scholarly journals Calibration of time domain reflectometry technique using undisturbed soil samples from humid tropical soils of volcanic origin

1997 ◽  
Vol 33 (6) ◽  
pp. 1241-1249 ◽  
Author(s):  
A. M. Weitz ◽  
W. T. Grauel ◽  
M. Keller ◽  
E. Veldkamp
Keyword(s):  
Time Domain ◽  
Tropical Soils ◽  
Time Domain Reflectometry ◽  
Soil Samples ◽  
Undisturbed Soil ◽  
Volcanic Origin ◽  
Humid Tropical Soils

scholarly journals Estimating the van Genuchten retention curve parameters of undisturbed soil from a single upward infiltration measurement

Soil Research ◽  
2017 ◽  
Vol 55 (7) ◽  
pp. 682 ◽  
Author(s):  
D. Moret-Fernández ◽  
C. Peña-Sancho ◽  
B. Latorre ◽  
Y. Pueyo ◽  
M. V. López
Keyword(s):  
Water Retention ◽  
Time Domain Reflectometry ◽  
Soil Samples ◽  
Water Retention Curve ◽  
Internal Diameter ◽  
Soil Cores ◽  
Undisturbed Soil ◽  
Retention Curve ◽  
Loam Soil ◽  
Undisturbed Soil Cores

Estimation of the soil–water retention curve, θ(h), on undisturbed soil samples is of paramount importance to characterise the hydraulic behaviour of soils. Although a method of determining parameters of the water retention curve (α, a scale parameter inversely proportional to mean pore diameter and n, a measure of pore size distribution) from saturated hydraulic conductivity (Ks), sorptivity (S) and the β parameter, using S and β calculated from the inverse analysis of upward infiltration (UI) has been satisfactorily applied to sieved soil samples, its applicability to undisturbed soils has not been tested. The aim of the present study was to show that the method can be applied to undisturbed soil cores representing a range of textures and structures. Undisturbed soil cores were collected using stainless steel cylinders (5cm internal diameter×5cm high) from structured soils located in two different places: (1) an agricultural loam soil under conventional, reduced and no tillage systems; and (2) a loam soil under grazed and ungrazed natural shrubland. The α and n values estimated for the different soils using the UI method were compared with those calculated using time domain reflectometry (TDR) pressure cells (PC) for pressure heads of –0.5, –1.5, –3, –5, –10 and –50kPa. To compare the two methods, α values measured with UI were calculated to the drying branch of θ(h). For each treatment, three replicates of UI and PC calculations were performed. The results showed that the 5-cm high cylinders used in all experiments provided accurate estimates of S and β. Overall, the α and n values estimated with UI were larger than those measured with PC. These differences could be attributed, in part, to limitations of the PC method. On average, the n values calculated from the optimised S and β data were 5% larger than those obtained with PC. A relationship with a slope close to 1 fitted the n values estimated using both methods (nPC=0.73 nUI+0.49; R2=0.78, P<0.05). The results show that the UI method is a promising technique to estimate the hydraulic properties of undisturbed soil samples.

Comparison of Soil Water Retention Functions for Humid Tropical Soils

2014 ◽  
Vol 567 ◽  
pp. 8-13 ◽  
Author(s):  
Nuraddeen Muhammad Babangida ◽  
Muhammad Askari ◽  
Khamaruzaman Wan Yusof ◽  
Raza Ul Mustafa Muhammad
Keyword(s):  
Soil Water ◽  
Water Retention ◽  
Tropical Soils ◽  
Soil Samples ◽  
Analytical Models ◽  
Water Retention Curve ◽  
Tropical Region ◽  
Soil Water Retention ◽  
Model Quality ◽  
Humid Tropical Soils

The determination of soil hydraulic properties is of paramount importance as they are needed in many models of water and solute transport in soils, however conventional methods are quite difficult, expensive and sometimes cumbersome to use. Most studies of soil water retention functions are for temperate soils and their soil water retention curve (SWRC) cannot be extrapolated to tropical region, as such this study focused solemnly on SWRC of soils of tropical region (Malaysia and Indonesia to be specific). The analytical models of Brooks & Corey, van Genuchten and Kosugi were applied to model the SWRC for humid tropical soils, parameters of the three models were optimised by fitting them to 191 soil samples, of 10 different classes (International society of soil science classification) using VBA & MS excel solver add in. A comparison of the fitting capabilities and model quality was made using the sum of square of errors (SSQE) between observed and modelled values and, Akaike information criterion (AIC) respectively. The Kosugi model was found to describe the SWRC of the tropical soil samples better than the other models, as it has the lowest SSQE and AIC values.

scholarly journals Measurement of Volumetric Water Content by Gravimetric and Time Domain Reflectometry Methods at Field Experiment with Biochar and N Fertilizer

