When it comes to fertility, among the most important factors influencing plant growth and stand life is soil pH. Maintaining proper soil pH levels is critical to legume growth in pastures, soil microbial activity and micronutrient availability.
Soil pH identifies the active acidity, or alkalinity, of a soil solution. The pH measurement is expressed as a measurement of hydrogen ion activity or concentration in a solution. The pH scale is from 1 to 14. A neutral solution of soil has a value of 7.0.
The ability of lime to neutralize pH is measured by the Effective Neutralizing Power. The effective neutralizing power of lime is expressed on the basis of pounds per ton as a percentage of the fineness index, multiplied by the total neutralizing power and percentage of dry matter.
Buffer capacity (buffer pH) or cation exchange capacity of the soil best explains differences in lime requirements. The buffer capacity of a soil reflects the resistance to a change in pH.
The amount of clay and organic matter influences buffer capacity. This simple notion explains why soils of the same pH may have a different lime requirement. For instance, much more lime may be required to raise the pH of a clay soil than will be required to raise the pH of a sandy soil.
Liming materials vary significantly in terms of purity, fineness and moisture. These factors help us select the most economical source of lime and determine the application rate of lime.
Fortunately, state law, sections 905.51 to 905.66 of the Ohio Revised Code, requires lime manufacturers to label lime products. The most important item on the lime product label for determining application rate and value is the Effective Neutralizing Power.
Lime application is usually provided on the soil test recommendation report as a calcium carbonate equivalent basis and is specific for the crop, soil, lime history and tillage depth indicated on the test submission form. This means that we must adjust the application of the liming material up or down based on ENP.
OSU Extension fact sheet ANR-9-02 uses a price for lime products then calculates the amount of each product needed to equal an application of 1 ton per calcium carbonate equivalent providing an example of how to make these adjustments.
In terms of fertility, lime should rank high on the priority list. Contact your local OSU Extension office for a soil test kit and assistance in the interpretation of your soil test results.