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This study investigates the hazardous effect of salinity on plant growth and soil moisture dynamics in the root zone. Field irrigation experiments on paddy (Oryza sativa L.—basmati variety) with varying levels of salinity of irrigation water (0.5, 5, 10, 15, 20, and 25 dS/m) were performed for studying the effect of salt water stress on crop growth. Throughout the crop's growth period, measurements of leaf area index (LAI), root depth (RD), and soil moisture status in the root zone were recorded. For the analysis, a numerical model was developed to simulate root water uptake (RWU) and soil moisture movement in the root zone, accounting for osmotic pressure developed as a result of the salinity. Nonlinear parameters for the RWU model were estimated based on these observations for each salinity level. By incorporating meteorological data and soil–crop parameters, the model simulated RWU and root zone soil moisture. The results of the irrigation experiments revealed that increased salinity levels in the irrigation water significantly hindered crop development, leading to a decrease in LAI and root depth. The maximum LAI in the growth period decreased markedly, from 5.19 m2m−2 at 0.5 dS/m to 2.01 m2m−2 at 25 dS/m, a decline of approximately 61%. Root depth also exhibited a substantial reduction, declining by up to 36%, from 69.5 cm at 0.5 dS/m to 44.5 cm at 25 dS/m. The simulation outcomes further demonstrated that higher salt concentrations in the irrigation water resulted in reduced root water uptake and decreased soil moisture content in the root zone, ultimately affecting crop yield. The reduction in root water uptake becomes notably pronounced, exhibiting an approximate decrease of 81% when salinity level increases from 0.5 to 25 dS/m. These findings shed light on the hazards posed by salinity in agricultural practices and emphasize the importance of effective management strategies to ensure sustainable crop production in the presence of salinity-induced hazards. Practical Applications: The results of our research yield significant insights with practical applications for real-life conditions. We find that increasing salinity levels in irrigation water have a pronounced adverse effect on paddy crop growth and root water uptake. As salinity levels rise, there is a noticeable effect on crop growth i.e., decrease in leaf area index (LAI), root depth (RD), and root water uptake (RWU), which are crucial parameters for crop development. Furthermore, our findings reveal a clear correlation between increasing salinity and reduced soil moisture content, particularly at the critical depths of 20 and 40 cm below the surface. The practical implications of our research are twofold. First, it underscores the importance of carefully managing salinity levels in irrigation practices to mitigate the negative effects on crop growth and water uptake. Secondly, our study provides valuable insights for crop selection, suggesting that paddy crops may be less suitable under high salinity conditions. These results offer practical guidance for agricultural decision makers, highlighting the need for salinity control measures and informed crop selection to optimize agricultural productivity in regions with saline water environments. [ABSTRACT FROM AUTHOR]

Assessing root sources of three uncertainties – parameterization of soil hydraulic characteristics, boundary conditions, and estimation of source/sink terms – is a significant challenge in soil water transport modeling. This study aims to evaluate the uncertainty of three each widely-used parameter estimation methods affecting plot-scale water dynamics. The study employs HYDRUS, a process-based hydrologic model, to incorporate these uncertainties and compare model predictions to measured values in a semiarid Inner Mongolia steppe, China. Soil hydraulic parameters are determined using two direct methods (laboratory-derived approach and evaporation method) and one indirect method (neural network). While each hydraulic parameter method generally simulates soil moisture dynamics, the evaporation method performed better, especially under dry conditions. This suggests that measuring the intensity properties, such as unsaturated hydraulic conductivity, with the evaporation method is crucial for reasonable soil moisture simulation. The study also demonstrates the impact of different applied boundary conditions on simulated soil moisture, specifically the partitioning of reference FAO evapotranspiration via one direct method (soil fraction cover) and two indirect methods (leaf area index and crop height). The partitioning via soil fraction cover reflected a better simulation. Additionally, the study compares the uncertainties of root water uptake function with root growth parameters and constant root depth referenced to grass and pasture, and finds no significant difference among them. Comparing three sources of uncertainty in predicting soil moisture, the study concludes that the input soil hydraulic parameter is more sensitive than evapotranspiration partitioning or representation of root water uptake function. Our study highlights that measuring soil intensity properties can better reflect the effects of land use change, such as compaction, on field water transports.

Salinity leaching is necessary to sustain agricultural production in irrigated croplands. Improving salinity leaching efficiency not only conserves water but also reduces groundwater contamination. Current leaching requirement (LR) calculations are based on steady-state and one-dimensional (1D) approaches, and consequently, this LR concept may not be applicable to drip irrigation (approximately 2D), which is becoming more common due to its higher water use efficiency. The aims of this study were to assess the salinity leaching fraction (LF) in clay, loam, and sand soils under 1D (to mimic sprinkler irrigation) and 2D (to mimic drip irrigation) transient conditions with a numerical model (HYDRUS). Water applications used the actual irrigation scheme in an almond orchard located in central California without considering precipitation. Model simulations showed that soil salinity at the lower boundary (depth of 150 cm) reached steady-state in 10 years in HYDRUS-1D simulations. The leaching fractions calculated from the ratio of drainage-water depth to irrigation-water depth (LFw = Ddw/Diw) and irrigation-water salinity to drainage-water salinity (LFEC = ECiw/ECdw) from HYDRUS-1D were similar among different textured soils. However, they were much higher under drip irrigation (2D) than under sprinkler irrigation (1D) when the same amount of water was applied, and LFEC values were much greater than the LFw values under 2D simulations. Salt balance (SB) and leaching efficiency (LE) indicated that sprinkler irrigation (1D) is more effective for salinity leaching than drip irrigation (2D). To improve salinity leaching efficiency, further evaluation of LRs under drip irrigation is needed.

