Can you tell me how alkaline soils are formed and if and how they are related to saline soils?
Saline soil may have a high pH, a characteristic shared with soils which are alkaline. You may find this information on soils and pH useful:
Diagnosing Saline and Sodic Soil Problems
Plant Materials for Saline-Alkaline Soils
- Alkaline soil: A soil whose reaction is greater than pH 7.
- Acid soil: A soil whose reaction is less than pH 7.
- Saline soil has a pH less than 8.5.
Saline soil, as defined in Soils: An Introduction, by Michael Singer and Donald Munns (Prentice Hall, 1999): “Saline soils …contain large amounts of soluble salts, appreciably more soluble than calcium sulfate. Most commonly, these are salts of Na, Ca, and Mg, with chloride, sulfate, and bicarbonate…soils are considered saline if their electrical conductivity exceeds 4 deciSiemens meter-1. Many plants suffer at this level.”
To answer your question about how alkaline soils are formed, here is what Clemson University Extension says:
“The pH value of a soil is influenced by the kinds of parent materials from which the soil was formed. Soils developed from basic rocks generally have higher pH values than those formed from acid rocks.”
Rainfall also affects soil pH. Water passing through the soil leaches basic nutrients such as calcium and magnesium from the soil. They are replaced by acidic elements such as aluminum and iron. For this reason, soils formed under high rainfall conditions are more acidic than those formed under arid (dry) conditions.
Application of fertilizers containing ammonium or urea speeds up the rate at which acidity develops. The decomposition of organic matter also adds to soil acidity.