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Serving: IA
field with young plants emerging
WHEN TO SWITCH: Although specific dates vary across regions, the consensus is to continue to plant full-season varieties until June 15 in central Iowa.

June-planted soybeans: 3 considerations

Adjust your planting plan to help preserve yield with late-planted soybeans.

This year due to the prolonged wet spring, June-planted crops were unavoidable. So, what can you do if you are planting soybeans well into June to preserve as much yield potential as you can?

If planting is delayed past June 15, the decision must be made to either plant soybeans using a shorter-maturity group that is well-adapted for your area, or consider taking the Delayed and Prevented Planting crop insurance provisions, says Mark Licht, Iowa State University Extension agronomist. 

Planting soybeans after May 20 will likely result in lost yield potential of 10% to 50% or more. For delayed and prevented planting, the late coverage decreases each day from June 16 to July 10. In prevented planting situations, crop insurance language states the “cause of loss must be insurable and common to the area.”

Remaining yield potential

If planting is delayed past June 15, make a realistic determination of the remaining soybean yield potential, and the feasibility of delayed and preventive planting options. Talk with crop advisers, Extension field agronomists and insurance providers to gather information to make the best decision given the situation.

“Over the years, we’ve learned that early-planted soybeans offer numerous benefits that ultimately lead to increased yield potential. An earlier canopy shades out weeds, increases light interception and conserves soil moisture,” says Melissa Bell, an agronomist for BASF. “Plus, more vegetative growth [or] nodes on the main stem support more pods. With wet spring conditions and delayed planting, you likely won’t have these opportunities. But you can tweak your management now to help save yield potential, if you decide to go ahead and proceed with late planting.”

Areas of improvement

Licht and Bell offer these tips to improve your management:

Yield potential. Be realistic about yield expectations, she advises. University studies show you can expect to lose 0.3 to 0.6 bushel per acre each day planting is delayed after the first week of May, with losses reaching 1 bushel per acre every day by July 1. This yield loss is a result of fewer nodes developed prior to flowering and slower canopy closure.

The good news: “August rains can do a lot for a soybean crop, and we’ve seen the positive effect a timely rain can have during seed fill by increasing seed size,” Bell says. “Therefore, favorable weather and conditions late in the growing season may allow us to still achieve respectable yield.”

Planting rates. Agronomists talk a lot about canopy closure. Reducing row width (if possible) and increasing planting population (within reason) can allow for faster canopy closure to help with weed control and light interception.

Most university agronomists agree soybean populations should be boosted by 10% to 20% when planting in the first three weeks of June. For example, if you generally plant at 140,000 seeds per acre, consider bumping your population to 155,000.

“Boosting population also provides the benefit of increasing plant height and, therefore, pod height,” Bell says. “This is an important consideration since soybeans are photoperiod sensitive. That’s the reason they begin flowering around summer solstice, June 21.

Maturity selection. A question many farmers have is: Do I need to switch maturities? “There is no need to switch the soybean maturity group if planting can occur before June 1 in northern Iowa,” Licht says. “In southern Iowa, well-adapted soybean varieties can be planted into June. Soybeans have the ability to adjust their development caused by late planting because they are photoperiod-sensitive.”

In recent trials conducted at seven ISU research farms over five years, the same soybean variety planted 40 to 60 days apart reached physiological maturity within seven to 10 days of each other. Moreover, a 0.5 to 1.0 maturity group spread resulted in a difference of only three to five days to reach maturity.

Although specific dates vary across regions, the consensus is to continue to plant full-season varieties until June 15. It may then be appropriate to swap for an earlier maturity group for the remainder of the month if prevented planting provisions do not pencil out.

To compare more planting date and maturity combinations and determine risk of fall frost at more specific regions across Iowa, see the Soybean Planting Decision Making Tool.




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