I.  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.

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. 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.

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.

"Hi-Cal" Lime. A term widely used 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 and calcitic limestones would be considered "hi-cal" aglimes.

III.  Factors Affecting the Reactivity of Lime

1. Purity is expressed as %

2. Fineness is based on mesh size

Mesh size	Reactivity
Coarser than 20 mesh	very little effect after 18 months
30-60	took 6-18 months to neutralize the acidity that was neutralized in 1 month by 80 mesh
100	reacts very rapidly

3. Neutralizing Value of Different Liming Materials

	Material	CaCO3 equivalent
Calcite	CaCO3	100
Dolomite	CaCO3 MgCO3	109
Hydrated	Ca(OH)2	136
Burned	CaO	179

*M.W. = Molecular Weight

Example using Ca(OH)2

4. Degree of Mixing and Reaction Time

Lime is very insoluble, therefore, it needs to be mixed throughout the root zone. If the recommended amount of limestone is properly mixed with the soil, planting may follow without delay because enough fine particles are present in limestone to raise soil pH immediately above toxic Al and Mn levels and to correct a Ca deficiency. In the past it was recommended that limestone be applied 2 to 3 months prior to planting. Because of improved tillage equipment for incorporating limestone and improved limestone quality this recommendation is no longer necessary. When limestone is properly incorporated into the soil, liming may be done anytime between the harvesting of one crop and the planting of the next.

Click on graph to enlarge

Click on graph to enlarge

Click on graph to enlarge

IV.  Effectiveness of Surface Liming For No-Till Fields and Pastures

In 1985 a study was initiated at Penn State to look at the effects of surface application of lime on a very acid, long-term no-till soil. Since 1977 this field had been in no-till corn production with no limestone applied. The initial pH of "plow layer" was 5.1 and the surface 2 inch pH was 4.5. The limestone recommendation, based on the SMP buffer pH and a target pH of 6.5, was 6000 lb calcium carbonate equivalent (CCE) per acre. The study included four limestone rates (0, 3000, 6000, 9000 lb CCE/A) and liming programs ranging from applying lime every year to once every five years. Each year the soil was sampled in the spring in 2 inch increments to a depth of 6 inches. No-till corn was grown from 1985 to 1991, no-till soybeans were grown in 1992 and 1993, oats was grown in 1994 and wheat in 1995 and corn in 1996, 1997 and 1998.

Soil pH results from soil samples taken in the spring of each year from 1985 through 1994 for selected liming programs are given in Figures 1 and 2. The soil pH results for the 6000 lb/A, every third year liming program are shown in Figure 1. This treatment was chosen for illustration because this would be the recommended limestone rate based on a plow depth soil sample and this frequency of liming is fairly common in many areas. The pH results in Figure 2 are from the every year, 3000 lb/A liming program. The every year program is of interest because there has been speculation that more frequent smaller applications of limestone may be necessary in no-till. Several observations can be made based on these results. First, it is clear that the recommended limestone application changed the soil pH in the surface 2 inches within the first year after application. Soil pH measurements taken within the first year indicated that most of the pH change in the surface layer occurred within the first two months after spring liming. This rapid increase at the surface was expected since this was a high quality finely ground limestone with 90% passing a 100 mesh sieve. Although the 0 to 2 inch layer was not subdivided for routine pH determination, spot checks of pH in this layer indicated that most of the pH change was in the surface 1/2 inch. However, there was little change in the soil pH below the surface 2 inches until about the fourth year of the study following subsequent limestone applications. Even after 9 years the soil pH in the 2 to 6 inch layers has not yet reached the target pH of 6.5 that was achieved rather quickly in the surface layer. There is little apparent difference between the standard, every third year liming program, and the more frequent every year liming program.

Figure 1.

Soil pH vs time for a no-till soil limed at 6000 lb/A every third year

Figure 2.

Soil pH vs time for a no-till soil limed at 6000 lb/A initially and then every year since 1987 at 3000 lb/A.

These pH effects from the liming treatments resulted in slight but generally insignificant increases in corn yield. The greatest yield response was in the wheat crop in 1995. Some negative responses were observed in the years when soybeans were the plots. However, it was speculated that this was due to compaction from the liming operation especially in the more frequent liming programs. A triazine weed control treatment was included in the early years of this study. This work showed that the initial liming which only affected the pH at the soil surface did improve the efficacy of the triazine herbicides. Similar to the effect observed with the triazine activity, there were significant effects on plant tissue concentrations immediately after liming even though the pH effect from the lime was limited to the soil surface. These plant nutrient effects were a significant increase in calcium and a decrease in manganese. From this work it was concluded that surface application of limestone will rapidly change the soil pH at the surface of the soil. It was also observed that even this shallow pH improvement could affect herbicide activity and nutrient availability. A second major conclusion is that a very long time is required to have much effect on the soil pH below the surface 2 inches in no-till crop production. Finally, there seems to be little justification for more frequent liming in no-till systems.

Thus, the current recommendation is that where possible on a very acid soil, limestone should be incorporated to adjust the soil pH to the desired level in the entire plow layer before no-till crop production in initiated. Other work has shown that if the soil pH is in the desired range to begin with, it can be maintained by surface applications of limestone in no-till systems. Thus, if a regular liming program is followed and soil pH is not allowed to drop to very low levels further incorporation of limestone should not be necessary. Where incorporation is not possible there are beneficial effects of surface application of limestone to acid no-till soils even though the immediate effect will only be near the soil surface. Also, with surface liming the standard every three year or so liming program based on a regular soil testing program should be adequate.

Prepared by:
Douglas B. Beegle, Professor of Agronomy
Department of Agronomy
Penn State University

V.  Individual State Lime Laws

NOTE: Each state has its own lime laws. Although the intent of the following text is to discuss the properties of common lime materials, some of the definitions are dependent on Florida state laws. Lime laws for some states can be found at the following links:

	South Carolina Lime Laws
		South Carolina Rules, Regulations and Standards
		For a comprehensive list of SC Fertilizer & Lime Law Links.
	Georgia Lime Code
	Alabama Lime Laws

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