WCN_Dec17WEB

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time, it is a slower process and results in
a less dense set of data point. The EM38
is a smaller device that can be carried
by hand. This allows it to be used in
a variety of situations. There are also
researchers that believe that the electromagnetic
is a more reliable measure of
conductivity.
When using either system, GPS
should be used to record the location of
each data point. Dataloggers are used
to record the two different values and
combined with a location from a GPS
receiver. These values can be mapped for
a visualization of soil variability. Georeferencing
of the mS/m is important as
it allows the transfer of the data in text
format and onto a GIS for mapping.
Photo Courtesy of Veris Technologies
It is important to remember that this
value is not in itself a measure of salinity or other common soil characteristic. But
because it is highly correlated to many of these characteristics, it can be used to estimate
or predict many of these characteristics of soil. EC is therefore a measure of soil
spatial variability. Areas with similar EC values also share soil characteristics such as
water, texture, OM (organic matter) and salinity. Any difference in these characteristics
show up on an EC map.
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Higher water content and salinity
allows higher conductivity. Clay particles
are smaller and form tighter bonds than
other types of soil particles, resulting in
higher conductivity. OM decreases the
conductivity. Each of these characteristics
specifically impacts the conductivity
of the soil. The problem is how to
separate and define the level of just one
of these characteristics since they are all
interrelated.
The good news is determining individual
characteristics can be done with
the proper protocol. Three basic uses of
an ECa map include identifying variability;
determining a soil sampling routine;
and determine level of salinity or other
soil characteristic.
Soil Spatial Variability
Precision farming or site specific
management is based on understanding
the variability that is present within a
field and then managing it for economic
efficiencies. A goal in managing variability
is identifying those areas that are
homogenous, i.e. areas that have more
in common than the area around it. ECa
works well to determine these zones
since areas with similar ECa values have
similar texture, organic matter, CEC
(cation exchange capacity) and water
content which means similar production
decision will be applicable.
This is the one application that
requires very little analysis on the part of
the user. The mapped points interpolated
within a GIS (geographic information
system) creates a map showing variability
of the field. Using a GIS reclassification
tool will create three to five zones of
homogenous areas to serve as management
zones.
Determine Spatial Variability
for EC Directed Soil Sampling
Completing a soil sampling using a
grid has been common in precision ag. A
more common technique is using zones
to determine placement of soil samples.
An EC map can be used to determine
the homogenous areas for targeted
sampling. The same management zones
previously discussed, can also be used
to determine where to take soil samples.
Usually a group of samples would be
taken from each zone and aggregated for
a composite sample. The nutrient values
from the samples would be used for fer-
18 West Coast Nut December 2017