Part 1, Section 2: Soil Fertility Management
Soil Fertility Management
SOIL ACIDITY AND LIMING
Calcium and magnesium
Although limestone is applied primarily to neutralize soil acidity, it also serves as a source of essential calcium (Ca) and magnesium (Mg). When a soil test indicates the need for magnesium, limestone is the most economical way to meet that need. The magnesium content of limestone varies considerably. Unfortunately, there is no official trade classification of limestone according to magnesium content. Local classification schemes often create confusion. Therefore, to select the proper limestone material, it's best to rely on the actual magnesium analysis rather than a name (e.g., dolomitic lime, high-magnesium lime, or high-calcium lime). Generally, if soils are limed to the recommended pH, there will be more than enough available calcium for agronomic crops. This is true even when a high-magnesium lime is used.
Penn State soil test recommendations not only indicate the amount of magnesium the crop requires, but also include a magnesium analysis of the limestone recommended to supply the needed magnesium.