Finding the source of soil salinity

How the problem came to be will determine how to deal with it in the field

Managing soil salinity might have a lot to do with how the problem started.

Attendees to a Brandon soil fertility update Jan. 30-31, one of several to run through Manitoba in the last month, were told to consider how old the salinity problem is before making a plan of attack.

“Salinity is not a soil problem. Salinity is a water problem,” Manitoba Agriculture farm production adviser Lionel Kaskiw said.

That problem might not appear as bad in wet years, Kaskiw said, but that same excess moisture can wick salts to the surface and raises the water table, leaving salts in the upper soil after water drops again or evaporates.

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A drop of hydrochloric acid solution, and the resulting fizz as it reacts with soil carbonates, may help diagnose if salinity is a recent problem or as old as the last ice age, both Kaskiw and Manitoba Agriculture agri-ecosystems specialist Mitchell Timmerman said.

“The reason to do the fizz test is to see at what depth carbonates are detected and that gives a clue, it’s not a test for soluble salts, but it gives a clue, as to what’s been happening with water movements since the glaciers left and then what are the implications for the water table bringing soluble salts higher in the profile, into the root profile which would then affect crop growth,” Timmerman said.

While both types of salinity will have soil salts close to the surface, long-term salinity will also have carbonates in the topsoil.

“Over the last 8,000 to 10,000 years, water has had difficulty moving down, if at all,” Timmerman said. “That means the carbonates haven’t moved down, so when I take that dilute acid and test it near the surface, I find fizz.”

In well-drained or imperfectly drained soils, where the water table fluctuates, that reaction will happen deeper in the soil.

The acid test alone does not certify there’s a salinity problem, Timmerman stressed, although it might be a red flag for producers.

“If there’s enough of a water problem, crop production’s already going to be affected, but we could then decide to, for instance, collect samples, have it tested for salinity at the lab,” he said.

Soils that are fighting salinity but have only deep carbonates hint that the land was once well drained — with water moving carbonates properly through the soil profile — but that something has changed in the last decades.

The existence of a B horizon, or subsoil, may offer another clue. Long-term salinity soils will not be fully developed and will have no B horizon, the room heard. Recent salinity, however, will show three developed soil horizons, another indication that the soil was once well drained.

“The carbonates are being found deeper in the profile, there’s a B horizon, and yet there are salts? It’s probably because of some change like road building, removal of vegetation, tillage, annual crop production that changes the hydrology such that the salts come up, but the carbonates don’t,” Timmerman said.

Famers have few options to deal with long-term salinity, mostly limited to returning the land to its natural vegetation or turning to salt-tolerant plants. Kaskiw cautioned, however, that salt tolerant does not mean an affinity with salts, and while plants can grow, they might not grow as well as they would in non-saline areas.

More recent salinity, however, comes with more hope of undoing the damage.

Strategic cropping and drainage can help manage water and drag salts farther into the earth, Kaskiw said. Some producers have turned to deep-rooted crops like tillage radish or perennial forage to jump-start infiltration.

Tile drainage has also been known to lower salinity, Kaskiw told attendees, pointing to Agvise data that showed a steady decline across 10 sampling sites between 2002 and 2011 after tile drainage was installed. Salts dropped in both the topsoil and the subsoil, the laboratory reported, but noted that subsoil levels stayed high until after salts in topsoil had leached.

Kaskiw suggested that partial tile draining in problem areas, such as low areas in the rolling terrain common in western Manitoba, might help producers cut salinity cost.

“Be skeptical of quick fixes… you may hear about adding chemicals or (that) a different commercial fertilizer or soil conditioner is going to improve the salinity,” he said. “Make sure if you’re going to try something like that, test it. Leave a spot. Try it in one spot. See if you’re going to see any advantages to it.”

About the author

Reporter

Alexis Stockford

Alexis Stockford is a journalist and photographer with the Manitoba Co-operator. She previously reported with the Morden Times and was news editor of  campus newspaper, The Omega, at Thompson Rivers University in Kamloops, BC. She grew up on a mixed farm near Miami, Man.

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