Les Henry: On salty ground

We’ve come full circle in the soil salinity cycle

This well data can be interpreted as a 30-year net cumulative drought from 1975 to 2005.

This topic was not on the to-do list for this winter. Soil salinity is a very hot topic right now and many farmers are concerned they will have no land to farm if it carries on like this.

The last time I remember such concern about soil salinity was during the late 1970s and early ’80s. We started the research program in 1982 at the University of Saskatchewan, where we would go out to actual farms to drill holes until we knew what was happening.

In this piece, we will talk about what we learned at that time and how we have come full circle in the cycle. I bought my Dundurn farm in 1993 and have witnessed one complete soil salinity cycle “down on the farm.”

What is soil salinity?

Soil salinity is actually a water problem, not a soil problem. Saline soils are very fertile (i.e. lots of plant nutrients). Salty soils often occur as small patches within a normal, annual crop field. With big equipment, it is much easier to go through those patches than around. If you have variable rate fertilizer capability, the first prescription is to completely cut the fertilizer application from the salty ground.

If there is no variable rate capability, then fertilizer is poured in each year but little, if any, of the nutrients are hauled off the field. The result is a continuous build-up of nutrients.

The fundamental problem with salty soil is the excess salt increases the osmotic pressure of the soil solution such that a plant root cannot take up nutrients. For the most part, it is not a toxicity problem but an osmotic problem.

What makes soil salty in the first place

Our precious sun is responsible. The process driving soil salinization is evaporation greater than precipitation when the water table is close to the soil surface. That means there is more water leaving the soil surface than is entering by precipitation.

A water table means all soil pores are full of water. The water table is the water level in a shallow dug or bored well in an unconfined surficial aquifer.

Now it is time to do some thinking. Think, think, think. If evaporation exceeds precipitation, how in the world does the water table remain close to the surface? For that to happen, there must be water continually replenishing the water table even in times of drought. If there is no water coming up from below, the water table drops and a well will go dry.

In most cases, that water is delivered to the soil surface from an aquifer with sufficient pressure to deliver water to, or above, the soil surface. If it is above the soil surface that is a flowing well.

The upward movement of water continues 24 hours a day, 365 days of the year, and in some cases, has been going on for thousands of years. To understand the process, we must think in terms of great depth over a long period of time.

The water in the aquifer need not be salty. It is the concentration by evaporation that leads to the soil salinity at the surface. The saline soils west of Radisson, Sask., are caused by discharge from the Fielding Aquifer, with salt content not much greater than the South Saskatchewan River.

How to fix salty soil, drainage plus leaching

The fix for salty soils has been known since at least 1935. We must install tile drains and then make sure there is enough water to flush the salts down and away. Drainage and leaching are the only real fix.

The “enough water” part in most of Saskatchewan and southern Alberta means irrigation. The Canada-Saskatchewan Irrigation Development Centre at Outlook, Sask., installed tile drainage on a small, problem field with a linear sprinkler setup. They monitored the soil and water leaving the site in great detail.

Barley would barely grow on that field in 1986 when the project started. They poured gobs of water on in the fall each year after the barley crop was off. By 1990 salt-sensitive pulse crops were growing on land that had been white crusts, kochia and Russian thistle in 1986. Readers with Henry’s Handbook can check out page 97 for details.

Thanks to a long-time experiment conducted by Agvise Laboratories in North Dakota, we now have a pretty decent answer for farmers in Manitoba with rainfall in the 18- to 20-inch range each year.

To be successful, the soils must be on the sandy side and, even then, the desalinization takes place mostly in the surface soil. During dry years, the salts sneak up again, but if enough wet years come along, salts will flush down. The North Dakota experiment carried on for 17 years and that was the experience. Thanks, again, to John Lee of Agvise Labs for sharing that data with me over the past 10 years or so.

The other fly in the ointment is there must be some acceptable place to dump the salty water. Much easier said than done.

Leaching alone

In the 1980s, we did a leaching-only experiment at the U of S Goodale Research Farm. Pages 94 and 95 of Henry’s Handbook provide a completely illustrated story of that project.

We actually used the water from the flowing well of the aquifer that was causing the problem in the first place. It worked swimmingly for the first few years. When I took bureaucrats out to see what we were doing, they were amazed and suggested we immediately upscale the garden patch experiment to a field scale.

