An Inverse Method to Estimate the Root Water Uptake Source-Sink Term in Soil Water Transport Equation under the Effect of Superabsorbent Polymer

Plants of Lupinus cosentinii Guss. cv. Eregulla were grown in a sandy soil in large containers in a glasshouse and exposed to drought by withholding water. Under these conditions stomatal closure had previously been shown to be initiated before a significant reduction in leaf water potential was detected. In the experiments reported here, no significant changes were found in water potential or turgor pressure of roots or leaves when a small reduction in soil water potential was induced which led to a 60% reduction in leaf conductance. The decrease in leaf conductance and root water uptake closely paralleled the fraction of roots in wet soil. By applying observed data of soil water and root characteristics, and root water uptake for whole pots in a single-root model, the average water potential at the root surface was calculated. Potential differences for water transport in the soil-plant system, and the resistances to water flow were estimated using the 'Ohm's Law' analogy for water transport. Soil resistance was negligible or minor, whereas the root resistance accounted for 61-72% and the shoot resistance accounted for about 30% of the total resistance. The validity of the measurements and calculations is discussed and the possible role of root- to-shoot communication raised.

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Using measured soil water contents to estimate evapotranspiration and root water uptake profiles – a comparative study

Hydrology and Earth System Sciences ◽

10.5194/hess-19-409-2015 ◽

2015 ◽

Vol 19 (1) ◽

pp. 409-425 ◽

Cited By ~ 17

Author(s):

M. Guderle ◽

A. Hildebrandt

Keyword(s):

Time Series ◽

Water Content ◽

Soil Water ◽

Soil Water Content ◽

Water Uptake ◽

Root Water Uptake ◽

Performance Criteria ◽

Sensor Calibration ◽

Vertical Flow ◽

Sink Term

Abstract. Understanding the role of plants in soil water relations, and thus ecosystem functioning, requires information about root water uptake. We evaluated four different complex water balance methods to estimate sink term patterns and evapotranspiration directly from soil moisture measurements. We tested four methods. The first two take the difference between two measurement intervals as evapotranspiration, thus neglecting vertical flow. The third uses regression on the soil water content time series and differences between day and night to account for vertical flow. The fourth accounts for vertical flow using a numerical model and iteratively solves for the sink term. None of these methods requires any a priori information of root distribution parameters or evapotranspiration, which is an advantage compared to common root water uptake models. To test the methods, a synthetic experiment with numerical simulations for a grassland ecosystem was conducted. Additionally, the time series were perturbed to simulate common sensor errors, like those due to measurement precision and inaccurate sensor calibration. We tested each method for a range of measurement frequencies and applied performance criteria to evaluate the suitability of each method. In general, we show that methods accounting for vertical flow predict evapotranspiration and the sink term distribution more accurately than the simpler approaches. Under consideration of possible measurement uncertainties, the method based on regression and differentiating between day and night cycles leads to the best and most robust estimation of sink term patterns. It is thus an alternative to more complex inverse numerical methods. This study demonstrates that highly resolved (temporally and spatially) soil water content measurements may be used to estimate the sink term profiles when the appropriate approach is used.

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Using measured soil water contents to estimate evapotranspiration and root water uptake profiles – a comparative study

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-11-10859-2014 ◽

2014 ◽

Vol 11 (9) ◽

pp. 10859-10902 ◽

Cited By ~ 1

Author(s):

M. Guderle ◽

A. Hildebrandt

Keyword(s):

Time Series ◽

Water Content ◽

Soil Water ◽

Soil Water Content ◽

Water Uptake ◽

Root Water Uptake ◽

Performance Criteria ◽

Sensor Calibration ◽

Vertical Flow ◽

Sink Term

Abstract. Understanding the role of plants for soil water relations, and thus for ecosystem functioning, requires information about root water uptake. We evaluated four different complex water balance methods to estimate sink term patterns and evapotranspiration directly from soil moisture measurements. We tested four methods: the first two take the difference between two measurement intervals as evapotranspiration, thus neglecting vertical flow. The third uses regression on the soil water content time series and differences between day and night to account for vertical flow. The fourth accounts for vertical flow using a numerical model and iteratively solves for the sink term. Neither of those methods requires any a priori information of root distribution parameters or evapotranspiration, which is the advantage, compared to common root water uptake models. To test the methods, a synthetic experiment with numerical simulations for a grassland ecosystem was conducted. Additionally, the time series were perturbed to simulate common sensor errors, like those due to measurement precision and inaccurate sensor calibration. We tested each method for a range of measurement frequencies and applied performance criteria to evaluate the suitability of each method. In general, we show that methods accounting for vertical flow predict evapotranspiration and the sink term distribution more accurately than the simpler approaches. Under consideration of possible measurement uncertainties, the method based on regression and differentiating between day and night cycles leads to the best and most robust estimation of sink term patterns. It is thus an alternative to more complex inverse numerical methods. This study demonstrates that highly resolved (temporal and spatial) soil water content measurements may be used to estimate the sink term profiles when the appropriate approach is used.

