Root Water Uptake Rate Research Articles

A model for root water uptake of alpine meadow on the Qinghai-Tibet Plateau considering soil temperature

Predicting root water uptake (RWU) of wide-distributed alpine meadow on the Qinghai-Tibet Plateau (QTP) is essential to precisely reveal the complex hydrothermal behaviors of alpine meadow soil under warming and humidifying climate. In this study, a model for RWU of alpine meadows on the QTP is proposed, which comprehensively considers the actual root characteristics of alpine meadow and the influence of soil temperature. In the proposed model, a root density function is newly derived to describe the root characteristics of alpine meadows, where root biomass (RB) is taken as root characteristics index. Meanwhile, a temperature-dependent reduction function is developed to reflect the impact of soil temperature on the RWU of alpine meadows. The proposed model for RWU is highly competent compared to the model for RWU not considering soil temperature. Furthermore, the proposed model for RWU is applied to explore the influence of RWU effect on the water movement of soil under different soil temperatures. Results indicate that the increment of soil temperature can lead to the exponentially increasing trend for the RWU rate of alpine meadows. Under the RWU effect, the alpine meadows with the thickness of 0.25 m have contributed to the moisture redistribution of soil layer within the range of 0.75 m. At the maximum soil temperature of 23 °C, the maximum RWU rate of 25.16 × 10−9 1/s leads to the maximum decline in volumetric water content of 6.31%. Higher soil temperature is beneficial to the stability of the shallow freeze-thaw slope covered by alpine meadows, which is the opposite of the influence of humidifying climate. It is helpful to disclose the failure mechanism of shallow freeze-thaw slopes of the QTP.

Simulating Tree Root Water Uptake in the Frame of Sustainable Agriculture for Extreme Hyper-Arid Environments Using Modeling and Geophysical Techniques

In order to ensure sustainability in the agricultural sector and to meet global food needs, a particularly important challenge for our time is to investigate the possibility of increasing agricultural production in areas with extreme hyper-arid environments. Warming air temperatures and sandy soils significantly influence tree root water uptake (RWU) dynamics, making accurate estimation of RWU depth distribution and magnitude crucial for effective resource management, particularly in the context of precision irrigation within agroecosystems. This study employed two non-invasive techniques, namely HYDRUS 1D and electrical resistivity tomography (ERT), to simulate RWU under controlled experimental conditions and under an extreme hyper-arid environment. The results revealed that the highest RWU rates occurred during the morning (08:00–11:00). RWU activity predominantly concentrated in the upper soil profile (0–30 cm), and the soil water content in this area was notably lower compared to the deeper soil layers. With increasing temperature, there was a tendency for the RWU zone to shift to lower depths within the soil profile. The findings of this study could have important implications for farmers, providing valuable insights to implement irrigation water management strategies.

Modeling and Analysis of Rice Root Water Uptake under the Dual Stresses of Drought and Waterlogging

The development of an accurate root water-uptake model is pivotal for evaluating crop evapotranspiration; understanding the combined effect of drought and waterlogging stresses; and optimizing water use efficiency, namely, crop yield [kg/ha] per unit of ET [mm]. Existing models often lack quantitative approaches to depicting crop root water uptake in scenarios of concurrent drought and waterlogging moisture stresses. Addressing this as our objective; we modified the Feddes root water-uptake model by revising the soil water potential response threshold and by introducing a novel method to calculate root water-uptake rates under simultaneous drought and waterlogging stresses. Then, we incorporated a water stress lag effect coefficient, φWs, that investigated the combined effect of historical drought and waterlogging stress events based on the assumption that the normalized influence weight of each past stress event decreases with an increase in the time interval before simulation as an exponential function of the decay rate. Further, we tested the model parameters and validated the results obtained with the modified model using data from three years (2016–2018) of rice (Oryza sativa, L) trails with pots in Bengbu, China. The modified Feddes model significantly improved precision by 9.6% on average when calculating relative transpiration rates, particularly post-stress recovery, and by 5.8% on average when simulating soil moisture fluctuations during drought periods. The root mean square error of relative transpiration was reduced by 60.8%, and soil water was reduced by 55.1%. By accounting for both the accumulated impact of past moisture stress and current moisture conditions in rice fields, the modified model will be useful in quantifying rice transpiration and rice water use efficiency in drought–waterlogging-prone areas in southern China.

