|Plant species vary in how well they tolerate salt-affected soils. Some plants will tolerate high levels of salinity while others can tolerate little or no salinity. The relative growth of plants in the presence of salinity is termed their salt tolerance.
Salt tolerances are usually given in terms of the stage of plant growth over a range of electrical conductivity (EC) levels. Electrical conductivity is the ability of a solution to transmit an electrical current. To determine soil salinity EC, an electrical current is imposed in a glass cell using two electrodes in a soil extract solution taken from the soil being measured (soil salinity). The units are usually given in deciSiemens per metre (dS/m).
Table 1 categorizes salinity into general ranges from non- saline to very strongly saline. These values are used for plant selection for saline soils. Salinity levels vary widely across a saline seep. Salinity also varies from spring to fall. Salinity usually appears on the soil surface just after spring thaw.
A high salt level interferes with the germination of new seeds. Salinity acts like drought on plants, preventing roots from performing their osmotic activity where water and nutrients move from an area of low concentration into an area of high concentration. Therefore, because of the salt levels in the soil, water and nutrients cannot move into the plant roots.
As soil salinity levels increase, the stress on germinating seedlings also increases. Perennial plants seem to handle salinity better than annual plants. In some cases, salinity also has a toxic effect on plants because of the high concentration of certain salts in the soil. Salinity prevents the plants from taking up the proper balance of nutrients they require for healthy growth.
Extensive research on salt tolerance for prairie conditions was done in 1988 (Table 2). It should be noted that crop tolerances developed for chloride-dominated soils, such as those in California, may not be applicable to crops grown on the sulphate-dominated soils typically found in western Canada.
|Table 1. Salinity rating and electrical conductivity value|
0-60 cm (0-2 ft)
60-120 cm(2-4 ft)
* ds/m = decisiemens per metre.
The dominant salts in prairie saline seeps are calcium (Ca), magnesium (Mg), sodium (Na) cations and sulfate (SO4) anions. If Na levels are high or not balanced with the Ca and Mg, soil tilth can also be effected. The positively charged Na cations attach to the negatively charged clay particles in the soil, causing the soil to be sticky when wet, and hard and impermeable when dry.
Table 2 gives salinity tolerance ratings for a range of plant species and a range of salinity levels. New research underway may modify the rating of some plant types. As a general rule, plants that have low drought tolerance will have low salinity tolerance.
|Table 2. Salt tolerance of various types of plants|
| ||beardless wildrye|
fulks altai grass
| || |
slender wheat grass
| ||Siberian salt tree|
laurel leaf willow
| ||meadow fescue|
|reed canary grass||cabbage||ponderosa pine|
|4||corn|| ||sweet corn|
Siberian crab apple
|white dutch clover|
|Colorado blue spruce|
|0|| || || ||black walnut|
Source: Agdex 518-17. November 2001.