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In the arid southwest, salinity is of primary concern when it comes to
plant selection. Salinity
or the relative level of various salts within a soil varies greatly from
one region to the next, and certainly the levels may change drastically
from one neighborhood to another.
The soil type, drainage and most importantly, rainfall or the lack
thereof, can affect the level of salinity.
Areas with little annual precipitation generally have higher
levels of salt in the soil than those with more precipitation.
Irrigation water also may play a role in salinity.
As the quality of water declines due to extended drought, each
irrigation cycle brings more salt into the equation.
In fact, it is estimated that each acre-foot of irrigation water
may contain as much as one ton of salt or more.
Soil testing laboratories can perform tests that will indicate the
relative salinity of the soil. Salinity
is measured by determining the electrical conductivity of the soil, as
the higher the conductivity, the greater the level of salt.
Request information from your local cooperative extension agent
on salinity and where you can secure soil and/or irrigation water
analyses.
Many plants have become adapted to saline soil conditions through
evolution. Plants native to
arid regions typically can tolerate higher levels of salts than those
indigenous to regions of higher rainfall.
In general, it would be safe to say that plants adapted to
drought are relatively tolerant of saline soils.
Plants that are not adaptive to salinity tend to have variable
responses. Typical symptoms
include a loss of vigor, stunted growth, overly thickened foliage,
foliar leaf burn often referred to as scorch, defoliation, limb die-back
and in severe cases, death of the plant.
Also, salinity levels may be managed by proper irrigation methods. Soils
may be leached of salts by applying clean or relatively low salt
irrigation water provided drainage is adequate.
As a rule of thumb, the application of six inches of water will
reduce the salinity of one foot of soil by 50%.
Twelve inches of water will reduce salinity by approximately 80%,
and the application of twenty-four inches of water will remove
approximately 90% of the soluble salts.
Long, slow applications of water tend to provide better leaching
of salts that brief cycles.
Unfortunately very little research has been conducted to determine the
best-suited ornamental plants for saline conditions, as primary research
has been focused on agricultural and forage crops.
As a result, most of the lists developed for salinity tolerance
are anecdotal. Please
consider the lists presented in this publication as a general guide,
developed by evaluating lists prepared by numerous governmental research
agencies and laboratories. Information
regarding other plants that are salt tolerant would be greatly
appreciated. Please send comments and suggestions to MSWN.
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