ACID SOILS

Soil acidity varies from about pH 2.0–10.0, acid soils have a pH of <7.0 but most acid soils with a wide distribution (acrisols, ferralsols and podzols) have a pH of 3.5–4.0 (see Figure). In the soil types with a wide distribution, the acidity comes from weakly acid rain water and is accentuated by the metabolism of roots and micro-organisms. In hyperacid soils the higher acidity levels come from the oxidation of sulfide-rich minerals, such as pyrites. High acidity is associated with low cation exchange capacity (CEC) and low base saturation, which lead to agricultural problems from the toxicity of aluminium (Al) and nutrient deficiency.

Acid soilsVarious types of soils in relation to their acidity (pH) and redox potential (Eh). The envelope for common mineral soils is indicated by the dashed line (as used in Chesworth, 2008).

[See alsoacid rain, acid sulfate soils, acidification, liming]