Souris River silt serves up free fertility

Farmers soil testing in the wake of floods have found the silt left behind contained 
surprisingly high levels of nutrients, including phosphorus and potassium

It appears there’s one upside from flooding — silt.

After the deluge from the Souris River dried up, staff at the Westman Agricultural Diversification Organization (WADO) wanted to know what effect the flood had on research plots that were completely under water last summer.

Soil tests of what appeared to be dark-coloured sand near the bridge on the creek that runs behind the main building yielded surprising results — the silt contained more nutrients than samples taken from other parts of the farm.

“You can’t assume that just because it looks like something from a distance, that’s what it is,” John Heard, a soil fertility specialist with Manitoba Agriculture, Food and Rural Initiatives, said in a presentation at the annual WADO field day.

“Some of this silt is bringing more nutrients to the farm than what it had to begin with. It’s not much of an impediment — I don’t know how we charge you for it.”

For farmers left in a similar situation, Heard advises them to stop speculating and start soil testing.

“We have science. Science is a tool. Simply measure it,” he said.

Testing found that the samples containing 91 per cent sand also had 1.6 per cent organic matter, 16 parts per million phosphorus, 250 ppm potassium, and a pH of 7.3.

The flat, rented land that is home to the WADO research plots on the south side of Melita looks uniform, but dramatic differences were uncovered by soil testing at depths down to two feet post-flood, said manager Scott Day.

Nitrogen levels varied from 60 pounds of available nitrogen to just 18 pounds in some spots.

On his own farm north of Deloraine, soil tests found an abundance of crop nutrients left over after last year’s washout, he added.

“All the fields were extremely high in nitrogen and all nutrients, actually,” said Day.

Many of his neighbours “took a leap of faith” and opted to skip fertilizer this spring after some tests showed up to 200 pounds of available N on high ground outside of the river valley.

On the other hand, some farmers eager to cash in on high grain prices “poured on the coal” to boost yields.

“I know some people who sowed their crops with no fertilizer this year and it looks just as good as any other,” said Day. “It will be really interesting at harvest.”

On the edges of the WADO plots, provincial weed specialist Nasir Shaikh found some less encouraging detritus possibly brought in by the flood — what may be herbicide-resistant weeds.

Shaikh’s bouquet included giant ragweed, Canada fleabane and kochia — the first, second and third glyphosate-resistant weeds discovered in Canada, respectively.

“We have to be very careful,” he said. “A lot of growers are using glyphosate year after year after year — and that creates selection pressure for creating weeds that have glyphosate resistance. We could lose that chemistry forever.”

Shaikh added that after last year’s very wet spring then very dry summer, many growers have been left with issues related to Group 2 herbicide residues that are damaging this year’s crops.

Group 14 herbicides such as Reflex and Authority are also very persistent in the soil, and may cause injury to consecutive crops, he added.

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