Salinity leaching is necessary to sustain agricultural production in irrigated croplands. Improving salinity leaching efficiency not only conserves water but also reduces groundwater contamination. Current leaching requirement (LR) calculations are based on steady-state and one-dimensional (1D) approaches, and consequently, this LR concept may not be applicable to drip irrigation (approximately 2D), which is becoming more common due to its higher water use efficiency. The aims of this study were to assess the salinity leaching fraction (LF) in clay, loam, and sand soils under 1D (to mimic sprinkler irrigation) and 2D (to mimic drip irrigation) transient conditions with a numerical model (HYDRUS). Water applications used the actual irrigation scheme in an almond orchard located in central California without considering precipitation. Model simulations showed that soil salinity at the lower boundary (depth of 150 cm) reached steady-state in 10 years in HYDRUS-1D simulations. The leaching fractions calculated from the ratio of drainage-water depth to irrigation-water depth (LFw = Ddw/Diw) and irrigation-water salinity to drainage-water salinity (LFEC = ECiw/ECdw) from HYDRUS-1D were similar among different textured soils. However, they were much higher under drip irrigation (2D) than under sprinkler irrigation (1D) when the same amount of water was applied, and LFEC values were much greater than the LFw values under 2D simulations. Salt balance (SB) and leaching efficiency (LE) indicated that sprinkler irrigation (1D) is more effective for salinity leaching than drip irrigation (2D). To improve salinity leaching efficiency, further evaluation of LRs under drip irrigation is needed.

Water scarcity is increasing in the world, which is limiting crop production, especially in water-limited areas such as Southern High Plains of the United States. There is a need to adopt the irrigation management practices that can help to conserve water and sustain crop production in such water-limited areas. A 2-year field study was conducted during the summers of 2019 and 2020 to evaluate the effect of deficit irrigation levels and cultivars on root distribution pattern, soil water depletion, and water use efficiency (WUE) of cucumber (Cucumis sativus). The experiment was conducted in a split-plot design with four irrigation levels [100%, 80%, 60%, and 40% crop evapotranspiration (ETc)] as main plot factor and two cultivars (Poinsett 76 and Marketmore 76) as subplot factor with three replications. Results showed that root length density (RLD) was unaffected by the irrigation levels in 2019. In 2020, the RLD was comparable between 100% and 80% ETc, and it was significantly higher in 100% ETc than both 60% Eand 40% ETc. Root surface area density (RSAD) was not significantly different between 100% and 80% ETc, and it was significantly lower in both 60% and 40% ETc than 100% ETc in both years. Soil water depletion was the highest in 40% ETc followed by 60% and 80% ETc, and it was least in 100% ETc in both years. Evapotranspiration (ET) was the highest in 100% ETc followed by 80%, 60%, and 40% ETc. The WUE was not statistically different among the irrigation treatments. However, numerically, WUE was observed in the following order: 80% ETc > 100% ETc > 60% ETc > 40% ETc. The RLD, RSAD, soil water depletion, and ET were not significantly different between ‘Poinsett 76’ and ‘Marketmore 76’. However, fruit yield was significantly higher in ‘Poinsett 76’ than ‘Marketmore 76’, which resulted in higher WUE in Poinsett 76. It can be concluded that 80% ETc and Poinsett 76 cultivar can be adopted for higher crop water productivity and successful cucumber production in SHP.

Evapotranspiration is the major component of the water cycle excluding precipitation. Evapotranspiration sub-processes represent important paths of water which have been poorly investigated and may play an important role in the water cycle. Two of these sub-processes are root water uptake (RWU) and root hydraulic redistribution (RHR), which were modelled and numerically explored in this study. Both RWU and RHR were evaluated using the source/sink term in Richards' equation coupled to a vegetation-atmosphere system. This coupling composes a model of water transfer in which the interplay between evapotranspiration and three different root density distributions (exponential, linear and constant scenarios) was simulated to understand, mainly, the influence of rooting systems on RWU and RHR. The results showed that the model consistently described the water dynamics and accurately estimated water fluxes, with evapotranspiration and RWU greater under the constant scenario. RHR contributed, from simulations, up to 21% of the evapotranspiration on a daily basis. Precipitation events may invert the direction of RHR from upward (hydraulic lift) to downward. The last process tends to conserve soil moisture in the root zone. The root systems modified the dynamics of the drainage, being the exponential scenario the greatest contributor to free drainage. [ABSTRACT FROM AUTHOR]

