Salt and Crops: Salinity Tolerance

Soils are delicate structures, and careless agricultural practices can destroy them. Crop decline resulting from increased soil salinity can be traced back thousands of years to Sumer and Babylonia. There, the original “Fertile Crescent” eventually turned into desert, destroyed by deforestation, unwise planting, and irrigation-induced soil salinity. Such decline in soil productivity also was evident in the U.S. Dust Bowl of the 1930s and is occurring in present-day Australia. Irrigation, currently practiced on about 15% of the world’s farmland, produces more than one-third of the world’s crops but often leaves soils with high salinity. Increased demand for fresh water for urban use not only decreases the amount available for agriculture but also requires that less suitable, often moderately saline, water serves as a replacement. In addition, replacing perennial native plants, which evaporate most of the rainwater, with crops that grow only part of the year can lead to a rise of saline groundwater that ultimately will kill many plants (Figure 1). Flooding, incursion of sea water into coastal fresh water reservoirs, and erratic weather patterns, which seem to increase and which add drought years, compound the effects of increasing soil salinity.