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What’s the Optimum Seeding Rate for Soybeans?

Lower than what you may think. Purdue University recommendations are 100,000 to 120,000 plants per acre at harvest.

If you’re aiming to raise soybean yields by increasing seeding rates to the stratosphere, think again. There are better ways to do it. 

“If we are in the 100,000- to 120,000-plants-per-acre (ppa) range (at harvest), we are fine,” says Shaun Casteel, Purdue Extension agronomist.

Casteel discussed Purdue seeding rate research at this month’s Top Farmer Conference at Purdue. In some areas, optimum harvest populations at a southeastern Indiana site have even been as low as 60,000 ppa, he says. However, the 100,000 to 120,000 ppa range is a good overall range for which to strive.

As with corn, though, stand counts for soybeans are essential, he says. Stand counts can help farmers make those hard-to-make replant decisions. Consideration is often given when soybean stand counts tally 70,000 ppa, he says. Even then, though, replanting always isn’t always a given. 

“By the VC (vegetative cotyledon) stage, with the cotyledons and unifoliates (leaves) fully extended, the plant has already made its decision to branch,” says Casteel. “So, as you replant over a stand of soybeans at V1 or V2, you take what the original stand has had—with the advantage of time with nodal development and branching—vs. what you have just replanted. The replanted beans will be delayed in development and will not have as many nodes. They will fill out and make the field look green. But by the time you get to the V2 stage (at a 50,000 ppa replanted rate), those replanted beans will only contribute to 5% of the overall yield; 95% will have come from the original stand. There is zilch yield difference. 

“I’ve had people come up to me and say, ‘I listened to half your advice. I replanted half the field when the (original) stand was 70,000 plants per acre. The yield monitor came up at 62 bushels at what I replanted and 65 for what I did not,’ ” Castell says.

There is one catch, though, when a field is not replanted with a compromised 70,000 ppa stand. 

“We have to make sure we need to keep up on weed control,” says Casteel. 

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