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Abstract Estimation of soil sorptivity (S) and hydraulic conductivity (K) is fundamental to model the water infiltration into the soil. This process can be affected by soil water repellency, which is defined as a reduction in soil wettability due to coating of soil particles by hydrophobic substances. Unlike to wettable soils, this phenomenon can generate infiltration curves with double-slope shape: a transient infiltration curve followed by a steady-state section. Because the topsoil final volumetric water content (θ 1) of the transient phase of the double-slope curve is not a measurable data, in principle, the standard model based on the Haverkamp et al. (1994) model cannot be used to estimate S and K. This work presents two different approaches based on the Haverkamp et al. (1994) equation, which allow estimating S and K from the first phase of a double-slope infiltration curve, when θ 1 data are not available. The methods, which are based on the analysis of both short-medium time transient infiltration curve (Tr) and the combination of both short-medium transient and steady-state infiltration steps (Mx), were applied on 20 soils affected by different degrees of water repellency. The Haverkamp et al. (1994) model was also valid for infiltration curves measured on hydrophobic soils, and the final volumetric water content was not an essential data to estimate K and S. Although the steady-state infiltration rate (q 1) calculated with Mx was about 26% larger than that estimated with Tr , comparable K and S values were obtained with both methods. Overall, a large dispersion on the estimate of θ 1 was observed with both methods. The gravimetric time, t grav , estimated in the studied soils was low, <500 s. While the Mx method required simpler numerical calculus, Tr looked like to be more robust and less subjective. Highlights • This work analyzes the first part of a bi-slope infiltration curve affected by SWR. • A first method (Tr) estimates K and S from the transient infiltration curve. • The second one (Mx) combines short-transient and steady-state infiltration analysis. • The methods were applied on 20 soils affected by SWR. • Mx requires less numerical calculus, but Tr was more robust and less subjective. [ABSTRACT FROM AUTHOR]

The soil sorptivity, S , which is defined as a measure of the capacity of a porous medium to absorb or desorb liquid by capillarity, is commonly estimated under laboratory conditions from upward infiltration measurements. The objective of this work is to compare different methods to estimate S from a single upward infiltration curve obtained from both theoretical and experimental soils. An additional analysis of the influence of synthetic infiltration noise on the estimation of S was also performed on the theoretical soils. Five different methods were compared: Short Time model for horizontal infiltration (ST), the Cumulative Linearization method (CL) and the Differentiated Linearization (DL) linear regressions models, Short-time (SIM) methods that use the simplified Haverkamp et al. (1994) model, and Complete-time (CIM) upward infiltration method that uses the quasi-analytical Haverkamp et al. (1994) function. Since finite soil columns were considered, the saturated hydraulic conductivity needed to estimate S with the Haverkamp et al. (1994) model was calculated from an overpressure step at the end of the water absorption process, using the Darcy's law. The methods were contrasted on four theoretical and six sieved experimental soils, ranging from sand to clay textures. Although all methods showed acceptable estimates of S on clean theoretical upward infiltration curves, the ST, SIM and CIM were the methods that gave significant ( p < 0.001) regression analysis on noisied infiltration curves, and only SIM and CIM presented a relative error < 1%. From these results we can conclude that although acceptable approaches of S were obtained with the simplest ST method, the CIM procedure was the most accurate method to estimate S in both clean and noised theoretical and experimental upward infiltration curves. [ABSTRACT FROM AUTHOR]

