ABSTRACT
Soil pH is a measure of soil acidity or alkalinity and is probably the single most important chemical characteristic of a soil. In the past, soil acidity or alkalinity, reported in pH units, was also referred to as “soil reaction” (Mason and Obenshain, 1939), and this term is occasionally still used in some publications. However, “soil reaction” is no longer used by soil chemists (SSSA, 2008). Because of the importance of acidity and alkalinity in soils, pH has been called a master variable (McBride, 1994), with knowledge of soil pH required to understand many chemical processes including ion mobility, precipitation and dissolution equilibria and kinetics, and oxidation-reduction equilibria. Soil pH also a¦ects nutrient availability to plants and the negative response of many plant species to soil acidity.
