Salt crusts are the most common type of chemical soil crusts. They occur throughout the world in arid and semiarid regions with intense evaporation and little precipitation. Salts accumulate in soils because of limited or reduced leaching. When salt crystals bond with soil particles on the surface or interior of the soil a cementing layer of soil and salt forms.
There are two types of salt crusts: efflorescence and subflorescence. The types of cations and anions available and the porosity of the soil determine the type of salt crust that forms. Efflorescence occurs when there are fine soil particles and quick evaporation. Small salt crystals form and are uniformly distributed on the soil surface resulting in a smooth, crusty appearance. Large soil particles result in slower evaporation and subflorescence. The slower evaporation leads to large salt crystals precipitating on areas of the soil surface and between the soil particles producing an uneven, patchy distribution of salts at and immediately under the soil surface.
Salt crusts improve soil resistance to wind erosion, inhibit soil evaporation and can change the chemical properties of the soil. “Salt-affected” soils are those where the total concentration of salts is high enough to retard plant growth, injure tissues and/or decrease plant productivity.
Most plants avoid areas with salt crusts and an excess of soluble salts while some can resist the salt effects within a certain range. However, a few plants can actually tolerate a high concentration of salts. In the next posts I will note plants that can survive in soils with salt crusts.
This area of salt crust was photographed at Ash Creek Wildlife Area (Lassen County CA) not far from the microbiotic soil crusts mentioned in my previous post (“Microbiotic Soil Crusts” 01-14-22).
In March Leonard and I will be camping at Death Valley where we plan to observe physical soil crusts, the third type of soil crust.