Management of Salt-Affected Soils - Practices of Irrigation and On-farm Water Management - page 286

Diagnosis of salt-affected soil can be performed by

• field observation, and/or

• laboratory examination

8.3.3.1 Diagnosis by Field Observation

Salinity may be a local problem, so a site visit is recommended regardless of the
availability of detailed soil information. Some visual symptoms can be used to help
diagnose these problems, but ultimately soil and irrigation water analyses are the
best ways to make an accurate diagnosis. When salinity is suspected to be caused
by a high water table, you may be able to measure groundwater depth by boring
holes with an auger. If free water collects in holes less than 1.5-2 m deep, a drainage
problem is indicated.

Field Symptoms
There are many visual indicators of salinity in affected areas. The absence of crop
or poor crop in seeded areas can be a good indicator that salts are present. Another
indicator of soil salinity is the presence of a “Bathtub ring” around sloughs or
depressions; this is an area around a slough where it is easy for salts to accumulate.
Check for poor crop growth, light gray, or white colors on soil surface, areas
that take longer to dry and growth of salt-tolerant weeds (foxtail barley, kochia,
Russian thistle, etc.). Vegetation is a good indicator of the location of these soils.
Dawson Gum ( Eucalyptus cambageana ), False Sandalwood ( Eremophila mitchel-
lii ), and Poplar Box ( Eucalyptus populnea ) are the main trees found on sodic soils.
Plants growing in saline soils may appear water stressed. In some cases, a white
crust is visible on a saline soil surface (Fig. 8.2 ) .
Salt-affected soils may inhibit seed germination and cause irregular emergence
of crop seedlings, particularly in sensitive crops such as beans or onions. Plants
sprinkler irrigated with saline water often show symptoms of leaf burn, particularly
on young foliage. If a soil is highly sodic, a brownish-black crust sometimes forms
on the surface due to dispersion of soil organic matter. By the time darkened crusts
are visible on the soil surface.
High soil pH sometimes may confuse with the symptom of salinity or sodicity,
as yellow stripes on middle-to- upper leaves or dark green or purple coloring of the
lower leaves and stems can be signs of high soil pH. Symptoms of salinity, sodicity,
and high soil pH are given in Table 8.4 .

8.3.3.2 Diagnosis by Laboratory Determination

Soil testing labs typically evaluate pH and EC (electrical conductivity) as part of a
routine program. If the pH is high (>8.5), sodium adsorption ratio (SAR) or ESP
should also be calculated. Proper soil sampling depth to diagnose saline conditions