The Value of Agricultural Limestone

ED RAYBURN
WVU Extension Service
Forage Agronomist
Revised June 1997

Different agricultural liming materials have different values. How can a manager decide which is the best buy for a given application? The value of agricultural limestone varies with the geological source of the limestone and how the limestone is processed. The geological source of the limestone determines how much calcium carbonate and magnesium carbonate, capable of neutralizing soil acidity, is in a ton of the material. The amount of these two carbonates determines the total neutralizing value (TNV) of the limestone. The processing of the limestone determines how fine the particles in the finished product are, which determines how fast the limestone will react with the acids in the soil to increase the soil pH.

By law, all agricultural liming materials sold must include a tag on the bag or truck weight slip that describes the material being sold. This tag must give the TNV of the material in calcium carbonate equivalent, the amount of material that passes different sieve sizes, and the percent of magnesium carbonate in the material.

The TNV is the percentage of the limestone capable of neutralizing an acid and is expressed as calcium carbonate equivalent. If a limestone has a TNV of 80 percent it means that 1 pound of it will neutralize the same amount of acid as 0.8 pound of pure calcium carbonate. Limestones differ in TNV since they all contain impurities which do not react with acid. The more impurities the lower the TNV. Also some limestones contain magnesium carbonate, that has a greater neutralizing value than calcium carbonate per unit of weight. One pound of pure magnesium carbonate will neutralize the same amount of acid as 1.2 pounds of calcium carbonate. Therefore dolomite limestone often has a higher TNV than calcium limestone and high-grade magnesium limestone can have a TNV over 100 percent. Hydrated and slaked limestone have been heated to drive off carbon dioxide, leaving oxide forms of calcium and magnesium. These have higher TNVs than limestone.

Fineness of a limestone (sieve size) determines how fast the lime can react with an acid. As a ton of limestone is ground finer there is more surface area. This increased surface area gives more places where the lime can react with the acids in the soil. The fineness of limestone is measured by how much will pass through different mesh screens or sieves. The screen mesh or sieve size is the number of wires in a 1-inch/length of screen. The larger the number of the mesh means the more wires per inch which results in smaller holes in the sieve. Soil and management conditions will affect how fast the different particle sizes react with your soil. However, based on plant response and laboratory studies we can expect the following to occur when lime is worked into the soil:

  1. particles that pass a 100-mesh sieve react 100 percent with the soil in six months or less;
  2. particles that pass a 60-mesh or finer sieve react 100 percent within the first year;
  3. particles that pass a 20-mesh but not a 60-mesh sieve react about 50 percent in the first year;
  4. particles not passing a 20-mesh sieve have little liming value and generally are not credited when evaluating lime materials.

Effective neutralizing value (ENV) is a way of combining TNV and fineness to estimate how much of a liming material will be available to change the soil pH within one year. The worksheet "Comparing the Effective Neutralizing Value of Agricultural Limestone" is available at the end of this fact sheet for making these calculations.

The three pieces of information we need to calculate a limestone's ENV are its TNV in percent calcium carbonate equivalent, the percent of the limestone that passes a 20-mesh sieve and the percent that passes a 60-mesh sieve. All of this information is available on the label provided with the sale of all ground agricultural limestone in the state. Enter the TNV and the percent passing the 20- and 60-mesh sieve in the blanks on the appropriate lines of the worksheet. The percent of limestone that passes a 60-mesh sieve is given a weighting value of 1.0 since it is considered to be completely available within one year. The amount passing a 20-mesh sieve but not a 60-mesh sieve (subtract that passing a 60 from that passing a 20-mesh sieve) is given a weighting value of 0.5 since only half of it is available in the first year. Multiply these weighting values by the percent material in that sieve class and enter the result to the right of the equal sign. Next add these values to get the "% Effectiveness of liming material". Divide this value by 100 to convert the number to a decimal fraction. This decimal is then multiplied by the "Calcium Carbonate Equivalent" to get the "Effective Neutralizing Value (ENV) of the liming material" or "% ENV". Liming recommendations are given in terms of 100% ENV limestone. To calculate the agronomic value of a liming material, divide its cost by the "% ENV" and multiply by 100 (to adjust for using a percent and not a fraction). This is the cost of this liming material to provide one ton of 100 % ENV limestone. To find the number of tons of this limestone needed to correct the soil pH, make this same calculation using 1.0 instead of the price of the limestone.

