Not All Lime Products Are Created Equal

Know the RNV value of lime so you know how to adjust rates.

Published on: Oct 2, 2013

The key to getting the right amount of lime applied where soil pH is low is to first check soil test reports to see how much you need, then ask about the quality of lime from the quarry where you are buying it. The two things you need to know most are the fineness of grind and the relative neutralizing value.

"There are definitely differences in lime," says Brian Early, production agronomist with DuPont Pioneer in northeast and east-central Indiana. He also operated a crops and soil consulting business for many years before joining Pioneer.

"The finer the grind of the lime, the higher the neutralizing value will be. That determines how quickly the product will begin to change soil pH levels in your field."

Fineness of grind: Finely ground ag lime will react faster than coarse-ground lime.
Fineness of grind: Finely ground ag lime will react faster than coarse-ground lime.

Quarries routinely test their products for fineness of grind. It's determined by the amount of material passing through a sieve. If the particles are course, it will take longer, sometimes measure in years, for all of the lime to break down and supply neutralizing power to help raise soil pH in the field.

Different quarries also vary on the contest of calcium and magnesium in their lime. Most have calcitic lime. Dolomitic lime is higher in magnesium. It typically doesn't become an issue in Early's area, but may be an issue in other parts of the state, particularly parts of southern Indiana.

"Typically you're not going to haul from more than one or two quarries near you because lime is bulky and a lot of the cost is transportation cost in getting it to the field," he says, "But if you know what the RNV value is then you can adjust your rate accordingly."

The higher the RNV value, the less total lime it will take to do the same job compared to lime products with lower RNV ratings, he concludes.