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Implementing small scale processes at the soil-plant interface – the role of root architectures for calculating root water uptake profiles

Hydrology and Earth System Sciences ◽

10.5194/hess-14-279-2010 ◽

2010 ◽

Vol 14 (2) ◽

pp. 279-289 ◽

Cited By ~ 45

Author(s):

C. L. Schneider ◽

S. Attinger ◽

J.-O. Delfs ◽

A. Hildebrandt

Keyword(s):

Soil Water ◽

Water Flow ◽

Water Uptake ◽

Soil Water Potential ◽

Root Systems ◽

Root Water Uptake ◽

Bulk Soil ◽

Small Scale ◽

Sink Term

Abstract. In this paper, we present a stand alone root water uptake model called aRoot, which calculates the sink term for any bulk soil water flow model taking into account water flow within and around a root network. The boundary conditions for the model are the atmospheric water demand and the bulk soil water content. The variable determining the plant regulation for water uptake is the soil water potential at the soil-root interface. In the current version, we present an implementation of aRoot coupled to a 3-D Richards model. The coupled model is applied to investigate the role of root architecture on the spatial distribution of root water uptake. For this, we modeled root water uptake for an ensemble (50 realizations) of root systems generated for the same species (one month old Sorghum). The investigation was divided into two Scenarios for aRoot, one with comparatively high (A) and one with low (B) root radial resistance. We compared the results of both aRoot Scenarios with root water uptake calculated using the traditional Feddes model. The vertical rooting density profiles of the generated root systems were similar. In contrast the vertical water uptake profiles differed considerably between individuals, and more so for Scenario B than A. Also, limitation of water uptake occurred at different bulk soil moisture for different modeled individuals, in particular for Scenario A. Moreover, the aRoot model simulations show a redistribution of water uptake from more densely to less densely rooted layers with time. This behavior is in agreement with observation, but was not reproduced by the Feddes model.

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Implementing small scale processes at the soil-plant interface – the role of root architectures for calculating root water uptake profiles

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-6-4233-2009 ◽

2009 ◽

Vol 6 (3) ◽

pp. 4233-4264 ◽

Cited By ~ 7

Author(s):

C. L. Schneider ◽

S. Attinger ◽

J.-O. Delfs ◽

A. Hildebrandt

Keyword(s):

Soil Water ◽

Water Flow ◽

Water Uptake ◽

Soil Water Potential ◽

Root Systems ◽

Root Water Uptake ◽

Bulk Soil ◽

Small Scale ◽

Sink Term

Abstract. In this paper, we present a stand alone root water uptake model called aRoot, which calculates the sink term for any bulk soil water flow model taking into account water flow within and around a root network. The boundary conditions for the model are the atmospheric water demand and the bulk soil water content. The variable determining the plant regulation for water uptake is the soil water potential at the soil-root interface. In the current version, we present an implementation of aRoot coupled to a 3-D Richards model. The coupled model is applied to investigate the role of root architecture on the spatial distribution of root water uptake. For this, we modeled root water uptake for an ensemble (50 realizations) of root systems generated for the same species (one month old Sorghum). The investigation was divided into two Scenarios for aRoot, one with comparatively high (A) and one with low (B) root radial resistance. We compared the results of both aRoot Scenarios with root water uptake calculated using the traditional Feddes model. The vertical rooting density profiles of the generated root systems were similar. In contrast the vertical water uptake profiles differed considerably between individuals, and more so for Scenario B than A. Also, limitation of water uptake occurred at different bulk soil moisture for different modeled individuals, in particular for Scenario A. Moreover, the aRoot model simulations show a redistribution of water uptake from more densely to less densely rooted layers with time. This behavior is in agreement with observation, but was not reproduced by the Feddes model.

