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Les Henry: The ground beneath our feet

To understand soil, we must understand what is beneath it

Your fearless columnist beside the 35-foot piezometer at Spiritwood, Sask., circa 1995. photo: Courtesy Les Henry

Hang on tight — this could be a rough ride. I will take you down some very deep gopher holes and hopefully stretch your mind a bit in the process.

We are not talking about those claustrophobic tubes that run underground in places like Toronto or New York or about criminal activities. We are talking about what is beneath our feet as we walk across our land.

Most soil textbooks define soil as the surface layer of the earth down to the more or less unweathered parent material. The parent material in the Canadian Prairies is mostly what the glaciers left behind (glacial till), which in central Saskatchewan is usually 100 to 300 feet thick and as much as 1,000 feet.

As the glaciers receded, water took over with glacial lakes, streams and rivers. In some cases, wind came along and reworked the sandy deposits into dunes or silty materials into loess (pronounced luss not Lois). Much of the U.S. corn belt is loess.

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After Mother Nature did her thing for approximately 10,000 years, we now have our current soil profiles: A=topsoil, B=upper subsoil, C=subsoil. For most soils, people think of the soil profile as about four feet deep, and to many the world ends at that point.

I am sorry, Virginia, but the world does not end when your knuckles hit the ground with a four-foot soil auger.

Top down or bottom up

We think of soils as a top down affair. Geology is a bottom up business. The elixir that ties soils to geology is water.

In our thickly glaciated, pothole country, there is often an aquifer (sand and gravel) between the layers of glacial material. These are referred to as intertill aquifers. These aquifers are what many farm wells are completed in and they result in lateral movement of water over long distances.

Bottom up Shaunavon, Sask.

It is not the depth of the aquifer that counts, but the pressure the water is under in the aquifer. When the pressure in the aquifer is high enough, it forces water up slowly but surely, 24 hours a day, 365 days of the year. If the pressure in the aquifer is enough to push water near the soil surface, salinity is the result.

Our first discovery of water as the elixir was in 1982 at Shaunavon, Sask. Those with Henry’s Handbook of Soil and Water can check out page 87 for details. The actor here was the Shaunavon aquifer at 53 feet deep. The pressure was enough to push water within a few inches of soil surface in 1982.

This photo was taken in 2016. It shows the Shaunavon drill site from 1982. The salinity in the area is also evident in this air photo. photo: Supplied

A few years ago, owner Bruce Poppy sent me photos with water spilling out the top of the pipe that was three feet above ground. The pressure from beneath was the cause of the salinity. The salinity in the area is evident from the air photo.

Our advice to Bruce at that time was to plant that 20 acres down to grass and carry on farming the rest of the land. He did just that and almost 40 years later, it is still yielding some grass with no expensive inputs, no getting stuck and no white crusts to stare at. And, the piezometers we installed in 1982 are still there also.

If readers want to see how the pressure level in aquifers can change over time, check out the Observation Well Network page at the Saskatchewan Water Security Agency. There are two observation wells in the Shaunavon aquifer. One is named Shaunavon, which is near the Shaunavon town, and is affected by the town use of water. The Garden Head well is away from any use and it has risen five metres since it was installed in 1966. You can bet that is affecting salinity in the area.

Top down Spiritwood, Sask.

For this example, we will go to Spiritwood, Sask., which is about a two-hour drive northwest of Saskatoon. I owned a quarter of land there for 30 years, so I am familiar with the country. My quarter was NE34 49 12W3 — six miles south and six miles west of Spiritwood.

It is at an elevation of 2,400 feet above sea level. The natural vegetation was white and black poplar and the soils are grey wooded. The grey soil has been attributed to the wooded condition and the leaching caused by the trees’ leaves. But, there is much more to it than that.

Soils and elevations at Spiritwood, Sask. photo: Supplied

Not long after I bought that quarter, Elk Point Drilling put in a farm well just a mile east of my place. The aquifer was an intertill sand and was 400 feet deep and the static level of water in the well was 200 feet. That aquifer continues on to the lower elevation of about 1,930 feet above sea level at Spiritwood.

