Lime vs Gypsum: Understanding the Right Soil Amendment for Your Fields
Farmers often face the question: should I apply lime or gypsum?
Understanding the differences is essential for pH management, soil structure improvement, and nutrient availability.
Both amendments contain calcium, but their mechanisms and effects differ:
| Amendment | pH Effect | Primary Function | Secondary Benefits | Use Cases |
|---|---|---|---|---|
| Lime | Neutralizes acidity | Raises pH | Supplies Ca, Mg (if dolomitic) | Acidic soils, pH-sensitive crops |
| Gypsum | Improves soil structure | Minimal | Supplies Ca, improves infiltration, displaces Na | Sodic soils, compacted soils, high Na soils |
Table 1. Key differences between lime and gypsum as soil amendments.
How Lime Works
Lime reacts chemically with hydrogen and aluminum ions in the soil:
- Raises soil pH
- Reduces exchangeable acidity
- Supplies calcium (and magnesium if dolomitic)
Key Considerations
- Requires lab testing: buffer pH, exchangeable acidity
- Reaction is slower in coarse or high-clay soils
- Effectiveness depends on CCE and particle size
How Gypsum Works
Gypsum primarily improves soil physical properties rather than pH:
- Adds soluble calcium without raising pH
- Displaces sodium in sodic soils
- Improves aggregation and water infiltration
- Supports deeper rooting and nutrient uptake
Key Considerations
- Best for sodic, compacted, or heavy clay soils
- Does not neutralize acidity
- Can be used in combination with lime for acidic sodic soils
Practical Decision Guide
| Soil Condition | Recommended Amendment | Notes |
|---|---|---|
| Acidic (pH < 6) | Lime | Adjust pH, supply Ca |
| Sodic/Na-affected | Gypsum | Improve structure, leach sodium |
| Acidic + Sodic | Lime + Gypsum | Lime corrects pH; gypsum improves structure |
| Compacted clay | Gypsum | Enhances water infiltration and root growth |
| High Mg deficit | Dolomitic lime | Supplies both Ca and Mg |
Table 2. Choosing between lime and gypsum based on soil conditions.
Application Tips
- Timing: Apply lime several months before planting to allow pH adjustment; gypsum can be applied anytime, preferably before intensive cultivation.
- Rate: Determine lime rate based on buffer pH or exchangeable acidity. Use our **Soil liming rate calculator by Growing Farm **for accurate calculations. gypsum rate depends on sodium content and soil structure goals.
- Tillage: Lime requires good incorporation; gypsum works both on the surface and incorporated.
- Combination Strategy: In acidic sodic soils, apply lime first to correct pH, then gypsum to enhance soil structure and calcium availability.
Monitoring and Follow-Up
- Re-test soil pH after 6–12 months when lime is applied.
- Monitor soil infiltration and sodium levels when using gypsum.
- Adjust future applications based on crop response and soil testing trends.
Conclusion
Lime and gypsum are complementary but not interchangeable.
- Use lime to correct acidity and provide calcium (and magnesium if dolomitic).
- Use gypsum to improve soil structure, water movement, and displace sodium.
- Soil tests are essential to decide which amendment — or combination — will maximize crop productivity and soil health.
For detailed guidance on lime application rates, see:
Adjusting Soil pH with Lime: Materials, Rates, and Tillage
Optimize Your Soil Management
Decide between lime and gypsum based on soil tests, crop needs, and field conditions
