What is lime?

Applications of limestone demand knowledge of different types and how each reacts chemically within the coil to alter the soil pH, calcium and magnesium.

Basically, limestone contains calcium or calcium plus magnesium. Rates of application and selection of limestone type must be based on soil test data that indicates a need to adjust calcium or both calcium and magnesium. Limestone should never be applied unless a soil analysis indicates a specific need. Limestone must not be applied indiscriminately, and above all those who preach that you cannot apply too much limestone must not be believed. Recommendations as high as ten to fifteen tons per acre of specific limestone per acre have been made, often without the benefit of a soil analysis for a guide.

Two basic type of liming materials must be examined because depending upon your soil analysis; a selection must be made between them whenever you apply limestone

1.  Calcium limestone.  This liming material may also be called “calcite,” “calcareous,” “high- calcium lime “or” calcium carbonate lime.” It contains most calcium carbonate (CaCO₃) and has little if nay, magnesium. Calcium is the only cation it contains and is the reason it is often referred to as “high- calcium limestone.” Pure calcium carbonate, but for practical purposes the mined calcium carbonate can be figured at forty percent calcium.

There are several sources of calcium carbonate limestone. It is available as regular agricultural limestone in several parts of the country. Other sources include sugar beet lime, paper mill sludge and the by products from city water treatment systems. Sugar beet lime results from using powdered calcium carbonate to purify the sugar solutions during beet processing. The same lime is used in processing wood pulp into paper. Water treatment plants use this lime in their purification systems. These byproducts carry impurities usually of an organic nature that are harmless to soils and plants. As a result of their impurities their calcium levels are lower than regular limestone. They are a powdered form and are calcium carbonate whether from the beet, paper mill or water processing industries and are good sources of high calcium limestone.

Another source of calcium is marl. Marl deposits are usually fond in association with swamps or bogs and can be an excellent source of calcium carbonate. Marl must be mined and allowed to dry before it can be conditioned for spreading.

1. Dolomite limestone. Dolomite limestone contains both calcium carbonate (CaCo₃) and Magnesium carbonate (MgCO₃). It always contains more calcium than magnesium. While all limestone which contains magnesium is referred to as “dolomitic limestone.”

Regular mined limestone always contains its calcium and magnesium in the carbonate forms. This will be important to remember when studying limestone reactions when applied to the soil. Pure calcium carbonate contains forty percent calcium and pure magnesium carbonate contains twenty-eight percent magnesium.

Limestone is often rated accordingly to their neutralizing powers. Magnesium carbonate will neutralize more soil acid than an equal amount of calcium carbonate, so dolomitic limestone will always have higher neutralizing rating than calcium carbonate limestone. Calcium carbonate limestone will be rated over one hundred, depending on how much magnesium carbonate it contains. Magnesium carbonate will neutralize 1.19 times the soil acidity of an equal weight of calcium carbonate.

The term, dolomite, does not infer a set level of magnesium carbonate. Dolomite limestone can vary from less than five percent to more than thirty percent magnesium carbonate. Regardless of the level it is all called dolomitic limestone.

While you should be aware of how the neutralizing values of limestone are derived, if applying limestone for either calcium alone or calcium and magnesium, you will seldom be concerned with buying limestone because of its neutralizing power alone. It would be a serious mistake to purchase dolomitic limestone just because it has a lower cost to apply to soils already too high magnesium.