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Aims: Assuming the saturated, θs, and residual θr volumetric water contents of a seed as known inputs, we present a methodology to determine the hydraulic properties of a seed: α, n parameters and hydraulic conductivity Ks. Methods: The seed is considered as a porous material in which water flow is governed with the same hydraulic properties defined for soils. Using the HYDRUS-2D software, the hydraulic properties of a seed were estimated from the inverse analysis of several cumulative seed imbibition curves measured at different seed water potentials, h. The optimum number of h was evaluated on synthetic seeds. The theoretical analysis was validated in laboratory experiments on barley, wheat and vetch seeds, where imbibition curves were measured with germination tests at seven levels of h (from 0 to -2.50 MPa). Results: The theoretical analysis showed that accurate estimates of α, n and Ks can be obtained if the most negative h-values are included in the optimization. The sensitivity analysis showed that the method allows obtaining a unique solution of α, n and Ks. The optimization error on the theoretical α, n and Ks was less than 1%. A satisfactory validation was also obtained on the experimental seed imbibition curves, with robust fits between the measured and optimized data. A unique solution of α, n and Ks was also obtained in all cases. Conclusions: A new method to determine the hydraulic properties of a seed is presented. This methodology could be used in different areas involving seed imbibition and also to simulate seed imbibition in different scenarios. [ABSTRACT FROM AUTHOR]

Background and aims: Germination as a function of soil water potential (h) is modelled using polyethylene glycol (PEG). But, PEG would not consider soil properties. Our objective is to show the limitations of PEG to model germination in real soils. Using a new device, the tension germinator (TG), we show the interaction between soil type, h and seed characteristics on seed germination.TG (A Mariotte reservoir that supplies water at constant h to a porous substrate on which seeds are deposited). Barley (Hordeum vulgare L.) and vetch (Vicia sativa L.) seeds were placed on TG with loam (TG-loam) and sand (TG-sand), and h of 0, -0.002, -0.006 MPa. Then, the imbibition curves were monitored. PEG experiments (0 to -2.5 MPa) were performed to estimate the critical h, hPEG, or h from which the imbibition curve decreases compared with that at 0 MPa. PEG curves for 0 > h > -0.01 MPa were compared with TG.PEG and TG curves were not different at 0 MPa. hPEG for barley and vetch was within [0, -0.01] MPa. While no differences were observed between PEG at [0, -0.01] MPa and TG-loam curves, TG-sand curves at -0.002 and -0.006 MPa were different to those of PEG. Conversely to PEG at -0.01 MPa, no imbibition was observed in TG-sand (-0.006 MPa). A negligible influence of h in TG-loam was observed.PEG is not adequate to describe seed germination in soil. But the TG allows monitoring seed germination in real soils and controlled h.Methods: Germination as a function of soil water potential (h) is modelled using polyethylene glycol (PEG). But, PEG would not consider soil properties. Our objective is to show the limitations of PEG to model germination in real soils. Using a new device, the tension germinator (TG), we show the interaction between soil type, h and seed characteristics on seed germination.TG (A Mariotte reservoir that supplies water at constant h to a porous substrate on which seeds are deposited). Barley (Hordeum vulgare L.) and vetch (Vicia sativa L.) seeds were placed on TG with loam (TG-loam) and sand (TG-sand), and h of 0, -0.002, -0.006 MPa. Then, the imbibition curves were monitored. PEG experiments (0 to -2.5 MPa) were performed to estimate the critical h, hPEG, or h from which the imbibition curve decreases compared with that at 0 MPa. PEG curves for 0 > h > -0.01 MPa were compared with TG.PEG and TG curves were not different at 0 MPa. hPEG for barley and vetch was within [0, -0.01] MPa. While no differences were observed between PEG at [0, -0.01] MPa and TG-loam curves, TG-sand curves at -0.002 and -0.006 MPa were different to those of PEG. Conversely to PEG at -0.01 MPa, no imbibition was observed in TG-sand (-0.006 MPa). A negligible influence of h in TG-loam was observed.PEG is not adequate to describe seed germination in soil. But the TG allows monitoring seed germination in real soils and controlled h.Results: Germination as a function of soil water potential (h) is modelled using polyethylene glycol (PEG). But, PEG would not consider soil properties. Our objective is to show the limitations of PEG to model germination in real soils. Using a new device, the tension germinator (TG), we show the interaction between soil type, h and seed characteristics on seed germination.TG (A Mariotte reservoir that supplies water at constant h to a porous substrate on which seeds are deposited). Barley (Hordeum vulgare L.) and vetch (Vicia sativa L.) seeds were placed on TG with loam (TG-loam) and sand (TG-sand), and h of 0, -0.002, -0.006 MPa. Then, the imbibition curves were monitored. PEG experiments (0 to -2.5 MPa) were performed to estimate the critical h, hPEG, or h from which the imbibition curve decreases compared with that at 0 MPa. PEG curves for 0 > h > -0.01 MPa were compared with TG.PEG and TG curves were not different at 0 MPa. hPEG for barley and vetch was within [0, -0.01] MPa. While no differences were observed between PEG at [0, -0.01] MPa and TG-loam curves, TG-sand curves at -0.002 and -0.006 MPa were different to those of PEG. Conversely to PEG at -0.01 MPa, no imbibition was observed in TG-sand (-0.006 MPa). A negligible influence of h in TG-loam was observed.PEG is not adequate to describe seed germination in soil. But the TG allows monitoring seed germination in real soils and controlled h.Conclusions: Germination as a function of soil water potential (h) is modelled using polyethylene glycol (PEG). But, PEG would not consider soil properties. Our objective is to show the limitations of PEG to model germination in real soils. Using a new device, the tension germinator (TG), we show the interaction between soil type, h and seed characteristics on seed germination.TG (A Mariotte reservoir that supplies water at constant h to a porous substrate on which seeds are deposited). Barley (Hordeum vulgare L.) and vetch (Vicia sativa L.) seeds were placed on TG with loam (TG-loam) and sand (TG-sand), and h of 0, -0.002, -0.006 MPa. Then, the imbibition curves were monitored. PEG experiments (0 to -2.5 MPa) were performed to estimate the critical h, hPEG, or h from which the imbibition curve decreases compared with that at 0 MPa. PEG curves for 0 > h > -0.01 MPa were compared with TG.PEG and TG curves were not different at 0 MPa. hPEG for barley and vetch was within [0, -0.01] MPa. While no differences were observed between PEG at [0, -0.01] MPa and TG-loam curves, TG-sand curves at -0.002 and -0.006 MPa were different to those of PEG. Conversely to PEG at -0.01 MPa, no imbibition was observed in TG-sand (-0.006 MPa). A negligible influence of h in TG-loam was observed.PEG is not adequate to describe seed germination in soil. But the TG allows monitoring seed germination in real soils and controlled h. [ABSTRACT FROM AUTHOR]