Design, development, and assessment of a High-Throughput Screening (HTS) system for the macroscopic root water uptake modeling

Climate change is responsible for the increasing frequency and intensity of abiotic stresses generating water scarcity conditions. There is a need to breed plants adapted to future environmental conditions and resistant to water stress. This study presents a High-Throughput Screening (HTS) system for continuously and simultaneously monitoring plant stress response to drought in a semi-controlled environment. The HTS system combines a gravimetric weighing system with soil moisture and atmospheric sensors. In operative terms, the system was tested on the Sage (Salvia officinalis L.) under two soil water deficit treatments managed according to a feedback control irrigation scheduling.The system was able to model the sage water stress function following the root water uptake macroscopic approach. The threshold of soil water status below which crop water stress occurred was also identified. The gravimetric-based daily evapotranspiration (ETa) and the time domain reflectometry (TDR)-based root water-uptake (RWU) rates showed a high correlation during the drying when the evaporation flux is minimal. Moreover, the effects of soil bulk density on the root density and the plant biomass were evaluated, indicating the importance of carrying out a homogeneous procedure of the pot-filling process.

Construction of root tip density function and root water uptake characteristics in alpine meadows.

Accurate calculation of root water uptake (RWU) is the key to improving vegetation water use efficiency and identifying water cycle evolution patterns, and root tips play an important role in RWU. However, most of the current RWU models in the alpine meadow are calculated based on the root length density (RLD) function. In this study, a large number of roots, soil hydraulic conductivity, and physicochemical property indices were obtained by continuous field prototype observation experiments for up to 2 years. It was found that the RLD and root tip density (RTD) in alpine meadows decrease by 16.2% and 14.6%, respectively, in the wilting stage compared to the regreening stage. The RTD distribution function of the alpine meadow was constructed, and the RWU model was established accordingly. The results show that the RTD function is more accurate than the RLD function to reflect the RWU pattern. Compared with RLD, the simulated RWU model constructed by using RTD as the root index that can effectively absorb water increased by 24.64% on average, and the simulated values were more consistent with the actual situation. It can be seen that there is an underestimation of RWU calculated based on the RLD function, which leads to an underestimation of the effect of climate warming on evapotranspiration. The simulation results of the RWU model based on RTD showed that the RWU rate in the regreening stage increased by 30.24% on average compared with that in the wilting stage. Meanwhile, the top 67% of the rhizosphere was responsible for 86.76% of the total RWU on average. This study contributes to the understanding of the alpine meadow water cycle system and provides theoretical support for the implementation of alpine meadow vegetation protection and restoration projects.

Evaluation of the applicability of the root water uptake model on alpine meadows and analysis of root water uptake characteristics

It is essential to quantify the rate of root water uptake (RWU) and characterize the variability of RWU, which benefits understanding the water use of alpine meadows and its response to environmental changes. In addition, model simulation is one of the feasible methods to obtain the RWU characteristics of alpine meadows. However, recent research on RWU models mainly focused on crops and trees, while barely on alpine meadows. Thus, it is of great significance to develop an RWU model applicable to alpine meadows, which can describe local plant water consumption processes. In this paper, we measured the distribution characteristics of root density and soil characteristics of alpine meadows in the Qinghai-Tibet Plateau (QTP) with prototype observation experiments. The root length density (RLD) of the wilting stage decreased by 16.2% on average compared to the re-greening stage, and the ability of root growth was poorer in the high altitude area. Based on the distribution characteristics of root length density (RLD) and the three soil resistance indexes (soil water potential, soil hydraulic diffusivity, and soil hydraulic conductivity), which have obvious impacts on RWU. The improved Feddes model, Selim-Iskandar model, and Molz-Remson model were selected to simulate the RWU in alpine meadows, which fully considered the above impact factors, but the applicability in alpine meadows was not discussed. The results showed that the model performance of the Selim-Iskandar model was better than the improved Feddes model and Molz-Remson model, and its simulation performance was improved by 44.76 and 22.16% compared to the improved Feddes model and Molz-Remson model, respectively. Based on the quantified RWU rate, the RWU characteristics showed that the top 50% of the rhizosphere was responsible for 72.65% of the water uptake of the entire rhizosphere. At the same time, the obvious difference in RWU rate in different phenological stages was obvious, showing that the RWU rate in the re-greening stage increased by 36.52% compared to that in the wilting stage. This study can provide technical support for a more accurate estimation of transpiration and water use efficiency in alpine meadows, and could provide theoretical support for the implementation of vegetation.

