By Shaun Casteel
Almost every farmer today knows that the growing point of corn stays below ground until about the fifth leaf stage. So if small corn is destroyed, it will grow back. But how much do they know about soybeans?
Shaun Casteel, a Purdue University Extension soybean specialist, contends it may not be as much as they know about corn. And with farmers concerned that it seems like they have more trouble pushing soybeans to higher yield levels than corn, he believes it would be helpful if they understood how soybeans grow and develop a bit better.
Here's a case in point. For example, the cotyledons, first unifoliate leaf and first trifoliate leaf are all in the embryo of the seed, ready to take off once the seed imbibes enough water to cause it to germinate. The hypocotyl pushes up through the soil, and brings out the cotyledons. Then the cotyledons are above the hypocotyl, or first stem. In corn, the first leaves spike through without help.
So if hail hits the soybeans in the cotyledon stage, is all lost? Many have been trained to say yes. However, as Casteel points out, it's more complicated than that. The trick is whether the unifoliate and trifoliate leaves at the base of the cotyledon are destroyed or not. If they're not, then the plant will still develop fairly normally.
In fact, the specialist notes that if both cotyledons are destroyed but the leaves remain intact at the upper part of the hypooctyl there may be as, little as a 2% yield loss, with that being primarily from delay compared to plants not hit with the delay. However, if only one cotyledon is lost and the leaf parts remain intact, there should be no yield loss.
The difference, of course, is if the soybean is broken at the base of the hypocotyls near the soil line. Since the growing point is above that, then the soybean is finished. You've got a zero yield situation. It's loss of the tiny leaves at the base of the cotyledon that doom the plant, not loss of the cotyledons themselves.
Hail is one situation where this comes into play. Crusting is another. Sometimes if crusts are hard enough a cotyledon may be lost during the emergence process. Crusting depends upon soil types, tillage and weather and combinations of these three factors.