Alkali, or alkaline, soils are
clay soils with high
pH (> 8.5), a poor
soil structure and a low infiltration capacity. Often they have a hard
calcareous layer at 0.5 to 1 metre depth. Alkali soils owe their unfavorable physico-chemical properties mainly to the dominating presence of
sodium carbonate, which causes the soil to swell and difficult to clarify/settle. They derive their name from the
alkali metal group of elements, to which
sodium belongs, and that can induce
basicity. Sometimes these soils are also referred to as
(alkaline) sodic soils.
Alkaline soils are
basic, but not all basic soils are alkaline; see
alkali for the difference between alkali and base.