• We present the SWRIM model for simulating infiltration curves in SWR substrates. • SWRIM represents the pore system as a set of disconnected pathways with dual K. • SWRIM estimates the K d distribution and the percentage of water-conducting pores. • SWRIM was validated on different substrates of 1.0 and 2.5 cm height. • Robust fits were obtained between experimental and modeled infiltration curves. The hydraulic characterization of hydrophobic substrates, which strongly depends on the water content, is an understudied topic in the field of soil physics. Based on laboratory experiments, this work presents a physically-based model, denoted as Soil Water Repellency Infiltration Model (SWRIM), to describe the double-slope cumulative infiltration curves commonly observed in hydrophobic substrates, whose behavior is conditioned by the dual hydraulic behavior (under dry and saturated conditions) of the water repellency materials. The experimental setup consists of 1D infiltration tests on hydrophobic substrates and tension of 0 cm, following by a free drainage. The SWRIM model assumes that water flow in the hydrophobic substrate is gravity driven, representing the pore system as a set of disconnected pathways or capillaries with dual behavior. Each capillary is governed by two hydraulic conductivity values corresponding to dry or partially saturated and saturated conditions, K d and K s respectively. During infiltration, water flow within each pathway is regulated by K d , but once the pathways are filled and the substrate is fully saturated, the water flow is governed by K s , whose value is directly measured from the slope of the drainage curve. In order to incorporate the variability of the pore system, unimodal and bimodal probability distributions of K d values were considered. The application of the SWRIM model allowed determining the distribution of K d and the percentage of water-conducting pores, δ , of the hydrophobic layer. Additional determinations of the soil hydraulic conductivity, K , and sorptivity under water repellent conditions were also obtained from the inverse analysis of the initial times of the infiltration test. The proposed model was validated on experimental soil columns of 5 cm internal diameter and 1.0 and 2.5 cm height filled with pine forest organic material, Pine, rosemary leaf litter, RS, and, blond peat, Peat. Overall, convex-to-linear curves with a monotonously increasing infiltration, typical of hydrophobic substrates, were obtained. SWRIM model allowed robust fits of the infiltration curves, showing in all cases a distribution of K d with a bimodal shape. Pine and Peat presented the largest values of δ. The estimated average K d was within the same order of magnitude as K values. Overall, the results showed that the proposed physically-based model allows to satisfactory describe and characterize the dynamic hydraulic behavior of hydrophobic soil substrates. [ABSTRACT FROM AUTHOR]

