Agricultural lime does not contain a significant amount of nitrogen. This soil amendment is primarily used to alter soil chemistry, not to supply a major nutrient like nitrogen. Lime is typically derived from pulverized limestone or chalk, which are rocks composed of specific mineral compounds.
The Primary Components of Agricultural Lime
Agricultural lime is composed almost entirely of minerals that lack nitrogen. The most common form is calcitic limestone, which is predominantly calcium carbonate (CaCO3). The chemical formula shows the presence of Calcium (Ca), Carbon (C), and Oxygen (O), with no Nitrogen (N).
Another widely used type is dolomitic limestone, which contains both calcium carbonate and magnesium carbonate (MgCO3). This form introduces Magnesium (Mg), but nitrogen is absent from the core chemical structure. Other forms, such as quicklime (calcium oxide) or hydrated lime (calcium hydroxide), are also nitrogen-free, confirming that lime’s composition is centered on alkaline earth metals and carbonates.
Lime’s Function in Soil Chemistry
The main purpose of applying lime to soil is to modify the soil’s chemistry by raising its pH. Many agricultural soils become acidic over time due to natural processes, rainfall, and the use of certain fertilizers. Lime works as a base, neutralizing the hydrogen ions that cause acidity and reducing the harmful effects of low pH.
This adjustment controls the availability of other nutrients already present in the soil. When the soil pH is too low, essential nutrients like Phosphorus and Potassium can become locked up and unavailable for plant uptake. Increasing the pH improves the solubility and accessibility of these nutrients. Furthermore, lime serves as a source of the secondary nutrients Calcium and Magnesium, which are necessary for plant cell wall strength and photosynthesis.
Nitrogen Sources in Soil
Nitrogen is a primary macronutrient, required in large amounts for processes like protein and chlorophyll synthesis. Plants absorb nitrogen from the soil primarily in the inorganic forms of ammonium (NH4+) and nitrate (NO3-).
Nitrogen must be introduced through other means to support plant growth. The most direct way to supply nitrogen is through synthetic fertilizers, such as urea or ammonium nitrate. Nitrogen is also naturally introduced through the decomposition of organic matter, like animal manure and compost, where soil microbes break down organic compounds into plant-available inorganic forms. Another process involves specialized bacteria, often associated with legume roots, that can “fix” atmospheric nitrogen gas (N2) into forms plants can use. Nitrogen management relies on these separate inputs and biological processes, which are distinct from the pH-adjusting role of lime.