Many of these reactions are dependent on a variety of soil chemical properties. Soil pH is generally related to the concentration of free hydrogen ions in the soil matrix. Hydrogen ions are made available to the soil matrix by the dissociation of water, by the chemical activity of roots, and by many chemical weathering reactions. The concentration of hydrogen ions determines the pH of the soil. Soils with a relatively large concentration of hydrogen ions tend to be acidic .
Alkaline soils have a relatively low concentration of hydrogen ions.
The pH scale. A value of 7.0 is considered neutral. Values higher than 7.0 are increasingly alkaline or basic. Values lower than 7.0 are increasingly acidic. The illustration above also describes the pH of some common substances.