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]

• A new method to simultaneously estimate soil hydraulic properties is presented. • K s , α and n are estimated from inverse analysis of an upward infiltration curve. • The method is evaluated on different synthetic and experimental soils. • Accurate estimates of K s , α and n are obtained in the theoretical curves. • The method allows accurate estimates of K s and n in all experimental soils. This paper presents a new laboratory method to simultaneously estimate K s and α and n parameters of the van Genuchten (1980) θ (h) from the inverse analysis of an upward infiltration curve measured in a 5-cm high soil column. The method was evaluated on synthetic 1D infiltration curves generated for a theoretical loamy sand, loam and clay soil. The influence of the soil initial condition on the inverse analysis was also studied. Next, an optimization method was presented and tested on eight theoretical soils (from loamy sand to clay). The method was subsequently applied to experimental curves measured on five sieved soils (from sand to clay) packed in 5-cm high and diameter cylinders. The K s , α and n values estimated from the inverse analysis of the experimental curves were compared to those measured by Darcy and the pressure cell method (PC). The initial soil tension, h i , which had an important influence on the optimization, was fixed to −6.0·105 cm. The optimization method resulted robust and allowed accurate estimates of the actual hydraulic parameters. A close to one relationship (R2 = 0.99) was observed between the theoretical K s , α and n and the corresponding values obtained with the inverse analysis. Regarding to the experimental soils, significant relationships close to one were obtained between K s and n (R2 > 0.98) estimated from inverse analysis and those measured with Darcy and PC. A non-significant relationship with slope away from one was found for α. [ABSTRACT FROM AUTHOR]

Highlights • This work analyses the influence of the β on the estimate of K and S. • Early infiltration times (i.e. 100 s) promoted good estimations for S. • Longer infiltrations (i.e. 1.000 s) were required to estimate accurately K s. • Only very long infiltration (i.e. 10.000 s) allowed defining the actual β value. • S and K s can be accurately estimated using a constant β. Abstract Soil water infiltration can be described with the quasi-analytical Haverkamp et al. (1994) equation, defined by the hydraulic conductivity (K s), sorptivity (S) and the β parameter. K s and S are commonly estimated from the transient cumulative infiltration curve, using a constant β value. The objective of this work was to study the influence of β on the estimation of K s and S. The study was first performed on synthetic 1-D infiltration curves generated at different infiltration times for loam sandy, loamy and silty soils, and next extrapolated to a 3-D loam synthetic soil and on 10 infiltrations curves measured on the field with a disc infiltrometer on different types of soils. The infiltration measurements lasted between 600 and 900 s. The results showed that, while early infiltration times (i.e. 100 s) promoted good estimations for S , longer infiltrations (i.e. 1.000 s) were required to estimate accurately K s. Only very long infiltration (i.e. 10.000 s) allowed defining the actual β value. A similar behaviour was observed for the 3-D infiltration measurements. Except for β , significant relationships (R2 = 0.99) were obtained between the K s and S of the three theoretical soils and the corresponding values calculated by optimizing the three hydraulic parameters on 2.000 s 1-D infiltration curves. The large confidence interval observed in β (between 0.3 and 2.0) resulted from the fact that β had a small effect on the infiltration curve. A significant relationship (R2 = 0.99) was also obtained between the K s and S optimized from the experimental curves using a β = 1.1 and the corresponding values obtained by simultaneous optimization of the three hydraulic parameters. These results demonstrated that S and K s can be accurately estimated using a constant β and that downward infiltration is not an appropriate procedure to estimate β. [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]

