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Les Henry: How does ground get salty?

What causes salty ground, and a two-step process to fix the problem in your fields

After scribbling for this many years, it is no surprise that I’ll repeat the same song several times. Perhaps if I sing the song in a different tune it will resonate with more people. Salty ground is one such topic and this time I’ll try a new approach.

A few years back this column predicted that ground that stays white after the snow melts would be back to haunt us. Discussions I had with a few folks at Crop Week in Saskatoon tell me that the topic is back as top of mind for many farmers.

Sometimes folks are buying land when under the snow in winter and lo and behold, when the snow melts in the spring, the ground is still white. Ouch!

What causes salty ground?

As it turns out the big red fire in the sky — the sun — is the driving force that makes soils salty. Sounds far-fetched but read on.

The sun provides the energy to drive evaporation. The fundamental cause is the concentration of salts that occurs as the water evaporates from the surface of the ground. The water supply for evaporation comes from a water table that is too close to the soil surface. When the water table is high, wick action can deliver water to the soil surface to feed the salt concentration process.

It is a little more complicated than that — evaporation must exceed precipitation for the concentration to occur. Now, stop and think.

If evaporation exceeds precipitation then the water supply should soon dry up and the concentration process would stop. Hmmm.

To solve that conundrum we must think in 3D. To maintain a high water table there must be water moving underground to keep the high water table even in dry times.

The actual salinization is concentration by evaporation during dry cycles. It is underground water movement that maintains the supply of water to keep feeding the evaporation process.

That means that to understand soil salinity we must understand the layers beneath the soil that move the water around underground. We farm in environments affected by many glaciations that came and went over the past million or so years.

In central Saskatchewan the thickness of the glacial deposits is often 300 feet or more. And the stratigraphy (layers) can alternate between sandy deposits and glacial clayey layers. It is the sandy layers that we complete our domestic wells in and those same layers can make our soils salty.

Artesian pressure

If the sandy layer (aquifer) is near a major river or creek the water will come out as a side hill spring and water will join the river/creek and no problem.

But, if the aquifer pinches out with no underground outlet, it will pressure up to the point that a drilled well will flow. That constant upward pressure delivers water slowly but surely through the glacial clayey layer to keep the water table high even in dry periods. Voila — salty soils are the result.

While there are other mechanisms such as slough “bathtub rings” and side-hill seeps that can cause salinity — in much of the thickly glaciated terrain artesian pressure is the main culprit.

Just recently I was asked to check out a quarter section that was being purchased under the snow. All the soils and groundwater information checked out OK for that quarter. When I checked out the water well maps we made in the 1980s/90s I noticed flowing wells only a few miles away. The new SKSIS on line soil survey maps and Municipal Assessment data were checked and sure enough — the area with flowing wells did have salinity mapped.

Intertill aquifers

The culprit is often sand and gravel layers that lie between two glacial clay layers from glaciers of different age. They can be regional in extent and cover sections and sections of land as in the Dafoe Salt Flats west of the problematic Quill Lakes. Or, they can be small and very local and affect only small areas of land.

How salty is the water

We sometimes hear folks say that it is the salt water coming up by artesian discharge that makes the soil salty. Not really. It is the concentration by evaporation of over hundreds and thousands of years that does the trick. We actually have to think in 4D (geologic time as well). Upward movement can be very slow, but in time it causes soil salinity.

Weather cycles and salty ground

In the mid 1970s I pounded a lot of pavement with Earl Johnson, soils specialist extraordinaire with Saskatchewan Agriculture. The topic was often soil salinity. Earl explained to me that soil salinity can appear at the end of wet cycles. In southeast Saskatchewan in the 1950s, soil salinity was the biggest call on his time.

I have now farmed long enough (25 years) in the Allan Hills area southeast of Saskatoon (Dundurn) to experience salty ground cycles for real.

When continuous cropping and zero till became common practice in the mid 1990s we noticed that salty patches shrunk and were less of a problem. We patted ourselves on the back, but a big part of it was the dry cycle. When the wet years came roaring back from 2005 to 2014 the wet areas got bigger and salinity increased. The white crusts did not show up until the dry years 2017 and 2018 came along.

So, weather cycles play a big role in the expression of salt at the soil surface.

Fixing salty ground

The solution to salty ground has been known since at least 1935. The two steps are:

  1. Tile drainage to keep the water table from rising too near the soil surface.
  2. Irrigation or enough natural rainfall to flush the salts out through the drains.

To see a report that shows how it is done and how much water it takes type “Reclamation of a saline irrigated field using subsurface drainage” into Google and click on “Archived Content…”

Thanks to John Lee of Agvise Labs in North Dakota, we now have a better answer for what rain is needed in a rain fed situation. He has a site in North Dakota where tile drains were installed 17 years ago and he has been measuring the soil salt each year since. He recently sent me the latest update and I will show readers that data in a future article.

That site gets an average of about 18 inches of rain per year (April to October). In years when rain is low, the salts tend to creep back up but over time it has been successful.

When someone talks about “reclaiming” a salty soil, drainage and leaching is the only real answer. What is technically possible may not be legally possible if there is no suitable outlet to deliver the salty water to. That varies by province so make sure you know your situation before spending money.

Living with salty ground

If the salty area is large enough and can be managed as separate field the best bet is to plant it down to a salt-tolerant grass for forage. But salty areas often occur in patches that are hard to separate and plant to grass.

Bare ground is the enemy so do everything possible to keep something growing. There are young folks working on new plant species to help keep a cover. I look forward to learning more about that in the near future.

One salt patch I deal with grows a fair stand of kochia. It is ugly to look at but we must resist the urge to dig out the cultivator or spray it out. I go out with a mower in July, before it sets seed, and mow it down. Sometimes a second mowing is necessary. That keeps something growing and prevents the kochia from spreading through the whole field.

If you have a quarter section that is a real pig and hard to make money on, the best bet is to sell it in the winter. That is only partly tongue in cheek. I regularly check out “Land For Sale” in weekly papers and other places and see it all the time.

If you are buying land under snow get some advice from someone who knows how to read a soil map, and in Saskatchewan knows how to read a Municipal Assessment report (samaview.ca, on line).

About the author

Columnist

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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