WCN August 2020

Continued from Page 13
on the surface of soil particles. A large
quantity of Ca is generally needed to
displace Na. Yet, because amendments
add salts to the soil, too much at once
can add to osmotic stress that limits
water uptake by trees. Also, any excess
applied Ca not displacing Na, has
potential to precipitate to form lime
or even leach with the irrigation water
dependent on soil conditions. The right
amendment or combination of amendments
largely depends on soil type, pH,
the balance of Na with Ca and Mg, and
whether there are appreciable amounts
of HCO 3
and CaCO 3
in the water and
soil.
Calcium amendments are most useful
to displace Na where soil pH is less
than 7.5, native calcite or lime is less
than 1%, and in areas with ultrapure
low EC (2 meq/L HCO 3
), as injection
may cause precipitation of lime and
clog irrigation lines. For dormant season
applications, growers may consider
using coarser sources such as ground
wallboard. The larger particle sized material
will slowly dissolve with repeated
irrigations throughout the season. Not
all sources are equal in terms of purity.
Ask your retailer for the bulk percentage
of soluble calcium in the product.
A lower grade with less Ca is generally
more economical, but will require
heavier application to achieve satisfactory
results.
NUT CROP LOSS
REDUCE LABOR COSTS
Acidifying amendments are generally
most useful in sodic soils with
a high pH with soil lime levels greater
than 1%. High levels of HCO 3
can also
be effectively neutralized by some
acids. If soils have less than 1% lime, Ca
must be added with the acid to create
gypsum in the soil for Na to be leached.
However, before these processes can
take place, acid-forming amendments
(for example sulfur, ammonium polysulfides,
and thio-sulfates) require an
initial biochemical oxidation of sulfides
(S 2
) by bacteria, named Thiobacillus,
to form the sulfuric acid that then
breaks down the lime to form free Ca
and gypsum. This is important to note
because soil temperature and moisture
greatly influence microbial activity and
the successful conversion of the acid
amendment to gypsum. Moist soil with
temperatures above 55°F for a period
of one to two weeks is needed for the
reaction to take place. Optimal soil
conditions are around 80°F, therefore a
fall application of sulfur will likely provide
Na leaching benefits the following
growing season rather than during the
dormant period when it is commonly
applied. Sulfur products, like gypsum,
are available in a variety of particle siz-
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Figure 2. Necrotic leaves are a characteristic of
photosynthetic capacity needed to support the
Giulia Marino, UCCE.)
14 West Coast Nut August 2020