Determination of saturated hydraulic conductivity,Ks, and the van Genuchten water retention curveθ(h) parameters is crucial in evaluating unsaturated soil water flow. The aim of this work is to present a method to estimateKs,αandnfrom numerical analysis of an upward infiltration process at saturation (Cap0), with (Cap0 + h) and without (Cap0) an overpressure step (h) at the end of the wetting phase, followed by an evaporation process (Evap). The HYDRUS model as well as a brute-force search method were used for theoretical loam soil parameter estimation. The uniqueness and the accuracy of solutions from the response surfaces,Ks–n, α–nandKs–α, were evaluated for different scenarios. Numerical experiments showed that only the Cap0 + Evap and Cap0 + h+ Evap scenarios were univocally able to estimate the hydraulic properties. The method gave reliable results in sand, loam and clay-loam soils. [ABSTRACT FROM PUBLISHER]

Determination of saturated hydraulic conductivity, Ks, and the shape parameters α and n of the water retention curve, θ(h), is of paramount importance to characterize the water flow in the vadose zone. This work presents a modified upward infiltration method to estimate Ks, α and n from numerical inverse analysis of the measured cumulative upward infiltration (CUI) at multiple constant tension lower boundary conditions. Using the HYDRUS-2D software, a theoretical analysis on a synthetic loam soil under different soil tensions (0, 0-10, 0-50 and 0-100 cm), with and without an overpressure step of 10 cm high from the top boundary condition at the end of the upward infiltration process, was performed to check the uniqueness and the accuracy of the solutions. Using a tension sorptivimeter device, the method was validated in a laboratory experiment on five different soils: a coarse and a fine sand, and a 1-mm sieved loam, clay loam and silt-gypseous soils. The estimated α and n parameters were compared to the corresponding values measured with the TDR-pressure cell method. The theoretical analysis demonstrates that Ks and θ(h) can be simultaneously estimated from measured upward cumulative infiltration when high (>50 cm) soil tensions are initially applied at the lower boundary. Alternatively, satisfactory results can be also obtained when medium tensions (<50 cm) and the Ks calculated from the overpressure step at the end of the experiment are considered. A consistent relationship was found between the α ( R2 = 0.86, p < 0.02) and n ( R2 = 0.97, p < 0.001) values measured with the TDR-pressure cell and the corresponding values estimated with the tension sorptivimeter. The error between the α (in logarithm scale) and n values estimated with the inverse analysis and the corresponding values measured with pressure chamber were 3.1 and 6.1%, respectively. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes a new method (NSQE) to estimate soil hydraulic properties (sorptivity, S, and hydraulic conductivity, K) from full-time cumulative infiltration curves. The technique relies on an inverse procedure involving the quasi-exact equation of Haverkamp et al. (1994). The numerical resolution is described and the sensitivity of the method is theoretically evaluated, showing that the accuracy of the estimates depends on the measured infiltration time. A new procedure to detect and remove the effect of the contact sand layer on the cumulative infiltration curve is also given. The method was subsequently compared to the differentiated linearization procedure (DL), which calculate K and S from the simplified Haverkamp et al. (1994) equation, valid only for short to medium times. A total of 264 infiltration measurements performed with a 10cm diameter disc under different soil conditions were used. Compared to the DL procedure, field measurements showed that the NSQE method allowed better estimates of soil hydraulic properties, independently on the infiltration noise and the presence of contact sand layer. Overall, although comparable S values were estimated with both methods, the longer infiltration times allowed by the proposed method made this procedure more accurate estimations of K. In conclusion, the NSQE method have shown to be a significant advance to accurate estimate of the soil hydraulic properties form the transient water flow. [Copyright &y& Elsevier]

Abstract: Time Domain Reflectometry is a technique widely used in hydrology and agronomy that allows real time estimation of soil volumetric water content (θ), which is related to soil's apparent permittivity (ɛa) and bulk electrical conductivity (σ). This work presents an enhanced release of TDR-Lab, software which controls instrumentation for field measurements of θ and σ, enabling a convenient recording and retrieving of data. TDR-Lab 2.0 supports Tektronics 1502C, TDR-100 Campbell Sci. and TRASE Soil-moisture Equipment Corp., which can be connected to a multiplexing system (SDMX50, Campbell Sci) allowing automated scheduled measurements from up to 251 different probes. This new release, when