613 Tight Soils – Sodacity, Salinity, and Alkali Explained

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#RealisticRegenAg | White patches in a field are often referred to as alkali patches. The underlying problem may be high pH – alkalinity – but the salt in and of itself is not at a high pH and therefore is not alkaline. When you see salt on the surface it is more properly called salinity. The reason for this is that alkalinity may or may not be there. If present it may be near the surface or it may be deeper down.

Compounding on this, alkalinity may not be present. Excess sodium cations – not excess sodium salts – could be the cause. Finally, just because you don’t see salt on the surface doesn’t mean salinity is not the problem. Regular soil testing helps to see these problems developing before they visibly manifest themselves.

Huge amounts of money are spent trying to fix these patches with products or practices that either don’t work or make it worse. Even if someone is not trying to fix it, they may be putting down fertilizer and seed every year with the hope of getting something, only to be disappointed at harvest time. Digging deeper – literally – and doing the proper tests will help you diagnose and decide. In this episode I’ll give an overview of how I approach this and why it is critical you get solid advice from a Certified Crop Advisor (CCA) or Professional Agrologist (P.Ag) that truly understands this issue.

Welcome to the sixth season of Plants Dig Soil, a podcast about #RealisticRegenAg. I’m your host, Scott Gillespie. I’m an author and independent agronomist from the Western Canadian Prairies specializing in Climate-Smart Agriculture. I focus on scientifically proven practices that benefit the planet and, just as importantly, farmers' economic sustainability. Be sure to visit my website, www.plantsdigsoil.com, to learn about my book “Practical Regeneration” and for services I that I offer for farmers and agribusiness.

Resources mentioned:
https://open.alberta.ca/publications/5333889
https://openpress.usask.ca/soilscience/chapter/soil-chemistry/
https://www.topcropmanager.com/solonetzic-soils-more-compact-more-complex-21506/
https://www.pioneer.com/us/agronomy/Base-Saturation-Cation-Exchange-Capacity.html

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Let’s start with salinity. When we see salts on the surface this is because they were once dissolved in water. Once the water is gone all that remains are the salts. Saline patches will always be in the lowest part of the landscape or where water gets pushed back up to the surface through underground flows. In periods of high rainfall, the water table moves higher, and you may see water stay in these areas for extended periods. Since it has nowhere to go it slowly evaporates off. Any salts that were dissolved in it end up sticking around.

Under regular rainfall the salts will keep getting washed down. However, if they can’t get very deep in the soil, they will get stuck a few feet or metres down. This will impede plant growth because the salts prevent the roots from taking up water. When it’s a few feet down it will affect plant growth later in the season because they can’t rely on the deep water. Since they don’t use this salty water it’s more likely water will accumulate here in the off season, which raises the water table, dissolving salts, then depositing them when it evaporates.

There are no magic cures for salinity. The only way to get rid of excess salts is to lower the water table and flush them down. If you can get them deeper than the root zone, they will be fine there as long as you can keep the water table low.

Where trees naturally grow, they can be used to help draw down the water and keep it from recharging. In my area of the prairies trees do not grow well.  Perennial forages or native grasses with deep roots are the best tool for lowering the water table here. These species don’t have to be salt tolerant. They can work from the area nearby – the recharge area – and help to prevent water from moving underground to the discharge area – the saline area. This is a fix that takes many years or decades to work. Salt tolerant species, like AC Saltlander, can help the change happen faster by starting closer to, or right inside, the more saline areas.

Tile drainage can be used instead of, or in conjunction with, the use of plants. This can work if you have a place for the water to go and you are permitted to put this water there. Since saline areas are usually at the lowest point in the landscape this makes it challenging to find a place for the water to go. Please check the regulations first. You cannot just start draining water without permission. You would not want an upslope neighbour improving their land but helping water bypass onto yours. Show the same respect for those downslope from you.

In the past clay tiles were used. They were small sections of pipe laid underground. The water seeped in between the sections and would get channeled away. Growing up on a farm in Ontario I recall having to do some work with dad and brothers on old clay tiles. They were installed early in the last century and while many still worked, some got clogged with sand and made underground springs in the middle of fields.

Whether clay or plastic, the pipe must decline towards a place that the water can drain into. Usually, multiple runs of pipe run into a header pipe that directs all the water to the drainage area.

Tile can work faster than plants, but it still takes a few years from installation for the salts to fully flush out with repeated rain or irrigation events. Once flushed out the tiles continue to keep the water table below the rooting zone. Combining plants and pipe can expedite the process. The plants pump excess water out at the recharge area and the pipes flush the salts away and keep the water table low in the lower area.

