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A Simplified Look at Soybean Maturity Groups

Top yields come from a range of groups in most areas, says this soybean expert.

Confused by soybean maturity groups? You’re not alone.

Don’t make it complicated, says Bill Wiebold, a plant science professor at the University of Missouri and director of the Missouri Soybean Center. His research shows that, in most locations, there’s a fairly wide margin of acceptability of maturity groups to maximize yield.

Following are Wiebold’s answers to four common questions.

1. Why are soybean maturity groups important?

Wiebold: Soybean plants respond to photoperiod – the day length. Because of the earth’s tilt on its axis, day length in the Midwest varies from about nine hours in the winter to 15 hours in the summer. In Missouri, the difference from north to south is just a few minutes, but it’s enough that the plants are quite different.

Soybeans have developed a sort of intelligence that lets them know if they have enough time to fill seed. A chemical in the leaves called phytochrome responds to day length and sends a signal to the meristem on nodes, where the flowers appear. That starts the reproductive process.

Plant breeders have identified and selected varieties that are just a little different in how the phytochrome reacts to day length. They’ve assigned maturity group numbers to them from 000 to 8 and developed zone maps across the country that correspond.

2. How does the maturity group impact yield potential?

Wiebold: Soybean yield is a product of the number of days of seed fill and the rate of fill. The vegetative growth – the leaves – are the plant’s factory. The more leaves, the greater the fill. So as you go up the maturity scale, from a group 1 to 2 and 3 and so on, you further delay the signal to start flowering. Each whole number as you move up adds about 10 days.

The significance of this is that as you move up the maturity groups, the plants have a bigger factory before flowering begins. That should maximize yields.

3. What is the yield response?

Wiebold: “I can speak for Missouri, but the principles are the same anywhere. Within certain maturity groups, we have a fair amount of leeway to get top yields. A few years ago, we did tests with three soybean varieties in maturity groups 1, 2, 3, and 4 and three planting dates of April, May, and June.

Groups 3 and 4 yielded almost identical and significantly better than groups 1 and 2.

More recently, we’ve done similar studies with groups 3, 4, 5, and 6. The average yields were 63.6, 61.7, 54.7, and 38 bushels per acre, respectively. Again, the 3 and 4 groups were about the same. The group 6 soybeans suffered frost damage because they flowered too late. They don’t belong in central Missouri.

Our soybean variety testing program in Missouri also sheds some light on this. Regardless of how you break out this data, groups 3 and 4 yield nearly the same in central and north Missouri.

Some seed companies break down maturity groups more precisely, such as 3.7 or 4.1. I don’t get too carried away with the decimal points. What one company calls a 3.7 might be a 3.9 somewhere else. Many other things can impact this anyway, such as weather and disease.

My bottom line is that you have a pretty wide range of maturity options, and planting a range may be a good thing in terms of adding some yield stability.”

4. What about delayed planting due to double cropping or weather?

Wiebold: We did some late planting last summer, at the end of June, in maturity groups from 3.4 to 4.8. It was a good year for late planting, and they all yielded between 54 and 57 bushels – essentially no difference. It’s just one year, but it leads me to recommend the same varieties and maturities that are normal for your area. If it is ultra-late planting in mid-July, maybe you drop that by 0.5 group.

Summer Scouting Tips

So it’s midsummer and you or your agronomist is scouting your soybeans. What should be on your lookout list?

Aborted pods for starters, says Jon Zuk, a Winfield United agronomist. “In mid- to late summer, soybeans live day to day.  If there is any stress in mid- to late season, you will find pods dropping on the ground, because the soybean plant isn’t able to feed itself,” says Zuk. “When you think about managing for higher yields, applications mid- to late season can help mitigate some of those pod abortions.”

For example, a fungicide application – particularly in the presence of fungal disease – could curb some of the mid- to late-season pod abortions, he points out.

Other maladies to scout for during this time are sudden death syndrome (SDS) and white mold.

“There’s not much you can do to save yield potential, but you can make a note of what’s going on in the field for future years,” he says.

Options include planting soybean varieties in problem fields that tolerate white mold and SDS. Ilevo is one planting treatment tool that can be used to target fields with SDS histories.

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