Version 5 of the Community Land Model (CLM5) introduces the plant hydraulic stress (PHS) configuration of vegetation water use, which is described and compared with the corresponding parameterization from CLM4.5. PHS updates vegetation water stress and root water uptake to better reflect plant hydraulic theory, advancing the physical basis of the model. The new configuration introduces prognostic vegetation water potential, modeled at the root, stem, and leaf levels. Leaf water potential replaces soil potential as the basis for stomatal conductance water stress, and root water potential is used to implement hydraulic root water uptake, replacing a transpiration partitioning function. Point simulations of a tropical forest site (Caxiuanã, Brazil) under ambient conditions and partial precipitation exclusion highlight the differences between PHS and the previous CLM implementation. Model description and simulation results are contextualized with a list of benefits and limitations of the new model formulation, including hypotheses that were not testable in previous versions of the model. Key results include reductions in transpiration and soil moisture biases relative to a control model under both ambient and exclusion conditions, correcting excessive dry season soil moisture stress in the control model. PHS implements hydraulic gradient root water uptake, which allows hydraulic redistribution and compensatory root water uptake and results in PHS utilizing a larger portion of the soil column to buffer shortfalls in precipitation. The new model structure, which bases water stress on leaf water potential, could have significant implications for vegetation‐climate feedbacks, including increased sensitivity of photosynthesis to atmospheric vapor pressure deficit. Key Points: An updated soil‐plant‐atmosphere continuum model based on hydraulic theory is implemented in the Community Land Model (version 5)Prognostic leaf water potential replaces soil matric potential as the basis for stomatal conductance water stressPrognostic root water potential is used to implement hydraulic root water uptake, replacing a "soil wilting point" approach [ABSTRACT FROM AUTHOR]

Abstract: Efficient extraction of soil water is essential for the productivity of plant communities. However, research on the complementary use of resources in mixed plant communities, and especially the impact of plant species richness on root water uptake, is limited. So far, these investigations have been hindered by a lack of methods allowing for the estimation of root water uptake profiles. The overarching aim of our study was to determine whether diverse grassland plant communities in general exploit soil water more deeply and whether this shift occurs all the time or only during times of enhanced water demand. Root water uptake was derived by analysing the diurnal decrease in soil water content separately at each measurement depth, thus yielding root water uptake profiles for 12 experimental grasslands communities with two different levels of species richness (4 and 16 sown species). Additional measurements of leaf water potential, stomatal conductance, and root traits were used to identify differences in water relations between plant functional groups. Although the vertical root distribution did not differ between diversity levels, root water uptake shifted towards deeper layers (30 and 60 cm) in more diverse plots during periods of high vapour pressure deficit. Our results indicate that the more diverse communities were able to adjust their root water uptake, resulting in increased water uptake per root area compared to less diverse communities (52% at 20 cm, 118% at 30 cm, and 570% at 60 cm depth) and a more even distribution of water uptake over depth. Tall herbs, which had lower leaf water potential and higher stomatal conductance in more diverse mixtures, contributed disproportionately to dynamic niche partitioning in root water uptake. This study underpins the role of diversity in stabilizing ecosystem function and mitigating drought stress effects during future climate change scenarios. Furthermore, the results provide evidence that root water uptake is not solely controlled by root length density distribution in communities with high plant diversity but also by spatial shifts in water acquisition. A plain language summary is available for this article. [ABSTRACT FROM AUTHOR]

The root water uptake profile (RWUP) reflects a plant's survival strategy and controls evapotranspiration and carbon fluxes. Despite its importance, there is still no reliable method for reconstructing this profile. In this study, we applied and compared two possible approaches to a case study in a conifer plantation: an isotope-calibrated mechanistic model and a mixing model with a bell-shaped approximation. Our results show that, after calibrating the hydrologically-active root density profile, the mechanistic model gave a good estimation of the xylem water isotope delta (δx); even though the measured root density was greater in shallower soils, water uptake occurred throughout the entire soil profile, with more uptake in deeper soils. The RWUPs estimated by the mixing model were different from those estimated by the mechanistic model and were unrealistic. However, when we constrained the minimum thickness of the water uptake zone, there was good agreement between the RWUPs from the two approaches. We can therefore conclude that the mechanistic model calibrated with isotopes gave better results, and that sole use of the mixing model is not recommended unless appropriate constraints are applied. [ABSTRACT FROM AUTHOR]

The amount of moisture transpired by vegetation is critically tied to the moisture supply accessible to the root zone. In a Mediterranean climate, integrated evapotranspiration (ET) is typically greater in the dry summer when there is an uninterrupted period of high insolation. We present a 1-D model to explore the subsurface factors that may sustain ET through the dry season. The model includes a stochastic parameterization of hydraulic conductivity, root water uptake efficiency, and hydraulic redistribution by plant roots. Model experiments vary the precipitation, the magnitude and seasonality of ET demand, as well as rooting profiles and rooting depths of the vegetation. The results show that the amount of subsurface moisture remaining at the end of the wet winter is determined by the competition among abundant precipitation input, fast infiltration, and winter ET demand. The weathered bedrock retains ~30% of the winter rain and provides a substantial moisture reservoir that may sustain ET of deep-rooted (>8 m) trees through the dry season. A small negative feedback exists in the root zone, where the depletion of moisture by ET decreases hydraulic conductivity and enhances the retention of moisture. Hence, hydraulic redistribution by plant roots is impactful in a dry season, or with a less conductive subsurface. Suggestions for implementing the model in the CESM are discussed. [ABSTRACT FROM AUTHOR]

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.