connected to TDR-100, allows increasing the waveform accuracy up to 2048 points/waveform. Multiple comparison of TDR waveform within the same TDR screen is now allowed. Graphical or numerical methods can be used for the estimation of θ and σ from soil measurements coming taken with different probes. Additional features to carry out water-surface-level measurements such as matric potential and soil solution electrical conductivity are also available when measurements are made using the corresponding specific probes. Two different versions, a lite and a full release, for field and laboratory applications have been developed. The light version with a reduced set of features (TDR-Lab Lite) was designed to run in low-end ultraportable devices. TDR- Lab Lite works with XML-files instead of the SQL database engine of the extended TDR-Lab, and has lower system requirements and a faster boot-up time. A robust import/export graphical user interface (GUI) facilitates transferring projects between the centralized SQL database and XML files. A new project manager window has been implemented, where the bar menu has been complemented with a useful set of icons. The display system projects has been improved and simplified. Within the project, a new friendly configuration manager for cables and TDR probes has been developed. Finally, an improved calibration procedure for TDR probes has been implemented. TDR Lab 2.0 supports more devices and provides additional estimated features from soil's measurements. Besides, the low hardware requirement of TDR-Lab Lite facilitates faster in-the-field tests and measurements. [Copyright &y& Elsevier]

The hydro-physical properties of gypseous soils, which are commonly associated with dry climates, determine the productivity of rangelands and croplands. The objective of this paper is to study, in the semiarid central Ebro Basin, NE Spain, some hydro-physical properties of gypseous soils under five different contrasted soil managements: soils of ungrazed (N) and grazed (GR) uncultivated lands, and freshly moldboard tilled (MB), cropped (C), and fallowed (F) agricultural soils. The gypsum content of the studied soils, with concentrations that are natural, ranged from 50 to 92%. The soil bulk density (ρb), saturated sorptivity (S10), hydraulic conductivity (K10), and the water retention curve (WRC) of undisturbed soil samples from the 0–10 cm deep soil layer after removing the soil surface crust were calculated. Soil penetration resistance (SPR) for the upper 10 cm soil layer was also measured. Additional measurements of soil surface crust sorptivity (Scrust) and hydraulic conductivity (Kcrust) were conducted. Livestock trampling in GR promoted the highest ρband SPR values. The lack of soil disturbance in N caused that this treatment showed the lowest values ofScrustandKcrust, but the highestS10andK10. The specific behavior of gypseous soils, whose loose aggregates easily collapse during the soil wetting process, showed that the MB freshly tilled soil produced the lowest values ofS10andK10. A typical bimodal function of the WRC was found. Pore size distribution was affected by the soil treatment, with the highest and lowest values under MB and GR treatments, respectively. [ABSTRACT FROM PUBLISHER]

This work presents a new design of disc infiltrometer, which, associated with a microflowmeter (MF) and a solenoid valve set, makes it possible to automate the infiltration rate ( Q) measurements at different soil pressure heads (ψ). The MF consists of a 13·8-cm long and 1·5 mm i.d. pipe, with a pressure transducer connecting the two ends of the MF, inserted in a water-flow pipe that connects the Mariotte tube and the water-supply reservoir of the disc infiltrometer. Water flow is calculated from the head losses in the MF. Changes in ψ in the bubble tower, automatically affected when the infiltration rate reaches steady state, are controlled by a datalogger connected to four solenoid valves. The new design was tested in laboratory and field conditions, and the results showed that the MF allows the soil water infiltration rates to be correctly estimated for different soil characteristics. The solenoid valve set plus datalogger system satisfactorily monitored the changes in ψ and allowed the measurement time to be optimized. