The primary use of gypsum (calcium sulfate) in acidic soil is not to neutralize the acidity or change the soil pH. According to the provided reference, gypsum is not acid soluble and will not change the soil pH. Instead, its benefits in acidic soils (and other soil types) relate to providing essential nutrients and improving soil structure indirectly.
Key Benefits of Gypsum in Acidic Soil
While gypsum doesn't correct acidity, it offers several valuable benefits:
- Provides Calcium: Gypsum is a source of readily available calcium (Ca). Calcium is a crucial secondary macronutrient for plant growth, essential for cell wall development, root growth, and nutrient uptake.
- Supplies Sulfate Sulfur: Gypsum also offers a readily available form of sulfate sulfur (SO₄⁻²). Sulfur is another vital secondary nutrient needed for protein synthesis, enzyme activity, and chlorophyll formation. Sulfate sulfur is a valuable secondary nutrient that benefits the soil and crop.
- Adjusts Calcium and Magnesium Balance: Gypsum helps to shift the Ca and Mg levels in soil. In some acidic soils, there might be an imbalance between calcium and magnesium. Adding gypsum can help improve the Ca:Mg ratio, which is important for healthy plant growth and nutrient availability.
- Potential for Subsoil Improvement: While not directly altering surface pH, calcium from gypsum can leach into the subsoil. In soils with subsurface acidity, this mobile calcium can help mitigate aluminum toxicity in deeper soil layers, encouraging deeper root growth.
Why Gypsum Doesn't Neutralize Acidity
Unlike liming materials such as calcium carbonate (agricultural lime), which directly react with and neutralize hydrogen ions that cause acidity, gypsum (calcium sulfate) does not have this chemical effect. Its lack of acid solubility means it cannot effectively raise the pH level of the soil.
Applying Gypsum
Gypsum can be applied using standard equipment. The reference states that gypsum can be spread with lime and litter spreaders.
Summary of Uses in Acidic Soil
Here's a quick look at what gypsum does and doesn't do in acidic soil:
| Gypsum in Acidic Soil | Effect |
|---|---|
| Soil pH | No change |
| Provides Calcium | Yes |
| Provides Sulfur | Yes |
| Balances Ca/Mg Ratio | Yes |
| Neutralizes Acidity | No |
In conclusion, while gypsum is not a substitute for liming when the goal is to raise soil pH, it is a valuable amendment for acidic soils to provide calcium and sulfur nutrients and improve calcium-magnesium balance, thereby supporting healthier plant growth.
