Because nutrients concentrate when water evaporates,
many pedocals are fertile if irrigation water is
available. However, salts often concentrate so much that
they become toxic to plants (Fig. 6–18). As mentioned
previously, all streams contain small concentrations of
dissolved salts. If arid or semiarid soils are intensively irrigated,
salts can accumulate until plants cannot grow.
This process is called salinization. Some historians argue
that salinization destroyed croplands and thereby
contributed to the decline of many ancient civilizations,
such as the Babylonian Empire.