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The water retention curve (θ(ψ)), which defines the relationship between soil volumetric water content (θ) and matric potential (ψ), is of paramount importance in characterizing the hydraulic behaviour of soils. However, few methods are so far available for estimating θ(ψ) in undisturbed soil samples. We present a new design of TDR-pressure cell (TDR-Cell) for estimating θ(ψ) in undisturbed soil samples. The TDR-Cell consists of a 50-mm-long and 50-mm internal diameter stainless steel cylinder (which constitutes the outer frame of a coaxial line) attached to a porous ceramic disc and closed at the ends with two aluminium lids. A 49-mm-long and 3-mm-diameter stainless steel rod, which runs longitudinally through the centre of the cylinder, constitutes the inner rod of a coaxial TDR probe. The TDR-Cell was used to determine the θ(ψ) curves of a packed sand and seven undisturbed soil samples from three profiles of agricultural soils. These θ(ψ) curves were subsequently compared to those obtained from the corresponding 2-mm sieved soils using the pressure plate method. Measurements of bulk electrical conductivity, σa, as a function of the water content, σa(θ), of the undisturbed soil samples were also performed. An excellent correlation ( R2 = 0·988) was found between the θ values measured by TDR on the different undisturbed soils and the corresponding θ obtained from the soil gravimetric water content. A typical bimodal θ(ψ) function was found for most of the undisturbed soil samples. Comparison between the θ(ψ) curves measured with the TDR-Cell and those obtained from the 2-mm sieved soils showed that the pressure plate method overestimates θ at low ψ values. The σa(θ) relationship was well described by a simple power expression ( R2 > 0·95), in which the power factor, defined as tortuosity, ranged between 1·18 and 3·75. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Pasture productivity depends on soil hydro-physical properties, which in turn are deeply affected by livestock grazing. However, the comparative response of different soil types, and particularly gypseous soil types, to grazing has hardly been studied before. This paper compares the effect of grazing on the soil hydro-physical properties of silty gypseous (Gy) and non-gypseous (NGy) soils located in a semi-arid region (Middle Ebro Valley, NE, Spain). Two different soil managements were selected: ungrazed natural shrubland (N) and grazed shrubland (GR) soils. The gypsum, CaCO3 and organic matter content (OM), soil texture, soil bulk density (ρ b ), penetration resistance (PR), saturated sorptivity (S), hydraulic conductivity (K), and the water retention curve (WRC) for undisturbed soil samples from 1 to 10cm depth soil layer were measured. The ρ b and PR in NGy soils were significantly higher than those observed in the Gy ones. Soil compaction due to grazing treatment tended to increase ρ b and decrease the K and S values. While no differences in PR were observed in the Gy soils between grazing treatments, the PR measured in the NGy soils under GR was significantly higher than the corresponding values observed under N. Differences in K and S between GR and N treatments were only significant (p <0.05) in NGy soils, where K and S values under the N treatment were almost four times greater than the corresponding values measured under GR. Overall, no differences in the WRCs were observed between soil types and grazing treatments. While the WRCs of NGy soils were not significantly affected by the grazing treatment, Gy soils under N treatment present a significantly higher level of soil macropores than under GR treatment. The hydro-physical features of Gy soils tended to be less affected by grazing than those of the NGy soils. These results suggest that livestock grazing, in both Gy and NGy soils, has a negative effect on the physical soil properties, which should be taken into account by land managers of these semi-arid regions where silty gypseous and non-gypseous areas coexist. [Copyright &y& Elsevier]

Time domain reflectometiy (TDR) is a technique that allows simultaneous estimates of apparent permittivity (ϵa) and hence volumetric water content (θ) and bulk electrical conductivity (σa). Difficulties arise for θ and σa determination, however, when uncoated TDR probes (UP) are used in highly conductive media. This work shows that σa can be estimated in highly conductive media using a TDR probe coated with a high-dielectric insulator (CP). To this end, the Dalton method for σa estimations was applied to a 10-cm-long three-rod TDR probe insulated with a 0.2-mm-thick epoxy-ceramic composite coating with a relative permittivity, ϵr, of 32.3. This method was calibrated on different NaCl-water solutions (0-15 dS m-1) and compared with the standard long-time TDR method for σa estimations using an UP. The method