WCN_Dec17WEB

Technology:
Using Electrical Conductivity
Sensors to Salinity
By Terry Brase | West Hills College Precision Ag Instructor
Photo Courtesy of Veris Technologies
West Hills College hosted an Open
Farm on October 25, 2017 on the
Farm of the Future to demonstrate some
of the latest technology. Technology just
for the sake of technology will rarely
bring benefit. However production or
management needs that can be satisfied
through the application of technology
should be considered. The Farm of the
Future tries to incorporate technology
we believe to have practical usefulness
to growers. Demonstrations at the Open
Farm event included: the use of wireless
sensors/control network with software to
determine power and water efficiencies;
use of infrared imagery to determine
plant stress and vigor; and the use of
electrical conductivity sensors to determine
salinity. It is this last technology
that is the subject of this article.
Crops, whether they be annual row
crops or permanent orchards, respond to
various factors. These can be categorized
as: anthropogenic (human impacts such
as compaction or irrigation), edaphic
(basic soil characteristics such as salinity,
texture, organic matter), meteorological
(rainfall, humidity, etc), biological (disease,
microorganisms), or topographical
(slope, elevation).
Identifying all of these factors and
understanding the impact each has individually
or interrelated to other factors
would allow the nut producer to control
and prescribe treatments that give the
maximum or optimum yield. The trouble
is that we do not know all of the interrelationship
and rarely have consistent and
accurate data on these characteristics.
Of special interest to most nut producers
is the amount of salinity and depth of
salinity in the soil profile.
Salinity is one of those edaphic
characteristics that is highly correlated to
other soil characteristics. Texture of the
soil and the water content are two other
characteristics that are highly correlated
to the level of salinity. Salinity affects the
uptake of water and nutrients by tree
roots, limiting the absorption of both.
There are several methods to determine
the extent of salinity. The most
accurate, though also the most labor
intensive and expensive, is to take soil
samples and test within a soils lab. A
faster and cheaper method that results
in a large number of spatially correlated
data points are variations of sensors
that automatically collect for “electrical
conductivity”.
What is EC?
Electrical conductivity (EC), as the
name implies, is the ease with which an
electrical current is conducted through
the soil and is measured in milliSiemens/
meter. Commercially available sensors
pass an electrical current through the
soil and record the resistance or conductivity
of the soil in “apparent Electrical
Conductivity (ECa).
There are three different paths that
an electrical current can take through
soil. First, it can follow the water within
the soil’s pore space. For this to occur,
the soil being tested must be at approximately
50-70 percent of field capacity,
otherwise there is not enough water for
an accurate test. Second, the current can
follow the solid soil particles that are
contacting each other. This can provide
information on the soil texture. Thirdly,
there can be an electrical pathway using
both solids and water.
16 West Coast Nut December 2017