Ohio's Effective Neutralizing Power for Aglime

Printable Word Doc - O.A.C. ENP Explanation

In 1997, the Legislature of the State of Ohio revised the 30 year-old laws governing Feed, Fertilizer and Agricultural Liming Materials. The primary change that affected Aglime was the inclusion of an Effective Neutralizing Power (ENP) value to be guaranteed for a lime producer's license and placed on their bulk sales label. The intent of creating an ENP guarantee was to provide a ‘yardstick', or comparison, by which the consumer could fairly evaluate various agricultural liming products and how effectively each would neutralize soil acidity. The formula used to arrive at an ENP value takes into account; Total Neutralizing Power (TNP, which is the same as calcium carbonate equivalent, TNP=CCE), moisture and the ‘fineness' of a given material. The final ENP calculation is expressed as a "pounds per ton" comparison of the liming material to a pure calcium carbonate. As ‘fineness' is considered the most important component of a liming materials' ability to neutralize high soil acidity (seen as low pH on a soil sample), a Fineness Index was created to give more importance to the finest particles found in a given product. For example, it is generally accepted that particles passing the #100 sieve (100 square openings, per square inch) will neutralize soil acid, and provide calcium and magnesium for plant uptake within 2-3 months. As such the Fineness Index assigns weighting averages to each particle size in a lime sample, with progressively coarser particles receiving a progressively lower average multiplier (1.0 to the #100 sieve, but only 0.2 to the #20 sieve sizes). Therefore the finer a product is, the higher its fineness index is. The higher the fineness index is, the higher its ENP will be. The reverse holds true for moisture in the final ENP calculation. The more moisture a liming material has, the lower its final ENP number will be. Therefore the Legislature actually created a ‘truth in labeling law', which should enable the consumer to fairly compare various agricultural liming products. The formula used by the Ohio Dept. of Agriculture to calculate ENP is as follows :

Pounds ENP / Ton = 2000 x (% ENP / 100) x (% Dry Matter / 100)

1) To determine Effective Neutralizing Power (ENP)

FI = (Fineness Index)        = 0.2 x (% Passing 8 Mesh - % Passing 20 Mesh)

                                              + 0.6 x (% Passing 20 Mesh -%Passing 60 Mesh) 

                                              + 1.0 x (% Passing 60 Mesh)

          2) Determination of Percent Moisture

a. Weigh the sample container (and approximately 600 gram sub-sample of Aglime) to the nearest 0.1 gram before placing in the oven.

              b. After drying, weigh the container and sub-sample to the nearest 0.1 gram.


Percent Moisture =  (Wet weight of sample - Dry weight of sample)

                                   ____________________________________              X 100

                                                  % Dry Matter = 100 - % Moisture


3) % ENP = (FI / 100) x % TNP

4) Pounds ENP / Ton = 2000 x (% ENP / 100) x (% Dry Matter / 100)