Study tracks irrigation timing for soybeans

OUTLOOK, Sask. — Knowing when and how much to water fababeans and soybeans are key questions for Dale Tomasiewicz.

The irrigation agronomist with Agriculture Canada is carrying out an irrigation study, and he said the answers are more complex than some might think because of differing soil moisture holding capacities and types of seasons.

Pulse crops were the theme during the annual field day at the Canada-Saskatchewan Irrigation Development Centre in Outlook July 14.

While lentils have centre stage in the province this year, dryland and irrigation production of fababeans and soybeans is slowly expanding.

Tomasiewicz’s three-year study is funded by Saskatchewan Pulse Growers. Tests have shown so far that showing that the two crops are productive under irrigated conditions.

Now in its second year, the study includes irrigation treatments that impose drought and excess moisture at various times during the season. It will help define moisture conditions that each crop is best adapted to or tolerant of for dryland and irrigation management.

“That will not only help us develop irrigation management recommendations for the crop, but it also tells us about where in the province for dryland conditions the crops are particularly adapted based on the moisture conditions throughout the province,” he said.

Admittedly, 127 millimetres of precipitation in the Outlook area during the first two weeks of July has curtailed the researcher’s mid-season drought stress, which he said is not going to happen.

“Five inches (100 millimetres) up to the first of July and five inches (100 mm) since the first of July and we’re only on the 14th.”

He said the plentiful rain is good for reducing the need for irrigation, but it has negative effects, including patchy lodging in fababeans.

But since the study has seven different moisture treatment plots with two varieties for each, Tomasiewicz doesn’t expect all of them to work out every year.

“So far from last year and this year’s work it doesn’t look like our excess moisture, at least visibly, is having any negative effect,” he said. “I think the reality is both of these crops are fairly tolerant of excess moisture unless it gets to the point of actual poor drainage where they’re sitting in saturated soil.”

Compared to other annual crops, fababeans and soybeans will use about 50 more mm of moisture by the end of the year because of their longer growing seasons.

“It’s the duration of the canopy and the length of the season that you have to keep it watered that’s the big difference,” he said.

“Keep in mind that water use in a day in September is not the same as water use in a day in early July. If it hits 25 degrees on the 10th of September your water use is going to be much less than 25 degrees on the 10th of July because the day is just so much shorter.”

He said pulses need some en-couragement during their development because they tend to stay green into September and run into problems with frost.

“You definitely want the crop to rely on the stored sub-soil moisture for that last period to try and en-courage it along to maturity and generally at that stage of the season there is a good rooting system in there,” he said.

Because soybeans and fababeans are both later maturing, Tomasiewicz said they are concerned about a heavy frost occurring in late August.

“That’s happened in the past in Manitoba, for example, where you’d have the acreages increasing a lot and then they’d have a setback like an early frost and it would go down,” he said.

However, he said breeding efforts are helping to lesson those worries.

“When we get that heavy August frost it’s going to be a setback for things, but I think the (newer) varieties are getting good enough that it won’t kill the whole crop,” he said.

“People will still recognize that there is still potential.”

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