We experienced one of the wettest springs on record across Illinois. This delayed planting and caused some replant conditions this season as well. With inevitable late planting of soybeans this year, here are some key points to remember:

  • As soybean planting is delayed population increases are necessary to maximize yields and ROI
  • Past research shows if you are planting the second and third week in June, a transition from 140,000 plants per acre to 180,000 has a positive ROI
  • Maintain maturity at our latitude through June for maximum yield
  • A one-week delay in planting translates into 2.8 days delayed maturation

You are all aware that the summer solstice triggers flowering in the soybean plant. June-planted soybeans will be encouraged to start reproductive activities immediately and will have less vegetative growth than an early planted soybean. This phenomenon diminishes the number of nodes (opportunity) for flowers and, ultimately, pods on a per-acre basis. The goal is to intercept 95 percent of the sunlight in the mid- to late-July timeframe (pod set) to maximize yield.

To compensate for shorter stature plants and achieve yield expectations, increase the number of plants per acre to return the number of nodes to an optimum level. Also, consider row widths narrower than 30 inches by interplanting or planting at an angle to the first pass if a narrower planter is unavailable or already in operation.

The chart below is from a recent article in Corn & Soybean Digest by Joe Byrum with Syngenta. Keep in mind that these figures are for plant populations, not planting populations. So, if you expect to get 85 percent of the plants out of the ground and growing, take the plant population divided by .85 to determine planting populations.


Todd Thumma is a product development agronomist for Syngenta.

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About the Author: Todd Thumma

A Certified Crop Adviser for 25 years, Thumma has been with Golden Harvest and its legacy brands for 15 years. He is passionate about helping Golden Harvest farmers in Northern Illinois address corn and soybean field challenges to maximize yield. Thumma is an Iowa State University graduate with a bachelor’s degree in agronomy and agricultural business.