The Spiritwood town wells flow and a few salty soils can be seen. The general area at that elevation has a combination of black and thick black soils. At an intermediate elevation, there are some grey-black soils.

The thick black soils will also have high water tables in wet cycles, and where that is true, they will yield good crops, even if rain is not timely. The water table issue was something we did not consider until recent years.

On my Spiritwood farm, there was evidence of old, shallow dug wells. When we were there with the rig in the 1990s to get five-foot undisturbed soil cores for teaching purposes, we installed a 35-foot piezometer to see where the water table was. It was at about five feet and is the reason alfalfa is such a good crop on those grey wooded soils — provided lots of phosphorus and sulphur fertilizer is used.

The water table is high simply because the 400 feet of glacial till has low permeability and water moves through it slowly. However, with the 400-foot well having a static level of 200 feet, there is a huge downward gradient. (Have I stretched your mind yet?)

In plain language, the downward movement of water carries on very slowly 24 hours a day, 365 days a year. If rain gets scarce, the water table could drop and shallow wells could go dry.

A really deep gopher hole

Hang on — we are headed down a really deep gopher hole. We will take you just a few miles east of Gardiner Dam at Diefenbaker Lake. In the late 1970s, the soil survey used part of a quarter section to do detailed soil sampling to test out the mapping.

As part of that study, Roland St. Arnaud (my MSc supervisor) did deep sampling of sloughs and found that the salts had all been leached to 20 feet. It takes a lot of water to wash salts that far down. Professional agrologist and certified crop advisor types that want to check it out, can look up Canadian Journal of Soil Science, 1979, Volume 59, pages 87-98.

I have since tied those deeply leached soils into the underground with a geologic cross section done as part of soils work we did in soil salinity days. It turns out there is no aquifer until a depth of approximately 500 feet. It is a pre-glacial aquifer (Ardkenneth Formation) and it drains to the South Saskatchewan River. The static water level is about 200 feet below surface.

That deep aquifer, with no shallow aquifer above it, is why those soils are so leached. Not far away there are shallow (approximately 50 feet) aquifers that intercept the water and move it to a slightly lower level, pinch out, pressure up and cause soil salinity.

Hydropedology, a new science

When I present such data to academic audiences, there are few believers. About 12 years ago, I started to read U.S. literature and a textbook about hydropedology — a new branch of study in soil science and hydrogeology. It was described as soil physics without the glass beads (they like to use glass beads to simplify experiments) and soil classification without the fancy names.

The father of hydropedology was Henry Lin (1965-2019). We lost him to cancer in the prime of his life at age 54. He was at Penn State University.

After that conference, I had a chance to show him the hydropedology in the environs of Saskatoon, Sask. At the time of his loss, we were working together on a formal paper of the Lake Diefenbaker site. His legacy will live on for generations in his published work.

Les Henry and Henry Lin at a conference in Saskatoon, Sask., in 2010, where we both gave talks. photo: Courtesy Les Henry

The punch line

Soils are considered to occupy the upper metre or so of planet Earth. However, soils are blockchain linked to what lies beneath them. The elixir that ties the soil to the underground is water. If we do not understand the groundwater and aquifers beneath the soil, we do not understand that soil.

I rest my case and hope I have stretched your mind a bit.

About the author

Columnist

Les Henry

J.L.(Les) Henry is a former professor and extension specialist at the University of Saskatchewan. He farms at Dundurn, Sask. He recently finished a second printing of “Henry’s Handbook of Soil and Water,” a book that mixes the basics and practical aspects of soil, fertilizer and farming. Les will cover the shipping and GST for “Grainews” readers. Simply send a cheque for $50 to Henry Perspectives, 143 Tucker Cres., Saskatoon, Sask., S7H 3H7, and he will dispatch a signed book.

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