8
Relative water
Content Mode
In addition to displaying volumetric water content
(VWC), the meter can also display the relative water content
(RWC) and Water Deficit (see MODE button, p. 5). RWC is
an index value calculated with respect to upper (wet) and low-
er (dry) VWC set points. The set points are configured with
the software (refer to Meter Settings, p. 10). An RWC of 0
indicates the soil is at the dry set point while an RWC of 100
indicates the soil has reached the wet set point. (Example: As-
sume the dry set point is VWC=25% and the wet set point is
VWC=40%. If the meter measured a VWC of 35%, this
would translate to a RWC of 67 because 35% is 2/3 between
25% and 40%.) If the soil’s volumetric water content is out-
side the range of the set points, it is possible to get a negative
RWC or an RWC greater than 100.
If the volumetric water contents for field capacity and
permanent wilting point are the wet and dry set points respec-
tively, the RWC value will be equivalent to Plant Available
Water (PAW). A general rule of thumb is to recommend irri-
gation when the soil has reached 50% of the PAW.
Also included on the first line is the Water Deficit.
The Water Deficit is the amount of rain or irrigation water
necessary to raise the soil water content to the wet set point.
This calculation applies to a soil depth equal to the probe rod
length. The water deficit can be extrapolated further into the
profile if the porosity and water-holding characteristics are
similar to the volume of soil sampled by the probe.
The second line of the LCD gives the Average (A) of
all readings taken, the Number (N) of readings taken and the 5
-symbol name given to this soil type in the Meter Settings
screen (see p. 12).
RWC=25.5 D=3.17in
A=23.4 N=06 Asnte