Stomatal conductance tracks soil-to-leaf hydraulic conductance in faba bean and maize during soil drying.

Although regulation of stomatal conductance is widely assumed to be the most important plant response to soil drying, the picture is incomplete when hydraulic conductance from soil to the leaf, upstream of the stomata, is not considered. Here, we investigated to what extent soil drying reduces the conductance between soil and leaf, whether this reduction differs between species, how it affects stomatal regulation, and where in the hydraulic pathway it occurs. To this end, we noninvasively and continuously measured the total root water uptake rate, soil water potential, leaf water potential, and stomatal conductance of 4-week-old, pot-grown maize (Zea mays) and faba bean (Vicia faba) plants during 4 days of water restriction. In both species, the soil-plant conductance, excluding stomatal conductance, declined exponentially with soil drying and was reduced to 50% above a soil water potential of -0.1 MPa, which is far from the permanent wilting point. This loss of conductance has immediate consequences for leaf water potential and the associated stomatal regulation. Both stomatal conductance and soil-plant conductance declined at a higher rate in faba bean than in maize. Estimations of the water potential at the root surface and an incomplete recovery 22 h after rewatering indicate that the loss of conductance, at least partly, occurred inside the plants, for example, through root suberization or altered aquaporin gene expression. Our findings suggest that differences in the stomatal sensitivity among plant species are partly explained by the sensitivity of root hydraulic conductance to soil drying.

Shallow roots of different crops have greater water uptake rates per unit length than deep roots in well-watered soil

PurposeCommonly, root length distributions are used as a first approximation of root water uptake profiles. In this study we want to test the underlying hypothesis of a constant water uptake rate per unit root length over depth.MethodsRoot water uptake profiles were measured using a novel sensor technology. Root length was measured with MRI and by scanning harvested roots. Experiments were performed with pot-grown barley (Hordeum vulgare), maize (Zea mays), faba bean (Vicia faba), and zucchini (Cucurbita pepo).ResultsFor barley, maize, and faba bean, we found that roots in the top 15 cm had significantly greater water uptake rates per unit length than roots in the bottom 30 cm. For zucchini, the trend was similar but not significant. Therefore, variation of root water uptake rates with depth could be explained only partly (61–71%) by a variation of root length with depth.ConclusionThe common approximation of root water uptake profiles by root length distributions relies on constant water uptake rates per unit root length. This hypothesis does not hold in our study, as we found significantly greater water uptake rates per unit length in shallower than in deeper roots. This trend was consistent among species, despite the partly strong variation in physiological parameters. We suggest that this is caused by a decreasing axial transport conductance with depth. This might result in a general underestimation of water uptake rates in shallow soil layers when they are approximated by the root length distribution.

Reactive transport modelling the oxalate-carbonate pathway of the Iroko tree; Investigation of calcium and carbon sinks and sources

The oxalate carbonate pathway (OCP) of the Iroko tree has been shown to function as a carbon sink, due to the precipitation of calcium (Ca) carbonate in the tree and the soil around its roots, a soil developed on a carbonate-free bedrock. A 1D reactive transport (RT) model of the Iroko OCP system was constructed and used in a sensitivity analysis to replicate the geochemical pathway of the OCP and carbon sequestration, constrained by the Ca mass balance. The sensitivity analysis examined ranges of contributions for Ca sources to the system, including rainfall, dust, plant decomposition, mineral weathering, and optionally groundwater Ca sources. The study focused on identifying possible scenarios by which the observed magnitude of accumulated soil calcite could be reproduced, related to the OCP geochemical pathway. In line with field observations of the Iroko, all model results showed a soil transition from acidic (pH 5.1) to mildly alkaline (maximum pH 8.1) conditions, as well as precipitation of calcite. The location of calcite precipitation remained within the upper reach of the soil column, and between 29% and 63% of carbon was retained as calcite. The magnitude of calcite precipitation was limited both by the availability of Ca from the various sources, and by the tree’s rate of root water and solute uptake. The sensitivity analysis confirms that surficial sources such as rainfall and dust deposition contribute only a small fraction of Ca, and indicate that mineral weathering and the extent of the root system, must play a dominant role in supplying Ca to facilitate carbon sequestration through calcium carbonate formation.

