Dolomitic lime

Dolomitic lime is ground from dolomite rock, a carbonate mineral containing both calcium and magnesium. Its neutralising value and the fineness of the grind determine how effectively and quickly it raises soil pH, and the exact calcium and magnesium content varies with the source deposit.

Mineral composition

Calcium magnesium carbonate, CaMg(CO₃)₂

Nutrients

Both calcium and magnesium, in proportions set by the deposit

Reaction speed

Slower than calcitic lime; finer grinding speeds the reaction

Effect on soil pH

Neutralises acidity, raising soil pH

As dolomitic lime reacts with soil acidity, its carbonate neutralises hydrogen ions and raises pH, while releasing calcium and magnesium onto the soil exchange complex. The magnesium contribution is what sets it apart from calcitic lime, addressing a common deficiency on acid, sandy soils.

• Neutralises soil acidity and raises pH over time
• Supplies both calcium and magnesium as it reacts
• Improves the availability of some nutrients as pH moves toward the optimal range

Dolomitic lime is applied to raise the pH of acid soils that also need magnesium, and it is typically incorporated ahead of planting because it reacts slowly and moves little in the soil. Because it acts gradually, it is usually applied well in advance of the crop that will benefit.

• Chosen over calcitic lime where the soil is both acid and magnesium-deficient
• Best incorporated and applied ahead of the season to allow time to react
• Finer grades react faster but are more expensive to spread

Because it reacts more slowly than calcitic lime, dolomitic lime is less suited to situations needing a rapid pH change. Over-applying it, or using it where magnesium is already high, can push the calcium-to-magnesium balance in a direction that impairs uptake of other cations such as potassium.