2019 ◽  
Vol 22 (2) ◽  
pp. 61-64 ◽  
Author(s):  
Lucia Toková ◽  
Dušan Igaz ◽  
Elena Aydin
Keyword(s):  
Field Experiment ◽  
Water Content ◽  
Time Domain ◽  
Soil Property ◽  
Time Domain Reflectometry ◽  
Soil Samples ◽  
Volumetric Water Content ◽  
N Fertilizer ◽  
High Concentration ◽  
Indirect Methods

Abstract There are many methods used for soil water content measurement which we can divide into direct gravimetric methods from using soil samples or indirect methods that are based on the measurement of another soil property which is dependent on soil moisture. The paper presents the findings of volumetric water content measurements with gravimetric and time domain reflectometry (TDR) methods. We focused on four variants in the field experiment in Dolná Malanta (Slovakia): control variant (B0+N0), variant with biochar at dose 20 t.ha−1 without N fertilizer (B20+N0), variant with biochar 20 t.ha−1 and N fertilizer 160 kg.ha−1 (B20+N160) and variant with biochar 20 t.ha−1 and N fertilizer 240 kg.ha−1 (B20+N240). TDR is nowadays a well-established dielectric technique to measure volumetric water content; however, its accuracy is influenced by high concentration of salts in soil. In this paper, we evaluated the effect of added N fertilizer on the measuring accuracy of HydroSense II device that is operating under the TDR principle.

scholarly journals Solute Transport Measurements in Different Soil Types using Time Domain Reflectometry

2001 ◽  
Vol 32 (2) ◽  
pp. 99-114 ◽  
Author(s):  
Magnus Persson
Keyword(s):  
Solute Transport ◽  
Time Domain ◽  
Calibration Method ◽  
Calibration Procedure ◽  
Solute Concentration ◽  
Time Domain Reflectometry ◽  
Soil Types ◽  
Undisturbed Soil ◽  
Transport Measurements ◽  
Calibration Methods

During recent years, time domain reflectometry (TDR) has proved to be a valuable tool for both water content (θ) and bulk electrical conductivity (σa) measurements. To allow resident solute concentration (Cr) measurements, a calibration procedure is necessary for the relationship between σa and Cr. Two main calibration approaches exist. Direct calibration allows for Cr measurements with varying θ, while the indirect calibration method is used for conditions with constant θ. In this paper, three methods of achieving direct calibration parameters are presented and evaluated in three different soil types. Calibrations are made in both disturbed and undisturbed soil columns as well as in the field. It was shown that there were only small differences between calibration methods in homogeneous sand. In other soils, choosing the correct calibration is important. In clay soils solute transport measurements are difficult to take under conditions with varying θ, therefore it is suggested that only the indirect calibration approach should be used. When using TDR it is important to be aware of the accuracy of the TDR system in order to interpret data correctly. Some error sources are thus also briefly discussed.

scholarly journals Construction and calibration of Time Domain Reflectometry probes for assessing soil humidity in distropheric red latosol

2020 ◽  
Vol 8 (12) ◽  
pp. 87-98
Author(s):  
Abinel Bianchessi Dagher ◽  
Arthur Carniato Sanches ◽  
Fernanda Lamede Ferreira De Jesus ◽  
Rodrigo Couto Santos ◽  
Fagner Lopes Theodoro ◽  
...  
Keyword(s):  
Time Domain ◽  
Time Domain Reflectometry ◽  
Soil Samples ◽  
Data Logger ◽  
Indirect Methods ◽  
Precise Method ◽  
Ceramic Capacitor ◽  
Cubic Polynomial ◽  
Red Latosol ◽  
Hydraulics Laboratory

Among the indirect methods of assessing soil moisture, Time Domain Reflectometry (TDR) stands out, which uses the soil dielectric constant to provide volumetric moisture efficiently, quickly and non-destructively. Despite a practical and precise method, TDR has a high cost due to the probes and its Data Logger. In view of this, the present work aims to build and calibrate TDR probes to assess moisture in a Dystrophic Red Latosol. The present work was carried out in the experimental area of the hydraulics laboratory of the Federal University of Grande Dourados (UFGD), located in Dourados-MS, at latitude 22⁰ 12 'south, longitude 54⁰ 59' west and altitude of 434 meters. Each probe built consisted of 3 stainless steel rods (Ø = 3 mm; L = 230 mm) RG 98 cable with 90% mesh and 50 ohm impedance, 4.7 pF ceramic capacitor and BNC connector. The construction procedures followed the following steps: 1- Making the cable, 2- Preparing the rods, 3- Welding the rods to the wires, 4 -Operating test and 5 - finishing phase. After construction, they were calibrated with the characteristic soil of the Region, proceeding with the Probe Reading in two depths (10 and 30 cm) and simultaneous collection of deformed soil samples to determine the moisture based on mass in Laboratory. Subsequently, calibrations with cubic polynomial adjustment were performed. The results showed adjustments with high determination coefficients, and the probes developed showed satisfactory performances.

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