WCN August 2020

positively charged
cations or negatively
charged anions that
have varying levels
of impact on overall
salinity stress, with
more or less effort
to manage. Soil
chloride (Cl) and
sodium (Na) levels
>30 milliequivalents
per liter (meq/L),
and B levels above 3
mg/L are problematic
for the
long-term health
and productivity
of pistachios. Cl
can be reduced
with clean water
alone, however
Figure 1. Stress in response to a high salt load starts with osmotic stress, where the ability to pull in water by osmosis
declines due to the low solute differential between the root sap and the soil water. This reduces tree transpiration,
which limits cell expansion for shoot growth. When the tree can no longer exclude salts, it begins to accumulate
in the FIGURE trunk 1and leaves. Symptoms of specific ion toxicity include leaf burn and nutritional disorders. (courtesy M.
Culumber, UCCE.)
B ions strongly hold (adsorb) to soil particles at higher pH
levels, and acid amendments with ample water are necessary
to flush excess B out of the rootzone. Na requires continual
management to mitigate current or future problems with toxicity
and declining soil structural stability and drainage. However,
sufficient levels of calcium (Ca) and magnesium (Mg)
can counter or reduce the severity of its effects. The sodium
absorption ratio (SAR) and exchangeable sodium percentages
(ESP) are indices used to compare the concentration of Na
with respect to Ca and Mg levels. A general rule of thumb is
SAR levels greater than five times the EC of irrigation water
indicates an imbalance of Na to Ca and Mg levels, and likely
problems with infiltration.
Elevated pH greater than 7.5, bicarbonate (HCO 3
) greater
than 2 meq/L, and soil lime (CaCO 3
) > 1% indicate potential
for reduced nutrient availability, as well as soil sealing and
reduced infiltration. High HCO 3
levels appear as a white
chalky substance on the soil surface and micro irrigation
emitters, which alone can be a major source of clogging
when not amended properly. When both Na and HCO 3
salts
are present, HCO 3
can tie up Ca in the soil and water, which
allows Na to become the dominant cation on soil particle
surfaces in the formation of saline-sodic or sodic soil conditions.
Calcium is a positively charged ion that is attracted to
negatively charged soil clay particles, this attraction aggregates
soil particles, giving soil structure that resists dispersal
and degradation. Unlike Ca, Na ions cause spaces between
soil particles to swell, and at elevated levels will eventually
disperse soil aggregates. When loose particles clog the pores
and cracks that usually allow soil water to infiltrate into
the ground, impermeable crusts can develop on the surface.
These crusts slow or stop water infiltration and decrease
oxygen levels needed by tree feeder roots to absorb nutrients.
These saline-sodic or sodic conditions require soil and or
water amendments to improve soil structure and leaching for
better tree health.
Soil and Water Amendments
The purpose of amendments is to provide a source of Ca
to replace the Na and remove it from the rootzone. This can
be accomplished with either the direct application of soluble
Ca (usually as gypsum) or by use of acidifying products that
react with Ca bound by HCO 3
or soil lime (CaCO 3
) to make
the Ca ion soluble. A combination of both amendments can
be beneficial. The sulfate binds with Na to form a compound
that is easily leached from the soil, while Ca takes its place
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