Reliable parameterizations of water uptake under osmotic stresses depend on the appropriate description of the interacting effects of root distribution and activity over the root zone. These effects should be evaluated under transient salinity conditions. To show that, a crop was irrigated with three salinity inputs using a randomized block design. Root-zone water storage and pressure heads measured at the bottom of the root zone allowed to calculate the evapotranspiration under the different salinity levels imposed. Root densities were measured by direct sampling twice during the growth season. Transpiration was distributed along the root zone according to a Feddes-type sink term and a reduction function accounting for osmotic stress. These data allowed evaluating the effects on the reduction function of (1) the actual salinity and root distributions under different osmotic stress and (2) discontinuous osmotic stress conditions occurring locally in the root zone because of salt leaching. When considering the space-time salinity distribution and the specific root distribution, a unique reduction curve was found, independently of the salinity level of the irrigation water. The effect of discontinuous stress was modelled by introducing (1) a hysteretic behaviour in the salinity reduction function, to be applied only to root compartments actually experiencing discontinuous stress and (2) a scaling factor acting on the whole root zone, based on the ratio of the actual (induced by salinity) to the potential root density. Results suggested that the reduction of transpiration under salinity may be partly caused by irreversible physiological adaption of the roots to saline stress and partly by reduced root density. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In arid and semiarid climate catchments, where annual evapotranspiration ( ET) and rainfall are typically comparable, modeling ET is important for proper assessment of water availability and sustainable land use management. The aim of the present study is to assess different parsimonious schemes for representing ET in a process-based model of coupled surface and subsurface flow. A simplified method for computing ET based on a switching procedure for the boundary conditions of the Richards equation at the soil surface is compared to a sink term approach that includes root water uptake, root distribution, root water compensation, and water and oxygen stress. The study site for the analysis is a small pasture catchment in southeastern Australia. A comprehensive sensitivity analysis carried out on the parameters of the sink term shows that the maximum root depth is the dominant control on catchment-scale ET and streamflow. Comparison with the boundary condition switching method demonstrates that this simpler scheme (only one parameter) can successfully reproduce ET when the vegetation root depth is shallow (not exceeding approximately 50 cm). For deeper rooting systems, the switching scheme fails to match the ET fluxes and is affected by numerical artifacts, generating physically unrealistic soil moisture dynamics. It is further shown that when transpiration is the dominant contribution to ET, the inclusion of oxygen stress and root water compensation in the model can have a considerable effect on the estimation of both ET and streamflow; this is mostly due to the water fluxes associated with the riparian zone. [ABSTRACT FROM AUTHOR]

Highlights: [•] Interaction between belowground and aboveground water ecohydrologic dynamics. [•] Water uptake simulation both at the microscopic and macroscopic levels. [•] Macroscopic models have moisture uptake pattern constant, linear and exponential. [•] Non-linear macroscopic models have improved moisture prediction efficiency. [•] To verify the modeled moisture uptake patterns, precisely obtained field data is vital. [Copyright &y& Elsevier]

Abstract: It is very important to identify the uncertainties of transpiration and root zone soil water for improving water, fertilizer and agricultural chemical management. The canopy transpiration, dominating over evapotranspiration in a close planting orchard, is the main input data of soil water movement simulation for the model based on the Richard equation. However, transpiration estimations are always uncertain because of uncertainties of input data and model structure, which bring the uncertainties of root zone soil water simulation, reduce the simulation accuracy and cause model instability. So, quantitative study of uncertainties of transpiration and root zone soil water simulations are very important to raise the reliability of the simulation. In this study, a Bayesian approach was used to fit the transpiration model to half-hourly cherry transpiration rates, probabilistically estimate its parameters and predict the uncertainties. The probabilistic transpiration model was extended by adding a normally distributed error term, and the Markov chain Monte Carlo simulation method was used to determine the posterior parameter distributions, and the estimated transpirations of average, 95% upper and lower confidence limits were obtained as the input data of the Richard equation, and the simulations of soil water and root water uptake were then obtained. The results showed there were a large number of uncertainties for the transpiration, soil water and root water uptake, and soil water greatly changed in the 30 and 50 cm soil layer for the intensive root system, but there was only minor change in 10 and 110 cm soil layers for small roots. The mean relative error (MRE) was 4.3%, 8.64%, 14.53% between simulated and measured soil water for average, 95% upper and lower confidence limit estimated transpiration as input data, and it was 11.68%, 19.55%, 25.35% for root water uptake, respectively. Moreover, there were also very large uncertainties for cumulative root water uptake, and the maximum difference can reach about 100 mm after 100 simulation days. So, the effect of transpiration uncertainties on soil water and root water uptake should be paid attention to for improving water management and contamination risk assessment. [Copyright &y& Elsevier]

