Soil pH and Lime Requirement

Soil pH is a measure of the activity of ionized H (H+) in the soil solution. Although other criteria are sometimes used as indices of lime needs of acid soils, the lime requirement (LR) is generally a measure of the base (lime) required to neutralize that fraction of the total acidity that must be neutralized to attain a desired soil pH that is favorable for crop growth. Hence the activity of H ion in the soil solutions is the intensity factor (index), whereas exchange acidity and LR are the capacity factors of soil acidity. Before the development of laboratory soil tests for determining the LR of individual soils, the amount of lime for a given soil condition and crop, or cropping sequence, was based on field experiments. Laboratory methods to determine LRs have involved soil-lime incubations, soil-base titrations, and soil-buffer equilibrations.