The water retention curve ( θ ( h )), which defines the relationship between the volumetric water content ( θ ) and the matric potential ( h ), is of paramount importance to characterize the hydraulic behaviour of soils. Because current methods to estimate θ ( h ) are, in general, tedious and time consuming, alternative procedures to determine θ ( h ) are needed. Using an upward infiltration curve, the main objective of this work is to present a method to determine the parameters of the van Genuchten (1980) water retention curve ( α and n ) from the sorptivity ( S ) and the β parameter defined in the 1D infiltration equation proposed by Haverkamp et al. (1994). The first specific objective is to present an equation, based on the Haverkamp et al. (1994) analysis, which allows describing an upward infiltration process. Secondary, assuming a known saturated hydraulic conductivity, K s , calculated on a finite soil column by the Darcy’s law, a numerical procedure to calculate S and β by the inverse analysis of an exfiltration curve is presented. Finally, the α and n values are numerically calculated from K s , S and β . To accomplish the first specific objective, cumulative upward infiltration curves simulated with HYDRUS-1D for sand, loam, silt and clay soils were compared to those calculated with the proposed equation, after applying the corresponding β and S calculated from the theoretical K s , α and n . The same curves were used to: (i) study the influence of the exfiltration time on S and β estimations, (ii) evaluate the limits of the inverse analysis, and (iii) validate the feasibility of the method to estimate α and n . Next, the θ ( h ) parameters estimated with the numerical method on experimental soils were compared to those obtained with pressure cells. The results showed that the upward infiltration curve could be correctly described by the modified Haverkamp et al. (1994) equation. While S was only affected by early-time exfiltration data, the β parameter had a significant influence on the long-time exfiltration curve, which accuracy increased with time. The 1D infiltration model was only suitable for β < 1.7 (sand, loam and silt). After omitting the clay soil, an excellent relationship (R 2 = 0.99, p < 0.005) was observed between the theoretical α and n values of the synthetic soils and those estimated from the inverse analysis. Consistent results, with a significant relationship (p < 0.001) between the n values estimated with the pressure cell and the upward infiltration analysis, were also obtained on the experimental soils. [ABSTRACT FROM AUTHOR]

• This method estimated K s , θ s , n and α dr of a soil column by inverse analysis. • 1D infiltration followed by successive steady-states drainages were measured. • The drainage curves are generated by a differential h between the top and the bottom. • The method was tested on 2.5 cm high synthetic and experimental soil columns. • Accurate estimates of θ s , K s , α dr and n were obtained. Determination of the saturated hydraulic conductivity, K s , and the water retention curve, θ(h) , is of paramount importance to characterize the hydraulic behavior of the vadose zone. Given the van Genuchten hydraulic model, defined by the residual, θ r , and saturated, θ s , volumetric water content and the α and n parameters, this work presents a new laboratory procedure to estimate K s , θ s , n and α for a drainage process, α dr , from the inverse analysis of successive drainage steady-states curves generated by a tension-gradient between the surface and the base of a soil column. To this end, a double disc system, one connected a bubbling tower and placed at the soil surface and the second one placed under the soil core, was employed. The second disc was connected to an air-vacuum system. The experiment presented two parts: a first 1D downward infiltration at saturation on a dry soil column, followed by successive drainage steps. During the drainage process, the tension of the upper and lower discs varied between 0 and −5 cm, and from −5 to −100 cm, respectively. The soil sorptivity, S , and θ s were calculated from the 1D transient infiltration measure, K s was calculated by Darcy's law, α dr and n were optimized from the inverse analysis of the steady-state curves under tension-gradient and α for a wetting process, α w , was calculated from previously obtained S , θ s , K s and n. Once K s estimated, α dr and n were optimized by minimizing the Q = h b - h n objective function, where h b and h n are the experimental and calculated tensions at the base of the soil core. Given a α dr value, the optimimum n was computed as the value that provides a minimum Q. By repeating this process for a sequence of α dr , different Q -isolines were obtained, one for each h b value, which crossing-point corresponded to the actual α dr and n values. The method was tested on 2.5 cm high columns of four different synthetic soils. Next, it was applied on an experimental sand column of 5 cm height and on 2.5 cm high columns filled with sieved loam, clay loam and clay soil. The estimated α dr and n were compared with corresponding values measured in the same soils with the pressure plate technique and α w was contrasted with the corresponding value calculated with an empirical hysteresis model. The method, which was fast (from 1 to 2 h) and easy to implement for small-scale experiments, was successfully applied to soil samples 2.5 cm high and allowed to explore a range of soil tensions from 0 to −100 cm. Overall, accurate estimates of θ s , K s , α dr and n were obtained in both synthetic and experimental soils. A significant relationship was also obtained between α w estimated from S and the corresponding value calculated from the hysteresis model. [ABSTRACT FROM AUTHOR]

