Successful soybeans need attention to seeding

The window of opportunity to seed soybeans is small, but farmers would do well to take it to heart, a researcher involved in a recent study told a people attending Crop Production Week in Saskatoon.

Mike Hall of the Essential Research Foundation and Parkland College in Yorkton, Sask., said farmers will likely get their best results by seeding soybeans in mid to late May.

“Seeding too early runs the risk of cold shock and damage from late spring frosts. Seeding too late reduces yield and increases the chance of fall damage and green seed,” he said.

The research foundation conducted several experiments during a five-year program using Northstar Genetics varieties.

A 2013 study demonstrated the importance of seeding soybeans into warm soil to avoid cold shock and improve plant vigour and yield.

Soybeans were planted into 21 C soil and kept at that temperature for 17 days. To produce a cold shock effect, soybeans were planted into 7 C soil for 20 hours and then 21 C for 17 days. They were also planted into 21 C soil for eight hours and then 7 C for four days followed by 21 C for the remaining 13 days.

“Unfortunately, we are never able to cold shock soybeans even when seeding in early May. We still had soil temperatures that were above the minimum amount required which is 8 C. But there was one year that if we had seeded at that time we would have been taken out by a frost May 30,” he said.

“As it turned out we did seed soybeans that year, but because we seeded at the optimum time, we avoided the frost and the soybeans yielded quite well.”

Multiple varieties were seeded into rotovated soil and undisturbed soil with the expectation that soybeans seeded into warmer rotovated soil would mature faster, be taller with a longer first internode and yield higher.

Soybeans seeded into rotovated soil did mature faster, but were shorter with a shorter first internode and yielded poorer quality.

Hall thinks rotovated plots performed worse because it may have resulted in deeper seeding, but it didn’t affect emergence or early stand establishment.

It’s also possible that breaking up the soil with a rotovator dried out the soil and reduced nitrogen fixation, which would result in earlier maturity and lower yield.

In 2015, the study looked at the effect of row spacing and seeding rate on bush, semi-bush and upright statured soybean types using three Northstar varieties. Target populations were 175,000 and 200,000 plants per acre. Row spacing was 10 and 20 inches.

“Bushy soybeans tend to yield better when they’re at a wider row spacing. But having said that, those soybeans weren’t yielding any better than an erect variety, solid seeded, 10 inches in row spacing. So, we didn’t really see any evidence to suggest people should be running out there and buying planters, for example,” he said.

A study in 2016 looked at the influence of fall cultivation and seeding date on soybean production.

Treatment list included soybeans seeded May 5, May 16 and May 24 into soil cultivated in the fall compared to the same seeding dates into standing stubble.

The study showed cultivation could benefit soybean production when soybeans were seeded early. The benefit may have been higher if the trash was heavier or there had been a frost, but benefits need to be weighed against soil conservation concerns.

Considering that soybeans shouldn’t be seeded until mid to late May, cultivated soil didn’t provide much of a benefit at those seeding dates.

Another study in 2017 looked at the importance of dual inoculation and seeding into warm soil, which means inoculant on seed and granular banded to the side.

Hall said the general recommendation in Manitoba is to dual inoculate soybeans if land doesn’t have a history of well inoculated soybean crops for at least two years.

“We weren’t able to demonstrate the benefits of dual inoculation. We saw a really strong response to granular inoculant but inoculant on the seed didn’t work too well, and there might have been some handling issues along the route. But in general, I really do like the granular inoculant,” he said.

“I always look at inoculant as cheap insurance.”

With a warming climate and more varieties to choose from, the number of seeded acres is increasing as the crop migrates further west and north across the Prairies each year.

“My main message to someone wanting to try soybeans is understanding it is a long-season crop. Don’t go out there and seed it too early because there are some risks out there. I know some seed growers that won’t even give you the seed until later, so that you don’t go out there and seed it too early,” he said.

It’s definitely going to be on the late side of crops that you’ll harvest, so you don’t want to grow a lot of acres of it when you’re just starting out.”

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