Agricultural lime is a common material used in farming and gardening to improve soil conditions. The answer to whether this material contributes calcium to the soil is yes. This rock-derived soil amendment serves as a direct source of calcium for plants. Its use corrects soil imbalances and supports healthy plant growth.
The Chemical Composition of Agricultural Lime
Agricultural lime is essentially ground limestone, a rock formed primarily of calcium carbonate. The term “lime” refers to this crushed material, not the caustic chemical calcium oxide. This composition makes lime an inherent source of calcium.
The calcium is chemically bound within the carbonate structure. When applied to the soil, the lime slowly dissolves, releasing calcium ions into the soil solution for uptake by plant roots. The purity and fineness of the ground rock determine how quickly this calcium is released.
Lime’s Primary Function: Adjusting Soil Acidity
While lime supplies calcium, its primary purpose in agriculture is modifying the soil’s acid-alkaline balance, known as pH. Many soils become acidic over time due to rainfall leaching basic minerals and the use of certain fertilizers. When soil pH drops too low, typically below 5.5, it becomes detrimental to plant health.
In acidic soil environments, the availability of major nutrients like phosphorus, magnesium, and calcium is reduced. Low pH also increases the solubility of elements like aluminum, which becomes toxic to crop roots. Liming is the direct method used to counteract these negative effects.
The neutralizing action comes from the carbonate component of the agricultural lime. This component reacts with the excess hydrogen ions that cause acidity in the soil. The chemical reaction captures the acid ions, forming water and carbon dioxide, which raises the soil’s pH level.
By raising the pH, lime reduces the concentration of toxic aluminum and improves the uptake efficiency of other nutrients. The ability of lime to stabilize soil pH is a more significant agronomic benefit than the direct calcium addition alone. This modification creates a soil environment where plants can access nutrients more freely.
Calcitic Versus Dolomitic Lime
Agricultural lime is categorized into two main types based on mineral content: calcitic and dolomitic. Calcitic lime, sometimes called high-calcium lime, is composed predominantly of calcium carbonate. This type is preferred when a soil test indicates a need for pH adjustment and calcium, but the soil’s magnesium level is adequate.
Dolomitic lime is derived from rock that contains significant magnesium carbonate in addition to calcium carbonate. This makes it a dual-purpose amendment, supplying both calcium and magnesium. A grower selects dolomitic lime if the soil test reveals both low pH and a magnesium deficiency.
Both types are equally effective at neutralizing soil acidity, but the choice depends on the specific nutrient profile of the soil. Applying dolomitic lime unnecessarily to soil with high magnesium levels can lead to a nutrient imbalance. Therefore, a current soil analysis is necessary to determine the correct product.
Alternatives for Soil Calcium Supplementation
There are situations where soil calcium levels are low, but the soil pH is already optimal or too high. Adding agricultural lime would over-correct the pH, potentially causing new nutrient availability problems. A different amendment is needed to provide calcium without significantly altering the soil’s acid-alkaline balance.
The most common alternative for calcium delivery is gypsum, which is calcium sulfate. Unlike lime, gypsum is a neutral salt and does not contain the carbonate component necessary to neutralize acidity. When gypsum dissolves, it releases calcium ions and sulfate ions, providing two beneficial nutrients without affecting the pH.
Gypsum is a good choice for improving the physical structure of certain soils, particularly those with high sodium content, where the calcium helps improve water infiltration. Other calcium sources include calcium chloride and calcium nitrate, though these are typically more expensive and can increase the soil’s salt content. Using a non-pH-altering calcium source ensures that a nutrient deficiency can be addressed without compromising the existing soil chemistry balance.