Salt Tolerance of Plants

 
 
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 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
Soil Depth
Non-Saline
Weakly
Saline
Moderately
Saline
Strongly
Saline
Very Strongly
Saline
0-60 cm (0-2 ft)
<2 ds/m*
2-4 ds/m
4-8 ds/m
8-16 ds/m
>16 ds/m
60-120 cm(2-4 ft)
<4 ds/m
4-8 ds/m
8-16 ds/m
16-24 ds/m
>24 ds/m

* 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
Salt Tolerance
EC (ds/m)
Field Crops
Forages
Vegetables
Trees, Shrubs
Very High
20
 beardless wildrye
fulks altai grass
levonns alkaligrass
alkali sucatan
  
High
16
kochia
sugar beets
altai wildrye
tall wheatgrass
Russian wildrye
slender wheat grass
 Siberian salt tree
sea buckthorn
silver buffaloberry
86-row barley
safflower
sunflower
2-row barley
fall rye
winter wheat
spring wheat
birdsfoot trefoil
sweetclover
alfalfa
bromegrass
garden beets
asparagus
spinach
hawthorn
Russian olive
American elm
Siberian elm
villosa lilac
laurel leaf willow
Moderateoats
yellow mustard
crested wheatgrass
intermediate wheatgrass
tomatoes
broccoli
spreading juniper
poplar
 meadow fescue
flax
canola
reed canary grasscabbageponderosa pine
apple
mountain ash
4corn sweet corn
potatoes
common lilac
Siberian crab apple
Manitoba maple
Viburnum
Lowtimothy
peas
field beans
white dutch clover
alsike clover
red clover
carrots
onions
strawberries
peas
beans
Colorado blue spruce
rose
Douglas fir
balsam fir
cottonwood
aspen, birch
raspberry
0   black walnut
dogwood
little-leaved linden
winged euonymus
spirea
larch

Source: Agdex 518-17. November 2001.

 
 
 
 
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This information published to the web on November 1, 2001.