Soil Liming And Lime Qualities

liming soil
Applying lime to soil helps increase the pH of soils — photo courtesy LSU AgCenter

After receiving a soil test report, the first thing to check is soil pH, which influences soil nutrient availability. Most nutrients are available at the soil pH of 6.5.

Therefore, soil pH needs to be adjusted to the target pH either by applying lime for low pH (less than 6.0) soils or with elemental sulfur for high pH (greater than 7.5) soils. Liming is the most common practice.

Soil Buffering Capacity

The lime rate depends on the initial and target soil pH and the soil’s buffering capacity (ability to resist the pH change). If the soil buffering capacity and the difference between initial and target soil pH are low, the lime rate would be low.

However, for soils with high buffering capacity (low buffer pH), the lime rate would be high even for a small change in soil pH. Clay soils have higher buffering capacity and require a greater amount of lime for each unit increase of soil pH than silt loam soils.

The Louisiana State University AgCenter Soil Testing and Plant Analysis Lab does not run buffer pH. It does indicate the unit change of soil pH with the addition of maximum 3 tons of lime and lets the farmers decide how much they want to spend, assuming more than 3 tons of lime may be too expensive.

Target soil pH should be set at 6.3 for soybean and 6.0 for corn and cotton. Lime is required if the target soil pH is 0.2 unit more than actual soil pH. Lime takes six to nine months — depending on liming materials — to react with the soils and raise soil pH. It should be applied uniformly and incorporated in the fall.

Purity And Particle Size

The quality of liming materials — purity and particle size — is important to raise soil pH. Purity is determined in relation to pure calcium carbonate — calcitic limestone — that is rated as 100%. This rating is called calcium carbonate equivalent.

The lime rate recommended by soil testing labs is based on pure calcitic limestone with 100% CCE. The lime application rate should be adjusted based on the CCE of the liming materials. For example, if the CCE is 80% and the recommendation is 2 tons of lime per acre, then 2.5 tons of lime (2 tons x 0.8) per acre should be applied.

Another lime quality is particle size, or fineness factor, and is expressed as the percentage of liming material that passes through various sized screens. Finer particles are more efficient in neutralizing soil acidity (increasing soil pH).

However, the liming materials should have a good distribution of both smaller and larger particles. The smaller ones can raise the soil pH quickly, and larger particles can have long-term control in neutralizing soil acidity.

Both purity (CCE) and particle size (fineness factor) of the liming material are expressed together as effective CCE or effective neutralizing value. The higher the ECCE or ENV of the liming material the more efficient it is in increasing soil pH. Like CCE, the actual lime rate also needs to be adjusted with the liming material’s ENV if the recommendations are based on ENV.

This feature is excerpted from an article by LSU AgCenter soil scientists Rasel Parvej, Brenda Tubana and Jim Wang.

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