There are a number of calcium products that can be used in your soil. Some, like oyster shell, provide a pretty pure calcium source. Wollastonite is a calcium silicate, meaning that you get a good supply of silica along with the calcium. Gypsum, is calcium sulphate, and has a sulphur content. Calcitic limestone is calcium carbonate, which provides a valuable additional role in neutralizing acids in a soil.
Dolomitic limestone is a combination of calcium carbonate, and magnesium carbonate, which means that the calcium here is found in the presence of magnesium. This limestone takes longer to dissolve in the soil than calcitic limestone, which also extends the length of time it takes to moderate the soil ph. With respect to their ability to neutralize soil acidity, there is little difference between the lime types.
The use of dolomitic limestone needs to be considered in conjunction with its magnesium content. In naturally high magnesium soils, its use can be a problem, as once magnesium levels climb, they can be very difficult to moderate. The overuse of magnesium in the soil causes soil to bind, and also encourages rampant weed growth. Soils that drain poorly- clay and clay loam soils- generally have a higher magnesium content. It is the magnesium that 'binds' the soil together, whereas adequate calcium helps to break apart soils, creating a lighter, 'fluffier' soil. Use of dolomitic limestone in clay soils is not recommended.
If your field contains a calcium-to-magnesium ratio of 6:1 or greater, your field is considered to be magnesium deficient, and you should strongly consider using dolomite lime to bring your mineral balance in line. In soils that have average or low magnesium levels, such as quick draining soils, especially those that are sandy- dolomitic limestone is able to provide both the calcium and the magnesium that the soil might require.
But before you decide on which calcium source is best for your application, give consideration also to the ph of your soil. If the ph is below 7, this means your soil is acidic, and a lime treatment is necessary in order to help balance the ph. Balancing the ph alone can substantially help encourage the growth of micro organisms that contribute to plant health and encourage strong crop production. But give careful consideration to the existing magnesium content of your soil before choosing a lime. Reversing a high magnesium soil or a dolomite lime treatment can be difficult, time consuming and expensive. If you don’t need dolomite lime, calcitic lime simply works better at restoring ph. So if you are merely looking to correct the pH balance, you are much better served choosing calcitic lime.