A few years back we predicted that the super wet years would lead to a marked increase in soil salinity. It is now happening.
In this piece I am not going to talk about Solonetzic soils or true Alkali (high pH , low salts) soils. I’m talking only about saline soils — soils that have too much salt and are waterlogged. Soil salinity is really not a soil problem but a water problem. Saline soils are often high in organic matter and loaded with nutrients.
Cause of soil salinity
There is only one fundamental cause of soil salinity: a high water table and conditions where evaporation exceeds precipitation. Now, before reading on stop and think. If evaporation exceeds precipitation how can a high water table be maintained?
To maintain a high water table in dry spells there must be water movement underground.
In areas of thin glacial deposits over salty bedrock shale side-hill seeps can form. The “tight” shale prevents downward movement of water and horizontal movement leads to side hill seeps. Southern Alberta and Montana have such conditions.
But in many areas of Western Canada the most common cause of soil salinity is artesian discharge from aquifers that can be shallow (50 feet or less) or deep (100 feet or more). One such aquifer is the Shaunavon aquifer in southwest Saskatchewan. Since installation in 1967 the piezometric (pressure) level of the Garden Head observation well has risen five metres. Two metres of that rise has taken place since 2010. The current water level elevation in the Garden Head observation well is 897 MetersASL or 2,942 FASL (feet above sea level). Land that is near or below that elevation is at risk for increased salinization.
To inspect the hydrograph see www.wsask.ca. From there, Water Info/Groundwater/Observation wells. There you are presented with a long list of wells. Click the Garden Head location for the Shaunavon aquifer, or go through the list and pick a location near you to examine groundwater changes over the years.
Alberta also has an observation well network which can be found at esrd.alberta.ca.
The Manitoba observation wells are in defined aquifers that are used for irrigation or other high use and are intended to monitor impact of water extraction rather than natural cycles. To my knowledge the data is not available online. If I’m wrong I am sure a reader will correct me.
Some shallow observation wells show the water table at that location but many measure the piezometric (pressure) level in an aquifer. Henry’s Handbook of Soil and Water has diagrams that explain it all.
Cures For Soil Salinity
Cure 1: Sell it in the winter time. That might seem like a glib statement but it does happen often. In the land price crash of the early 1990s the back page of the weekly Western Producer was devoted to ads for distress lands. A scan of those ads with soil map in hand found many examples of salty soils. It was bought at high price in heady times and under the snow and sold years later at a much lower price. So, do be careful buying land under the snow — it might turn out to be the same colour in July!
Cure 2: Tile drainage and leaching. This is the only cure. Drainage alone or leaching alone does not do the job. In the brown and dark brown soil zones leaching usually means irrigation.
A few years ago a farmer near Glenboro, Manitoba asked: “Would our 18 inches of rain here in Manitoba be enough to flush the salts without irrigation?” My answer was a rather vague “maybe.”
Thanks to John Lee of Agvise Labs in North Dakota we now have a much better answer. They have monitored a tile-drained field in North Dakota since the drains were installed in 2002. The site is 25 miles west of Grand Forks, ND. The soil is sandy loam to loam texture with a pH of 7.9 to 8.2 and Organic Matter of four to 5.5 per cent.
The April to October rain at that site has averaged 17.2 inches through 2002 to 2013. The high was 22.5 inches in 2010 and the low was 13.9 inches in 2012. In 2014 John Lee sent me updated data and the following conclusions, which are taken verbatim from his Powerpoint:
- Topsoil salt levels decreased over the years as long as excessive rainfall was received.
- Several crops now produce good yields — corn, soybeans, sunflower.
- Subsoil salt levels take longer to decrease.
- High subsoil salt levels do not affect crop growth as much as high topsoil salt levels.
- Salinity stayed the same or increases in dryer years, even with tile drainage.
It seems clear that in much of the brown and dark brown soil zones of Saskatchewan and Alberta it would take a series of unusually wet years in a row to get much reclamation by tile drainage alone. With hindsight, tile drains installed in 2009 on my farm would have resulted in much leaching and removal of salts via the excess rainfall. We had five irrigation years from 2010 to 2014. Are we going to get more such years? I doubt it.
In my rolling land there is lots of grade to move water. One area about 10 acres in size could easily be tile drained via a road ditch to a natural waterway that leads eventually to Blackstrap Lake. In the process it passes through land owned by two different neighbours. I doubt very much if others care to see my salty water.
And, therein lies the rub in many cases. There may be no place to drain and if there is, who wants it?
To be sure there are areas where there is a natural outlet and the impact of the drained water would be minimal. But, caution must be used.
Before tile drains are installed it makes sense to me that a few shallow observation wells be installed to see where the water table is currently sitting. See my column in Grainews October 2015 to learn how to install such wells.
As well, the appropriate permits should be in place. A recent tile drain project just south of Melfort will, in time, give results that will take theory into practice. That project was well planned in advance with all ducks in order including appropriate permits.
I have seen demonstration projects that planted salt tolerant forage crops in a saline area to “reclaim” the land. That is not reclamation it is coping.
We used to refer to it as “management” but I think “coping” describes it better.
Planting salt tolerant crops — usually barley — does produce some crop. Canola is actually quite salt tolerant if it gets established. Bulletins describing salt tolerance of crops are available on provincial ag websites.
In the last outbreak of soil salinity in 1970s we talked a lot about continuous cropping. At that time summerfallow was almost half the acreage in Saskatchewan. The switch to continuous cropping took place at the same time as a natural desalinization was in progress. The dry years of the 1980s lowered the water tables and any rain in excess of crop use resulted in salt leaching. Continuous cropping is a plus on all fronts. It helps to “cope” with but does not “reclaim” salty ground.
In a small salty patch of mine the best crop I ever had was peas. That was in 2005 when water tables were down. Very good late May and early June rains washed the salts down far enough to support a fair pea crop.
Keeping something green whenever possible is important. I mow kochia patches before seed set in place of cultivation. And late broadcast and cultivating in of canola in sloughs will keep it green and keep down the weeds.
So, that is why I call all of the above “coping.” It is better to do those things than not do them but do not suffer under the delusion that such practices are going to “reclaim” salty ground.
Hmmm… sell it in the winter time… Maybe you can catch someone that does not read Grainews?