Salt is secretly sapping prairie soils and along with it the Canadian economy.
Secret soil salinity, which lies hidden in the crop’s root zone, affects 22.25 million acres of prairie farmland, according to Agriculture Canada.
Assuming those fields were planted to traditional cereal and oilseed crops, the problem would cost the Canadian economy as much as $400 million annually.
An additional 3.7 million acres of prairie farmland are white and crusty. On that land, the costs are even higher.
When average crop yields are calculated at 30 bushels per acre and returns from those fields are assigned at $185 per tonne, the value of crops grown with average yields and below average prices is $3.4 billion.
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Harold Steppuhn, an agricultural engineer at the Agriculture Canada research centre in Swift Current, Sask., said yields on the secretly salty acres are at least 12 percent below average.
Based on those figures, salinity annually costs western Canadian agriculture about $408 million. Steppuhn’s estimates are in line with United States Department of Agriculture research data.
Despite this, less than $300,000 per year is spent on research into Canadian agricultural soil salinity.
Each one percent increase in yield on those farmed acres would return $34 million in additional revenue, said Steppuhn.
He told agrologists attending the Saskatchewan Soil Conservation Association’s Crop Adviser Workshop in Saskatoon on Dec. 2, that new research and agricultural extension training could reduce the effects of salinity by as much as four percent annually. That could add up to $136 million more for prairie agriculture, even in a poorly priced crop year.
Garry Lawrence of Rosetown, Sask., has seen the problem on his farm.
“We got a combine yield monitor in 1996 and started seeing something we couldn’t explain. Yield would drop off suddenly in a field for no reason.”
Lawrence said even after applying more fertilizer to those areas they couldn’t explain continued lower than expected yields.
Salinity was the culprit.
“It wasn’t salt that you could see always. But it was in the root zone of the crop,” he said.
Steppuhn said the problem develops when dissolved solids in water available to plants, mainly sulfate, chloride and carbonate salts, exceed what the plants can use.
The salt deposits come from ancient seas that once covered the region. Glacier movement spread some of the surface deposits around and in some cases blended them into silt.
Other salts pooled on impermeable clay layers and were then covered with soil.
When moisture in the soil reaches these often hidden salt deposits, the salts dissolve and the water pools on the clay.
This is where salt begins its migration toward the soil surface. The water evaporates or is taken up by plants and the salt is deposited into the cropping root zone.
Salinity can pollute surface and ground water and cause subsurface water to collect, bogging down farm implements, said Steppuhn.
He said mildly saline areas of a field might be found by a thinning of crop and the salt tolerant weeds that begin to dominate the area.
“By the time you find the weeds, you may already be in the worst of it. If you begin measuring crop height in the surrounding area, it likely gets taller as you move away from the weedy spot,” he said.
Planting salt-tolerant crops helps break the saline cycle of moisture travelling down and salt coming up.
When crops use the available, seasonal moisture for growth, in some cases that can sever the moisture connection to the saltier water.
Some salt-tolerant crops such as alfalfa can absorb salt and carry it away in the forage harvest, eventually reducing the amount in the root zone. But often there is more salt in the soil than the plants can carry.
Drainage strategies that draw water into specific areas and wash the salt downward toward a mechanical drain or pool it into an area where salt-tolerant crops are planted can reduce the damage in the surrounding field.
This is one of the most effective management techniques and can be enhanced by adding snow fences to collect water for rinsing.
Irrigation is also effective and in some cases either adding deep tillage or ceasing tillage may aid in breaking the salinity cycle.
The Lawrence farm has chosen to plant saline areas with barley and canaryseed rather than wheat and to use minimal tillage and continuous cropping to keep excess subsurface moisture from collecting.
Steppuhn said producers don’t have to eliminate salt but they do have to keep it out of the root zone.
“I’m sure some of the best methods of dealing with salinity have yet to be fully developed. But that takes research money and that is in short supply,” he said.