The place where it may not work is if you are dealing with sodic soils. These are soils so tight that water does not flow through them well. Tile could be installed, but the water will still be impeded from flowing. This is because sodic soil has no structure. It is a soil with too many sodium cations. This is not sodium salt. This is sodium that causes clay and organic matter to collapse, sealing the soil from water flow.

A tougher beast is a solonetzic soil. This is a soil that has a saline layer over a sodic layer. This is incorrectly referred to as an alkali patch in the common usage of the term. So, what is an alkali patch? An alkali patch in the technical definition is a soil with a high pH. In fact, these are very likely solonetzic soils. They are sodic soils that are below the surface, impeding water flow due to high sodium cations, causing salts, usually made up of sodium salt, to accumulate on the surface when the water evaporates. Sodium salts affect plants by not allowing them to take up water. Sodium cations affect water by not allowing it to move through the soil.

This is where an agronomist who understands all of this is critical. Too many times I see people applying products or amendments that are not going to help. In some cases, they may temporarily relieve the symptoms and appear to work but if the underlying issue is not dealt with the money is wasted. Well, not wasted, because the person that sold the product still makes their money. In other cases, what is added may make the problem worse.

When you have soil like this the key is soil testing. You need to get samples at different layers, and you need to compare the problem area to a good area. They must be sent to a lab that has a test for the Sodium Adsorption Ratio (SAR) or the Exchangeable Sodium Percentage (ESP). An Electrical Conductivity (EC) test tells us salt levels and a test of free lime and pH tells us the level of alkalinity. With these numbers a proper diagnosis can be completed.

While some labs calculate base saturation ratios (BSR), this is unnecessary. There is a direct correlation between the BSR and pH, which we already have. BSR’s are also a poor predictor of the underlying sodium problem. The SAR ratio (Sodium Adsorption Ratio) correctly puts a number to the severity of the problem and helps guide the type and quantity of amendment needed.

If free lime is present (high pH - alkalinity) then an acidic amendment such as elemental sulfur (low pH) will often be the solution. It frees up calcium to displace the sodium. If free lime is not present, then gypsum is usually needed to add calcium to displace the sodium. In both cases – adding elemental sulfur or adding gypsum – you still need to flush the sodium out with water. This takes many years to do, and it needs a place to go. If you can only affect the surface layer but the underlying layer is still tight you haven’t achieved anything.

When the layers are shallow and the salinity or sodacity (or both) is not severe there are options such as manure, compost, deep ripping, deep plowing, or a combination of the practices. If this allows plants to establish it can be worth it. In the case of organic ammendments they can help in the short term but in time as the organic matter decays the soil can seal up again. Before trying this be sure to get a soil test. This only works if you can affect the layer that is causing the problem and it only works in mild cases of salinity or sodacity.

I think the draw of deep tillage is to be able to use very powerful tractor with a very large plow and get in there and try to fix things. I’ve seen some of these at work on YouTube. They go up to a meter deep and are often just one blade. Sometimes they have two large tractors pulling a single blade. However, mixing saline soil with sodic soil is unlikely to create good agricultural soil. It will only work if the upper layer has calcium to react with the sodium once together. Before doing this please get a soil test. You may have fun doing it, but if it doesn’t improve crop growth, what’s the point? And a final, very important note: If you do decide to do this, call before you dig. Underground pipelines and utilities are often shallower than these plows go.

There are links to the four key resources I used in creating this episode. “Solonetzic soils: more compact, more complex” is an article from Top Crop Manager that covers the basics. “Management of Sodic Soils in Alberta” is a factsheet from Alberta Agriculture that goes more in depth with some solutions that I have mentioned. Chapter 5 “Soil Chemistry” from the book “Digging Into Canadian Soils: An Introduction to Soil Science” gets very technical but is a great resource for those that really want to understand this issue.

Finally, “Base Saturation and Cation Exchange Capacity” is a resource that goes into the history and the science behind base saturation ratios. If you believe they work then I’m sure this will not sway you, but for everyone else, this helps explain how a good idea, with an initial promise, did not stand the test of time. All are free to download. Again, I’ll put links to them in the episode description.

If you’re dealing with these types of soils get a hold of me. Yes, I charge money to help you diagnose and decide on what to do with these types of soil. Charging for my advice is how I’m able to make a living and put out these free podcasts.  

I hope this helps, and I’ll talk to you again next time.