By-product lime and lime analysis

Fall is almost here, and so is the season for lime applications. I sometimes get the question about whether or not by-product lime can be applied to crop fields and pastures. The answer is, it depends, since these liming materials will need to be handled differently compared to ag lime.

Lime by-products are leftover materials from processes used by municipal water facilities, steel plants or coal operations. Usage will also depend on other factors, such as whether these products are contaminated and if your operation requires approved lime products to remain certified organic.

Benefits

Lime for a long time was considered to “sweeten the soil.” However, this does not make lime a fertilizer product, and, as with most things in life, too much is detrimental. Lime is used to correct soils with a low pH.

Soils with proper lime applications are more productive — nutrient availability to plants is improved, as is the habitat for soil microorganisms. Ag lime, which usually consists of either calcitic limestone or dolomitic limestone, is commonly used to correct pH in crop and pasture fields.

Labels

Lime manufacturers are required to label commercial ag lime products in Ohio.

The lime label is important for applications — in Ohio, manufacturers are required to list the Effective Neutralizing Power of that product. ENP determines the quality of that lime and how much will be needed to correct the soil pH listed on a soil test report. Other states may use different metrics to describe lime quality.

For example, several states may use Neutralizing Value, which is given as a percentage. If lime is purchased out-of-state, you may see a different metric than what is used in Ohio.

By-product

Lime produced as a by-product of a process may not come with a lime label, so we may have no idea of what the quality of that final product is. Before we apply it, we need to know the ENP, if the lime texture is similar to ag lime, so we can apply the right amount needed. Otherwise, we run the risk of over or under applying lime, which can be costly to fix.

Some by-products are derived from industrial chemical precipitates and will react with the soil more quickly than ag lime. Even though particle size is not as important in these cases, we still need to know the calcium carbonate equivalent.

If by-product lime is used and the supplier does not provide the analysis of that lime, the lime will need to be tested for quality.

One example of a lime by-product is the hydrated lime used in municipal water treatment after the water softening process. Oftentimes, this liming agent has a similar neutralizing value compared to ag lime, or even greater.

The downside to this type of lime is that while it might raise the soil pH faster compared to pelletized lime, it does not maintain the soil pH for three to five years. Due to this issue, multiple applications of this lime product will be required.

Contamination

Coal combustion by-products, such as fly ash, can also be used to increase soil pH. However, quality differs among coal combustion materials. These materials may contain contaminants such as arsenic or boron.

With any lime by-product where there is a question of contamination, environmental testing for metals and other contaminants should be conducted. Lime by-products that are wet (moisture is about 50%) may be difficult to spread evenly in a field without a special type of spreader. Uneven applications can result in a banding affect, with some areas having a soil pH that is too high.

Testing

There are several laboratories that will test lime quality for a fee in Ohio, which usually ranges somewhere between $80-120, depending on what testing selections are made. The Ohio Department of Agriculture Consumer Protection Laboratory will also test lime quality for a similar fee.

Whichever lab you use, follow their protocols for submitting samples. For dry samples, this often requires sending material in a sealed plastic bag with the air removed or squeezed out. Wet samples will need to be placed into containers for shipment.

If you use a lab that is out-of-state, make sure they can provide you with the ENP of that product. There may be options to select between several lime packages or to purchase individual tests al la carte.

ENP is calculated from calcium and magnesium content, water content and particle size. Since we need to know the particle size, it is important to make sure that a sieve analysis is included in the package. Particle size is related to effectiveness of the liming product as it determines how much of that lime product comes into direct contact with the soil.

Gypsum

I will end this article mentioning gypsum, as it often comes up in conversations about lime. Gypsum can be a by-product obtained from coal-fired power plants and is often used to condition sodic soils in some of the western states.

Sodic soils tend to have poor soil structure due to the sodium ion exchange that causes soil particles to deflocculate.

A common misconception is that gypsum functions similarly to lime and can be used to condition the soil in Ohio. It can be used as an agricultural amendment in Ohio for soils that are calcium deficient that do not need the pH corrected. However, gypsum does not correct soil pH and is not a substitute for a good liming product.

Ohio also does not have sodic soils that gypsum products are used to condition. Before applying any lime product in the field, make sure you understand the ENP of that product and how it can be used to determine how much lime is needed in your hay field or pasture.

References and resources

References and resources include “Applying lime to raise soil pH for crop production” from Oregon State University Extension, “Use of byproduct lime on agricultural soils” from Michigan State University Extension, “Understanding Value in Lime” from Ohio State University Extension and “Use of Industrial Byproducts in Agriculture” from the Water Quality Information Center, National Agricultural Library, ARS-USDA.