Simultaneous monitoring of soil water content and salinity with
a low-cost capacitance-resistance probe
E. Scudiero, A. Berti, F. Morari
Dept. of Agronomy, Food, Natural Resources, Animals and Environment, University of Padova, Legnaro, Italy
P. Teatini
Dept. of Civil, Environmental and Architectural Engineering,
University of Padova, Padova, Italy
ABSTRACT
Capacitance and resistivity sensors can be used to continuously monitor
soil volumetric water content (θ) and pore-water electrical conductivity
(ECp) with non-destructive methods. However, dielectric readings of
capacitance sensors operating at low frequencies are normally biased
by high soil electrical conductivity. A procedure to calibrate
capacitance-resistance probes in saline conditions was implemented
in contrasting soils. A low-cost capacitance-resistance probe
(ECH2O-5TE, 70 MHz, Decagon Devices, Pullman, WA, USA) was used in
five soils at four water contents (i.e., from dry conditions to saturation)
and four salinity levels of the wetting solution (0, 5, 10,
and 15 dS·m-1). θ was accurately predicted as a function of the
dielectric constant, apparent electrical conductivity (ECa),
texture and organic carbon content, even in high salinity conditions.
Four models to estimate pore-water electrical conductivity were
tested and a set of empirical predicting functions were identified
to estimate the model parameters based on easily available soil
properties (e.g., texture, soil organic matter). The four models
were reformulated to estimate ECp as a function of ECa,
dielectric readings, and soil characteristics, improving their
performances with respect to the original model formulation.
Low-cost capacitance-resistance probes, if properly calibrated,
can be effectively used to monitor water and solute dynamics
in saline soils.
