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Horizontal and Vertical TDR Measurements of Soil Water Content and Electrical Conductivity
Author(s) -
Nadler Arie,
Green S. R.,
Vogeler I.,
Clothier B. E.
Publication year - 2002
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2002.7350
Subject(s) - reflectometry , loam , water content , soil science , electrical resistivity and conductivity , saturation (graph theory) , soil water , reproducibility , infiltration (hvac) , materials science , environmental science , geology , geotechnical engineering , chemistry , mathematics , time domain , composite material , physics , quantum mechanics , combinatorics , computer science , computer vision , chromatography
When time domain reflectometry (TDR) is used to measure soil water content (θ) and salinity, the probes can be installed either horizontally or vertically. We tested the common convention that θ values averaged from horizontal probes will be equal to a vertical direct measurement. In a laboratory experiment, a sandy loam soil, packed uniformly (0.02‐m layers to 0.18‐m depth) into a box, was gradually wetted to saturation by CaCl 2 solutions of 0, 0.5, 1.1, 2.1, 3.1, 4.5, 5.9, and 8.4 dS m −1 Horizontal and vertical TDR probes for measuring θ and electrical conductivity of the bulk soil (σ a ) were installed during soil packing. A comparison between θ values averaged from three horizontal probes and from two vertical ones showed deviations of 0.02 (L L −1 ). A simple water redistribution model was used to attribute this deviation to the process of averaging the horizontal results. The best practical attainable reproducibility, under our experimental conditions, were close to the theoretical limit 0.005 (L L −1 ) but the average experimental reproducibility of θ was 0.01 to 0.02 (L L −1 ). Width of the soil layer affecting the moisture measurement was reconfirmed to be close to 30 mm. The resistors‐in‐series model was found to be a good approximation to describe the soil profile σ a from separately measured horizontal σ a Final values of the electrical conductivity of the soil solution (σ w ) after sufficient leaching were in good agreement with σ w values calculated by an empirical protocol that uses σ a , θ, and a soil texture property.