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coefficients. The R2 value is a measure of how well the trend line fits the data (above 0.98 is
good, the closer to 1, the better the fit is).
Note (what polynomial order to use):
Depending on the data collected, it may be better to use a second order polynomial rather than
a third order polynomial. Some third order polynomial trend lines result in a downward curve at
high moisture levels, which is not representative of how the sensor will actually perform. If this
appears to be the case with your data, it is recommended to instead use a second order polyno-
mial (degree 2).
Entering Coefficients into the Probe
O
nce the soil coefficients have been determined they must be entered into the probe’s non vol-
atile memory. This is done using the extended SDI-12 command a
XC
i! where a=sensor address
(default address is 0) and i is the coefficient to modify. Please refer to the extended commands
section for more details. (A USB to SD-12 interface product (part 6300) is available that simpli-
fies the task of viewing and cha
nging the probe’s coefficient. Contact
RioT Technology for more
information).
General Observations to Note
Loamy Clay / Clay Soils
Loamy Clay/Clay soils can be very time consuming to work with. Although the loamy clay does
not stick to the gloves and trowel below about 32% moisture, it can form clumps that are diffi-
cult to reduce to smaller size, especially at lower moisture levels. At around 32% it may turn
very stiff and required a lot of hand strength to pack the soil around the probes so that there
are no air spaces, so be aware of this to ensure accurate readings from the probes. Above
around 32% the soil will start getting softer, and easier to work with. Above 36%, consistency
may be much softer, but it will become very sticky. Take care not to lose soil at this stage.
See Also
Resources on Soils
•
A Compendium of On-Line Soil Survey Information - Soil Classification for Soil Survey
