Investigation Of The Effects Of Soil, Salinity And Disturbance On The Estimation Of Water Content Using A 50 MHz Impedance Sensor.

ABSTRACT

The Hydra Probe (HP) is an electrical impedance sensor that operates at a fixed frequency of 50 MHz. It is not clear if water content estimations using the HP are soil, salinity or disturbance independent. The main objective of this research was to investigate the mixed effects of soil, salinity and disturbance on the estimation of soil water content using the HP. Disturbed and undisturbed replicate samples from a range of soil textures (Clay, Silty Clay Loam and Sandy Loam) were saturated with distilled-deionized water and saline solutions at four concentrations: KCl and CaCl₂ at 0.01 and 0.02 Mol L^-1 for three days and then air dried under laboratory conditions, generating monotonic drying curves. Real and imaginary components of the dielectric permittivity were recorded every 5 minutes using the HP connected to a datalogger. Load cells were also connected to the datalogging system, recording changes in sample weight over time, which were later converted into volumetric water content. Regression analysis and analysis of variance (ANOVA) were used to test for soil, salinity and disturbance effects on the volumetric water content - dielectric permittivity function. Our main conclusions were that there was no benefit in including the imaginary dielectric permittivity, or a correction for the loss tangent, in models for estimating water content at 50 MHz. Soils with higher clay content should be assessed independently when developing calibration equations for the Hydra Probe. The sensor’s water content estimations are not disturbance independent.