Choosing Liming Materials

Last week we talked about soil pH and how important it is to keep your soil pH at an appropriate level. We occasionally have to add acidifying compounds to lower the soil pH but this isn’t very often or very cheap. Neutralizing acid soils, however, is something that we do on a regular basis using calcium carbonate materials, often called lime. In recent years there have been some changes in lime application technology and this has created a fair amount of confusion and occasional misleading advertising.

Liming materials differ in their effectiveness based on purity and fineness of grind. A standard measure has been developed called effective calcium carbonate or ECC. Very pure, finely ground calcium carbonate may have an ECC rating of 99 or even 100. For every pound of material applied you’ll have 0.99 to 1.00 pounds of effective liming material. A more traditional liming material may have an ECC of 50. This product is either not pure calcium carbonate or more coarsely ground or both. Since the second material has an ECC of 50 you’ll need two pounds of it for every pound of ECC required by the soil test.

Now, to understand how liming works we have to briefly delve into a little chemistry, please bear with me. In a very simplified explanation, soil acidity is caused by the presence of "free" hydrogen ions in the soil solution. The liming material acts as a hydrogen "sponge". It reacts with the hydrogen ions in the soil and replaces them with calcium or magnesium, releasing water vapor and carbon dioxide. Over time the calcium and magnesium are taken up by plants or leached out of the soil by rainfall/irrigation, hydrogen ions start to become numerous again, the pH drops and a new application is required. This process may take anywhere from 3 to 20 years.

The liming materials themselves are not very mobile in the soil. They aren’t like nitrogen fertilizer - spread it on the surface and rain will carry it in. To work effectively lime needs to be tilled into the soil so it can interact with the soil particles. If just applied to the soil surface the liming material will only interact with the top ¼ inch of soil. Not what we really need for most plants. Ideally the lime would be incorporated into the top 5 to 6 inches of soil.

One of the basic concepts of physics is that the more finely something is ground, the more surface area there is to react with. That is true with liming materials as well. Fineness of grind is one of the calculations of the ECC value. In reality, we don’t see that big of a difference between a very high grade liquid suspension and a more standard 45 to 55 ECC grade dry product. One pound of ECC lime is going to work effectively regardless of whether it is 99 ECC or 50 ECC. If the soil test calls for 3,000 pounds per acre of ECC it doesn’t matter what form of lime is applied as long as it is 3,000 pounds per acre of ECC. A higher test material would use less material, BUT you still have to apply 3,000 pounds per acre.

So what do you use? The cheapest material you can have applied. Calculate cost on an ECC basis. Whatever you can apply at the cheapest cost per acre, and still apply the total amount needed, is what you should use. I’ve seen some sales pitches where companies have advertised that since their product is so pure you only need half as much. Remember to have everything priced on an ECC equivalent and the amount needed is actually applied. Lime is often needed to raise soil pH. Make sure you wind up getting what you need, or your plants and profits will suffer!

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