Putting Plant Roots at Light: Temporal Imaging of Plant Roots and Soil Water with a Light Transmission Technique for Linking Water and Root Observations to Soil-Plant Models.

Estimating how the "hidden half" of plants, that is the roots, take up water or the influences of root system architecture or root physiological properties (such as root hydraulic conductance) on efficiency of water uptake is of prime importance for improving crops against water deficits. To unravel soil-root interactions for water, we describe a system that enables a dynamic imaging of the soil water content and of the root system, from the single root to the whole root system scales.This system uses plants grown in rhizotrons filled with sandy soil and is based on the variable attenuation of the intensity of light transmitted through the rhizotron with soil water content (the rhizotron is nearly translucent when saturated and becomes darker as soil water content decreases). Images of the transmitted light during plant water uptake (or exudation) phases are recorded with a camera, showing a qualitative pattern of water content variations. The gray levels of the image pixels are then quantitatively related to water content with a calibration.This system is affordable and can be easily implemented without specific equipment. It is scalable and quick to allow the phenotyping of a range of plant genotypes relative to their water uptake pattern. This pattern can be then related with root system properties (soil colonization, root architecture ) at different plant stages. In combination with modeling , imaging results help in obtaining physiological parameters such as root hydraulic conductivity, distributed root water uptake rates or root xylem water potential. Combination of modeling and experiment further helps in testing biological and physiological assumptions and in predicting the uptake behavior of plants in the field.

Modeling tomato root water uptake influenced by soil salinity under drip irrigation with an inverse method

The influence of soil salinity on plant root water uptake (RWU) must be considered in order to promote efficient irrigation management. However, due to challenges in parameterization, modeling RWU response to salinity is problematic. We set out to characterize the influence of soil salinity on tomato RWU under conditions of irrigation with high salinity water and to improve methods for optimizing parameters of RWU model. Experiments were conducted in a greenhouse over two seasons (2016 and 2017). Three irrigation water salinity treatments [0.4 (S1), 3.4 (S2) and 6.4 (S3) mg cm−3] were evaluated. The results showed that soil water content and salinity increased with the irrigation water salinity, especially in the top soil layers, and that RWU was reduced by the increased root zone salinity. An inverse method based on a one-dimensional equation of soil water movement was used to estimate the RWU rate distribution under drip irrigation and determined to be reliable. The parameter value of the normalized root length distribution (NRLD) function was fitted through the estimated RWU rate distributions for treatment S1 without the effect of salinity stress. The fitted NRLD function was used to optimize the parameters of the salinity stress reduction factor (β) through the measured soil moisture and salinity of treatments S2 and S3 in 2016. With the optimized parameters of β, the RWU rates of treatments S2 and S3 in 2017 were simulated. The simulated RWU rates based on the RWU model agreed well with the estimated RWU rates using the inverse method, with root mean squared error (RMSE) and normalized root mean squared error (NRMSE) less than 0.00067 cm3 cm−3 d−1 and 12.36%, and index of agreement (IA) higher than 0.94. These findings can be used to estimate the NRLD distribution and determine actual crop water requirements under saline conditions with no root distribution data required. This should contribute to efficient and sustainable irrigation scheduling.

Evaluation of the Effect of Low Soil Temperature Stress on the Land Surface Energy Fluxes Simulation in the Site and Global Offline Experiments

