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  • 1
    In: Water Resources Research, August 2010, Vol.46(8), pp.n/a-n/a
    Description: Wetting and redistribution of water in air‐dried wettable, slightly repellent, and strongly repellent soils was investigated by tracking the spatial and temporal moisture‐content variation in a transparent flow chamber. Water was applied as a subsurface point source. The degree of water repellency had a substantial effect on the plume's shape, dimensions, and internal moisture‐content distribution. The high uniform moisture content in the repellent soil's plume surrounded by a narrow transition layer within which moisture content was sharply decreasing indicates that unstable flow shapes a finger‐like wetting front. Moisture redistribution in the repellent soils was limited and took place mainly in the vertical direction. The repellent soils were wetted immediately, very likely by local positive pressure buildup induced by the hydraulic resistance imposed by the initial 〉90° contact angle. The plume shape dimensions and internal moisture‐content distribution should be considered in the design and operation of subsurface drip irrigation in water‐repellent soils.
    Keywords: Water‐Repellent Soil ; Subsurface Drip Irrigation ; Unstable Flow ; Effluent Irrigation
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 2
    Language: English
    In: Journal of Colloid And Interface Science, April 15, 2013, Vol.396, p.270(8)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jcis.2013.01.022 Byline: Qiuling Wang (a), Ellen R. Graber (b), Rony Wallach (a) Keywords: Capillary flow; Sinusoidal capillaries; Dynamic contact angle; Wettability; Geometry effect; Hysteresis Abstract: Display Omitted Author Affiliation: (a) Department of Soil and Water Sciences, The R.H. Smith Faculty of Agriculture, Food, and Environment, The Hebrew University of Jerusalem, Rehovot 76100, Israel (b) Institute of Soil, Water and Environmental Sciences, The Volcani Center, Agricultural Research Organization (ARO), Bet Dagan 50250, Israel Article History: Received 21 August 2012; Accepted 10 January 2013
    ISSN: 0021-9797
    Source: Cengage Learning, Inc.
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  • 3
    Language: English
    In: Journal of Hydrology, Feb 23, 2012, Vol.422-423, p.30(13)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jhydrol.2011.12.010 Byline: Yunwu Xiong (a), Alex Furman (b), Rony Wallach (a) Keywords: Unstable flow; Water-repellent soil; Moment analysis; Drip irrigation Abstract: a* Plumes shape and moisture content distribution were measured for repellent soils. a* Center of mass and spatial variances were calculated for the measured plumes. a* Ellipses around the stable and unstable plumes' centers of mass were plotted. a* Ellipses' eccentricity indicated the gravity role over the diminished capillarity. a* A single probability describes fractions of added water in the different ellipses. Author Affiliation: (a) Department of Soil and Water Sciences, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Israel (b) Civil and Environmental Engineering, Technion-Israel Institute of Technology, Israel Article History: Received 16 April 2011; Revised 24 October 2011; Accepted 5 December 2011 Article Note: (miscellaneous) This manuscript was handled by Philippe Baveye, Editor-in-Chief
    Keywords: Universities And Colleges -- Analysis ; Soils -- Analysis
    ISSN: 0022-1694
    Source: Cengage Learning, Inc.
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  • 4
    Language: English
    In: Journal of Hydrology, 2011, Vol.410(1), pp.92-104
    Description: ► Self-organizing map was used to map moisture content for wettable and repellent soils. ► Hybrids of MLP or MNN with SOM were used to predict the moisture contours. ► MLP and MNN were applied to predict the spatial moments of water content distribution. This study examined the use of three different classes of artificial neural networks for modeling water flow in wettable and water-repellent soils, using both synthetic numerical data and experimentally measured data. The 1D self-organizing maps (SOM) successfully rendered the moisture contour in the transition zone of the wetting plumes for all soil types at different flow rates. Due to SOMs inability to generate external output data, multilayer perceptrons (MLP) and modular neural networks (MNN), respectively, were combined with SOM to predict the moisture contour for both wettable and water-repellent soils. Due to dimensionality reduction, the 1D SOM failed to capture high moisture content classes of water-repellent soils with anomalous wetting patterns, whereas spatial moment analysis succeeded in providing an accurate, albeit indirect, description. Hence, the MLP and MNN networks were applied to predict the spatial moments. The comparison between the predicted and the experimental measures demonstrated the capability of the MLP and SOM to predict the spatial moments. Comparison of the two different artificial neural networks indicated no significant difference between their results.
