What Causes Low pH Soils in Western Canada?

Date: February 17, 2025

Low soil pH can reduce crop yields, limit the availability of nutrients, and even increase the toxicity of certain elements. Understanding the processes behind soil acidification can help you manage and mitigate its effects. Here’s a breakdown of the causes of low pH.

Regional Variability in Low pH Soils Across Western Canada

Low pH soils are not uniformly distributed across Western Canada. Variability in soil types, rainfall, and farming practices means that areas in Alberta, Saskatchewan, and Manitoba each face unique challenges when it comes to soil acidification.

Alberta: Low pH soils are often concentrated in regions with sandy or lighter-textured soils. These areas are more prone to leaching and nutrient loss, which accelerates acidification.
Saskatchewan: The northern and central parts of the province, where rainfall is higher, are more likely to experience soil acidification. Soils in these regions often have lower natural buffering capacities.
Manitoba: Acidification hotspots are commonly found in areas with intensive crop production and high fertilizer usage, particularly in the Red River Valley.

For more information: Grainnews – Les Henry: Geography of acid soils in the Prairie provinces

Natural Causes of Soil Acidification

Rainfall and Carbonic Acid Formation

Rainwater is naturally slightly acidic because it dissolves carbon dioxide (CO₂) from the atmosphere to form carbonic acid. The carbonic acid breaks down into bicarbonate and hydrogen ions (H⁺). While the bicarbonates leach away, the hydrogen ions remain in the soil, making it more acidic.
Over time, areas with higher rainfall experience more acidification because of this process.

Acid Rain

Acid rain from industrial emissions has significantly decreased over recent decades, making it less of a concern for soil acidification. (Source: Grain News)
These industrial emissions contain sulfuric and nitric acids, which can intensify the natural acidification process, especially in areas downwind of industrial activity.

Soil Composition and Aluminum (Al³⁺) Release

When soil pH drops below 5.5, aluminum naturally present in the soil starts to break down from minerals like feldspar and mica.
This process releases more hydrogen ions into the soil, further lowering the pH. It becomes a chain reaction: the more aluminum is released, the more acidic the soil becomes.

Human-Induced Causes of Acidification

Nitrogen Fertilizers

Many nitrogen-based fertilizers, such as ammonium nitrate, ammonium sulfate, and monoammonium phosphate (MAP), release hydrogen ions during their conversion in the soil.
This is part of the nitrogen cycle, where microbes convert ammonium into nitrate, releasing acidity in the process.

Crop Removal

Crops take up nutrients like calcium, magnesium, and potassium, which act as natural buffers against acidity.
When these crops are harvested, the buffering capacity of the soil decreases, causing the pH to drop over time.

Intensive Farming Practices

Repeated cultivation of high-yield crops without replenishing lost nutrients can accelerate acidification.
Over-reliance on chemical fertilizers without balancing organic matter input can further upset the soil pH balance.

Manure and Organic Decomposition

Manure and organic residues can have dual effects on soil pH. While some residues produce organic acids that contribute to soil acidity, properly managed manure and organic matter can improve low pH soils by buffering acidity and adding essential nutrients like calcium and magnesium.
Applying manure strategically can help counteract acidification, especially when paired with other soil health practices.

Take Action to Improve Your Low pH Soils

Curious about how to address low pH on your farm? Learn more about how H-Start can help improve soil health and productivity. Contact Us to learn more.