A nonprofit publication of the Kentucky Center for Public Service Journalism

University of Kentucky grain crops specialist offers soybean planting tips to help growers maximize yield


By Katie Pratt
University of Kentucky

As full-season soybean planting gets underway in Kentucky, Carrie Knott, University of Kentucky grain crops specialist, offers Kentucky producers some advice to help them get the crop off to a good start.

“We know that to maximize yields of full-season soybeans, producers need to plant before early May in Western Kentucky and mid-May in Central Kentucky, but they need to make sure that soil temperatures are warm enough before they start,” said Knott, an associate extension professor in the UK College of Agriculture, Food and Environment. “Soil temperatures 2 inches below the ground need to reach and sustain at least 50 degrees F, and there needs to be no risk for a killing freeze.”

Ideal soil temperatures for soybean planting are between 50 and 60 degrees. (Photo by Steve Patton, UK agriculture)

This year, a warm March resulted in soil temperatures across much of the state reaching 50 degrees March 26, and some producers planted. But this date was well before the last killing freeze date for most of the state. On April 15, temperatures dropped into the low to mid-20s across Kentucky, which caused soil temperatures to drop to 45 degrees. As a result, producers who planted soybeans early this year should assess their crop for freeze damage.

“If soybeans were still below the ground on that date, their chances for survival are good, but if they were above ground on April 15, damage may have likely occurred,” Knott said.

Ideally, producers should plant soybeans when ground temperatures are between 50 and 60 degrees F. If they plant on the cooler end of this range, producers may need to take extra precautions to ensure they get good germination and emergence.

“If they plant early, they may want to increase their seeding rates to offset anticipated higher stand losses than if they had waited to plant when temperatures were closer to 60 degrees.” Knott said. “They may also want to select seed that is treated with a fungicide and insecticide, as cool, wet conditions typical of this time of the year slow germination and plant growth. This increases the risk for seedling diseases and insect damage to young plants.”

Producers should plant soybeans between 1 and 2 inches deep in the soil. If they plant deeper, the risk increases for the seed not emerging from ground. For maximum yields, they should choose a seeding rate that will give them at least 100,000 plants per acre at harvest. To determine their seeding rate, they must factor in anticipated stand losses and the variety’s germination rate.

If planting into a field that has had soybean sudden death syndrome, producers need to select varieties that are disease tolerant and use the newer seed treatment ILeVO.

Producers planting into fields that have been extremely wet all winter, fields that have not produced soybeans in 3 to 5 years or fields that have a history of poor nodulation should use a Bradyrhizobium japonicum inoculant on their seed to help maximize yields.

Additional information is available in UK extension publication ID: 249: Soybean Management in Kentucky. It is available at http://www2.ca.uky.edu/agcomm/pubs/ID/ID249/ID249.pdf or by contacting a local office of the UK Cooperative Extension Service.

Katie Pratt writes for the University of Kentucky College of Agriculture, Food and Environment


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