Summary In-situ measurements of soil hydraulic properties on covered soil surfaces (i.e. vegetated or residue covered surfaces) are of paramount importance in many agronomic or hydrological researches. These soil parameters are commonly estimated with the tension infiltrometry technique. This paper presents a portable and modified design of the hood infiltrometer (MHI) that, unlike to the original hood infiltrometer, allows estimating the soil hydraulic properties from the transient cumulative infiltration curve. The MHI consists of a water-supply reservoir attaches to a hat-shaped base placed on the soil surface. The base of the hat is closed by a system of sticks and a malleable material ring. To test the viability of this new design, the hydraulic conductivity ( K s ) estimated with MHI in a loam soil using the multiple head approach was compared to the corresponding values calculated from the transient infiltration curve analysis. Next, the MHI was tested on three different soils at saturated conditions, and the sorptivity ( S ) and K s estimated by the transient infiltration curve analysis were compared to the corresponding values obtained with a disc infiltrometer (DI). An additional field experiment was performed to compare the hydraulic properties measured with MHI on a bare soil and a soil covered with plants. Results demonstrated that this design allows hermetically closing the base of the hat without disturbing the soil surface. The K s estimated with the multiple head approach was not statistically different ( p = 0.61) to that obtained with the transient infiltration curve analysis. No significant differences between the K s ( p = 0.66) and S ( p = 0.50) values estimated with DI and MHI were observed. The S values measured with MHI on the covered soil surface were significantly higher than that measured on the adjacent bare soil. These results indicate that MHI can be a viable alternative to estimate the hydraulic properties of covered soils from the measured transient infiltration curve. [ABSTRACT FROM AUTHOR]

Summary Many gypsiferous soils occur in arid lands, where the water retention capacity of the soil is vital to plant life and crop production. This study investigated the effect of gypsum content on the gravimetric soil water retention curve (WRC). We analyzed calcium carbonate equivalent (CCE), equivalent gypsum content (EG), soil organic carbon content (SOC), and electrical conductivity of 43 samples collected from various horizons in soils in the Ebro Valley, NE Spain. The WRC of the fine earth was determined using the pressure-plate method (pressure heads = 0, −33, −100, −200, −500, and −1500 kPa), and the gravimetric water retention curves were fitted to the unimodal van Genuchten function. Soil gypsum content had a significant effect on water retention. Soils that had high gypsum content made WRC with higher water retention at near saturation conditions, and steeper WRC slopes. The EG threshold at which gypsum content had an effect on WRC was about 40%, and EG was positively and negatively correlated with the α and n parameters of the WRC, respectively. [ABSTRACT FROM AUTHOR]

