Recent wet and dry cycles have increased topsoil salinity in many parts of the Prairies over the past few years.
“Salinity is not a salt problem, it’s a water problem,” says Marla Riekman, soil management specialist with Manitoba Agriculture and Resource Development. “Wet years bring the water table closer to the roots, and salinity wicks up to the soil surface.”
If this wicking action and evaporation of surface water exceeds the downward movement of water – or “infiltration” – from rainfall or irrigation for significant periods of time, the result is increased salinity.
“This becomes especially noticeable when saline-susceptible crops are grown in those areas,” Riekman says. “If we didn’t have plants susceptible to soil salinity, we wouldn’t have a salinity problem.”
In general, pulses, sunflowers and soybeans are more susceptible. Canola is quite a bit more tolerant, but not as tolerant as cereals. Forage grasses like wild rye and some wheat grasses are the best choices for areas with very high salinity.
Farmers can ask for electrical conductivity (EC) tests with their soil samples as a test of salinity, but farmers do not usually take soil samples from saline areas. Probably the best way to identify these areas is visually. “Farmers will often know where their saline areas are because they’re full of foxtail barley and kochia,” Riekman says.
What to do with saline patches?
The first thing to do is stop wasting fertilizer in those areas where crop growth is chronically poor due to salinity. Second, consider steps to improve the situation. Growers have some options.
Tile drainage in saline patches will lower the water table. “Tile drainage is one thing that can actually fix salinity,” Riekman says, but notes it can take a decade or more to see major improvement unless you also have irrigation to increase water infiltration.
Another way to manage saline patches is to seed them to perennials that are saline tolerant or that root deeply to use up a lot of that excess water that can bring salts to the surface. AC Saltlander, for example, is a wheatgrass variety with exceptional salt tolerance. (See the table.)
Riekman says a strip of perennial forage in saline-prone areas around sloughs or along roadways can actually work to treat the area and contain the size of the saline patch. Keys to success, she says, are to leave these areas in perennial forage for the long term and choose species with good feed value.
Riekman says that letting the weeds work for you could be a low-cost management option. “Mow them, don’t spray them, so they stay in a vegetative state but don’t set seed.” She adds that kochia has very good feed value.
But you have to be careful that weeds don’t set seed – especially kochia which is Group-2 and potentially Group-9 resistant – and then spread those seeds through the rest of the field. The better choice for salinity and herbicide/weed stewardship is to use forage species to manage salinity and out-compete the herbicide-resistant weeds that also thrive in those saline patches.
Finally, definitely stop tilling saline patches. Tillage encourages evaporation that brings up even more salt through capillary action. You can also decrease evaporation by placing mulch, manure or straw over the saline patches, but Riekman says this is a less effective solution in the long term.
Ian Epp is an agronomy specialist with the Canola Council of Canada. Email firstname.lastname@example.org. This canola management tip is brought to you by canolawatch.org, a collaboration of the Canola Council, SaskCanola, Alberta Canola and Manitoba Canola Growers.