The water table was very near the soil surface and we were adding 700 pounds per acre of salt for every inch of irrigation water. As long as we were pouring on the water we grew some great crops. But I shut the whole thing down. How many times have you heard someone say, “Give me more money and in a few years we will have the solution to your problem,” but it does not happen.

It did not take long to realize that in the long term this experiment would fail unless we installed tile drainage and had someplace to dump the salty water. The installation of the tile drainage would be a simple matter; however, we were already at the low point in the landscape and with no reasonable place to dump the water. The extra water needed to do the leaching would bring the water table to the soil surface and the salts would have no place to go.

Turning bad news into good news

The fundamental problem is the osmotic pressure caused by the salts, which prevents the plant from taking up water. Plants vary greatly in their abilities to suck up some water, even with the high-salt concentration.

Coping with most serious soil salinity problems means the production of salt-tolerant forage crops, mostly grasses. The kicker in the past has been most salt-tolerant grasses were not great as a cattle feed. We now have AC Saltlander green wheatgrass, which is very salt tolerant and also a good cattle feed. Thanks to Harold Steppuhn and the Swift Current Research and Development Centre for this great advance. It is a game changer for sure.

For salty patches on the Dundurn farm, I am in the process of establishing a stand of AC Saltlander. By this fall, I may have something to report. In the meantime, I have learned patience and a good mower are important requirements in establishing a grass stand.

With a good, salt-tolerant grass stand, the salty acres can produce some income and you stop pouring expensive inputs down a rathole. Many losing acres can produce a bit of profit. Many farmers are already doing it with good success.

Cycles, cycles, cycles

As the decades fly by (now eight for me), there is more appreciation of Mother Nature’s cycles. What goes around comes around is the common saying. I bought my Dundurn farm just south of Saskatoon in 1993 and have now experienced first-hand one cycle. The land is hilly glacial till with sloughs and stones. Patches of soil salinity are common in that general area.

The mid-1990s were the start of zero till. Neighbours who had farmed there for decades concluded that with the conversion to zero till and the abolishment of summerfallow, soil salinity mostly went away. For the most part, it did. However, we cannot take all the credit. Mother Nature intervened big time.

On a salty patch near the road, I dug a nine-foot hole in 2005 to see where the water table was. To my surprise, that nine-foot hole was dry. Hmmmmmm. The book says salty soils have high water tables. What’s up, Doc?

The net cumulative dry years allowed the water table to drop big time. On May 3, 2005, we seeded peas and could plant right through that area, no problem. Seedbed moisture was excellent as was subsoil moisture. From May 1 to July 3 we had 8.4 inches of rain. Nice gentle rains, well spaced out and with significant amounts. Ideal rains to wash down the salts and with the water table down, it was no problem. That salty patch produced a fair crop of peas. Herbicides worked well so the crop was clean.

The field yield that year was 57 bushels per acre of peas — net sold bushels. The salty patch did not yield 57 bu./ac., but it was acceptable. I often joked that I could show that peas were fairly salt tolerant, if I picked the right data.

Check out the graph on page 18, which shows a continuous record of water levels in a shallow observation well (i.e. the water table) from 1967 to 2020. During the 30-year time period from 1975-2005, the water table trended downward with a couple of spikes at about 10-year intervals. I interpret that data to show a net cumulative drought from 1975 to 2005.

At my Dundurn farm from 1995 to 2005, we spent a lot of time staring at the sky looking for rain. Then came 2005 with a big snow job, 2010 with 20 inches of rain and 2013 was another big snow year. “Irrigation” crops without the pivot were common. Starting in 2015, we have had some dry years but good crops because of soil moisture and high water tables from previous wet years. Water table data suggests the party may soon be over.

The punch line: The cycles continue

Wet years in the early 1970s raised water tables and when the dry cycle started the white crusts of soil salinity were “in your face.” Even white, eroded knolls were being diagnosed as saline. The white colour was just lime from the subsoil exposed by erosion.

“Soil salinity is taking over the farm and we must do something about it” was the consensus. In 1982, we started the salt patrol at U of S to go out on individual farms and determine what the real cause was. At many sites, we were able to use old air photos to show that soil salinity had been present and “in your face” before. During the wet cycle, the salts are dissolved and not visible. As soon as it starts to dry up, they turn white and are in your face for all to see.

So, here we are in 2021, right back where we were in the early 1980s.

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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