• This work presents an upward infiltration method to estimate K PF = K T - K s. • K s and K T are measured from the transient infiltration and an overpressure step. • It was satisfactorily validated on packed soil with and artificial PF channel. • It was applied on soil cores collected from a grazing and tillage experiment. • 5, 35 and 60% of soil cores presented significant, moderate and negligible PF. Soil water preferential flow, PF, is the phenomenon where water moves along certain pathways, while bypassing a fraction of the porous matrix. This work presents a laboratory procedure to estimate the hydraulic conductivity of the soil water preferential flow, K PF. Using an upward infiltration curve followed by an over-pressure step, K PF is calculated as the difference between the total hydraulic conductivity, K T , measured with the constant head method, and the soil matrix hydraulic conductivity, K s , calculated from the inverse analysis of the transient upward infiltration curve. Previous to this analysis, a new approach to detect and remove the effect of possible overpressures due to the soil core placement on the sorptivimeter on the hydraulic properties estimate was presented. This consisted on searching the best fitting between the experimental infiltration curve after removing successive early time steps and the corresponding simulated function. The method to estimate K PF was validated on four different 5-cm height soil columns packed with 2-mm sieved clay loam and loam soils traversed longitudinally by a closed/opened pipe of 1.5 mm and 2.5 mm internal diameter, respectively. This same experiment was also repeated on the same soils without artificial preferential channel. Next, the method was applied on 20 undisturbed soil cores collected from two fields with different grazing intensity and soil tillage management (conventional, CT, reduced, RT and no-tillage, NT, practices). Results showed that correction made to remove the infiltration curve jump due to an overpressure step allowed more accurate and realistic estimates of the soil matrix hydraulic properties. On the other hand, both K T and K s , which could be satisfactorily calculated from a single upward infiltration curve followed by an overpressure step, where satisfactorily employed to quantify K PF. While no significant effect of grazing intensity on K PF was observed, the CT K PF was significantly larger than those obtained in RT and NT. [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]

Summary: The arid agricultural lands of the Monegros Desert, in the central Ebro Basin (NE Spain), show contrasting white patches (WPs) and dark patches (DPs), evidencing their different soil composition. The white patches have shallow soils with low or nil crop development in most years. Soil at the dark patches uses to be deeper, and winter cereal attains better development. This paper analyzes soil hydro-physical features in order to identify differences in soil physical properties between white and dark soils. For this purpose, 20 pairs of WP/DP soils were studied on several agricultural plots. Each sampled pair was under the same soil condition. Three soil treatment (ST) were studied: freshly tilled soil (MB), cropped (C), and fallowed soil (F). The gypsum and calcium carbonate content, organic matter (OM) content, and particle size distribution for the 0–10cm depth soil were determined. Field measurements for the 1–10cm depth soil layer were soil bulk density (ρb ), soil penetration resistance (SPR), saturated hydraulic conductivity (K 1–10) and sorptivity (S 1–10). The water retention curve (WRC) was determined in the lab on undisturbed soil cores for the 1–10cm depth soil layer. Additional field measurements of soil surface crust sorptivity (Scrust ) and hydraulic conductivity (Kcrust ) at saturation were also performed. The results show that WP soils have significantly (p <0.05) higher contents of gypsum, lower contents of calcium carbonate and OM, and a coarser texture than DP soils. Compared to DP, the WP soils have higher values of SPR but lower ρb , K and S values in both the surface crust and the 0–10cm depth soil layer. On average, K 1–10 in DP was 1.4times higher than that measured in WP. DP showed a better-defined microstructure and retained more water retention at near saturation conditions than WP. Soil treatments have a significant effect on ρb , SPR, S 1–10, K 1–10 and on the WRC parameters. Overall, ρb and SPR was the lowest under MB, with maximal S 1–10 and K 1–10 values under C. Compared to C and F, MB presented the highest volume of structural porosity and the lowest water retention at near saturation conditions. [Copyright &y& Elsevier]

