Agriculture Reference
In-Depth Information
Dolomite Lime
(22% Calcium and 12% Magnesium —
Varies)
I don't know how dolomite lime has come to be used by so many gardeners. Maybe it's
just because the dolomite industry has done a wonderful marketing job. Maybe it's because
it was promoted by some of the early organic proponents who have had a big influence on
the rest of us. It's in the same price range as calcitic lime, but personally, I almost never use
it.
It's approximately 22% calcium and 12% magnesium, a 1.8:1 calcium to magnesium ra-
tio, whereas calcitic lime is approximately 30% calcium and 4% magnesium, a 7.5:1 ratio.
Actually, magnesium has 1.7 times more exchange capacity than an equal amount of calci-
um, so we use correspondingly less magnesium when we're trying to raise magnesium
levels. This was shown in the last chapter when we looked at how we would need 400
pounds per acre of calcium to occupy 100% of the cation exchange sites in a soil with a
CEC of 1, but only 240 pounds of magnesium. In a way, that makes the effective calcium
to magnesium ratio of dolomite less than 1:1, and more like 4.5:1 for calcitic lime.
Too much magnesium in the soil can cause nitrogen to volatize into the air and soil to
compact. Dolomite generally brings in too much magnesium for what we need. If you had
a soil with extremely low magnesium in relation to calcium, such as a 12:1 calcium to mag-
nesium ratio, then it might make sense to use dolomite.
