New method for monitoring soil water infiltration rates applied to a disc infiltrometer

The definitive version is available at: http://www.sciencedirect.com/science/journal/00221694. - 8 Pages, 8 Figures, 3 Tables.Disc infiltrometers commonly use low-capacity water-supply reservoirs made of small diameter tubes. This reservoir geometry allows accurate measurements of water levels, but makes it necessary to stop the infiltration measurements to refill the water-supply reservoir when long-term infiltration experiments are conducted. The purpose of this study is to determine if a double Mariotte system provides accurate infiltration rate data from disc infiltrometer. To this end, infiltration rates (Q) is calculated from the head losses (ΔHT) produced by the water flowing along a flexible silicone pipe that connects a high-capacity water-supply reservoir and the disc of the infiltrometer. The method was calibrated in the laboratory using 2- and 3-mm internal diameter (i.d.) and 50- and 100-cm-long silicone pipes by comparing the measured ΔHT with the corresponding theoretical values, for different Q measured from the drop in water level in the water-supply reservoir. This method was next applied to field conditions, where the infiltration rates (at four supply pressure heads in five different soils) measured from the water-level drop in the water-supply reservoir of a double Mariotte disc infiltrometer (using 2- and 3-mm-i.d. and 100-cm-long silicone pipes) were compared with the corresponding values calculated from ΔHT measured in the Mariotte tube. An excellent correlation was found in the laboratory experiment between the calculated and the measured ΔHT (r2 = 0.99), and between Q measured from the water-supply reservoir and that calculated from the measured ΔHT (r2 = 0.99). In the field experiments, excellent correlation was shown between the infiltration rates measured from the water-level drop in the water-supply reservoir and the corresponding values calculated from the ΔHT measured in the Mariotte tube. This correspondence indicated that this method would be a consistent alternative to the standard procedure used in the disc infiltrometry technique.This research was supported by the Ministerio de Ciencia e Innovación of Spain (Grants AGL2007-66320-CO2-02/AGR; 200840I214).Peer reviewe

Un método sencillo para la estimación de la porosidad de un agregado de suelo

4 Pags.- 2 Figs. Trabajo originalmente presentado en las XII Jornadas de Investigación en la Zona No Saturada del Suelo (Alcalá de Henares, 18-20 de nov. de 2015). © de los textos: sus autores[ES] Este trabajo presenta un nuevo método (AM) para estimar la porosidad de agregados de suelo, , expresada como el cociente entre el volumen interno de poros (Vi) y el volumen externo del agregado (VT). VT se calcula a partir de la densidad de partícula, el peso del agregado y el Vi, estimado este último a partir del peso del agregado saturado en alcohol. El método se validó comparando VT por AM con el VT medido por fotogrametría (PHM), sobre 36 agregados de 8-16 mm procedentes de un suelo bajo laboreo tradicional (CT), reducido (RT) y no laboreo (NT). Los resultados muestran una buena relación entre el VT medido con PHM y AM (y = 0,94 x + 0,01; R2 = 0,99). El método fue suficientemente sensible para detectar diferencias entre los sistemas de laboreo. Los agregados de suelo bajo NT y RT presentaron una significativamente mayor que bajo CT.[EN] This work presents a new method (AM) to estimate the soil aggregate porosity, , expressed as the quotient between the internal pore volume (Vi) and the aggregate volume (VT). VT is calculated from the particle soil density, and the aggregate weight and Vi, the last one estimated form the weight of the ethanol-saturated agregate. The method was validated by comparing the VT estimated with AM with the corresponding value estimated by the photogrammetry technique (PHM), on 36 aggregates of 8- 16 mm size collected from conventional tillage (CT), reduced tillage (RT) and no tillage (NT). Results show a good relationship between VT measured with PHM and with AM (y = 0.94 x + 0.01, R2 = 0.99). The values were significantly higher in soil aggregates under NT and RT than those under CT.Este trabajo ha sido financiado por el Ministerio de Economía y Competitividad de España (AGL2010-22050-C03-02).Peer reviewe

Water balance simulation of a dryland soil during fallow under conventional and conservation tillage in semiarid Aragon, Northeast Spain