Example

Limestone #1
Percent Calcium Carbonate Equivalent             105.6% TNV
% Passing a 20-mesh sieve 100%            
% Passing a 60-mesh sieve 85% x 1.0 =   85.0  
% 20- to 60-mesh
(substract 60 from 20 mesh)
15% x 0.5 = + 7.5  
% Effectiveness of liming material           92.5  
(to convert percentages to decimal)           / 100 = x 0.925
Effective Neutralizing Value (ENV)             97.68% ENV

$ 26.00 / 97.68 x 100 = $ 26.62/ton ENV
(Cost/ton) (%ENV)

1.0 / 97.68 x 100 = 1.02 tons of this lime equals 1 ton of 100% ENV lime.
      (%ENV)


Limestone #2
Percent Calcium Carbonate Equivalent             87.0% TNV
% Passing a 20-mesh sieve 45%            
% Passing a 60-mesh sieve 26% x 1.0 =   26.0  
% 20- to 60-mesh
(substract 60 from 20 mesh)
19% x 0.5 = + 9.5  
% Effectiveness of liming material           35.5  
(to convert percentages to decimal)           / 100 = x 0.355
Effective Neutralizing Value (ENV)             30.88% ENV

$ 16.00 / 30.88 x 100 = $ 51.81/ton ENV
(Cost/ton) (%ENV)

1.0 / 30.88 x 100 = 3.24 tons of this lime equals 1 ton of 100% ENV lime.
      (%ENV)

Comparing the Work Sheet for Agricultural Limestone

To calculate the effective neutralizing value of (ENV) of agricultural limestone enter the information from the label describing the limestone and perform the indicated calculation.

Limestone #1
Percent Calcium Carbonate Equivalent             _______%
% Passing a 20-mesh sieve ______%            
% Passing a 60-mesh sieve
(substract 60 from 20 mesh)
______% x 1.0 =   ______  
% 20- to 60-mesh ______% x 0.5 = + ______  
% Effectiveness of liming material           ______  
(to convert percentages to decimal)           /100= x_______
Effective Neutralizing Value (ENV)             _______% ENV
$ cost per ton / % ENV x 100 = $ cost/ton ENV

$ _____ / _____ x 100 = $ _____/ton ENV
(Cost/ton) (%ENV)

1 / _____ x 100 = _____ tons of this lime equals 1 ton of 100% ENV lime.
  (%ENV)

 

Limestone #2
Percent Calcium Carbonate Equivalent             _______%
% Passing a 20-mesh sieve ______%            
% Passing a 60-mesh sieve
(subtract 60 from 20 mesh)
______% x 1.0 =   ______  
% 20- to 60-mesh sieve ______% x 0.5 = + ______  
% Effectiveness of liming material           /100= x______
(to convert percentages to decimal)             ______% ENV
Effective Neutralizing Value (ENV)              
$ cost per ton / % ENV x 100 = $ cost/ton ENV

$ _____ / _____ x 100 = $ _____/ton ENV
(Cost/ton) (%ENV)

1 / _____ x 100 = tons of this lime equals 1 ton of 100% ENV lime.
  (%ENV)

Programs and activities offered by the West Virginia Cooperative Extension Service are available to all persons without regard to race, color, sex, handicap, religion, age or national origin. Cooperative Extension Work in Agriculture and Home Economics, West Virginia University and the United States Department of Agriculture, Cooperating. Rachel B. Tompkins, Director, Morgantown, West Virginia. Published in Furtherance of Acts of Congress of May 8 and June 30, 1914.

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