Late Soybean Planting Recommendations and Adjustments

Soybeans flower and mature in response to photoperiod, also known as, day length. Shorter days after June 21st trigger flowering in soybean products. North Dakota State University reports a 0.6% yield loss per day when soybean planting takes place in late May. Switching soybean maturities at the appropriate time may help avoid these problems and help maintain yield potential with later planting. Switching product maturity in North Dakota and northern Minnesota shouldn’t be considered until early June.

The time span from flowering to harvest maturity is controlled by the maturity group for a specific product. Because soybeans are day length sensitive, days from flowering to harvest maturity will only differ slightly from planting dates between May 10 and June 10. For each three to five-day delay in planting, flowering and maturity are delayed only about one day. Unless the planting or replanting date is very late, it is usually not necessary to change to an earlier maturing soybean product.

However, planting rates should increase 10 to 15% to compensate for plants that may not reach optimum yield potential and to help establish a good canopy. Narrow row spacing is another good agronomic management tool that can hasten canopy closure, increase sunlight interception and biomass accumulation. Ideally, the crop canopy should be closed by July 1st. When a field originally intended for corn is being switch to soybeans, it is important to know plantback restrictions for the specific herbicides that have already been applied. Herbicide plantback restrictions found on the labels should be followed to prevent any carryover damage from further delaying the crop.

In conclusion:

  1. Consider switching to an earlier maturing soybean product after the first week of June.
  2. If choosing to switch to a shorter maturity soybean product, shorten the maturity group by 0.5 RM earlier until mid June or move 1.0 RM group earlier for late June planting to help maximize height and yield potential.
  3. Increase planting rate by 10 to 15% by June 1st.
  4. Use narrow or drilled rows where feasible to promote faster canopy closure.
  5. Implement a timely weed management program.
  6. Follow the herbicide label instructions regarding plant back (the time period between when herbicides are sprayed and when a specific crop can be planted) restrictions.

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Josh Lamecker

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