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Corn+Soybean Digest

Soybeans May Have Stebacks, Will Recover

WEST LAFAYETTE, Ind. – Cold soil temperatures in early June slowed soybean growth; however, last week’s warmer weather will help make up for lost time, says a Purdue University agronomist.

Ellsworth Christmas, Purdue Extension soybean specialist, says cloudy and cold conditions have delayed nitrogen fixation in early-planted soybeans causing them to turn a light green color. But he says the crop will recover.

"There should not be any significant impact on yield potential," says Christmas. "When soil temperatures warm to a level suitable for nodule activity, the leaves will become a darker green color indicating adequate nitrogen levels in the plant. The plant will resume normal growth."

During late May and early June, soil temperatures dipped to or below 50 degrees, making germination and emergence a slow process. Christmas says the major risk of slow growth at low temperatures is the increased probability of injury to seedlings from fungi and insects. Once the plant emerges, air temperature is the driving force for the speed at which the plant grows, he says.

Because soybeans had a slow start this growing season, Christmas says plant internodes may be shortened near the soil surface. He says this will result in low podding on some plants. At harvest, this means the sickle bar may cut through those beans and cause some field loss.

Christmas says producers are seeing thin soybean stands in some fields and may want to replant. Some thin stands have 80,000 to 85,000 plants per acre where there should be 160,000 to 165,000 plants per acre in drilled soybeans, he says.

Full-season soybeans in thin stands planted in mid-May or earlier will have

94 percent normal yield, assuming weeds are controlled, he says.

"If farmers tear up a soybean field with a 50 percent stand and replant it with a full-season soybean during mid-June, yield potential would be 92 percent," Christmas says. "The drop in yield is related to the planting date."

Therefore, the most profitable solution is to keep the lower number of plants per acre since the yield potential is higher than a replant, and any additional investment will be related to extra weed control, Christmas says.

With the exception of fungal disease, Christmas says most of these stresses should not have long-term affects on the soybean crop.

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