George Kargas

Performance Analysis and Calibration of a New Low-Cost Capacitance Soil Moisture Sensor

AbstractSeveral newly developed sensors based on capacitance and frequency techniques have simplified real-time determination of soil water content (θ). The 10HS sensor is one of the most recent developments in capacitance sensors. However, up to now, little is known about the accuracy of this sensor, and the dependency of its measurements on soil type and environmental factors. In this study, the performance of the 10HS sensor was investigated through experiments using liquids with known dielectric properties and experiments in a set of porous media exhibiting a wide range of properties. The response of the 10HS sensor in bilayered systems was also investigated. The experimental results suggested that there is a distinct instrument sensitivity to soil type, indicating the need for individual soil calibration. A set of specific calibration equations for the various porous materials studied were proposed. It was shown that the 10HS sensor is able to provide reasonably accurate relative permittivity (er) me...

Soil texture and salinity effects on calibration of TDR300 dielectric moisture sensor

Newly developed sensors have simplified real-time determination of soil water content (θm). Although the TDR300 is one of the most recent dielectric sensors, little is known with regard to the accuracy and dependency of its measurements of soil type and other environmental factors. In this study, the performance of TDR300 was investigated using liquids of known dielectric properties and a set of porous media with textures ranging from sandy to clayey. The experiments were conducted in the laboratory by mixing different amounts of water with each soil to obtain a sufficient range of soil water contents. For sand, the calculated permittivity values (er) correlated adequately with Topp’s equation derived for time domain reflectometry. However, for the remaining inorganic porous media, er values were overestimated compared with those resulting from Topp’s equation, especially for water contents exceeding 0.2 cm3/cm3. The results suggested that the relationship between θm and √er was strongly linear (0.953 2 dS/m, the relationship θm–√er was not linear, and, thus the TDR300 device calibration became increasingly difficult. Therefore, rather than operating as a time domain device, TDR300 operates as a water content reflectometer type device.

Evaluation of a Dielectric Sensor for Measurement of Soil-Water Electrical Conductivity

The salinity status of soil can be obtained through the measurement of the pore-water electrical conductivity σp . In the present study the WET sensor’s capability in predicting σp through the simultaneous measurements of the soil bulk electrical conductivity ( σb ) and the soil dielectric constant (K) is investigated. The estimation of σp is based on a model by Hilhorst, which relates σp to the two other quantities K and σb and an extra fitting parameter K0 which is incorporated in the software of the device. The study involved experimental measurements in the laboratory using four different soils with a large range in soil texture and volumetric water content θ . In each soil type four different electrical conductivity aqueous solutions were used. The results exhibited a rather strong linear relationship between K and σb . The slope of this linear relationship appeared to depend on both the soil type and the electrical conductivity of the pore water. The value of K0 seems to be soil specific and increas...

Effect of tillage practices on the hydraulic properties of a loamy soil

AbstractThe knowledge of soil hydraulic properties is essential for modeling the water flow in unsaturated porous media for hydrological applications and agricultural water management. Long-term tillage practices have been shown to affect the hydraulic properties of soil. In this study, a field experiment was conducted to evaluate the effect of roto-tillage and no-tillage practices on the hydraulic properties of a bare loam soil. Two field plots were used with different tillage practices. In the first one, the field has been in roto-tillage for three years and in the other in continuous no-tillage for two years. From the hydraulic properties determined, water retention curves indicated that the water retention capacity was greater in tilled than in no-tilled (NT) soil. Both soil–water diffusivity and hydraulic conductivity values were greater in tilled than in NT soil at relatively low to moderate water contents, and lower in tilled than in NT soil at relatively high water contents—near saturation. The hy...

Prediction of soil solution electrical conductivity by the permittivity corrected linear model using a dielectric sensor

AbstractIn the present study, the electrical conductivity of the soil solution (σp) was predicted using a linear model in which the bulk soil electrical conductivity (σb) effect on the apparent die...

Evaluation of porous medium hydraulic properties using experimental methods and RETC code

ABSTRACT Two experimental procedures were used to determine both hydraulic properties, soil water retention θ(h) curve and unsaturated hydraulic conductivity K(θ), of a sand sample. Knowledge of hydraulic properties is essential, since they generally control soil water dynamics. A steady-state laboratory method was used for the simultaneous determination of θ(h) and K(θ). A one-step outflow method was used for the determination of diffusivity D(θ) and subsequently K(θ) from soil water retention data which were measured independently on the same sample and using the same apparatus. The comparison of K(θ) measured values from the above-mentioned methods showed very good agreement of the results. Also, the comparison between the experimental K(θ) and θ(h) functions and the predictions obtained using retention curve (RETC) code by simultaneous fit of experimental soil water retention and hydraulic conductivity data from outflow data, assuming the Mualem-van Genuchten model, showed very good agreement. It is noted that the main disadvantage of the one-step outflow method is the weakness to predict K(θ) values near saturation. This disadvantage could be overcome using RETC code with the above procedures, since the K(θ) values between the predictive approach and the steady-state method were similar.

Investigation of the Relationship between Three- and One-Dimensional Infiltration Using a Mini Disc Infiltrometer

Disc infiltrometer experiments were conducted in the laboratory on two disturbed soils, a loam and a silty clay loam soil, in order to investigate the relationship between three- and one-dimensional infiltration using the proposed equation of Smettem et al. A mini disc infiltrometer of a radius of 45 mm with suction ranged from −5 mm to −70 mm was used. Three- and one-dimensional infiltration tests were performed on repacked cores by applying pressure heads −70, −40 and −10 mm for loam soil, and −30 and −10 mm for silty clay loam soil. Analysis of the results showed that the difference between the three- and one-dimensional infiltration is linear with time confirming the equation of Smettem et al. [1]. Also, this difference is used to calculate the value of an additional infiltration parameter.