Alkali, or alkaline, soils are clay soils with high pH (greater than 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 to be difficult to clarify/settle. They derive their name from the alkali metal group of elements, to which sodium belongs, and which 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.
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Alkali soil in the context of Cupressus sempervirens
Cupressus sempervirens, the Mediterranean cypress (also known as Italian cypress, Tuscan cypress, or Persian cypress), is a species of cypress native to the eastern Mediterranean region and Iran. It is well-adapted to the environmental conditions that it lives in due to its ability to survive in both acidic and alkaline soils and withstand drought. Cupressus sempervirens is important in Mediterranean and Middle Eastern culture, most notably in Iran, where it is both a sacred tree and a metaphor for "the graceful figure of the beloved".
Alkali soil in the context of Acidic soil
Soil pH is a measure of the acidity or basicity (alkalinity) of a soil. Soil pH is a key characteristic that can be used to make informative analysis both qualitative and quantitatively regarding soil characteristics. pH is defined as the negative logarithm (base 10) of the activity of hydronium ions (H
or, more precisely, H
3O
aq) in a solution. In soils, it is measured in a slurry of soil mixed with water (or a salt solution, such as 0.01 M CaCl
2), and normally falls between 3 and 10, with 7 being neutral. Acid soils have a pH below 7 and alkaline soils have a pH above 7. Ultra-acidic soils (pH < 3.5) and very strongly alkaline soils (pH > 9) are rare.
Soil pH is considered a master variable in soils as it affects many chemical processes. It specifically affects plant nutrient availability by controlling the chemical forms of the different nutrients and influencing the chemical reactions they undergo. The optimum pH range for most plants is between 5.5 and 7.5; however, many plants have adapted to thrive at pH values outside this range.