Simultaneous measurement of soil water and soil hardness using a modified time domain reflectometry probe and a conventional cone penetrometer

Abstract

Soil strength and water content are important indices for assessing soil resistance to root growth and soil compaction both of which affect other soil properties. Therefore, simultaneous measurement of soil penetration resistance (PR) and soil water content can aid agricultural land management. We measured PR with a conventional cone penetrometer, followed immediately by determining water content using a modified TDR probe inserted into the penetrometer hole. From the results of a field feasibility test, soil water content was measured satisfactorily and correlated well with data obtained by the gravimetric method, except for those data from near the surface owing to soil disturbance when the cone penetrometer was extracted after the PR measurements. Field results demonstrate that PR and soil water content have three‐dimensional variability, with a markedly different distribution pattern between cultivated and subsoil layers at the field scale. Overall, the variability in the PR and soil water data is similar to that reported in previous studies. We conclude that our method produces results helpful to field management of soil and water because it is based on a simple and easy technique for the simultaneous measurement of soil water content and PR.

Evaluation of measurement sensitivity and design improvement for time domain reflectometry penetrometers

“…[2006], and C resembles the probe proposed by Redman and Deryck [] and Miyamoto et al . []. Each of the TDR penetrometers consists of a 30 mm diameter nonconductor shaft and several conductors.…”

“…Therefore, it would be significant to develop techniques that measure the distribution of the dielectric permittivity and the electrical conductivity along the depth in situ. Recently, scholars developed time domain reflectometry (TDR) penetrometers suitable for TDR measurements of soils at various depths [ Redman and Deryck , ; Nissen et al, ; Young et al, 2000; Vaz and Hopmans , ; Persson and Wraith , ; Topp et al ., ; Lin et al ., ; Kosugi et al ., ; Miyamoto et al ., ]. The general practice of using a TDR penetrometer was to place conductors around a nonconductor shaft.…”

“…The general practice of using a TDR penetrometer was to place conductors around a nonconductor shaft. The current TDR penetrometers have been primarily constructed in three types: (a) two or three parallel copper wires are coiled around a nonconductor core, as indicated in Figure a [ Vaz and Hopmans , ; Topp et al ., ; Kosugi et al ., ; Persson and Wraith , ]; (b) two straight grooves are produced on the nonconductor shaft surface in which stainless steel rods are embedded, as indicated in Figure b [ Redman and Deryck , ; Miyamoto et al ., ]; and (c) four straight strips are produced on the nonconductor shaft surface in which four similar copper strips are embedded, as indicated in Figure c [ Young et al, 2000; Lin et al ., ].…”

“…Therefore, minimizing the effect of materials inside the shaft and maximizing the influence zone in the surrounding medium are important to consider when designing the TDR penetrometer. Currently, most of the research focuses on the innovation of conductor styles [ Vaz and Hopmans , ; Lin et al ., ; Miyamoto et al ., ] or the disturbance caused by penetration [ Rothe et al ., ]. Insufficient attention was given to the measurement sensitivity of the TDR penetrometer.…”

Modelling soil moisture – soil strength relationship of fine-grained upland forest soils

“…Obviously, the proportion of organic substrate affects PR as well, but its role is thought to be more important as the clay content decreases (Smith et al 1997). Due to the dominant role of moisture content affecting PR, many researchers have suggested specific correction factors (Busscher 1990;Busscher et al 1997;Vaz et al 2011) or tools for the simultaneous measurement of PR and moisture content (Vaz et al 2001;Hummel et al 2004;Miyamoto et al 2012) to make the PR results more versatile. Of these numerous investigations, only a few have been carried out in forest soils.…”