Red Rock, Half a Mile Down

More than half a mile under the prairie of Saskatchewan, Canada, machines cut red rock out of the floor of a sea that dried up more than 380 million years ago, long before the first dinosaurs. The rock is potash, and most of the potash used in the United States comes from here.

Fertilizer sounds like something made in a factory, and some of it is. Nitrogen fertilizer is made from nitrogen in the air. Potash cannot be made at all.

It carries potassium, one of the three nutrients crops use most, and potassium is a chemical element. Chemistry can rearrange elements, but it cannot create them. Every pound has to be found in nature, dug out of old seabeds or drawn from salty water.

What comes up the shaft is red rock, a mix of potash and ordinary rock salt, and only about a third of it is potash. A mill on the surface strips out the salt and leaves potash, sold as red, pink or white grains.

Every bag of fertilizer lists three numbers, for nitrogen, phosphate and potash, in that order. A bag of straight potash, for example, reads 0-0-60.

The name comes from "pot ashes." Plants draw potassium from the soil, so wood ashes hold some of it. The old way to get it out was to soak the ashes in water and boil the water off in iron pots. The first patent the United States ever issued, signed by George Washington in 1790, was for a process for doing it.

A shallow sea once spread across what is now western Canada. A reef grew across its mouth and slowed the flow of ocean water into it. The sea evaporated faster than the ocean could refill it, and the water left behind grew saltier and saltier, laying down bed after bed of rock salt.

As seawater dries up, its salts come out in turn. Rock salt starts once about 90 percent of the water is gone. Potash comes out only at the very end, once about 95 percent is gone.

Those beds run from Alberta across Saskatchewan into North Dakota and Montana. Near Saskatoon they lie about 3,300 feet down. They sink deeper to the south, to about 5,200 feet near Regina and deeper still across the border.

In the 1940s, drilling for oil in Saskatchewan turned up potash instead. Reaching it took about 20 years. Between the surface and the salt lies a layer of sand soaked with water under heavy pressure, 475 pounds per square inch or more, more than 30 times the pressure of the air at sea level. When miners dug shafts through it, water poured in.

One company dug for nine years before water burst in at about 1,800 feet. To get through, miners froze the wet sand solid around the shaft and dug down through the frozen ground.

Even frozen ground leaked. The first mine started producing in 1958 but had to stop within a year when water seeped into its shaft. Not until 1962 did a mine run without stopping. That mine, too, fought leaking water for more than 30 years, until its owner moved to newer shafts nearby in 2021.

Below ground, machines cut long rooms through the potash, about 16 feet high at one mine, leaving pillars of potash standing between them to support the rock above. Conveyor belts carry the ore to the shaft and up more than half a mile to the mill.

Nutrien runs six mines in Saskatchewan. More and more, its cutting machines are steered by remote control or run on their own, and the company says it mined 49 percent of its potash ore with automation in 2025.

Canada mines nearly a third of the world's potash, more than any other country. Russia, China and Belarus follow, and together the four mine about three-quarters of it.

The United States mines little potash of its own, mostly in southeastern New Mexico. Near Moab, Utah, potash dissolved deep underground is pumped up as brine into ponds dyed blue to soak up more sunlight.

The trip south starts on a train. Nutrien says most of its potash for North American customers goes by rail, to about 370 distribution points it owns or leases. The railroads CN and CPKC both haul potash out of Saskatchewan, and CPKC says the potash it carries for North American buyers goes mainly to the US Midwest, for use on farms there.

At the end of the line, farmers spread potash on their fields. Inside a plant, potassium does many jobs, and the picture below numbers four of them. It helps open and close the tiny pores on the leaves, speeds sugars through the plant, strengthens stalks against falling over and disease, and helps roots grow so the plant holds up through dry spells. A corn plant that runs short shows it first on its lower leaves, which turn yellow and then die along their edges.

Soil holds plenty of potassium, but most of it is locked inside minerals that plants cannot use. Every harvest carries more away. A good soybean crop takes about 70 pounds of potash an acre out of the ground, and a big corn crop nearly 50.

More potash is on the way. The mining company BHP is building a new mine east of Saskatoon and says the first stage is 87 percent complete, on track to produce in mid-2027, though building it is costing more than expected.

The United States relies on imports for about 92 percent of its potash, most of it from Canada. Potash returned to the federal list of critical minerals last year, and when Washington put 50 percent tariffs on many Canadian goods this summer, the White House said potash would be left out. Tariffs on Canada have shifted several times this year and may shift again.

None of that changes the chemistry. "No substitutes exist for potassium as an essential plant nutrient," the US Geological Survey says. The potash on a Midwestern field this fall most likely came out of a sea that dried up more than 380 million years ago and lies today beneath the Saskatchewan prairie.

Anthony

The Luniter Observatory

Nutrien (NTR), CN (CNI) and CPKC (CP) are among the 200 companies Luniter follows.

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