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An Inverse Method to Estimate the Source-Sink Term in the Nitrate Transport Equation

Soil Science Society of America Journal ◽

10.2136/sssaj2005.0395 ◽

2007 ◽

Vol 71 (1) ◽

pp. 26-34 ◽

Cited By ~ 9

Author(s):

Jianchu Shi ◽

Qiang Zuo ◽

Renduo Zhang

Keyword(s):

Transport Equation ◽

Inverse Method ◽

Nitrate Transport ◽

Sink Term ◽

Source Sink

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Analysis of Soil Water Response to Grass Transpiration

Soil and Water Research ◽

10.17221/6510-swr ◽

2013 ◽

Vol 1 (No. 3) ◽

pp. 85-98

Author(s):

Dohnal Michal ◽

Dušek Jaromír ◽

Vogel Tomáš ◽

Herza Jiří

Keyword(s):

Soil Water ◽

Water Uptake ◽

Preferential Flow ◽

Water Movement ◽

Control Volume ◽

Water Pressure ◽

Lower Boundary ◽

Root Water Uptake ◽

Water Dynamics ◽

Soil Water Dynamics

This paper focuses on numerical modelling of soil water movement in response to the root water uptake that is driven by transpiration. The flow of water in a lysimeter, installed at a grass covered hillslope site in a small headwater catchment, is analysed by means of numerical simulation. The lysimeter system provides a well defined control volume with boundary fluxes measured and soil water pressure continuously monitored. The evapotranspiration intensity is estimated by the Penman-Monteith method and compared with the measured lysimeter soil water loss and the simulated root water uptake. Variably saturated flow of water in the lysimeter is simulated using one-dimensional dual-permeability model based on the numerical solution of the Richards’ equation. The availability of water for the root water uptake is determined by the evaluation of the plant water stress function, integrated in the soil water flow model. Different lower boundary conditions are tested to compare the soil water dynamics inside and outside the lysimeter. Special attention is paid to the possible influence of the preferential flow effects on the lysimeter soil water balance. The adopted modelling approach provides a useful and flexible framework for numerical analysis of soil water dynamics in response to the plant transpiration.

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Modelling the Impact on Root Water Uptake and Solute Return Flow of Different Drip Irrigation Regimes with Brackish Water

Water ◽

10.3390/w11030425 ◽

2019 ◽

Vol 11 (3) ◽

pp. 425 ◽

Cited By ~ 3

Author(s):

Fairouz Slama ◽

Nessrine Zemni ◽

Fethi Bouksila ◽

Roberto De Mascellis ◽

Rachida Bouhlila

Keyword(s):

Water Content ◽

Soil Water ◽

Soil Water Content ◽

Water Uptake ◽

Brackish Water ◽

Deficit Irrigation ◽

Root Zone ◽

Root Water Uptake ◽

Return Flows ◽

Semi Arid

Water scarcity and quality degradation represent real threats to economic, social, and environmental development of arid and semi-arid regions. Drip irrigation associated to Deficit Irrigation (DI) has been investigated as a water saving technique. Yet its environmental impacts on soil and groundwater need to be gone into in depth especially when using brackish irrigation water. Soil water content and salinity were monitored in a fully drip irrigated potato plot with brackish water (4.45 dSm−1) in semi-arid Tunisia. The HYDRUS-1D model was used to investigate the effects of different irrigation regimes (deficit irrigation (T1R, 70% ETc), full irrigation (T2R, 100% ETc), and farmer’s schedule (T3R, 237% ETc) on root water uptake, root zone salinity, and solute return flows to groundwater. The simulated values of soil water content (θ) and electrical conductivity of soil solution (ECsw) were in good agreement with the observation values, as indicated by mean RMSE values (≤0.008 m3·m−3, and ≤0.28 dSm−1 for soil water content and ECsw respectively). The results of the different simulation treatments showed that relative yield accounted for 54%, 70%, and 85.5% of the potential maximal value when both water and solute stress were considered for deficit, full. and farmer’s irrigation, respectively. Root zone salinity was the lowest and root water uptake was the same with and without solute stress for the treatment corresponding to the farmer’s irrigation schedule (273% ETc). Solute return flows reaching the groundwater were the highest for T3R after two subsequent rainfall seasons. Beyond the water efficiency of DI with brackish water, long term studies need to focus on its impact on soil and groundwater salinization risks under changing climate conditions.

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