Many growers need to use lime in order to increase low soil pH.
However, there are many liming materials, differing in their composition and effectiveness.
How can you determine the quality of the liming material?
Which liming material is best for your soil?
Which product will give you the best value for your money?
In order to answer these questions, we first need to understand some basic concepts and terminology:
Soil pH affects many reactions in the soil. Soils with pH lower than 5.4 are considered to be acidic.
Low soil pH is associated with problems such as aluminum and manganese toxicities as well as with calcium and magnesium deficiencies.
Soil pH of 5.8 to 6.5 is favorable for most crops. In order to maintain the soil pH in this range acidic soils require liming.
Lime reduces the acidity in the soil and raises soil pH.
The effectiveness of a liming material is directly related to its purity. Purity of a liming material is a measurement of the calcium carbonate equivalent (CCE). It is a measure to the amount of acid that the liming material will neutralize, compared to pure calcium carbonate (CaCO3).
The higher the calcium carbonate equivalence, the more effective the product in neutralizing acidity.
Pure calcium carbonate would have a CCE of 100%. Some materials can have a CCE higher than 100%.
Impurities, which have no neutralizing power, reduce the CCE value.
The CCE values of several common liming materials are presented in the table below:
|Pure calcitic lime (CaCO3)||100|
|Pure dolomitic lime CaCO3*MgCO3||108|
|Quicklime / burned lime (CaO)||179|
|Hydrated lime CaOH2||136|
The liming material has to be grounded in order to be effective. Fineness refers to the particle size distribution of the liming material
Fine particles react faster in soil than large particles, as they have greater surface area.Therefore, liming materials containing more fine particles will be more effective.
The fineness is determined by passing the liming material through a set of sieves, usually 60 and 8 mesh sieves.
‘Mesh’ refers to the number of openings in the sieve (i.e. 60 mesh means 60 openings in one inch), therefore only fine particles will pass through a 60 mesh screen.
The classification of liming materials, based on their fineness depend on local regulations.
In general, a liming material is considered to be fine if about 95% of it passes a 20-mesh screen, 60% passes 60-mesh screen and 50% passes 100-mesh screen.
Lime particles that do not pass through an 8-mesh screen are considered to be ineffective.
This index allows comparison of different liming materials.
The terms ENV (Effective Neutralizing Value), RNV (Relative Neutralizing Value), NI (Neutralizing Index) and Effective CEE all refer to an index that allows comparing different liming materials.
The calculation of this index varies between countries and states. However, it is always determined by combining the fineness and purity properties of the liming material.
Example for a common method for calculating ENV:
ENV= CCE * [(A/100)*0.5 + (B/100)]
A = % particles that pass through a 8-60 mesh size
B = % particles that pass through a 60 mesh screen
Lime recommendations are usually made based on 100% effectiveness.
The ENV is used to calculate the actual amount of liming material that has to be applied.
For example, if the recommended lime application is 2 tons/acre and the ENV of the liming material is 67%, then the required application rate would be:
Let’s see an example of how ENV can be used to compare prices of liming materials.
Liming material A: ENV 65%, Price $18/ton
Price per ton of effective lime: 18/0.65=$27.7
Liming material B: ENV 85%, Price $22/ton
Price per ton of effective lime: 22/0.85=$25.88
Material B has more effective lime and therefore a lower application rate is required. We can see that even though material A is cheaper than material B, applying material B will be more economical.