Bumper yields start with basics

Not happy with your soybean yields compared to corn? Shaun Casteel, Purdue University Extension soybean specialist, believes the keys to bumping yields higher start with understanding the soybean plant better. Since it grows differently than corn, both when you make agronomic decisions and the type of decisions you make must be different.

Bumper yields start with basics

Not happy with your soybean yields compared to corn? Shaun Casteel, Purdue University Extension soybean specialist, believes the keys to bumping yields higher start with understanding the soybean plant better. Since it grows differently than corn, both when you make agronomic decisions and the type of decisions you make must be different.

This series is devoted to getting back to basics. Each installment will provide a tip to making a more informed management decision based upon understanding soybean growth habits. It will also include a short “check yourself” quiz.

Key Points

Understanding soybean basics leads to better decisions.

Losing cotyledons is not significant if unifoliate, trifoliates remain.

Check damaged soybean seedlings carefully before writing off a stand.


“Sometimes we forget that the soybean seed embryo has the first three vegetative parts inside — the cotyledons, unifoliate leaves and first trifoliate leaf,” Casteel says. “You may also not realize that compared to corn, which spikes through the ground, the hypocotyl pulls the cotyledons and growing point through the soil. The hypocotyl takes its position below the cotyledons.”

Management decision

Suppose it rains after planting and soils crust. Hypocotyls have more problems than usual pulling cotyledons out of the ground. Some cotyledons break off. Is that the end of plants where cotyledons break?

Your fast reaction may be “yes,” since the growing point is encompassed by the cotyledons. The soybean’s growing point is above the soil surface as soon as it emerges, unlike corn, where the growing point stays below ground until about the fifth-leaf stage.

However, the loss of a cotyledon or two doesn’t mean the growing point is destroyed. If the unifoliate and trifoliate leaves aren’t damaged, the plant should develop normally.

“If one cotyledon breaks off, there may be no yield loss,” Casteel says. “If both break, it might impact yield about 2% to 7%, mainly because it delays growth.”

If the hypocotyl breaks at ground level, then, yes, the plant is done and won’t regrow.

So when you’re making decisions after bad crusting, don’t let a few missing cotyledons influence you, he notes. First check to see if actual growing points are still intact.

Test your knowledge

Here’s a “soy teaser.” How much has Indiana soybean yield increased per year since the 1920s? Is it 0.1 bushel per year, 0.3 bushel per year, 0.4 bushel per year, or 1 bushel per year?

While some would prefer the latter, it’s about 0.4 bushel per year, Casteel notes. “It’s really about the same trend line as corn yield over time based on a percentage gain,” he notes. “Actual gains are larger for corn because corn is more efficient in converting light into energy, and yields about three times as much dry matter.”


02113440a.tif

Down, but not out: Note that the cotyledon is gone, but the unifoliate and trifoliate leaves near the top of the hypocotyl are intact. This seedling should recover and produce near-normal yield.

This article published in the February, 2011 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.

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