Dolomitic lime (garden lime) is most often used and it adds Ca and Mg, along with usually insignificant amounts of other trace elements present as impurities. It tends to raise pH but how much it raises it depends on the starting pH, buffering capacity of the soil, and how much you use.

Al

A "soil sweetener" would be lime of one kind or another, a Calcium source. Since the balance between your soils Calcium and Magnesium also affects your soils pH you need to know about that so you know which, Calcitic or Dolomitic, limestone to use. Dolomitic limestone has Magnesium as well as Calcium and is what is used in soils that test low for Magnesium. Calcitic limestone is used on soils with adequate or more levels of Magnesium but lack sufficient Calcium. Spreading a Dolomitic limestone on a soil with optimal levels of Magnesium will not help.

"Dolomitic limestone has Magnesium as well as Calcium and is what is used in soils that test low for Magnesium.

As long as we're splitting hairs, I suppose we should add that we wouldn't necessarily use dolomite to correct a Mg deficiency unless there was also a Ca deficiency. Adding dolomite to a soil with adequate levels of Ca but low in Mg could easily create an antagonistic deficiency of Mg.

Also, I'm wondering how the 'balance' between Ca and Mg affects pH?

Al

All plants need Magnesium to properly utilize Calcium and if they are not in balance then you can have problems. There are those that believe the Blossom End Rot in tomatoes is caused by a Calcium deficiency, but you can have lots of available Ca in your soil and still see BER if the Mg is not there to help the plant utilize that Ca.
Too much Ca in the soil can also keep a plant from getting the needed Mg and vice versa, just as too much Nitrogen can keep a plant from properly utilizing many of the other essential plant nutrients.
If you add Dolomitic lime to a soil that is deficient in Magnesium you can, according to the soil scientists at Michigan State University, bring the quantity of Mg into balance, if the right amount of that dolomitic lime is added to your soil. Adding more Mg to a soil that is deficient in Mg will not create a deficiency of Mg.

"All plants need Magnesium to properly utilize Calcium"

Technically, this is not true, unless you split another hair and say that plants need ALL the essential nutrients (and you may as well add "in the proper ratios") to properly utilize _______ (fill in the blank).

I touched on antagonistic deficiencies in my post above. Plants do not need Mg to utilize Ca. This is especially true because Mg is mobile in plants, while Ca is generally considered immobile. If Mg is deficient and Ca present, plants will still be able to take up all the Ca they need, but the Mg deficiency will limit growth. It is when the BALANCE between Ca:Mg is skewed that uptake of one or the other may become difficult. Too much Ca can limit Mg uptake, and too much Mg can limit Ca uptake. Favorable ratios vary by soil type, but somewhere around 3-5:1, Ca:Mg would be considered favorable. K is also a player in this triangular ratio.

You also skirted explaining how the balance between Ca:Mg affects pH. If you had said, "The total amounts of Ca and Mg present in soils affects pH", not the balance between them, you would have been correct.

Al

If you are adding hundreds of pounds of dolomitic lime to correct pH, how much mg are you adding? And how much mg does the soil need?

Is this a test? ;o)

All dolomite is not created equal, so it depends on the ratio of Ca:Mg in the lime. Plus, there are too many other "it depends" to answer w/o a soil test. Some of the Ca will be reactive in the soil, and it's mainly the residual (exchangeable) fraction we're concerned with. Starting pH needs to be known and the soils buffering capacity needs to be considered as well.

There are minimum amounts of both Ca and Mg required in soils, but there are also ratios of Ca, Mg, (and K) to consider as well. IOW, both (all 3) cations may be low along with a low ratio indicating calcium needs proportionately more attention, or vice versa - if both cations are low but the ratio high, then magnesium would need proportionately more attention. If the levels of both Ca and Mg are high, but the ratio disproportionate (ie outside of guidelines), you may still need to add one or the other to prevent an antagonistic deficiency.

Al