Plant water uptake is a crucial process linking water fluxes in the soil-plant-atmosphere continuum. Soil water extraction by roots affects the dynamics and distribution of soil moisture. Water supply of plants controls transpiration, which makes up for an important fraction of the energy balance at the land surface, and influences soil-vegetation-atmosphere feedback processes. Therefore, efficient algorithms for an accurate estimation of root water uptake are essential in land-surface models that are coupled with climate models, in agricultural crop models that predict water budget and plant growth at the field and plot scale, and in hydrological models. Due to different purposes and demands on computational time, the degree of detail in representing belowground processes varies considerably between these model types. This study investigates the impact of the degree of detail in process descriptions of root growth and water uptake and of information about soil hydraulic properties on simulated seasonal patterns of evapotranspiration and soil moisture in a field study with winter wheat ( Triticum aestivum L. cv. Cubus). Evapotranspiration was well simulated by CLM3.5 until the beginning of crop senescence, but it overestimates the water flux through plants in the last three weeks of the vegetation period and showed a lower performance in simulating soil moisture compared to crop models. The best simultaneous fit of soil moisture and latent heat flux was achieved by the crop model XN-SPASS, which consists of the most detailed representation of root growth dynamics. The results indicate the importance of implementing improved belowground process descriptions for advanced simulations with coupled hydrological and atmospheric models. [ABSTRACT FROM AUTHOR]

Abstract: Weighable lysimeters are powerful measurement systems for identifying soil hydraulic processes and properties, because the boundary fluxes (precipitation, actual evapotranspiration, and seepage across the bottom) can be determined very precisely. However, root water uptake by plants and the soil water flux are interrelated. Thus, the simultaneous estimation of root water uptake parameters and soil hydraulic parameters from macroscopic state observations is a challenge. In this study we investigated the possibility of simultaneously estimating root water uptake and soil hydraulic parameters by inverse simulation of soil water flow in monolithic lysimeters under atmospheric boundary conditions. We used the Richards equation and a macroscopic root water uptake model to simulate the processes. The amount of information needed for the unique identification of parameters was analyzed and the magnitude of their uncertainties was investigated. To check the principal feasibility of our approach, we first examined synthetic data sets for different scenarios and instrumentation campaigns that differed in their information content and complexity of soil properties. The investigations of synthetic data showed that for homogeneous profiles, cumulative outflow and profile-averaged water content data contained enough system information to allow the simultaneous estimation of soil hydraulic properties and root-distribution parameters. In contrast, for soil profiles consisting of two layers, unique soil hydraulic parameters and the correct rooting depth could only be estimated if matric potential measurements from both layers were included in the objective function. To test the procedure with real data, soil hydraulic properties of the grass-reference lysimeter at Wagna (Austria) were estimated using actual measurements. Water dynamics in the lysimeter could be described well by an effective parameterization assuming a homogeneous soil profile. Furthermore, the system behavior under different boundary conditions could be predicted adequately with the estimated parameters. [Copyright &y& Elsevier]

A tension-saturated water slug descends through a homogenous soil after a rainfall (irrigation) event and shrinks due to transpiration by a distributed root-sink and evaporation. The upper (drainage) and lower (imbibition) sharp fronts of the slug separate it from the superjacent and subjacent vadose zones, where water is immobile. In the slug, the hydraulic conductivity is constant according to the Green-Ampt model. The capillary pressures as well as effective porosities on the fronts are given (generally, different) constants that can be viewed as a kind of hysteresis. A volumetric sink models mild (no desaturation of the slug) soil water withdrawal by the plant roots. The sink intensity varies with the depth from the soil surface and with time. Mathematically, the hydraulic head is immediately expressed by double integration of a governing 1-D flow equation. The pressure and kinematic conditions on the fronts result in a Cauchy problem for a system of two ODEs, which is solved by computer algebra routines. [ABSTRACT FROM AUTHOR]

Different spatial distributions of soil moisture were imposed on field-grown grapevines by applying the same irrigation volumes to the entire (DI; deficit irrigation) or part of the (PRD; partial root zone drying) root zone. Five treatments were applied: controls irrigated at 60% ETc (crop evapotranspiration) for the whole season (308 mm year−1); DI-1 and PRD-1 that received the same irrigation as controls before fruit set, 30% ETc from fruit set to harvest and 45% ETc post-harvest (192 mm year−1); and DI-2 and PRD-2 that were the same, except that 15% ETc was applied from fruit set to harvest (142 mm year−1). Compared with DI-1, PRD-1 maintained higher leaf area post-veraison and increased root water uptake, whole-plant hydraulic conductance, leaf transpiration, stomatal conductance, and photosynthesis, but decreased intrinsic gas exchange efficiency without causing differences in leaf xylem abscisic acid (ABA) concentration. Compared with DI-2, PRD-2 increased leaf xylem ABA concentration and decreased root water uptake, whole-plant hydraulic conductance, leaf transpiration, stomatal conductance, and photosynthesis, mainly at the beginning of PRD cycles. Distinctive PRD effects (e.g. greater stomatal closure) depended on the volumetric soil water content of the wet root zone, as predicted from a model of root-to-shoot ABA signalling. [ABSTRACT FROM AUTHOR]

