Soybeans receive moisture stress help

Researchers are developing genetic resistance to negative moisture stress that could help production in drier areas

August of 2018 was dry in Weyburn, Sask.

Crazy dry.

Data from Environment Canada shows that Weyburn recorded 1.9 millimetres of rainfall for the entire month.

That sort of dry spell is extreme, but weeks without rain is a common occurrence in Saskatchewan and in most parts of the Prairies during the summer months.

Such periods in July and August the last couple of years is one reason why Saskatchewan farmers abandoned soybeans in 2019.

“I had 8,000 acres of beans two years ago. Now I have 160 acres of soybeans,” said Howie Mercer, FarmLink marketing adviser in southeastern Saskatchewan, referring to the acreage of his farmer clients.

“We can’t get the yield out of them. Eight to 20 bushels an acre…. We seed them too early and the ground is too cold. And we don’t get the rains when we need them. Other crops have more forgiveness (than) soybeans.”

In June, Agriculture Canada pegged Saskatchewan soybean acres at 160,000, down from 400,000 in 2018 and 850,000 in 2017.

In previous years, like 2016, soybeans performed well in Saskatchewan, with growers posting yields of 35 to 40 bu. per acre.

Soybean yields will likely be decent in Saskatchewan this year because of ample rainfall in June and July.

But, as Mercer said, other crops seem to have more forgiveness for dry conditions, which is why many growers are pessimistic about soybeans right now.

Agriculture Canada research may help change that perception as plant breeders and other scientists in Ottawa try to develop soybeans more tolerant of drought stress.

Malcolm Morrison, one of the Ag Canada scientists leading the effort, said “drought stress” isn’t the correct term.

“Moisture-stress tolerance” is more accurate.

“Maybe two in 10 years, in the Prairies, you might have real drought. But I guarantee you every year in the Prairies, you’re going to have moisture stress … two to three weeks without enough moisture for plant growth,” he said from his office at the Ottawa research station.

“That’s what we’re really aiming at. Getting the plant through that period, with the least detrimental effect.”

The most critical period for soybeans is the time after flowering. If it doesn’t rain in late July and early August, soybean pods don’t fill and yield drops dramatically.

“Ten days … to 24 days after the beginning of flowering,” Morrison said. “That’s a real sensitive period.”

Morrison and his Agriculture Canada colleagues, including soybean breeder Elroy Cober, are building upon research in the United States on moisture stress in soybeans.

Tom Sinclair, a plant scientist at North Carolina State, found that one trait is critical when it comes to soybean tolerance of dry conditions.

“The trait that showed the most consistent and greatest yield advantage for soybean was enhanced drought tolerance of nitrogen fixation. This trait resulted in the greatest yield increases with virtually no risk of yield loss in wetter seasons,” Sinclair wrote in a 2010 research paper.

U.S. researchers have determined that certain breeding lines of soybeans are able to fix nitrogen for the plant, even when soil conditions are dry. That’s crucial because, for most soybeans, nitrogen fixation slows or shuts down in dry soils.

“If it doesn’t have nitrogen it doesn’t have building blocks, (like) amino acids, to develop new seeds or put protein into development of stems,” Morrison said.

“(The plant) doesn’t have the nitrogen to produce a new leaf or seed.”

Ag Canada plant breeders are using the U.S. soybean lines, which can fix nitrogen in dry soils, and crossing them with varieties used in Canada’s shorter growing season.

However, scientists don’t know which gene or genes are responsible for nitrogen fixation under moisture stress. So, they’re relying on traditional plant breeding.

While that work continues, Morrison is studying another way to improve moisture stress in soybeans.

Using an approach developed by Pioneer, for corn, Morrison is growing plots of soybeans in dryland and irrigated conditions. The objective is to identify soybean lines with excellent yield under irrigation and very good yield in dryland conditions.

A line with the smallest yield difference, between irrigated and not, likely has more tolerance for moisture stress.

“It could be better root structure, increased water movement within the cells … it doesn’t really matter. The bottom line is yield,” Morrison said.

“We are doing this with soybean here (in Ottawa). And we have shown there are lines that have superior yield under normal conditions, as well as under moisture stress conditions.”

It will take time to get moisture-stress tolerant soybeans onto the market. But that trait, alone, won’t cause a soybean boom in Saskatchewan, Morrison said.

There are other pieces to the puzzle.

“Soybean is a tropical to temperate crop. And we’re growing them in conditions that are, in Saskatchewan … very cold soils that take a long time to warm up,” he said. “The current plant we have requires warmer temperatures to establish a root system…. It’s moisture stress susceptible because it might not have an extensive root system because (of cool soils).”

There are challenges to overcome before millions of acres of soybeans are grown in Saskatchewan, but Morrison believes the problems are solvable.

Breeders and plant scientists have developed soybeans suitable for Manitoba and they can do the same for Saskatchewan.

“Ag Canada has a long history of changing (plant) adaptation to suit different (geographic) areas,” he said.

“The future is bright for soybean. It’s a great crop.”

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