Soil Alkalinity

Abstract

Soil alkalinity or salinity is a condition that results from the accumulation of soluble salts in soil. Most of the alkaline soils are found in the desert environments throughout the world. Although saline soils do occur in humid regions in areas affected by sea water, the most extensive occurrences are in arid regions, where they usually are found in low-lying areas where evaporation concentrates the salts received from more elevated locations in surface water, ground water, or irrigation water. Since low-lying areas are most easily cultivated and irrigated, they have the greatest agricultural value. The problems connected with soil salinity in these low-lying areas are of major importance in highly developed agriculture in desert regions. The degree of alkalinity of a soil is conveniently expressed in terms of pH values. The pH scale is divided into 14 divisions or pH units numbered from 1 to 14. Soils with a pH of 7 are neutral. Soils with pH values below 7 are acid or “sour” and soils with pH values above 7 are alkaline or “sweet”. A pH of 9 is ten times more alkaline than a pH of 8 and a pH of 10 is ten times more alkaline than a pH of 9. Thus, a soil with a pH of 10 is 100 times more alkaline than a soil with a pH of 8 (Black 1957; National Plant Food Institute 1962).