Water redistribution from bare soil to vegetation patches is a key feature of semi-arid ecosystems, and is responsible for their patchy vegetation patterns. The magnitude of water redistribution depends on the properties of the bare soil (which determine the amount of water run-off) and the capacity of vegetation patches to trap water run-on. We examined the relationships between plant spatial patterns, water infiltration into bare soil, and plant community composition in semi-arid sites with different hydro-physical properties (silty and gypseous soils) in NE Spain. We also studied the effect of two stressors, aridity and grazing, on water infiltration and plant spatial patterns. Our results indicate a negative correlation of bare soil sorptivity (the capacity to absorb water by capillarity) and vegetation aggregation. There was a strong positive correlation between perennial grass cover and the spatial aggregation of vegetation, but aggregation was not associated with positive associations of different plant types. The aggregation of vegetation was positively correlated with species richness and the overall extent of vegetation cover. Grazing reduced water infiltration into silty soils, which are prone to compaction. In contrast, soil crust affected the hydrology of gypseous soils, especially in the most arid sites, where grazing increased infiltration, reducing surface sealing due to breaking of the soil crust. Together, our results suggest that biotic and abiotic factors affect the hydro-physical properties of soils in the semi-arid ecosystems of NE Spain, which is linked to the plant communities through the spatial distribution of plants. [ABSTRACT FROM AUTHOR]

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]

Summary: The measurement of the soil solution electrical conductivity (σw ) is critical for a better management of irrigation water and the effective monitoring and control of soil salinity. The objective of this work is to present the design and validation of a new time domain reflectometry (TDR) probe (WECP) for accurate and non-destructive measurements of σw . The probe consists in 14 porous ceramics disks (0.5bar bubbling pressure) arranged along the axis of a three-rod TDR probe. Using the model, σw was estimated from the volumetric water content (θ) and the bulk electrical conductivity (σa ) measured in the ceramic disk set of known pore-geometry. The τ and β factors, which describe the complex geometry of the ceramic matrix, were calculated by immersing the probe in NaCl solutions of different electrical conductivities, and in a pressure cell wetted and drained with these NaCl solutions, respectively. The reliability of the WECP was validated under laboratory and field conditions. The laboratory experiment consisted of the TDR probe inserted in a pressure cell packed with mixed sand and 2-mm sieved loam soil that was subsequently wetted and drained with different NaCl solutions at various pressure heads. The σw estimated by WECP was compared to the σw measured in the draining solutions after they stabilized in the soil porous system. The field experiment compared the σw estimated by WECP with the corresponding σw values measured in the soil solution extracted with three ceramic tension lysimeters (TLs) after successive wetting and drainage cycles. The τ and β factors calculated for the ceramic disks set were 1.957 and 4.282, respectively. High and significant correlations were found in both laboratory (R 2 =0.98; P <0.001) and field (R 2 =0.97; P <0.001) experiments between the σw estimated by the WECP and the corresponding σw values measured in the column-drainage or TL-extracted soil solutions, respectively. These results demonstrate that the WECP is a feasible instrument to accurately estimate soil solution salinity independently of the soil water content and the porous medium in which the TDR probe is installed. [Copyright &y& Elsevier]

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]

• This work analyzes the influence of layered soils on K s and S estimates. • The Sequential Infiltration Analysis (SIA) method was proposed. • SAI was tested on synthetic and laboratory columns and experimental soils. • Estimates of K s and S improved when the SIA method was applied. • Method also allowed determining the thickness of the upper soil layer. The soil sorptivity, S , and saturated hydraulic conductivity, K s , can be estimated from the inverse analysis of a cumulative infiltration curve using the quasi-exact implicit (QEI) formulation or its corresponding 4-Terms (4T) approximation. Although these models consider the soil as homogeneous media, there is no information about how heterogeneous profiles can affect the inferred soil properties. This work analyzes the influence of layered soils on K s and S estimates using QEI and 4T models, and designs a new procedure for treating infiltration curves measured on layered soil profiles. The Sequential Infiltration Analysis (SIA) method considers a sequence of increasing time series from the cumulative infiltration data to estimate K s and S , and its corresponding RMSE as a function of the number of samples used. A procedure to estimate the thickness of the upper uniform soil layer from the estimated wetting front advance (WFA) is also reported. The SIA method was applied on: (i) synthetic homogeneous profiles of loam soil and six layered profiles involving a 1, 2 and 3 cm thickness loam layer over silty or sandy loam soils, respectively, (ii) stratified laboratory soil columns, and (iii) 20 experimental infiltrations performed in a semiarid region of North-Eastern Spain. Similar results were found between QEI and 4T models for all cases. Erroneous estimates of K s and S were observed when the total infiltration time series was considered for the analysis, regardless of the presence of soil layering. In opposite, estimates improved when the SIA method was applied to the layered systems. The SIA method exploits the fact that the RMSE increases when the wetting front reaches the interface between the soil layers. Such increase allows: (i) detection of the soil heterogeneity, (ii) determination of the infiltration time, t o , required for the wetting front to reach the lower layer, and, (iii) accurate estimates of the upper layer K s and S along with its thickness. Laboratory experiments on layered soils and field measurements demonstrated that the SIA method could be satisfactorily applied on different curves with contrasting shapes and magnitudes. Although soil layering encountered on most field samplings restricted the treatment of the observed infiltrations to short-medium times, the SIA method allowed robust estimates of K s and S. These results indicate that the proposed method is a promising tool for characterizing the hydraulic properties of layered and heterogeneous soil profiles. [ABSTRACT FROM AUTHOR]

