears that are out there that gives you the yield."

Plants per acre matter: Begin thinking in terms of final stands in plants per acre instead of seeding rates, Bob Nielsen tells farmers.

Nielsen started research last year on something he hadn't looked at for some time – ideal final harvest populations. He says it's time to revisit it because plant breeders have improved hybrids and their ability to take stress from 30 years ago. The ability to take stress and still yield well includes withstanding higher populations than were harvested years ago.

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"Hybrids 30 years ago responded to more population to a point, then crashed and fell off the edge as you pushed them higher," he says. "What we're seeing now in today's hybrids is that yields respond to more plants to a point, then level off. They typically don't crash unless you push them very far out on population."

Nielsen's new research so far, which continues this year, largely in field-size testing, shows that the sweet spot today is somewhere around 31,000 to 32,000 plants per acre. That's more than he was recommending not that long ago.

"You convert it to seeding rate," he says. "I don't want to give seeding rates because everybody is different at how well they manage planting, and how much of the seed they plant actually ends up as final population producing ears.

"If you are 95% efficient, that's one thing. If you only achieve 80% of what you plant, then that's something else, and if that's where you're going to be, you will need a higher seeding rate."

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Nielsen says in his studies so far, which includes date from a number of farmers participating in the trials, the average for final plants harvested of seeds dropped is about 95%.

If you achieve 95% then the seeding rate falls somewhere around 33,000 to 34,000 seeds per acre, Nielsen says. If you only achieve 80%, then you will need to plant somewhere from 36,000 to 38,000 seed per acre.

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