AbstractThe root water uptake (RWU) rate of plants is influenced by various environmental factors. Low soil temperature stress can reduce RWU rate by inhibiting the growth of plant roots and increasing the hydraulic resistance of water transport among the soil‐plant‐atmosphere continuum. Given that low soil temperature stress is not accounted for in current land surface models (LSMs); in this study, we introduce three functions to represent low soil temperature stress, and modify the RWU scheme of the Common Land Model to quantify the role of low soil temperature stress on water and energy exchange between land and atmosphere. The simulated water and energy fluxes are evaluated using both in situ and global observational data sets. The results from in situ simulations show that ignoring effects of low soil temperature stress, latent, and sensible heat fluxes in spring are overestimated and underestimated, respectively, with the root mean square error up to 40 W/m2. By incorporating the low soil temperature stress functions into the RWU scheme, nearly 40% of the simulated errors are reduced. The global simulated results also highlight the importance of accounting for low soil temperature stress on increasing the accuracy of the modeled latent heat flux over high latitude areas. While uncertainties from related physical processes and parameters warrant further investigations, our results indicate that consideration of low soil temperature stress significantly affects water and energy transport from land to atmosphere by restricting RWU rate, emphasizing the need to integrate it in LSMs to increase the model reliability, especially over cold regions.

Application of a root water uptake model and numerical simulation to walnut trees in arid areas of northwest China

Water shortages restrict the sustainable development of agriculture in arid areas of northwest China. Quantitative studies of root water uptake (RWU) and soil water dynamics can guide the optimal regulation of irrigation. We studied walnut trees under drip irrigation in Hongqopo Farm Experimental Base in Aksu Prefecture, Xinjiang. Our aim was to parameterize the root distribution of walnut trees, establish a flexible and practical macroscopic two-dimensional RWU model, and numerically simulate soil moisture. Multiple regression analysis was applied to establish the root length density (RLD) distribution function and RWU model. The finite difference method was applied to the RWU rate inversion solution, and the alternating direction implicit difference (ADI) method was applied to numerically simulate soil moisture. The RLD distribution function accurately described the location of maximum root density and zero root density using four spatial distribution parameters (R2 = 0.86). The RWU model comprised three parameters: transpiration intensity, RLD distribution, and soil moisture distribution. There was a close agreement between simulated and measured RWU rates. The RWU was concentrated at depths of 10–60 cm. The mean absolute error of soil moisture numerical simulation for 16 days was 0.027 cm3·cm-3, which indicated that the proposed RLD distribution function, RWU model, and numerical simulation method were reliable. These approaches have the advantages of simple parameter measurement and flexible consideration of the spatial variability of the RWU rate and are applicable to other fruit trees. They provide a theoretical basis for water-saving irrigation and scientific management of orchards in arid areas.

Reduced root water uptake of summer maize grown in water-repellent soils simulated by HYDRUS-1D

Soil water repellency (SWR) is an ubiquitous soil property, that has major effects on surface and subsurface water flow, soil erosion, and therefore also affects plant growth and development. Soil water repellency has been recently observed to decrease summer maize growth, especially when the initial persistence of soil water repellency was high. However, mechanics implicated in maize biomass limitations are still unclear due to limited field observations and measurements of plant water use. This research aims to explain the possible mechanisms that impede the growth of summer maize in water repellent soils by examining soil water content, soil water evaporation and root water uptake (RWU) and comparing the measurements to simulations using HYDRUS-1D. Data from five increasing levels of SWR (CK, WR1, WR2, WR3 and WR4) from a two-year experiment were used. The soil hydraulic parameters described with the van-Genuchten model were calibrated inversely based on the observed volumetric soil water content at 26, 47 and 68 days after sowing (DAS) in 2016 and validated by water content values on 33, 62 and 91 DAS in 2017. The results showed the daily and cumulative RWU values ranked in an order of CK > WR1 > WR2 > WR3 > WR4. The RWU rates and cumulative RWU decreased with an increase of initial water droplet penetration time (persistence), which indicated weaker RWU ability of summer maize in the water repellent treatments. Thirty days after sowing, higher evaporation was observed in water repellent soils compared to CK. Weak RWU of summer maize grown in the water repellent soils and strong soil water evaporation were found. This research demonstrates the possible mechanisms that impede summer maize growth in water repellent soils could include weak RWU and high evaporation.