• A new compact 10 cm height and diameter tension disc infiltrometer is presented. • The water level is monitored by a smartphone camera. • The device was satisfactory compared in laboratory with V and PT methods. • Accurate estimate of hydraulic conductivity and sorptivity were obtained. • The method is an accurate, low-cost, portable and easy to use in field. The tension disc infiltrometer has become a widespread method to measure soil hydraulic properties under unsaturated conditions. Although several automated devices have been developed, most designs include an elongated water reservoir and a pressure transducer with electronic components to register the water level, increasing its cost and limiting its application. The objective of this work is to present a new tension disc infiltrometer with a compact design of 10 cm diameter and height, where the water level is monitored by a smartphone camera. The infiltration curve is determined from the automated analysis of the images recorded by the smartphone without additional electronic components. The device was first validated in the laboratory by comparing visual measurements (V), the camera imagery (Ca) and a pressure transducer (PT). Next, it was tested on field infiltration experiments. Robust fits (R2 = 0.99) were found between the water level measured with Ca in the laboratory and those obtained with V and PT procedures. The Ca method is accurate, robust and independent of the relative camera position. Good fits were also observed between Ca water level and those obtained with PT in the field experiments. Similar hydraulic conductivity and sorptivity values were obtained with both sensors using the numerical solution of the Haverkamp (NSH) equation. The compact infiltrometer, in conjunction with the smartphone camera, is an accurate, accessible, portable and easy-to-use field-based device for soil hydraulic characterisation. [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]

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]

Summary Based on the analysis of Haverkamp et al. (1994), this paper presents a new technique to estimate the soil hydraulic properties (sorptivity, S , and hydraulic conductivity, K ) from the full-time cumulative infiltration curves. The proposed method, which will be named as the Numerical Solution of the Haverkamp equation (NSH), was validated on 12 synthetic soils simulated with HYDRUS-3D. The K values used to simulate the synthetic curves were compared to those estimated with the NSH method. A procedure to detect and remove the effect of the contact sand layer on the cumulative infiltration curve was also developed. A sensitivity analysis was performed using the water level measurement as uncertainty source and the procedure was evaluated considering different infiltration times and data noise (e.g. air-bubbling in the infiltrometer). The good correlation between the K used in HYDRUS-3D to model the infiltration curves and those obtained by the NSH method ( R 2 = 0.98) indicates this technique is robust enough to estimate the soil hydraulic conductivity from complete infiltration curves. The numerical procedure to detect and remove the influence of the contact sand layer on the K and S estimates resulted to be robust and efficient. A negative effect of the curve infiltration noise on the K estimate was observed. The results showed that infiltration time was an important factor to estimate K . Smaller values of K or lower uncertainty required longer infiltration times. In a second step, the technique was tested in field conditions on 266 different soils at saturation conditions, using a 10 cm diameter disc infiltrometer. The NSH method was compared to the standard differentiated linearization procedure (DL), which estimates the hydraulic parameters using the simplified Haverkamp et al. (1994) equation, valid only for short to medium times. Compared to DL, NSH was considerably less affected by the infiltration bubbling and the contact sand layer, and allowed more robust estimates of K and S . Although comparable S values were obtained with both methods, the NSH technique, which is not limited to short times, resulted in more accurate and robust estimates for K . This paper demonstrates the NSH method is a significant advance to estimate of the soil hydraulic properties from the transient water flow. [ABSTRACT FROM AUTHOR]