The definitive version is available at: http://www.sciencedirect.com/science/journal/01671987In Central Aragon, winter cereal is sown in the autumn (November–December), commonly after a 16–18 months fallow period aimed at conserving soil water. This paper uses the Simple Soil–Plant–Atmosphere Transfer (SiSPAT) model, in conjunction with field data, to study the effect of long fallowing on the soil water balance under three tillage management systems (conventional tillage, CT; reduced tillage, RT; and no-tillage, NT). This was on the assumption that soil properties would remain unchanged during the entire fallow season. Once the model was validated with data obtained before primary tillage implementation, the differences between simulated and observed soil water losses for the CT and RT treatments could be interpreted as the direct effect of the soil tillage system. The model was calibrated and validated in a long-term tillage experiment using data from three contrasting long-fallow seasons over the period 1999–2002, where special attention was paid to predicting soil hydraulic properties in the pre-tillage conditions. The capacity of the model to simulate the soil water balance and its components over long fallowing was demonstrated. Both the fallow rainfall pattern and the tillage management system affected the soil water budget and components predicted by the model. The model predicted that about 81% of fallow seasonal rainfall is lost by evaporation in long-fallow periods with both a dry autumn in the first year of fallow and a rainfall above normal in spring. Whereas, when the fallow season is characterised by a wet autumn during the first year of fallow the model predicted a decrease in soil water evaporation and an increase in water storage and deep drainage components. In this case, the predicted water lost by evaporation was higher under NT (64%) than under RT (56%) and CT (44%). The comparison between measured and simulated soil water loss showed that the practice of tillage decreased soil water conservation in the short term. The long-term analysis of the soil water balance showed that, in fallow periods with a wet autumn during the first year of fallow, the soil water loss measured under CT and RT was moderately greater than that predicted by the model.This research was supported by the Comisión Interministerial de Ciencia y Tecnología of Spain (grants AGF98-0261-CO2-02 and AGL2001-2238-CO2-01 and PNFPI pre-doctoral fellowship awarded to the first author) and the European Union (FEDER funds).Peer reviewe

Estimate of soil hydraulic properties from disc infiltrometer threedimensional infiltration curve: theoretical analysis and field applicability

9 Pags., 3 Figs., 2 Tabls. The definitive version is available at: http://www.sciencedirect.com/science/journal/18780296/19/supp/CThis 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.This research was supported by the Ministerio de Ciencia e Innovación of Spain (Grant AGL2010- 22050-C03-02) and by the Aragón Regional Government and La Caixa (Grant 2012/GA LC 074).Peer reviewe

Water balance simulation of a dryland soil during fallow under conventional and conservation tillage in semiarid Aragon, Northeast Spain

The definitive version is available at: http://www.sciencedirect.com/science/journal/01671987In Central Aragon, winter cereal is sown in the autumn (November–December), commonly after a 16–18 months fallow period aimed at conserving soil water. This paper uses the Simple Soil–Plant–Atmosphere Transfer (SiSPAT) model, in conjunction with field data, to study the effect of long fallowing on the soil water balance under three tillage management systems (conventional tillage, CT; reduced tillage, RT; and no-tillage, NT). This was on the assumption that soil properties would remain unchanged during the entire fallow season. Once the model was validated with data obtained before primary tillage implementation, the differences between simulated and observed soil water losses for the CT and RT treatments could be interpreted as the direct effect of the soil tillage system. The model was calibrated and validated in a long-term tillage experiment using data from three contrasting long-fallow seasons over the period 1999–2002, where special attention was paid to predicting soil hydraulic properties in the pre-tillage conditions. The capacity of the model to simulate the soil water balance and its components over long fallowing was demonstrated. Both the fallow rainfall pattern and the tillage management system affected the soil water budget and components predicted by the model. The model predicted that about 81% of fallow seasonal rainfall is lost by evaporation in long-fallow periods with both a dry autumn in the first year of fallow and a rainfall above normal in spring. Whereas, when the fallow season is characterised by a wet autumn during the first year of fallow the model predicted a decrease in soil water evaporation and an increase in water storage and deep drainage components. In this case, the predicted water lost by evaporation was higher under NT (64%) than under RT (56%) and CT (44%). The comparison between measured and simulated soil water loss showed that the practice of tillage decreased soil water conservation in the short term. The long-term analysis of the soil water balance showed that, in fallow periods with a wet autumn during the first year of fallow, the soil water loss measured under CT and RT was moderately greater than that predicted by the model.This research was supported by the Comisión Interministerial de Ciencia y Tecnología of Spain (grants AGF98-0261-CO2-02 and AGL2001-2238-CO2-01 and PNFPI pre-doctoral fellowship awarded to the first author) and the European Union (FEDER funds).Peer reviewe

