scholarly journals Optimizing Water Consumption in Richards’ Equation Framework with Step-Wise Root Water Uptake: A Simplified Model

2022 ◽  
Author(s):  
Marco Berardi ◽  
Marcello D’Abbicco ◽  
Giovanni Girardi ◽  
Michele Vurro
Keyword(s):  
Water Uptake ◽  
Water Consumption ◽  
Unsaturated Soils ◽  
Equilibrium Points ◽  
Root Water Uptake ◽  
Richards Equation ◽  
List Type ◽  
Algebraic Equations ◽  
Sink Term ◽  
Steady Solutions

Abstract This work arises from the need of exploring new features for modeling and optimizing water consumption in irrigation processes. In particular, we focus on water flow model in unsaturated soils, accounting also for a root water uptake term, which is assumed to be discontinuos in the state variable. We investigate the possibility of accomplishing such optimization by computing the steady solutions of a $$\theta$$ θ -based Richards equation revised as equilibrium points of the ODEs system resulting from a numerical semi-dicretization in the space; after such semi-discretization, these equilibrium points are computed exactly as the solutions of a linear system of algebraic equations: the case in which the equilibrium lies on the threshold for the uptake term is of particular interest, since the system considerably simplifies. In this framework, the problem of minimizing the water waste below the root level is investigated. Numerical simulations are provided for representing the obtained results. Article Highlights Root water uptake is modelled in a Richards’ equation framework with a discontinuous sink term. After a proper semidiscretization in space, equilibrium points of the resulting nonlinear ODE system are computed exactly. The proposed approach simplifies a control problem for optimizing water consumption.

scholarly journals Diurnal variation in xylem water isotopic signature biases depth of root-water uptake estimates

2019 ◽  
Author(s):  
Hannes De Deurwaerder ◽  
Marco D. Visser ◽  
Matteo Detto ◽  
Pascal Boeckx ◽  
Félicien Meunier ◽  
...  
Keyword(s):  
Diurnal Variation ◽  
Soil Water ◽  
Water Uptake ◽  
Sap Flow ◽  
Soil Water Potential ◽  
Root Water Uptake ◽  
Isotopic Signature ◽  
Stem Length ◽  
Individual Plant ◽  
List Type

SummaryStable water isotopes are a powerful and widely used tool to derive the depth of root water uptake (RWU) in lignified plants. Uniform xylem water isotopic signature (i-H2O-xyl) along the length of a lignified plant is a central assumption, which has never been properly evaluated.Here we studied the effects of diurnal variation in RWU, sap flow velocity and various other soil and plant parameters on i-H2O-xyl signature within a plant using a mechanistic plant hydraulic model.Our model predicts significant variation in i-H2O-xyl along the full length of an individual plant arising from diurnal RWU fluctuations and vertical soil water heterogeneity. Moreover, significant differences in i-H2O-xyl emerge between individuals with different sap flow velocities. We corroborated our model predictions with field observations from French Guiana and northwestern China. Modelled i-H2O-xyl varied considerably along stem length ranging up to 18.3‰ in δ2H and 2.2‰ in δ18O, largely exceeding the range of measurement error.Our results show clear violation of the fundamental assumption of uniform i-H2O-xyl and occurrence of significant biases when using stable isotopes to assess RWU. As a solution, we propose to include monitoring of sap flow and soil water potential for more robust RWU depth estimates.

Variability assessment of Irrigation Requirement for Winter Wheat Cropping Under Changing Climate.

2020 ◽  
Author(s):  
Kaushika Gujjanadu Suryaprakash ◽  
Hari Prasad Kotnur Suryanarayana Rao
Keyword(s):  
Climate Change ◽  
Water Uptake ◽  
Root Water Uptake ◽  
Water Requirement ◽  
Richards Equation ◽  
Emission Scenarios ◽  
Irrigation Requirement ◽  
Moisture Movement ◽  
The Future ◽  
The Impact

<p>India is primarily an agronomic country and most of the cropping in the Rabi season depends on the rainwater availability. With the ill effects of climate change cropping up, the agriculture sector is expected to take a major hit. This study takes a technical approach on the impact of climate change on the irrigation requirement of wheat cropping by studying the future irrigation requirement based on the temperature and rainfall that can be expected to occur in the future timelines. A root water uptake model involving the solution of the non-linear Richards equation to assess the root-zone moisture movement is formulated and validated. The inputs of the model include the crop data, which, in this case is obtained by field experimentation at the irrigation field laboratory at IIT Roorkee and weather data, which is obtained from the CANESM2 General circulation model for the historical and projected timescales. The historical GCM data for thirty years is bias corrected using the observed data from the India Meteorological department (IMD). The validated root water uptake model is applied to the historical and projected data for a 60 year span for two emission scenarios for RCP 4.5 and 8.5. The output was obtained as soil moisture profiles and frequencies of irrigation required. It was seen that for both the mild and high emission scenarios, the number of irrigation events per cropping period increased. This increase is assessed using variability analysis and for its impacts on the water resources management systems. The variability assessment showed the variation of the irrigation water requirement on annual and decadal scales. This is useful in understanding the historical and expected crop water requirement in view of the climate change effects.</p>

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

2015 ◽  
Vol 19 (1) ◽  
pp. 409-425 ◽  
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.

Functional-structural modelling of root water uptake based on measured MRI images of root systems

2020 ◽  
Author(s):  
Tobias Selzner ◽  
Magdalena Landl ◽  
Andreas Pohlmeier ◽  
Daniel Leitner ◽  
Jan Vanderborght ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Drought Tolerance ◽  
Soil Water ◽  
Water Uptake ◽  
Root Architecture ◽  
Soil Water Potential ◽  
Computational Cost ◽  
Root Water Uptake ◽  
Extreme Weather Events ◽  
Richards Equation

<p>In the course of climate change, the occurrence of extreme weather events is expected to increase. Drought tolerance of crops and careful irrigation management are becoming key factors for global food security and the sustainable resource use of water in agriculture. Root water uptake plays a vital role in drought tolerance. It is influenced by root architecture, plant and soil water status and their respective hydraulic properties. Models of said factors aid in organizing the current state of knowledge and enable a deeper understanding of their respective influence on crop performance. Water uptake by roots leads to a decrease in soil moisture and may cause the formation of soil water potential gradients between the bulk soil and the soil-root interface. Although the Richards equation in theory takes these gradients into account, a very fine discretization of the soil domain is necessary to capture these gradients in simulations. However, especially during drought stress, the drop in hydraulic conductivity in the rhizosphere could have a major impact on the overall water uptake of the root system. In order to investigate computationally feasible alternative approaches for simulations with source terms that take these hydraulic conductivity drops into account, we conducted experiments with lupine plants. The root architecture of the growing plants was measured several times using an MRI. Subsequently, these MRI images were used in a holobench for manual tracing of the roots. We were able to mimic the root growth between the measurement dates using linear interpolation. In addition to root architecture, soil water contents and transpiration rates were monitored. We then used this data to systematically compare the computational effort of different approaches to consider the hydraulic conductivity drop near roots in terms of accuracy and computational cost. Eventually we aim at using these results to improve existing root water uptake models for the presence of hydraulic conductivity drops in the rhizosphere in an efficient and accurate way.</p>

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

2014 ◽  
Vol 11 (9) ◽  
pp. 10859-10902 ◽  
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.

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

2010 ◽  
Vol 14 (2) ◽  
pp. 279-289 ◽  
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.

Sign in / Sign up

Export Citation Format

Share Document