What is the Most Common Agricultural Liming Material?
The most common material used for liming agricultural soils is finely ground limestone, a material composed of varying concentrations of calcium and magnesium carbonates. Limestone has all the desired characteristics of an agricultural liming material.
Why are There so Many Confusing Terms Used When Referring to Aglime?
"Lime," "calcitic limestone," "calcite," "dolomite," "dolomitic limestone," "aragonite," "hi-cal"
all are names of aglime materials. As with any widely used material, there is considerable room for confusion. Natural materials can differ considerably in composition from one mine to the next. Technically correct definitions are frequently cumbersome, so everyday-use definitions develop which may be fine in local situations but which can cause confusion when used elsewhere. Legal definitions, as found in state aglime laws, are frequently different from one state to the next.
How About Some Definitions of Aglime Terms?
Although brief definitions are also subject to the limitations stated above, here's an attempt at clarifying some common aglime terms used in Florida.
Lime. A material which, upon reaction with the soil, increases pH (decreases soil acidity) and does not add harmful elements to the soil. Usually, lime consists of finely ground carbonates of calcium and magnesium, although the term also includes oxides and hydroxides of calcium. In Florida, the term "lime" is often incorrectly used to imply calcitic limestone exclusively.
Calcitic Limestone. A term widely used by agronomists when referring to agricultural limestone with high calcium content. It contains mainly calcium carbonate but may also contain small amounts of magnesium carbonate. The term is not as restrictive in definition as calcite. It is often used to distinguish materials of low magnesium carbonate content from those of high content, the latter being referred to as dolomitic limestone. The Florida lime law (Chapter 5E - 1.001) contains the two following specifications: (a) "Standard calcitic liming material shall contain a minimum of 86% calcium carbonate expressed as CaCO3," and (b) "Calcitic liming material shall contain a minimum of 70% calcium expressed as CaCO3."
Calcite. A mineral which occurs in nature. Pure calcite is 100% calcium carbonate (CaCO3) which is crystallized in hexagonal form. Calcite is a common constituent in calcitic limestone, dolomite, marble, chalk, marl, seashells, and similar substances. Because the mineral calcite is pure CaCO3, it is the standard by which the acid-neutralizing capability of all other liming materials is measured.
Dolomite. A mineral composed of calcium and magnesium carbonates. Pure dolomite contains 40 to 45% MgCO3 and 54 to 58% CaCO3.
Dolomitic Limestone. A material containing MgCO3 in lesser concentrations than found in dolomite. In the aglime trade, a concentration of 15 to 20% MgCO3 is common for material termed dolomitic limestone. Florida law requires that a material "contain a minimum of 36% magnesium carbonate expressed as MgCO3" in order to be sold as "standard dolomitic liming material," and "a minimum of 30% magnesium expressed as MgCO3" to be sold as "dolomitic liming material."
Aragonite. A mineral which in its pure form is 100% CaCO3. It differs from calcite in its orthorhombic crystal form. Large deposits of aragonite found in the shallow waters of the Bahamas are mined for industrial uses, including use as aglime. The Bahamian aragonite is competitive in price with other forms of aglime in many areas because it is mined by dredges, does not need grinding, and is transported by barge directly to Florida's east-coast ports.
"Hi-Cal" Lime. A term used widely in Florida to identify an agricultural limestone having a high concentration of calcium. It is usually used to distinguish the material from dolomite or dolomitic limestone. Calcite, aragonite, and calcitic limestones would all be considered "hi-cal" aglimes.
What Factors Influence Aglime Quality?
The two principal factors influencing aglime quality are:
- Its acid-neutralizing capacity.
- The fineness to which it is ground.
The acid-neutralizing capacity is usually measured as the calcium carbonate equivalent (CCE). The CCE is defined as the acid-neutralizing capacity of a liming material expressed as percent by weight of pure CaCO3. Thus, pure calcite or pure aragonite have a CCE of 100%. The fineness to which aglime is ground determines in large part the rate at which it will react in soil. As particle size decreases, aglime dissolves more rapidly and changes pH over a shorter period of time. This translates into increased yields on soils where limestone applications are needed. Particle size is such an important aspect of aglime quality that particle size specifications are part of most aglime laws. It might be noted here that limestone crushed for road-building is far too coarse to be effective in lowering agricultural soil pH, even if applied at several times the recommended aglime rate per acre.
What are Typical Calcium Carbonate Equivalents (CCE) of Some Liming Materials?
The following table presents typical CCE values of some common liming materials and the tons of each material needed to produce the same neutralizing power as one ton of pure CaCO3.
|
Typical Calcium Carbonate Equivalent (CCE) of Selected Liming Materials |
|---|
|
Liming Material | Typical CCE (%) |
Tons Required to be Equivalent
to 1.0 Ton of CaCO3 |
|---|
| Calcite (pure) | 100 | 1.0 |
| Calcitic limestone | 75 to 100 | 1.3 to 1.0 |
| Dolomitic limestone | 75 to 108 | 1.3 to 0.9 |
| Aragonite | 95 to 100 | 1.1 to 1.0 |
| Hydrated lime (Ca(OH)2) | 120 to 136 | 0.8 to 0.7 |
| Wood ash | 30 to 70 | 3.3 to 1.4 |
How is CCE Determined?
To determine CCE, a carefully weighed sample of the lime material is reacted with an acid under laboratory conditions prescribed by a standardized procedure. Based on the amount and strength of the acid consumed in the reaction the CCE can be calculated. For example, if a 1 gram sample of limestone was reacted with 50 ml of 0.5 N HCl and titrated with 0.25 N NaOH. The titration required 30 ml of 0.25 N NaOH. The calculations would be:
| %CaCO3 Equivalent | = 2.5 x (ml HCl
- ml NaOH/2)
= 2.5 x (50 - 30/2)
= 87.5 |
Is It Possible to Have a CCE Greater than 100?
Yes. When a material contains appreciable amounts of magnesium carbonate, calcium hydroxide, calcium oxide, or magnesium oxide, it will have greater neutralizing power than the same weight of calcium carbonate. This will result in a CCE greater than that of pure CaCO3, which is 100.
How is Particle Size of Aglime Measured and Expressed?
The usual testing procedure is to pass a sample through a series of standard sieves and express the results as percentage passing through, or remaining on the variously sized sieves. Sieves are typically made of wire cloth and are designated by the number of openings per linear inch (mesh) in the cloth. For example, a 60-mesh sieve has 60 openings per linear inch (i.e., 3,600 per square inch). A particle passing through a standard 60-mesh sieve would have a diameter of less than 0.0098 inch (less than 0.25 mm). Such material would have the consistency of flour. An aglime will ordinarily be composed of particles of many different sizes, ranging from very fine, dust-like particles to coarse, sand-like ones.
Factors Affecting Reactivity of Lime
South Carolina Lime Laws
South Carolina Rules, Regulations and Standards