    Keywords: Multilayer Perceptrons ; Self-Organizing Maps ; Modular Neural Networks ; Water-Repellent Soil ; Spatial Moment Analysis ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 5
    Language: English
    In: Journal of colloid and interface science, 2013, Vol.396, pp.270-277
    Description: Understanding the role of geometry, inertia, and dynamic contact angle on wetting and dewetting of capillary tubes has theoretical and practical aspects alike. The specific and synergistic effects of these factors were studied theoretically using a mathematical model that includes inertial and dynamic contact angle terms. After validating the model for capillaries of uniform cross section, the model was extended to capillaries with sinusoidal modulations of the radius, since in practice, capillaries rarely have uniform cross-sections. The height of the meniscus during wetting and dewetting was significantly affected by the relations between the local slope of the capillary surface and the Young contact angle. Non-dimensional variables were defined using viscous effects and gravity as the scaling parameters. Simulations using the dimensionless model showed that the inertial and dynamic contact angle terms can be neglected for narrow capillaries of uniform cross-section but not for uniform, wide cross-section capillaries. Moreover, nonuniformity in cross-sectional area induced hysteresis, deceleration, blocking, and metastable equilibrium locations. An increase in contact angle further amplified the effect of geometry on wetting and dewetting processes. These results enable characterization and modeling of fluid retention and flow in porous structures that inherently consist of capillaries of varying cross section. ; p. 270-277.
    Keywords: Hysteresis ; Synergism ; Mathematical Models ; Contact Angle ; Gravity
    ISSN: 0021-9797
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 6
    Language: English
    In: Journal of Colloid And Interface Science, 15 April 2013, Vol.396, pp.270-277
    Description: ► Integrated Navier–Stokes equation is used for uniform and sinusoidal capillaries. ► Inertia and dynamic contact angle have opposing effects on capillary flow. ► Nonuniform geometry significantly affects the kinetics of capillary flow. ► Nonuniform geometry induces wetting/dewetting hysterisis. ► Wettability decrease amplifies the effects of nonuniform geometry. Understanding the role of geometry, inertia, and dynamic contact angle on wetting and dewetting of capillary tubes has theoretical and practical aspects alike. The specific and synergistic effects of these factors were studied theoretically using a mathematical model that includes inertial and dynamic contact angle terms. After validating the model for capillaries of uniform cross section, the model was extended to capillaries with sinusoidal modulations of the radius, since in practice, capillaries rarely have uniform cross-sections. The height of the meniscus during wetting and dewetting was significantly affected by the relations between the local slope of the capillary surface and the Young contact angle. Non-dimensional variables were defined using viscous effects and gravity as the scaling parameters. Simulations using the dimensionless model showed that the inertial and dynamic contact angle terms can be neglected for narrow capillaries of uniform cross-section but not for uniform, wide cross-section capillaries. Moreover, nonuniformity in cross-sectional area induced hysteresis, deceleration, blocking, and metastable equilibrium locations. An increase in contact angle further amplified the effect of geometry on wetting and dewetting processes. These results enable characterization and modeling of fluid retention and flow in porous structures that inherently consist of capillaries of varying cross section.
    Keywords: Capillary Flow ; Sinusoidal Capillaries ; Dynamic Contact Angle ; Wettability ; Geometry Effect ; Hysteresis ; Engineering ; Chemistry
    ISSN: 0021-9797
    E-ISSN: 1095-7103
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  • 7
    Language: English
    In: Journal of Hydrology, 23 February 2012, Vol.422-423, pp.30-42
    Description: ► Plumes shape and moisture content distribution were measured for repellent soils. ► Center of mass and spatial variances were calculated for the measured plumes. ► Ellipses around the stable and unstable plumes’ centers of mass were plotted. ► Ellipses’ eccentricity indicated the gravity role over the diminished capillarity. ► A single probability describes fractions of added water in the different ellipses. Water repellency has a significant impact on water flow patterns in the soil profile. Transient 2D flow in wettable and natural water-repellent soils was monitored in a transparent flow chamber. The substantial differences in plume shape and spatial water content distribution during the wetting and subsequent redistribution stages were related to the variation of contact angle while in contact with water. The observed plumes shape, internal water content distribution in general and the saturation overshoot behind the wetting front in particular in the repellent soils were associated with unstable flow. Moment analysis was applied to characterize the measured plumes during the wetting and subsequent redistribution. The center of mass and spatial variances determined for the measured evolving plumes were fitted by a model that accounts for capillary and gravitational driving forces in a medium of temporally varying wettability. Ellipses defined around the stable and unstable plumes’ centers of mass and whose semi-axes represented a particular number of spatial variances were used to characterize plume shape and internal moisture distribution. A single probability curve was able to characterize the corresponding fractions of the total added water in the different ellipses for all measured plumes, which testify the competence and advantage of the moment analysis method.