Estimation of water content profiles by inverse analysis of TDR waveforms: application to infer soil hydraulic properties

La medida de las propiedades hidráulicas del suelo, curva de retención (θ(ψ)) y conductividad hidráulica (K) tiene una importancia fundamental para la simulación de procesos hidrológicos. La técnica de Reflectometría de Dominio Temporal (TDR) es una herramienta ampliamente utilizada para la medida no destructiva de contenido volumétrico de agua en el suelo (θ) y de conductividad eléctrica (σ). El objetivo de este trabajo es desarrollar una nueva metodología basada en el uso de la técnica TDR para estimar las propiedades hidráulicas del suelo (α, n and K) por análisis inverso de la dinámica de los perfiles de humedad (WCPs ) durante un proceso de infiltración de agua. Los WCPs se estiman a partir del análisis inverso de ondas TDR empleando un modelo físico de propagación electromagnética. Posteriormente, los parámetros α, n and K se calculan empleando una interfaz HYDRUS-1D-Matlab por medio del análisis inverso de los TDR-WCPs. Esta interfaz calcula los parámetros hidráulicos a partir del mejor ajuste entre los TDR-WCP registrados y los simulados por HYDRUS-1D. Para este fin, se emplea el método de optimización de fuerza bruta, el cual permite barrer un rango amplio de parámetros hidráulicos. El método fue probado en tres medios porosos distintos (tierra franca tamizada a 2 mm, arena y microesferas de vidrio) durante un proceso de infiltración. Las propiedades hidráulicas estimadas con este método se compararon con aquellas medidas en los mismos medios porosos empleando técnicas convencionales de laboratorio: cámaras de presión-TDR y mini-infiltrómetro de disco. Aunque se obtuvieron resultados satisfactorios para la mediad de K, los resultados obtenidos para la medida de n y α fueron imprecisos. Estas discrepancias se pueden atribuir a las siguientes causas (i) el uso de una función unimodal en lugar de una bimodal en HYDRUS-1D; (ii) el fenómeno de histéresis del suelo; (iii) incertidumbres en la función “puente” empleada para estimar WCP a partir del modelo de simulación de ondas TDR. Este método necesita nuevos esfuerzos para mejorar su precisión y así poder probarse en muestras de suelo inalterado

An automated disc infiltrometer for infiltration rate measurements using a microflowmeter

19 Pag., 1 Tabl., 4 Figs. The definitive version is available at: http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1099-1085This 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.This research was supported by the Ministerio de Ciencia e Innovación of Spain (grants AGL2007-66320-CO2-02/AGR; 200840I214).Peer reviewe

Hydro-physical responses of gypseous and non-gypseous soils to livestock grazing in a semi-arid region of NE Spain

20 Pag., 4 Figs., 1 Tabl. The definitive version is available at: http://www.sciencedirect.com/science/journal/03783774Pasture 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 ( b), penetration resistance (PR), saturated sorptivity (S), hydraulic conductivity (K), and the water retention curve (WRC) for undisturbed soil samples from 1 to 10 cm depth soil layer were measured. The 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 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.This research was supported by Aragón regional government and La Caixa (Grants: GA-LC020/2010; GA-LC-010/2008) and the CSIC (Grant: PIE-200930I145).Peer reviewe

Testing of a commercial vector network analyzer as low-cost TDR device to measure soil moisture and electrical conductivity

