September/October 2017

Figure 3 (pg. 26) perfectly illustrates
the insufficiency of using the classic ECe
threshold concept as the main driver for
tree growth and yield decline. The Area
1 tree has almost double the canopy volume
of Area 4, but the average rootzone
ECe from 2014-16 is actually higher
for Area 1 (12.9 dS/m) compared to
Area 4 of the same field with an average
rootzone ECe of 9.0 dS/m. Whoa—that
makes no sense—the tree with less salt
is smaller?! What the lab ECe salinity
does not take into account is the high
pH, bad sodic silty clay structure that
makes Area 4 prone to water-logging.
We used a somewhat novel approach
taking EM38 measurements right at the
single-line drip hose and 30 inches away
from the hose to get a larger snapshot
of the rootzone. We then summed the
resulting four horizontal and vertical
EMa readings for a “summed” conductance.
Doing this we find Area 1 has a
summed EMa of 241 mS/cm and Area 4
was 877 mS/cm—fully 360 percent higher
conductance for Area 4 compared to
Area 1, and higher conductance means
more salt and water logging. Thus, the
EM38 provided a superior integration of
the combined impact of salinity and soil
structure on final tree growth.
hundreds of measurements per hour as
opposed to three to four soil cores—and
it’s integration of excessive water logging
problems.
Blake L Sanden, Farm Advisor
UCCE Kern County
1031 South Mount Vernon Avenue
Bakersfield, CA 93307, USA
(661) 868-6218
blsanden@ucdavis.edu
Louise Ferguson, Pomology Extension
Specialist
Department of Plant Sciences
3045 Wickson Hall
Davis, CA 95616
530-752-0507
lferguson@ucdavis.edu
Craig E. Kallsen, Farm Advisor
UCCE Kern County
1031 South Mount Vernon Avenue
Bakersfield, CA 93307, USA
(661) 868-6221
blsanden@ucdavis.edu
Comments about this article? We want
to hear from you. Feel free to email us at
article@jcsmarketinginc.com
Figure 4 illustrates the three-year
summed yield decline as a function of
rootzone ECe to a depth of five feet. The
trend is highly significant, and similar
to the 10 year field trial preceding this
survey: resulting in a yield reduction
of 144 to 351 lb/ac (three year cumulative
inshell yield) for every unit ECe >
6.5 dS/m. Definitely a lower yield loss
salinity “threshold” then we published
13 years ago, but the scatter under the
curve is large (R2 = 0.107)—indicating
the multiple other factors affecting tree
growth and yield. Figure 5 uses the
“summed” EM38 conductivity (EMa)
as an estimator of yield decline and
improves the R2 to 0.207 (Regressing the
natural log transformed EM38 readings
with the lab ECe rootzone salinity gave
an R2 = 0.695, data not shown.)
Figure 4. Three year cumulative pistachio yield as a function of rootzone salinity.
No Perfect Tool
So there is no perfect tool for
indexing soil and salinity impacts on
pistachio yield, but the use of the EM38
shows promise both in it’s ease of use—
Figure 5. Three year cumulative pistachio yield as a function of EM38 “summed”
EMa readings.
September/October 2017
www.progressivecrop.com
27