Abstract: This modeling study used recent observations at a temperate broad-leaved forest in Central Germany to calculate water balances of a Fagus sylvatica monoculture and mixed stands of F. sylvatica, Tilia spp., Acer spp., Carpinus betulus, Fraxinus excelsior and Quercus robur. To simulate soil water flow the modeling framework Expert-N was applied which combines models that describe the physiological and hydrological processes of the plant-soil system including models of evapotranspiration (Penman–Monteith equation), interception (revised Gash model) and soil water flow (Richards equation). Measurements of rainfall partitioning, volumetric soil water content, evapotranspiration and tree transpiration provided reliable data for the parameterization and the calibration of the model for three stands of different diversity levels. They allowed to include species specific physiological (transpiration rates, response to dry soil water conditions) and structural (leaf area dynamics) characteristics. During the 3-year long observation period 2005–2007 the mean yearly precipitation was 652mm, the simulated mean yearly interception loss of the three observed forest stands was between 219 and 272mm, the transpiration accounted for 197–225mm, the forest floor evaporation for 96–104mm, the drainage for 16–60mm and the runoff for 13–50mm. The calculations of the water balance were sensitive to the species composition of the forest and showed differences of rainfall interception and root water uptake between the stands. The applied stand-level model was able to simulate the water dynamics of the monospecific and mixed forest stands. It was shown that differences in drought tolerance of tree species can have a strong impact on the simulated soil water extraction during periods when available soil water is low. [ABSTRACT FROM AUTHOR]

Abstract: Bioengineering features of native vegetation are currently being evolved to enhance soil stiffness, slope stabilisation and erosion control. The effects of tree roots on soil moisture content and ground settlement are discussed in this paper. Matric suction induced by tree roots is a key factor, governing the properties of unsaturated soils, directly imparting stability to slopes and resistance for yielding behaviour. A mathematical model for the rate of root water uptake that considers ground conditions, type of vegetation and climatic parameters has been developed. This study highlights the inter-related parameters contributing to the development of a conceptual evapo-transpiration and root moisture uptake equilibrium model that is then incorporated in a comprehensive numerical finite element model. The developed model considers fully coupled-flow-deformation behaviour of soil. Field measurements obtained by the Authors from a site in Victoria, South of Australia, are used to validate the model. In this study, the active tree root distribution has been predicted by measuring soil organic content distribution. The predicted results show acceptable agreement with the field data in spite of the assumptions made for simplifying the effects of soil heterogeneity and anisotropy. The results prove that the proposed root water uptake model can reliably predict the region of the maximum matric suction away from the tree axis. [Copyright &y& Elsevier]

Abstract: Hydrological simulations at multi-temporal time scales by a widely used land surface model (LSM) are investigated under contrasting vegetation and meteorological conditions. Our investigation focuses particularly on the effects of two different representations of root water uptake and root profile on simulated evapotranspiration (ET) and soil moisture by the Integrated BIosphere Simulator (IBIS). For this purpose, multi-year eddy covariance measurements, collected at four flux-tower sites across North America, were used to gauge IBIS simulations with: (a) its standard version (IBIS2.1), in which static root water uptake (RWU) and root profile schemes are incorporated; and (b) a modified version in which dynamic RWU and root profile schemes replaces the static schemes used in the standard version. Overall, our results suggest that the modified version of the model performs more realistically than the standard version, particularly when high atmospheric demand for evaporation is combined with high atmospheric vapour pressure deficit and low soil water availability. The overall correlation between simulated and measured monthly ET rates at the simulated sites reached 0.87 and 0.91 for the standard and the modified versions, respectively. Our results also show that the incorporation of the dynamic RWU in IBIS yields improved simulations of ET under very dry conditions, when soil moisture falls down to very low levels. This suggests that adequate representations of vegetation responses to drought are needed in LSMs as many state of the art climate models projections of future climate indicate more frequent and/or more intense drought events occurring in some regions of the globe. Our analysis also highlighted the urgent need for adequate methodologies to correct field measurements that exhibit energy imbalances in order to provide rigorous assessments of land surface model simulations of heat and mass exchanges between the land surface and the atmosphere. [Copyright &y& Elsevier]

