ekS - Instytut Agrofizyki im. Bohdana Dobrzańskiego PAN w Lublinie ...

Therefore there might be two competing phenomena that take place in the soil
subjected to the temperature change:
− the soil refractive index for wet soil decreases with the temperature
increase following the decrease of the water refractive index of free
capillary water in the soil,
− the soil refractive index increases with the temperature because of the
increase of free water particles and the simultaneous decrease of bound
water particles.
Susceptibility of the refractive index, n, for soil on temperature causes the
error of reflectometric soil water content measurement values, θ TDR . Taking into
account the calibration function of the TDR meter according to [29]:
n=1,491+7,675θ, the equation:
dθ dθ
dn = (50)
dT dn dT
and (49) the range of the temperature error of the soil water content determined
by TDR meter, dT
dθ :
1
dθ
− 0,0014 < < 0,0001deg
dT
−
(51)
For extreme situations, for example for saturated sand soil, the increase of the
soil temperature ∆T=50 °C will be reflected by the decrease of TDR meter soil
water content readout of ∆θ=0,0014· 50·100%=7% related to the corresponding
value determined by thermo-gravimetric method.
The temperature influence on the soil dielectric constant, and indirectly on the
reflectometric measurement of soil water content depends on its water content and
its texture. The influence of temperature on the TDR measured value may be
taken into account or not, which depends on the assumed accuracy of
measurements and type of the measured soil. In extreme conditions, ex for
saturated sand soil, where bound water is almost not present, this error should be
accounted for. The available TDR soil water content measurement devices may
simultaneously measure temperature of the same soil sample. In this case the
application of proposed temperature correction of is easy to implement and also
required.
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