    Keywords: Unstable Flow ; Water-Repellent Soil ; Moment Analysis ; Drip Irrigation ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 8
    In: Plant Journal, February 2017, Vol.89(4), pp.839-850
    Description: We present a simple and effective high‐throughput experimental platform for simultaneous and continuous monitoring of water relations in the soil–plant–atmosphere continuum of numerous plants under dynamic environmental conditions. This system provides a simultaneously measured, detailed physiological response profile for each plant in the array, over time periods ranging from a few minutes to the entire growing season, under normal, stress and recovery conditions and at any phenological stage. Three probes for each pot in the array and a specially designed algorithm enable detailed water‐relations characterization of whole‐plant transpiration, biomass gain, stomatal conductance and root flux. They also enable quantitative calculation of the whole plant water‐use efficiency and relative water content at high resolution under dynamic soil and atmospheric conditions. The system has no moving parts and can fit into many growing environments. A screening of 65 introgression lines of a wild tomato species () crossed with cultivated tomato (), using our system and conventional gas‐exchange tools, confirmed the accuracy of the system as well as its diagnostic capabilities. The use of this high‐throughput diagnostic screening method is discussed in light of the gaps in our understanding of the genetic regulation of whole‐plant performance, particularly under abiotic stress. Fast and accurate phenotyping remains a bottleneck in the effort to enhance yields in water‐limited and other stressful environments. Here we present a non‐invasive high‐throughput platform for simultaneous and continuous monitoring of water relations in the soil–plant–atmosphere continuum of numerous plants under dynamic environmental conditions.
    Keywords: Phenotyping Plant Stress Response ; Whole‐Plant Water Relation ; Transpiration ; Root Flux ; Soil–Plant–Atmosphere Continuum ; Genotype‐By‐Environment Interaction ; Functional Phenotyping ; Technical Advance
    ISSN: 0960-7412
    E-ISSN: 1365-313X
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  • 9
    In: Plant Journal, September 2013, Vol.75(6), pp.977-988
    Description: Stomata, composed of two guard cells, are the gates whose controlled movement allows the plant to balance the demand for for photosynthesis with the loss of water through transpiration. Increased guard‐cell osmolarity leads to the opening of the stomata and decreased osmolarity causes the stomata to close. The role of sugars in the regulation of stomata is not yet clear. In this study, we examined the role of hexokinase (), a sugar‐phosphorylating enzyme involved in sugar‐sensing, in guard cells and its effect on stomatal aperture. We show here that increased expression of in guard cells accelerates stomatal closure. We further show that this closure is induced by sugar and is mediated by abscisic acid. These findings support the existence of a feedback‐inhibition mechanism that is mediated by a product of photosynthesis, namely sucrose. When the rate of sucrose production exceeds the rate at which sucrose is loaded into the phloem, the surplus sucrose is carried toward the stomata by the transpiration stream and stimulates stomatal closure via , thereby preventing the loss of precious water.
    Keywords: Stomata ; Guard Cells ; Hexokinase ; Sucrose ; Abscisic Acid ; Transpiration
    ISSN: 0960-7412
    E-ISSN: 1365-313X
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  • 10
    Language: English
    In: Geoderma, Jan 15, 2016, Vol.262, p.1(11)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.geoderma.2015.08.002 Byline: Theodor Bughici, Rony Wallach Abstract: Water-repellent (hydrophobic) soils do not wet instantaneously, but only after some time (a few seconds to hours) of soil-particle contact with water. Some plant species can render soils hydrophobic but in this respect, olive trees have scarcely been examined. Measurements of water repellency in olive orchards of different ages in different locations in Israel using the water drop penetration time (WDPT) test have shown that soils tend to become hydrophobic, regardless of texture and structure. A comprehensive study was then performed for an irrigated young and mature olive grove and nearby uncultivated bare soil in the southern part of Israel. The study included intensive WDPT measurements, initial (repellency intensity) and rate of decrease (repellency persistence) for sessile drops placed on the soil surface, cumulative infiltration using tension disc infiltrometer, and monitoring flow in a transparent flow chamber packed with soils from the different plots. The soil from the mature olive plot was noticeably more water repellent than the young plot's soil, and both differed from the uncultivated soil that was fully wettable. The contact angle of a drop placed on the surface of a single layer of soil particles decreased exponentially with time, with a lower decay rate for the mature orchard soil. Cumulative infiltration had a convex pattern for wettable soils and a concave pattern for water-repellent ones. The difference in infiltration pattern was attributed to water/pressure buildup behind the wetting front as a result of the dynamic contact-angle-induced pore resistivity to wetting. The supplemental pressure, also known as dynamic water-entry pressure, increases the infiltration rate beyond that obtained by the capillary pressure per se. The significant correlation between soil sorptivity and the asymptotic infiltration rate, both calculated from the cumulative infiltration curves, and the WDPT substantiates the dependence of pressure overshoot and the rate at which the contact angle decreases prior to pore wetting. The considerable differences in plume shape, size, and internal saturation distribution between the wettable and water-repellent soils, indicating unstable flow in the latter, were also explained by the wettability-dependent water-entry pressure. The outcome of this study indirectly supports the findings that higher surface runoff and erosion are associated with no-till farming in olive orchards, due to the combination of no-till cropping and the near-surface accumulation of hydrophobic organic carbon compounds. Article History: Received 30 March 2015; Revised 30 July 2015; Accepted 1 August 2015
    Keywords: Conservation Tillage ; No-Tillage ; Infiltration (Hydrology)
    ISSN: 0016-7061
    Source: Cengage Learning, Inc.
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