Tritium is mainly produced from nuclear facilities apart from nuclear tests. After being released to the environment, tritium would cause water & food contamination due to its radioactivity and mobility. This study investigated dynamic characteristics of tritiated water (HTO) migration in the soil and evapotranspiration effect based on realistic environmental conditions. The influences of soil types and time-varying environmental factors such as precipitation and evapotranspiration on tritium migration behaviors were specially discussed under normal continuous and accidental short-term release conditions. Radiation dose caused by dynamic tritium evapotranspiration was evaluated. The results show that tritium migration velocity in the soil is much higher than other particles such as cesium due to negligible adsorption of tritium by the soil. Tritium migration in the soil from up to down is attributed to precipitation. On the contrary, evapotranspiration factor would carry tritium movement along the opposite direction. A considerable fraction approximately 55% of tritium deposited in the soil would be reemitted into the air from bare soil and plant leaves due to evapotranspiration effect. Subsequently, the radiation dose caused by second plume due to evapotranspiration effect might be higher than the first plume due to direct release from the nuclear facility under routine discharge. [Display omitted] • Dynamic tritium migration characteristics in the soil were investigated. • Dynamic tritium transfer characteristics through plant root uptake were explored. • Tritium migration velocity vector is attributed to precipitation and evapotranspiration. • The question where the tritium in the soil has gone was first real-time quantitatively answered. • A numerical method describing dynamic tritium behaviors in air-soil-plant system was introduced. [ABSTRACT FROM AUTHOR]

The article presents a study that calibrates a root water uptake model composed of the K. J. Kristensen and S. E. Jensen evapotranspiration model paired to a solution of Richard's equation that controls flow in variably saturated soils. The study is carried out in a semiarid rangeland, giving the opportunity to test the Kristensen and Jensen model and originally proposed parameter values in a different environment from which the original model was created and calibrated. Its goal is to see how a different balance of the different sources of information on the calibration problem impacts the parameter estimates and the model output.

• HYDRUS-1D coupled APSIM could be used for projection water dynamics in water repellent soils. • Climate change shortened the summer maize growth period in the Northwestern China. • Soil water repellency increased soil water storage and evaporation. • Soil water repellency decreased evapotranspiration and root water uptake. Soil water repellency greatly affects crop growth and soil water movement. The aim of this study was to estimate dynamics of soil water storage (SWS), actual evapotranspiration (ET a), root water uptake (RWU) and actual evaporation (E a) under an annual crop grown in water repellent (WR) soils at future climate scenarios. The soil hydraulic parameters were calibrated and validated for HYDRUS-1D based on the experimental data in 2016 and 2017. The summer maize growth periods and irrigation schedules were generated with Agricultural Production Systems Simulator (APSIM). The daily SWS, ET a , RWU and E a values from five water repellent treatments were simulated for summer maize growth periods during 1981–2000, 2030–2059 and 2060–2089 using eight selected global climate models under two representative concentration pathways (RCP 4.5 and RCP 8.5). Due to the increased temperature, the growth period reduced by 12–27 days, the total SWS, ET a , RWU and E a decreased by 8.1%-21.1%, 2.2%-11.1%, 0.5%-9.7% and 0.8%-9.6% compared to the baseline period, respectively. Changes of total SWS, ET a , RWU and E a during the whole summer maize growth periods under RCP 4.5 were greater than RCP 8.5 during the same period. Values of total SWS, ET a , RWU and E a in 2030–2059 were higher than 2060–2089 for the same RCP scenario. With increasing initial water droplet penetration time, total SWS and E a increased, while ET a and RWU decreased. The global circulation model (GCM) and Period contributed greatly to uncertainty. The results implied that it is necessary to adjust the planting date of summer maize. [ABSTRACT FROM AUTHOR]

In agriculture, soil evaporation is considered a loss of water, and crop transpiration is a crucial factor affecting crop growth and yield. Although there have been numerous studies on evapotranspiration (ET) on farmland, only a few have been conducted on field crop transpiration because of the difficulties in the direct measurement of transpiration and in separate evaluation of evaporation and transpiration under field conditions. In this study, we used the heat-pulse method to measure the sap velocity in sugarcane stems to evaluate field transpiration during summer at the study site on Tanegashima Island (at about 31° N) in Japan. The reference crop ET was determined by the Food and Agriculture Organization (FAO) Penman–Monteith method from on-site meteorological data and was compared with the measured transpiration. The daily transpiration in August ranged from 3.3 mm d−1 to 6.6 mm d−1; the corresponding sap flow varied from 0.27 L d−1 to 0.55 L d−1 per stalk. The daily analysis of ET showed that a standard value of 1.25 for the crop coefficient presented by the FAO is acceptable as the crop coefficient for the mid-season growth stage of sugarcane in the study site. Numerical simulations of Richards equation with the sink term were conducted to examine the response of root water uptake to atmospheric transpiration demand throughout 20 consecutive clear and dry days in August. The decrease in the soil moisture in the root zone depends on the transpiration demand during daytime, and soil moisture is redistributed and recovered during the nighttime. The hourly numerical results in August support a standard value of 1.20 for the basal crop coefficient in the mid-season growth stage, as proposed by FAO. The simulations showed that roots extract water preferentially from the deep and wet soil layers to meet the transpiration demand; transpiration predicted from the sink term agreed well with the actual transpiration measured by the heat-pulse method. Therefore, the numerical analysis of soil moisture dynamics under the atmospheric transpiration demand based on the reference crop ET can be an effective tool to evaluate field sugarcane water consumption. • Daily sap flow per stalk in August ranged from 0.27 L d-1 to 0.55 L d-1. • The standard values of crop coefficients by FAO are acceptable at the study site of Japan. • Roots extract water preferentially in the deep, wet soils for transpiration demand. • A step-shaped soil moisture depletion with time was recognized during clear days. [ABSTRACT FROM AUTHOR]

