Calcitic vs Dolomitic Limestone

By:  Eddie Ayers, County Extension Agent

A few weeks ago I discussed that it’s important to have your soil tested this time of year to insure that the pH will be correct for spring planting; pH is a measure of acidity.  The scale ranges from 1-14 with 7 being neutral.  Most plants grow best with a slightly acid pH.  Generally the soils in this area are actually more acid than plants prefer, so in order to raise the pH, lime must been added to the soil.  It takes 3 to 6 months for the lime to affect the pH, so the fall is the best time to apply lime if it is needed.

So this week as the discussion turns to lime, several questions come up.  The main question is what type of lime to use.  Lime or limestone is carbonates of calcium or magnesium.  Some limestones contain little or no magnesium.  They are practically pure calcium carbonate.  These materials are called calcitic limestones.  Other limestones also contain magnesium carbonate in varying amounts.  If considerable amounts of magnesium are present, the limestone is called a dolomitic material.  The question in many peoples’ minds is whether one is better than another.

The value of any liming material is determined by its ability to neutralize soil acidity.  There are some differences in this ability, but in our area most of the liming material is very similar in the ability to neutralize soil acidity. It is the carbonate content in a limestone that neutralizes acidity.  Therefore, for all practical purposes, a calcitic limestone and a dolomitic limestone of the same carbonate content are equal in ability to neutralize soil acidity.  However, limestone does contain plant nutrients, calcium and magnesium, and both are needed by plants.  The calcitic stone supplies mostly calcium.  The dolomitic stone supplies both calcium and magnesium.  Should one material be preferred over another?  Well, for the purpose of neutralizing soil acidity, there is very little difference so buy the material that gives you the most neutralizing power for your money.  If you also need magnesium, then a dolomitic material may be the best buy.  But what if you don’t need magnesium, should you use only a calcitic limestone?  Research with most crops indicates that even though the soil is high in magnesium, the additional magnesium in dolomitic limestone does help plant growth and does not reduce crop yields.  It really comes down to a matter of price.  Because of high transportation costs, the best limestone is generally a locally mined, quality material.

Once the decision has been made as to what kind of lime to use, the next decision is powdered or pelletized?  Let’s look at the merit of each one.  Assuming that they both have the same neutralizing quality, it comes down to cost and convenience.  As a general rule, powdered lime gets into the soil and starts to work quicker.  This is because of the small particle size.  The powder can be dissolved quicker by moisture and therefore move into the soil faster.  One drawback with powdered lime is that it is harder to spread, and because it is lighter, it can be blown into your face.  If it gets into your eyes, it can cause a lot of irritation.  On the other hand, pelletized lime is easier to handle because it is in pressed pellets.  It is still the fine powder, but it has been pressed together for ease of handling.  It will work the same as powdered lime, but it takes a little longer to dissolve and move into the soil.  Because it has gone through an extra processing step, it sometimes costs more.

The bottom line is that soil pH is very important in determining plant growth.  The only sure way to know the pH is to take a soil test.  If the pH is low, lime is needed to raise the pH to the proper level and hopefully you can find a lime that will fit your needs.

For more information about which limestone to use and taking a soil sample, contact me in the Gilmer UGA Extension office.

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