was subsequently used for determining σa in four different soils with different values of θ and σa (0-6 dS m-1) and again compared with the standard TDR procedure. The low error (RMSE = 1.5) for the comparison between the ϵa measured with the CP and that calculated with the analytical solution for coaxial probes indicates that the CP is accurate enough for ϵa estimations. For σa values <4 dS m-1, the UP allows determinations of ϵa and the most accurate estimations of σa using the standard TDR method (R2 = 0.99). For higher σa values, however, estimations of ϵa were only possible using the CP, where σa was satisfactorily determined (R2 = 0.99) using the Dalton method. To this end, a previous calibration between the real and the apparent bulk electrical conductivity estimated with the CP was required. [ABSTRACT FROM AUTHOR]

• Effect of grazing on soil hydraulic properties of gypseous soils were studied. • Three grazing intensities, High, Medium and Low, were compared. • Soil surface S and K c and subsurface ρ b , K s , θ s , α and n were measured. • H presented the highest ρ b and the lowest K c values. • In semiarid gypseous soils M did not have a negative effect of soil properties. Although is well known that grazing has a significant effect on the soil hydraulic properties and through them on the pasture productivity in semi-arid regions, there is still little data about the effect of this management on soils with high gypsum content. This work compares the effect of three increasing grazing intensities (low, medium, and high) on the hydraulic properties of the upper soil layers, measured on two areas with increasing gypsum content (56 and 73%, respectively) located in a semi-arid region of the Middle Ebro Valley (NE, Spain). 90 soil samplings were taken on bare soil surface areas. The measured soil parameters included the saturated sorptivity (S c) and hydraulic conductivity (K c) of the soil surface layer and the soil bulk density (ρ b), saturated hydraulic conductivity (K s), saturated volumetric water content, θ s , and α and n parameters of the water retention curve of the 1–8 cm depth soil layer. Increasing gypsum content increased the soil water infiltration but did not affect the water retention capacity and total porosity. All studied gypseous soils presented low water retention. High grazing intensities decreased the soil water infiltration. While soils with high gypsum content tended to attenuate the effect of the livestock trampling on ρ b , a significant influence of grazing on ρ b was observed in the fields with moderate soil gypsum content. No effect of livestock trampling on the soil water retention characteristics was observed. Moderate grazing, which did not show negative effects on the soil hydro-physical properties, could be an acceptable management for soil conservation in these semiarid regions of soils with high gypsum content. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a new type of pressure cell associated with a zigzag-shaped time domain reflectometry (TDR) probe for determining the soil-water retention (θ(ψ)) curve of disturbed thin soil samples. The pressure cell, designed for pressures ranging between 0 and −500kPa, consisted of a zigzag copper rod (150-mm long, 2mm in diameter) vertically installed in a clear plastic cylinder (60-mm high, 50mm in internal diameter) with six vertical copper rods (60-mm long, 2mm in diameter) arranged around the inner wall of the plastic cylinder. The cylinder was closed at the base with a nylon cloth and placed on a porous ceramic disc. The inner rod and the six-rod grille of the cell were connected respectively to the inner and outer conductors of a coaxial cable. The results showed that the correlation between the apparent dielectric constant measured with a standard three-rod TDR probe and the zigzag-shaped TDR probe, both immersed in five different non-conductive fluids, was excellent (R 2 =0.99). On the other hand, the volumetric water content measured with the TDR probe of the pressure cell filled up with sand, 2-mm sieved loam and clay-loam soils was highly correlated to the corresponding values calculated from the gravimetric water content and the soil bulk density (R 2 =0.97; RMSE=2.32×10−2). The parameters of the θ(ψ) curves measured for these three different soils with the TDR-pressure cell were within the range of values found in the literature. The cell was also used to study the θ(ψ) changes of a 2–4-mm sample of loam soil aggregates after a slow and a fast-wetting process. While negligible changes in both the soil structure and θ(ψ) were observed following slow wetting, fast wetting resulted in disintegration of aggregates and drastic changes in the shape of the θ(ψ) curve. [Copyright &y& Elsevier]