One of the classical methods for estimating groundwater evapotranspiration (ETg) by phreatophytes is based on diurnal water table fluctuations (WTFs). This method was initially introduced by White in 1932 and has recently been improved. However, vegetation‐induced disequilibrium between groundwater and capillary fringe (CF) water is not considered under White's assumptions. In this study, we propose an approach that considers root‐driven water depletion in the CF using the soil moisture profile (hereafter referred to as the SMP method). The SMP method is demonstrated to perform equally well for both long‐term water table rises and declines. The apparent advantages of the SMP method over traditional WTF‐based methods include its greater effectiveness in revealing physical mechanisms and its omission of specific yield determination. However, appropriately determining the boundary condition, which is related to active root‐zone thickness, is crucial for the SMP method. Further development of the SMP method requires a deeper understanding of the interactions among roots, groundwater, and soil moisture. [ABSTRACT FROM AUTHOR]

Various issues related to oil palm production, such as biodiversity, drought, water scarcity, and water and soil resource exploitation, have become major challenges for environmental sustainability. The water footprint method indicates that the quantity of water used by plants to produce one biomass product could become a parameter to assess the environmental sustainability for a plantation. The objective of this study is to calculate the water footprint of oil palm on a temporal scale based on root water uptake with a specific climate condition under different crop age and soil type conditions, as a means to assess environmental sustainability. The research was conducted in Pundu village, Central Kalimantan, Indonesia. The methodology adopted in carrying out this study consisted of monitoring soil moisture, rainfall, and the water table, and estimating reference evapotranspiration (ETo), root water uptake, and the oil palm water footprint. Based on the study, it was shown that the oil palm water usage in the observation area varies with different crop ages and soil types from 3.07–3.73 mm/day, with the highest contribution of oil palm water usage was in the first root zone which correlates to the root density distribution. The total water footprint values obtained were between 0.56 and 1.14 m3/kg for various plant ages and soil types. This study also found that the source of green water from rainfall on the upper oil palm root zone delivers the highest contribution to oil palm root water uptake than the blue water from groundwater on the bottom layer root zone. [ABSTRACT FROM AUTHOR]

Soil water content (SWC) distribution plays an important role in root water uptake (RWU) and crop yield. Reasonable deep irrigation can increase the yield of winter wheat. The soil water movement model of winter wheat was established by considering the root water uptake and the different soil depths of irrigation and using the source term of the soil water movement equation to simulate irrigation at different soil depths. For model verification, experiments on three treatments of winter wheat growth were conducted at irrigation soil depths of 0% (T1), 40% (T2), and 70% (T3) of the distribution depth of the winter wheat root system. The SWC calculated by the model is in accordance with the dynamic change trend of the measured SWC. The maximum absolute error of the model was 0.022 cm3/cm3. The maximum average relative error was 7.95%. The maximum root mean square error was 0.28 cm3/cm3. Therefore, the model has a high simulation accuracy and can be used to simulate the distribution and dynamic changes of SWC of winter wheat in irrigation at different soil depths. The experimental data showed that irrigation soil depth has a significant effect on the root distribution of winter wheat (p < 0.05), and deep irrigation can reduce the root length density (RLD) in the upper soil layers and increase the RLD in the deeper soil layers. The dynamic simulation of RWU and SWC showed that deep irrigation can increase the SWC and RWU in deep soil and decrease the SWC and RWU in upper soil. Consequently, deep irrigation can increase the transpiration of winter wheat, reduce evaporation and evapotranspiration, and increase the yield of winter wheat. [ABSTRACT FROM AUTHOR]

Satellite-based observations indicate that seasonal patterns in canopy greenness and productivity in the Amazon are negatively correlated with precipitation, with increased greenness occurring during the dry months. Flux tower measurements indicate that the canopy greening that occurs during the dry season is associated with increases in net ecosystem productivity (NEP) and evapotranspiration (ET). Land surface and terrestrial biosphere model simulations for the region have predicted the opposite of these observed patterns, with significant declines in greenness, NEP, and ET during the dry season. In this study, we address this issue mainly by developing an empirically constrained, light-controlled phenology submodel within the Ecosystem Demography model version 2 (ED2). The constrained ED2 model with a suite of field observations shows markedly improved predictions of seasonal ecosystem dynamics, more accurately capturing the observed patterns of seasonality in water, carbon, and litter fluxes seen at the Tapajos National Forest, Brazil (2.86°S, 54.96°W). Long-term simulations indicate that this light-controlled phenology increases the resilience of Amazon forest NEP to interannual variability in climate forcing., Organismic and Evolutionary Biology