Time Domain Reflectometry (TDR) is a non-destructive technique to determine the soil apparent dielectric constant, εa, the volumetric water content, θ, and bulk electrical conductivity, σ. However, the high cost of TDR devices may limit its use. This study evaluates two different low-cost Vector Network Analyzers (VNA) commercially available (NanoVNA), with 1.5 (VNA1.5) and 3.0 (VNA3.0) GHz maximum operating frequency. NanoVNA can be used for measurements of Frequency Domain Reflectometry (FDR) or, after suitable post-processing, for θ and σ TDR measures. Although FDR and TDR are dual procedures, TDR is easier to interpret for soil experiments. The TDR waveforms and εa measured with NanoVNA connected to 10 and 20 cm length three-rod probes immersed in air, distilled water, and a soil column with different θ were compared to those measured using a TDR100 (Campbell Sci.) instrument. The capacity of VNAs to measure σ was evaluated by immersing a 10 cm length three-rod probe in different NaCl-water solutions. Measurements obtained with the VNA and TDR100 were compared in a field test using two-rod 22 cm length TDR probes inserted in soil plots with increasing water content. A robust fit was observed between TDR waveforms registered with the two VNAs and the TDR100. Although VNA3.0 doubles the frequency range of VNA1.5, both devices allowed for good estimates of εa (εaVNA1.5, 3.0 = 1.001 εaTDR100 – 0.2125; R2 = 0.999). These results indicate that the low-cost VNA devices can measure soil water content with similar accuracy and precision as the TDR100. A good agreement (σVNA1.5, 3.0 = 0.999 σCM + 0.0023; R2 = 0.999) was also observed between the σ measured using a conductivity meter (CM) and that estimated with the VNAs. Finally, a good correlation was also observed between θ measured in the field experiment with TDR100 and the VNA1.5 and VNA3.0 devices

Dos métodos para estimar las propiedades hidráulicas del suelo a partir de: un proceso de (I) humectación por capilaridad más evaporación, y (II) humectación por capilaridad con multitensión: análisis teórico

6 Pags.- 1 Tabl.- 7 Figs. Trabajo originalmente presentado en las XII Jornadas de Investigación en la Zona No Saturada del Suelo (Alcalá de Henares, 18-20 de nov. de 2015). © de los textos: sus autores[ES] La determinación de la curva de retención θ(h) y conductividad hidráulica saturada (Ks) del suelo es fundamental para caracterizar la zona no saturada. Esta comunicación presenta dos métodos para estimar Ks y los parámetros α y n de θ(h) a partir de: (i) un proceso de humectación por capilaridad a saturación seguido de una sobre-presión, más un proceso de evaporación, considerando el fenómeno de histéresis, y (ii) un proceso de humectación por capilaridad a tensión negativa seguida de una tensión a saturación. El análisis inverso se realizó sobre un cilindro de 5 cm de altura y 5 cm de diámetro con suelo franco, utilizando el programa HYDRUS-2D. Los mapas de error de la función objetivo (Ks, α, n) para los planos Ks-α, α-n y Ks-n obtenidos para ambos métodos mostraron un único mínimo, lo que indica que estos métodos permiten estimar de forma precisa los parámetros hidráulicos del suelo.[EN] The determination of the soil water retention curve, θ(h), and the saturated hydraulic conductivity, Ks, are of paramount importance to correctly characterize the vadose zone. This communication presents two methods to estimate Ks and the water retention curve α and n parameters from: (i) a capillary rise wetting process at saturation followed by an overpressure step, plus an evaporation process, taking into account the hysteresis phenomena; and (ii) a capillary wetting process at negative tension plus a saturation step. The theoretical analysis was performed on a 5-cm diameter and 5 cm high cylinder of loam soil, using the HYDRUS-2D software. The responses surfaces of the objective function (Ks, α, n) for the planes Ks-α, α-n and Ks-n obtained with both methods showed a unique and well defined minimum, which indicates these methods allow accurate estimates of the soil hydraulic properties.Este trabajo ha sido financiado por el Ministerio de Economía y Competitividad de España (AGL2010-22050-C03-02).Peer reviewe