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What to expect from May 15 planting date

Tom J. Bechman young soybean plants
GOOD STARTING DATE: For the first time in three years, weather cooperated and the Soybean Watch field was planted in mid-May, not June.
Soybean Watch: This year’s field was no-tilled into cornstalks on May 15.

Everyone remembers what happened in 2019. It was one of the latest starts for soybean planting in 40 years in the eastern Corn Belt. Last year was much better, except for a few isolated spots. The Soybean Watch cooperator farms in one of those spots. So, the Soybean Watch field was planted in June the past two seasons.

Finally, a better weather window opened in 2021. He no-tilled the 50-plus-acre field into cornstalks on May 15 using a planter with 15-inch split rows. Multiple varieties were planted, but maturity ratings were similar.

Related: 2021 soybeans: Tale of 2 crops

“It’s good to have the field we’re following planted in what should be a more favorable window,” says Steve Gauck, a regional agronomy manager for Beck’s, based near Greensburg, Ind. Beck’s sponsors Soybean Watch ’21. Gauck is the agronomist and certified crop adviser who will visit the field on a regular basis during the season.

“It’s exciting to visit a field where I’m going just to evaluate how well they’re growing, and am not examining a particular problem,” Gauck notes. “Sometimes we find issues, and we can help the grower address them. More often, we just make general observations on crop maturity and growth.”

Soybean planting date

How important is it to have soybeans planted in mid-May vs. early or mid-June? Each year is different, but here is what history says. A table published in the Purdue University Corn & Soybean Field Guide, based on long-term research, says that if stands are uniform, there should be no loss in yield potential for soybeans planted by May 20.

However, yield drops to 96% of full potential for midseason beans planted May 30, and to 94% for full-season beans. The varieties in the Soybean Watch ’21 field are in the mid-Group 3 category. Yield drops to 92% and 90%, respectively, for beans planted June 10, and to 82% and 78% of full potential, respectively, for June 20-planted beans.

Other sources have also reported advantages for earlier-planted beans, or disadvantages for later-planted beans, depending upon your point of view. Beck’s Practical Farm Research data compiled for soybean planting dates over 20 years at multiple locations points to a distinct advantage for planting by May 15.

PFR agronomists determined the mean yield for those 20 years, with all locations combined. Then they grouped studies planted in various windows together and determined the yield for that window as a percentage compared to mean yield.

The planting date windows were March 16-31; April 1-15; April 16-30; May 1-15; May 16-31; June 1-15; and June 16-30. The percentages for yield in the planting window of mean yield were 98%, 108%, 108%, 107%, 99%, 92% and 79%, respectively. That means that soybeans planted anytime from April 1 through May 15 ranked above the mean yield for the entire 20-year period. Yields for March 16-31 and May 16-31 were neck-and-neck. What this data set says is that it’s better to plant in late March than early June! Yields fell off quickly in June, as they did in the Purdue data.

“Earlier planting dates tend to drive yields,” Gauck says. “We saw it in 2020 in many areas. One of the biggest advantages is a higher node count.

“Node count typically correlates with yield. It’s hard to make up extra nodes if soybeans get a late start in most years.”

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