Calcium Carbonate (Calcite/Limestone)
Calcium carbonate is the main mineral component of limestone. It is a widely used amendment to counteract soil acidity and to provide calcium for plant nutrition. Though the term “lime” may refer to different products, in agriculture it generally refers to ground limestone. Though aragonite calcium carbonate is not as readily available as limestone it does provide more benefits over limestone in the agricultural market.
Limestone, a common sedimentary rock that can be found in extensive geologic deposits, has been mostly utilized as a cementing agent, a building material, and in agriculture to improve acid soils. An agricultural liming material (ag lime) is widely defined as any substance containing calcium or magnesium and has the capability to neutralize acidity. Numerous materials can be classified as an agricultural liming material.
Ag lime is sourced from mines or quarries and typically needs to be crushed using a mechanical apparatus. The fineness of the ag lime is essential in finding out how fast it reacts with soil acidity. Smaller particle-sized limestone reacts quickly due to the larger surface area exposed to chemical reaction. Meanwhile, larger-sized particles react slower but provide a sustained, longer-term source of acid neutralization. The product label typically contains information about a measurement of particle size.
Clay is among the several other materials in the ag lime that will reduce its purity and decrease the acid-neutralizing capacity. The effectiveness of the ag lime is rated based on its comparison with pure calcium carbonate (CaCO₃), a value expressed as the percent calcium carbonate equivalent (CCE). Unlike in alkaline or neutral soils, the ag lime is more soluble in acid soils. The presence of CaCO₃ in soil is detected by the effervescence when you put in a strong drop of acid.
Ag lime’s main use is to elevate the pH value of acid soils and diminish the concentration of aluminum in soil solution. Substandard crop growth in acid soils largely results from an abundance of soluble aluminum, which is toxic and harmful to the root system of numerous plants. Lime will lower soluble aluminum through two reactions: CaCO₃ + H₂OICa²⁺ + 2OH⁻ + CO and Al₃ + [soluble] + 3OH – IAl(OH)₃ [insoluble]. Where Ca = calcium & Al = aluminum.
Additions of ag lime also provide valuable calcium (and possibly magnesium) for plant nutrition. Using ag lime to neutralize soil acidity has secondary benefits. These include the following:
- Increased phosphorus (P) availability
- Improved nitrogen (N) fixation by legumes
- Enhanced mineralization and nitrification of N
- Greater water use, nutrient recovery and plant performance with a healthier root
Lab testers can easily determine the quantity of ag lime required to bring a soil to a desirable pH value. Farmers usually spread the lime uniformly on the soil and then mix it through the root zone. However, neutralizing soil acidity is not done only once and needs to be repeated regularly depending on soil and environmental conditions. Most commonly, application rates are measured in tons per acre.
As one of the most widely utilized of all earth materials, limestone has many uses other than in building and construction. Its diverse applications include, but are not limited to, soil stabilization, air pollution control, soil stabilization, cosmetics, medicines, antacids, and treatment systems for drinking water and wastewater.