Enhancing the Noah‐MP Ecosystem Response to Droughts With an Explicit Representation of Plant Water Storage Supplied by Dynamic Root Water Uptake

AbstractPlants are able to adapt to changing environments and thus survive droughts. However, most land surface models produce unrealistically low ecosystem resiliency to droughts, degrading the credibility of the model‐predicted ecohydrological responses to climate change. We aim to enhance the Noah‐MP modeled ecosystem resilience to droughts with an explicit representation of plant water storage supplied by dynamic root water uptake through hydrotropic root growth to meet the transpiration demand. The new model represents plant stomatal water stress factor as a function of the plant water storage and relates the rate of root water uptake to the profile of model‐predicted root surface area. Through optimization of major leaf, root, and soil parameters, the new model improves the prediction of leaf area index, ecosystem productivity, evapotranspiration, and terrestrial water storage variations over most basins in the contiguous United States. Sensitivity experiments suggest that both dynamic root water uptake and groundwater capillary rise extend the plants' “memory” of antecedent rainfall. The modeled plants enhance their efficiency to use antecedent rain water stored in shallow soils mainly through more efficient root water uptake over the U.S. Southwest drylands while use that stored in deep soils and aquifers with the aid of groundwater capillary rise in the Central United States. Future plant hydraulic models should not ignore soil water retention model uncertainties and the soil macropore effects on soil water potential and infiltration.

High water uptake ability was associated with root aerenchyma formation in rice: Evidence from local ammonium supply under osmotic stress conditions

Root water uptake is strongly influenced by the morphology and anatomical structure of roots, which are regulated by nitrogen forms and environmental stimuli. To further illustrate the roles of different nitrogen forms on root water uptake under osmotic stress, a split-root system was supplied with different nitrogen forms and osmotic stress simulated by adding 10% (w/v) polyethylene glycol (PEG, 6000). The local effects of nitrogen form and osmotic stress on root morphology, anatomical structure, root lignin content, and water uptake rate were investigated. Under osmotic stress conditions, ammonium markedly promoted the formation and elongation of the lateral root, whereas a significant decrease in numbers of lateral roots was observed under local nitrate supply. Under nitrate supply in split-root systems, osmotic stress significantly promoted root cell death and more aerenchyma formation, as well as accelerated the lignification of the root. However, osmotic stress had no negative effect on the root anatomical structure under ammonium supply. The root water uptake rate was significantly higher in split-root supplied with ammonium than nitrate under osmotic stress conditions. In conclusion, the high water uptake ability in local ammonium supply was associated with the more lateral roots development and the lower cell death, aerenchyma formation and lignification under osmotic stress.

Soil conditions affect cotton root distribution and cotton yield under mulched drip irrigation

Film-mulched drip irrigation with brackish water has been used widely for cotton (Gossypium hirsutum L.) production in arid regions. Full consideration of the promise of brackish water irrigation requires consideration of the dependence of cotton root characteristics on soil conditions. To date, these dependences are complex and poorly understood. The present study compared the impacts of soil temperature, water and salinity on root characteristics on cotton yield for brackish water irrigation treatment (BWT) and fresh water irrigation treatment (FWT). Spatial differences were observed for cotton root mass, root length, root surface-area and root volume distribution that corresponded with differences in the distributions of soil conditions. There existed a strikingly linear relationship between cotton root length and root mass. Soil temperature did not exert clear control on root system growth. Lower average root density and coarser roots were observed for BWT than for FWT as a result of the reduced soil temperature and the elevated soil salinity associated with BWT. Cotton shoot growth was more sensitive than root growth to salt stress for BWT. Higher root density and fine root proportion for FWT than BWT led to higher cotton yield. That is, more cotton roots were observed in the shallow mulched zone, which corresponded with high root water uptake rate and salt accumulation. Our study indicated that the easily-measured cotton root mass could be used as a practical surrogate for root length under mulched drip irrigation. Subsurface drip irrigation with drip tapes set in the shallow mulched zone may further promote cotton root system growth, allowing for sustainable cotton production with brackish water irrigation.