• A method to estimate θ s , α , n and K s from an upward infiltration is presented. • The influence of θ s, θ r and h i , on the α , n and K s optimization was studied. • It was applied to 50 mm high undisturbed cores under different soil management. • θ s and h i affected α , n and K s , and h i should be located the d θ dh ≈ 0 region. • It was sensible to different texture and structure due to the soil management. Estimation of the α and n van Genuchten (1980) parameters and the saturated hydraulic conductivity, K s , of undisturbed soil samples is critical for realistic water flow simulations in the vadose zone. Given the Latorre and Moret-Fernández (2019) method, which allows estimating K s , α and n from the inverse analysis of a single upward infiltration, the objective of this work is to advance on the theoretical understanding of this method and to apply it on undisturbed soil cores. To this end, the influence of the saturated, θ s , and residual, θ r , water content and initial soil tension, h i , on the α , n and K s optimization was first studied on synthetic soils. A procedure to simultaneously estimate θ s , α , n and K s , which consisted on optimizing α , n and K s for a range of θ s values, was proposed. To this end, α , n and K s were optimized leaving each θ s as a fixed value. The method was next applied to experimental curves measured from sieved and undisturbed soil cores of 50 mm high and diameter, sampled the last ones from three fields with different management: bare vs. under plant soil; agricultural soil under conservation vs. conventional tillage; and overburden soil from mine vs. topsoil formed by the original soil. Results showed that θ s had an important effect on α , n and K s optimization, where the minimum error within the selected θ s interval corresponded to the theoretical θ s. An important effect of h i on the optimization was also observed. However, this influence was omitted by using a h i value located in the θ r region, where d θ dh ≈ 0. Under this assumption, θ r only affected the θ s optimization, which value varied with θ r. A robust relationship (R2 = 0.99; p < 0.0001) was found between theoretical and optimized θ s , K s and α and n calculated for the synthetic soils. Thus, the method allowed estimating four of the five van Genuchten (1980) parameters. An absolute minimum was also observed when the method was applied on experimental infiltration curves. The θ s measured gravimetrically on the undisturbed samples was, on average, 8.1% higher than the optimized one. Overall, the method allowed detecting significant differences (p < 0.05) in hydraulic properties between bare and under plant soils and among tillage treatments. The large variability found in the mine's soils prevented to find significant differences within this scenario. [ABSTRACT FROM AUTHOR]

The time domain reflectometry (TDR) technique allows simultaneous estimation of apparent permittivity (εa) and bulk electrical conductivity (δa). In highly conductive media, however, the signal is completely attenuated, which precludes permittivity measurements. This study showed that δa can be estimated in conductive media by applying long-time TDR waveform analysis to a TDR probe partially insulated with a high-dielectric coating. Four 10-cm-long three-rod TDR probes with identical geometry but different percentages of rod coating were tested: an uncoated sensor (P0) and probes with 50% (P50), 75% (P75), and 95% (P95) of the rod length coated with an insulator with a relative permittivity (εr) of 32.3. A good relationship (r² = 0.99) was found between the εa estimated, if possible, with P0 immersed in several conductive and nonconductive media and the corresponding values estimated with P50, P75, and P95 The results also show that, for δa values ranging between 0.4 and 0.75 S m-1, simultaneous measurements of εa and δa were only possible using the partially coated probes. A good correlation was found between the δa estimated with P0 inserted in different soil columns wetted with highly saline solutions (i.e., δa > 0.2 S m-1) and those values estimated with P50, P75, and P95 (r² = 0.96, RMSE = 1.08, and SD = 0.38). For δa < 0.2 S m-1, the accuracy of the partially coated TDR probes for estimations of δa decreased as the percentage of the rod coating increased, with errors up to 292% when δa determined by P95 was compared with that estimated by P0. [ABSTRACT FROM AUTHOR]