Use Gypsum to Amend High Sodium Soils

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06 0709 Use Gypsum - MAIN

In parts of eastern Ontario, on certain soils, tile drains don’t work. To drain excess water, farmers traditionally have ditches every 60 or 70 feet. “That’s all right with small equipment, but the first thing new European farmers do when they arrive is take out the fences, level the fields off and put in tile drains. But those tile drains don’t work,” says Bob Dalton, Agr., an independent crop consultant based in Gatineau, Quebec.

“The soils are not too bad when they’re dry, but with a little bit of moisture, like an inch of rain, the soil on top gets quite hard. It’s extremely difficult to get a probe in, and pulling it out is just as difficult. And it’s not very pleasant for the farmer to work with. He needs lots of horsepower.”

Dalton says when he was hired by some farmers in the area, he took soil tests and came back with some interesting results.

“Nobody was paying attention to sodium levels. In fact, they were rarely included in any soil tests. Magnesium levels were up too, but when you throw in the sodium, then you’ve got something a little unusual,” says Dalton.

In certain conditions, where soil tests indicate high sodium and magnesium levels, this agronomist says addition of gypsum can improve the soil significantly

“The first thing I did was have Senior Agri-Coach Doug Penney look at them. He zeroed in on the sodium and magnesium levels. With the sodium and magnesium, when the soil gets wet, they
swell up, no air passes through and no water can pass through, so it doesn’t get down to the tile drains. In wet years, you’d have a tile drain with nothing coming out, yet the fields were quite wet.”

Something else caught Dalton’s eye. When taking the soil samples and driving across a wet field, the grower said he wouldn’t have any problem crossing the field with his Jeep.

“When you’ve got water splashing up on you in this country, that usually means you’re up to your axles in mud. When I got out of that wet spot and looked back, I thought it was kind of strange. I hadn’t made any ruts. I got out and looked and there wasn’t any ruts. That was another clue that there is high magnesium, high sodium or both. It’s like cement,” he says.“In my case, it’s not coming from the soil surface. It’s an old sea bed – in eastern Ontario they call it the Alfred Bog and anything around Prescott County has it coming up from below.”

Penney suggested trying gypsum as a soil amendment. Gypsum is a soft mineral composed of calcium sulfate dihydrate.

Dalton says he wants to both increase the amount of calcium in the soil and decrease the magnesium and sodium levels. When the amendment is applied to the soil, calcium is released and the sulfate from the gypsum attaches to the sodium first. If it can’t find sodium, it will attach to magnesium.

“Both are highly soluble materials and we want them to move out the tile drains and off the field. The only problem is, there’s about 24 inches from the soil surface down to the tile drain,” says Dalton.

Experience with farmers on some of this land has shown him that as little as two inches of soil with high sodium and magnesium levels will stop water from flowing through to the drainage tiles.

“What we had to do to get more efficient removal of the sodium and/or magnesium was provide easy access down to the tile drain. So what we’ve started to do is open the soil above the tile
drain, use a certain sized stone plus gypsum mixed in with it, to form a channel down to the tile drain,” says Dalton.

“On the base saturation, the bad soils will have six to 10 percent sodium and magnesium as high as 36 or 38 percent. The goal is to get the calcium as close to 65 or 70 percent as possible, get the magnesium under 20 percent and the sodium down to 0.4 or 0.5 percent.”

“In a lot of the soil tests I look at, sodium is down around 0.2 or 0.1 percent, until you hit that Alfred Bog.”

Dalton is still experimenting, trying to find out how much gypsum it’s going to take to get the land amended sufficiently.

“I started out with one tonne per acre, because it was costing $70/tonne to bring in. I’ve got one client persuaded to try even higher rates across some fields, to see what works best,” he says.

Farmers in his area broadcast apply the gypsum with a lime spreader. He says it’s an extremely fine product, but there’s no dust because it’s quite moist. Dalton says gypsum is water-soluble and an application, even without incorporation on no-till land, moves through the soil.

“You see results down six to eight inches in no-till, very quickly. It should be worked in, but on some of the fields it wasn’t and I didn’t see any difference between fields where it was worked in and fields where it wasn’t worked in.”

Dalton says that in some of the areas where he has trenches dug down to the drainage tiles, magnesium and sodium levels in the soil two feet below the surface are extremely high. He thinks
those farmers will have the best luck amending the top foot of soil and working with that.

“When you’re down around 20 to 24 inches, the magnesium and sodium levels are so high, I don’t know how you’d ever get enough gypsum on to amend it,” he says.

“If we can get the top 12 inches half decently amended and have an opening where the water can quickly get out whenever it’s there, then it will be fine. Maybe apply gypsum every few years across the field, or closer to the holes, when they need it. It will be something that has to be done every so many years is how I’m looking at it.”

Selenite, satin spar, desert rose, and gypsum flower are four varieties of gypsum

Dalton says in parts of western Canada, problems sometimes occur with irrigation, when there’s high sodium levels in the water and the land tightens up.

“I understand in Michigan, they have high sodium soils, and in Australia – we don’t have anything close to high sodium soils, compared to what they sometimes have to deal with. I showed some Australians my soil test and said I start with one tonne per acre of gypsum. They said they start at 2.5 tonnes per acre,” he says.

Dalton says he’s heard that at the Toronto airport, before building the runways they mixed clay and magnesium to make a firm base. And during the Second World War, to build runways for Air Force training bases in western Canada, magnesium was mixed into the soil rather than using pavement.

Dalton would prefer to see the gypsum applications made in July, when the soil is relatively dry. He likes to see it worked in fairly deep, rather than a shallow working or left as a surface application.

While electricity in his area mostly comes from hydro dams, Dalton says in areas like western Canada, with coal-generated electricity, gypsum can be a by-product of flue gas desulfurization at these power plants and may be available at a reasonable price.

“Even when it’s wet, this soil is extremely hard. It’s worse than a golf ball. But you put some gypsum on that hard ball of soil and it turns into nice crumbles,” he says.

“These soils are beautiful soils, once they’ve been amended. You increase the calcium content, bring the sodium and magnesium down, it’s a nice fine soil that makes a nice seedbed.”

About the Author
Bill Strautman

Bill Strautman is an ag journalist with more than three decades of experience in the western Canadian agriculture industry. Originally from a mixed farm in north-west Saskatchewan, Bill has lived and worked in all three prairie provinces.

He currently owns a fifth-generation century farm east of North Battleford.

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