Spatial Heterogeneity Enables Higher Root Water Uptake in Dry Soil but Protracts Water Stress After Transpiration Decline: A Numerical Study

AbstractA common assumption in models of water flow from soil to root is that the soil can be described in terms of its representative or effective behavior. Microscale heterogeneity and structure are thereby replaced by effective descriptions, and their role in flow processes at the root‐soil interface is neglected. Here the aim was to explore whether a detailed characterization of the microscale heterogeneity at the scale of a single root impacts the relation between flow rate and pressure gradient. Numerical simulations of water flow toward a root surface were carried out in a two‐dimensional domain with a randomized configuration of spatially variable unsaturated hydraulic conductivities and varying boundary conditions, that is, increasing and decreasing root water uptake rates. By employing Matheron's method, the soil hydraulic properties were varied, while the effective hydraulic conductivity (corresponding to the geometric mean) remained unchanged. Results show that domains with a uniform conductivity could not capture important features of water flow and pressure distribution in spatially variable domains. Specifically, increasing heterogeneity at the root‐soil interface allowed to sustain higher root water uptake rates but caused a slower recovery in xylem suction after transpiration ceased. The significance of this is that, under critical conditions, when pressure gradients and flow rates are high, microscale heterogeneity may become an important determinant and should not be neglected in adequate descriptions of water flow from soil to root in dry soil.

Modelling soil water dynamics and root water uptake for apple trees under water storage pit irrigation

Water storage pit irrigation is a new method suitable for apple trees. It comes with advantages such as water saving, water retention and drought resistance. A precise study of soil water movement and root water uptake is essential to analyse and show the advantages of the method. In this study, a mathematical model (WSPI-WR model) for 3D soil water movement and root water uptake under water storage pit irrigation was established based on soil water dynamics and soil moisture and root distributions. Moreover, this model also considers the soil evaporation, pit wall evaporation and water level variation in the pit. The finite element method was used to solve the model, and the law of mass conservation was used to analyse the water level variation. The model was validated by experimental data of the sap flow of apple trees and soil moisture in the orchard. Results showed that the WSPI-WR model is highly accurate in simulating the root water uptake and soil water distributions. The WSPI-WR model can be used to simulate root water uptake and soil water movement under water storage pit irrigation. The simulation showed that orchard soil water content and root water uptake rate centers on the storage pit with an ellipsoid distribution. The maximum distribution region of soil water and root water uptake rate was near the bottom of the pit. Distribution can reduce soil evaporation in the orchard and improve the soil water use efficiency in the middle-deep soil. Keywords: root water uptake, soil water dynamics, numerical simulation, water storage pit irrigation, apple tree DOI: 10.25165/j.ijabe.20191205.4005 Citation: Guo X H, Lei T, Sun X H, Ma J J, Zheng L J, Zhang S W, et al. Modelling soil water dynamics and root water uptake for apple trees under water storage pit irrigation. Int J Agric & Biol Eng, 2019; 12(5): 126–134.

Extension of cosmic-ray neutron probe measurement depth for improving field scale root-zone soil moisture estimation by coupling with representative in-situ sensors

Accurate estimation of field-scale root-zone soil moisture (RZSM) is essential for hydro-meteorological and agricultural management. The cosmic-ray neutron probe (CRNP) is an innovative technique for field-scale soil moisture observation. However, it is limited at deeper depths, and requires suitable methods for scaling the CRNP effective depth to represent the root-zone layer (up to 100 cm depth). A merging framework was developed in this study for improving field-scale RZSM with the CRNP via coupling the representative ancillary RZSM information with cosmic-ray soil moisture. By using ancillary RZSM retrieved at the most time stable location, this approach alleviates the problems associated with lack of independent datasets, while maintaining scale representativeness. A linear autoregressive model was adopted to forecast the errors between two input datasets (the cosmic-ray soil moisture and ancillary RZSM) and a reference product, which was computed by spatially weighting the deepest in-situ soil moisture measurements apart from the most time stable location. The variances of estimated errors were then used to compute a suitable weight for each single product by following the original linear combination of forecasts, and subsequently merging the ancillary RZSM and cosmic-ray soil moisture. Performance of the merged RZSM in comparison to input datasets and exponential filter-based RZSM over three different environments was evaluated against the reference RZSM product. The results indicated that differences in vegetation coverages related to total aboveground and belowground biomass accumulation, root water uptake rate and canopy density are the major factors controlling the temporal variation in merged RZSM, and they can be partly interpreted via the framework procedure. Superior performance achieved by the merging framework demonstrated its robustness in improving field-scale RZSM measurement compared to other products. This study also underlines the strong relationship between input data quality and the performance of the selected merging method, with respect to variations of CRNP effective depths. Overall, the merging framework is simple to apply, enables unrestricted-use in different environments, and is flexible to combine further standalone data sources.