How does calcium remediate pH problems associated with an acid subsoil?
Soils can be acid or alkaline. Acid soils occur where there has been a lot of rainfall over the centuries. Acid soils are highly weathered, and many minerals and bases have been leached. Alkaline soils develop in arid areas that lack rainfall. Alkaline soils can be managed but not corrected. Acid soils can be neutralized with lime.
Growers apply lime to neutralize or raise pH. They generally apply enough lime to raise pH to 6.2 to 6.5 for a period of 4 years and then reapply. Neutralizing pH only targets the top 6 to 8 inches of soil and does nothing for the subsoil that can still be acid. Acidity, particularly when below 5.5, reduces nutrient solubility while increasing solubility of aluminum and iron, which can be damaging for growing root tips. While gypsum can’t increase the pH of acid subsoils, in can reduce aluminum toxicity in these same soils.
If acid neutralization is the goal, then lime is the material of choice. However lime is not very soluble or mobile in the soil. Therefore, neutralizing acid subsoils requires incorporation and deep mixing in the subsoil. This is not something that most farmers can easily or cost-effectively accomplish. Gypsum is more soluble and mobile in a shorter time frame and will leach into the subsoil by irrigation or rainfall.
In acid subsoils, soluble aluminum is toxic to plant roots and causes root pruning. Calcium will displace aluminum, allowing it to be leached below the rooting depths as long as there is enough moisture to draw it downwards. The more calcium that leaches through the subsoil, the more aluminum is leached. Lime can do the same in the topsoil but not the subsoil.
Gypsum is calcium sulfate, and lime is calcium carbonate. Both are soil amendments, and both provide calcium that can be used to displace excess aluminum in acid subsoil. However, only gypsum is soluble enough to move quickly down into the subsoil, and you can see the benefits in a few months. Lime is less soluble and can take 18 months to move down and give the same benefit as gypsum.
Calcium plays a crucial role in addressing pH problems in acid subsoils. While lime (calcium carbonate) is commonly used to neutralize acidic soils, its effectiveness is limited to the top 6-8 inches of soil due to its low solubility. Lime works by raising the soil pH, but it can take up to 18 months for it to move deep enough to impact the subsoil. In comparison, gypsum (calcium sulfate) is more soluble and can move deeper into the soil profile much faster, especially with the help of rainfall or irrigation.
When gypsum is applied to acid subsoils, it dissolves more quickly than lime, releasing calcium ions that displace toxic aluminum ions. Aluminium toxicity in acid soils is a major issue, as it causes root pruning and stunted plant growth. By displacing aluminium, calcium helps to prevent this toxicity, allowing plants to develop healthier roots. The benefits of gypsum can be seen within a few months, as calcium works its way deeper into the soil profile, leaching aluminum below the root zone. This makes gypsum a preferred solution for remediating pH problems in acid subsoils, especially in areas where rapid improvements are needed.
Gypsum is particularly effective in improving acid subsoils, as it dissolves faster than lime, releasing calcium ions that displace toxic aluminum ions. In acidic soils, aluminum toxicity can severely stunt plant growth by damaging roots, causing root pruning, and limiting nutrient uptake. When gypsum is applied, the calcium displaces these harmful aluminum ions, allowing plants to grow healthier roots and develop more robust plants. The benefits of gypsum are often visible within a few months, as the calcium works its way deeper into the soil, leaching aluminum below the root zone. This rapid action makes gypsum an ideal choice for correcting pH imbalances in acid subsoils, especially when quick improvements are needed for optimal crop growth.
