Dolomite lime is a naturally occurring mineral compound composed of calcium magnesium carbonate used as a soil amendment by gardeners and farmers. It is a type of agricultural lime derived from dolomitic limestone, which contains significant amounts of both calcium and magnesium carbonates. The primary function of this finely ground material is to improve soil conditions, mainly by correcting soil acidity and supplying two essential plant nutrients.
How Dolomite Lime Adjusts Soil Acidity
Soil acidity is measured by pH; a value below 7 indicates acidic conditions that limit plant growth and nutrient availability. When soil pH is too low, typically below 5.5, many nutrients become inaccessible for plant uptake. Acidic soil also increases the solubility of toxic elements like aluminum and manganese, which can harm plant roots and stunt development.
Dolomite lime neutralizes acidity through a chemical reaction involving its carbonate component. When applied, the calcium carbonate and magnesium carbonate react with hydrogen ions present in the soil water. This reaction removes the hydrogen ions, the source of acidity, and replaces them with calcium and magnesium ions.
This exchange raises the soil pH toward a neutral range (6.0 to 7.0), which is optimal for most cultivated plants. Dolomite lime is distinct from calcitic lime (regular agricultural lime) because calcitic lime primarily contains calcium carbonate and is used when only calcium is needed. While both types are effective at raising pH, dolomite lime offers the added benefit of supplying magnesium. The effectiveness of the lime is influenced by how finely the rock is ground.
The Role of Calcium and Magnesium Supply
The secondary function of dolomite lime is supplying two secondary macronutrients directly to the soil: calcium and magnesium. These elements are incorporated into plant structure and metabolic processes, supporting overall health and development. Dolomite lime is often selected specifically when a soil test indicates a deficiency in both of these nutrients.
Calcium maintains the structural integrity of plant cell walls. It is important for healthy root development and is involved in enzyme activation and signaling within the plant. A lack of calcium can lead to issues like blossom end rot in fruits such as tomatoes and peppers.
Magnesium is a component of the chlorophyll molecule, the pigment responsible for capturing sunlight during photosynthesis. Without sufficient magnesium, a plant cannot produce chlorophyll efficiently, leading to reduced energy production and yellowing of the leaves. Dolomite lime provides this nutrient, which is often leached out of sandy or highly acidic soils.
Practical Guidance for Application
Before applying dolomite lime, conduct a comprehensive soil test to determine the current pH level and nutrient concentration. Guessing the soil’s needs can be detrimental, as applying lime unnecessarily can raise the pH too high and cause other nutrients, such as phosphorus or iron, to become unavailable to plants. A laboratory soil analysis will provide specific recommendations on the type and quantity of lime required for the soil type and target crops.
The application rate depends on the soil’s texture, initial pH, and the desired pH change. For instance, sandy soils generally require less lime to adjust the pH than heavy clay soils. The results from the soil test dictate the precise amount to use, preventing the issue of over-liming.
Dolomite lime should be spread evenly over the soil surface and incorporated into the top four to six inches of the soil profile for the best results. This mechanical mixing is important because lime does not move downward through the soil very quickly. Applying the lime in the fall or well in advance of the growing season allows sufficient time for it to dissolve and react fully, a process that can take several months for complete pH correction.