Unsaturated Hydraulic Conductivity Research Articles

Impact of Hillslope Agriculture on Soil Compaction and Seasonal Water Dynamics in a Temperate Vineyard

Major losses of agricultural production and soils are caused by erosion, which is especially pronounced on hillslopes due to specific hydrological processes and heterogeneity. Therefore, the aim of this study was to assess the impact of agricultural management on the compaction, infiltration, and seasonal water content dynamics of the hillslope. Measurements were made at the hilltop and footslope, i.e., soil water content and potential were measured using sensors, wick lysimeters were used to quantify water flux, while a mini-disk infiltrometer was used to measure the infiltration rate and calculate the unsaturated hydraulic conductivity (K_unsat). Soil texture showed differences between hillslope positions, i.e., at the hilltop after 50 cm depth, the soil is classified as silty clay loam, and from 75 cm onward, the soil is silty clay, while at the footslope, the soil is silt loam even at the deeper depths. The results show a higher K_unsat at the footslope as well as higher average water volumes collected in wick lysimeters compared to the hilltop. Average water volumes showed a statistically significant difference at p < 0.01 between the hilltop and the footslope. The soil water content and water potential sensors showed higher values at the footslope at all depths, i.e., 8.0% at 15 cm, 8.4% at 30 cm, and 27.3% at 45 cm. The results show that, even though the vineyard is located in a relatively small area, soil heterogeneity is present, affecting the water flow along the hillslope. This suggests the importance of observing water movement in the soil, especially today when facing extreme weather (e.g., short-term high-intensity rainfall events) in order to protect soil and water resources.

Hydropedological Characterization of a Coal Mining Waste Deposition Area Affected by Self-Burning

Coal mining often produces severe environmental effects, including impacts on the soil system and, specifically, on hydropedological conditions that control the leaching of significant ions and Potentially Toxic Elements (PTEs). The research objective is to assess changes in the hydropedological conditions in an area with a coal mining waste pile that underwent self-burning. An integrative approach was implemented, starting with the definition of hydropedological zoning based on field observations of soil formation factors (namely, parent material, relief, biological activity, anthropic influence, and time). The soil profile in each hydropedological zone was characterized regarding morphological features. The upper mineral horizons were sampled and characterized in terms of mineralogy and PTE geochemistry. Field measurements of unsaturated hydraulic conductivity, soil water content, and hydrophobicity were performed. Afterwards, the hydrogeochemistry of leachates was determined, and the soil leaching potential was evaluated. The research outcomes express substantial differences regarding the hydropedological zones: development of different soil profiles, diverse mineralogy and PTE geochemistry, higher unsaturated hydraulic conductivity and leaching of major ions, and PTEs in soils affected by coal mining activities. Finally, a Principal Component Analysis confirmed the existence of significant contrasts according to hydropedological zoning.

Comment on “Modified expression for unsaturated hydraulic conductivity according to Mualem–van Genuchten to allow proper computations at low pressure heads” by M. Heinen

Comment on “Modified expression for unsaturated hydraulic conductivity according to Mualem–van Genuchten to allow proper computations at low pressure heads” by M. Heinen

A percolation model of unsaturated hydraulic conductivity using three-parameter Weibull distribution

Accurate estimation of unsaturated hydraulic conductivity, K(Sw), is crucial for modeling water and solute transport in variably-saturated soils. In this study, a new model for the estimation of K(Sw) based on percolation theory and critical path analysis is presented, in which the pore-throat size distribution is described by the three-parameter Weibull probability density function. To evaluate the performance of the proposed K(Sw) model, two datasets including more than three hundred samples are analyzed. The first dataset includes 240 pore-network simulations, while the second dataset consists of 101 soil samples from the UNSODA database. For the pore-network simulations, for which both pore-throat size distributions and capillary pressure curves are available, we estimate K(Sw) from the capillary pressure curve with RMSLE = 0.54 slightly better than the estimations obtained from the pore-throat size distribution with RMSLE = 0.6. For the soil samples, since only the capillary pressure curve is measured, we estimate K(Sw) from the capillary pressure curve and evaluate three previously proposed approaches for determining the exponent, α, in Poiseuille's law. We find that RMSLE = 0.98 for α = 3, RMSLE = 0.87 for α = 2(4 − D) − (3 − D)/(2D − 3), and RMSLE = 1.06 for α = 4 − 0.74D, in which D is the fractal dimension characterizing the pore space. Comparing the results with previous studies in which the power-law probability density function was used to characterize capillary pressure curve and pore sizes shows that the proposed three-parameter Weibull distribution, in conjunction with the CPA analysis, may more accurately estimate K(Sw) for a wide variety of soils ranging from very fine to very coarse textures.

Averaging or adding domain conductivities to calculate the unsaturated soil hydraulic conductivity

AbstractRecent models of the unsaturated hydraulic conductivity curve (UHCC) are the sum of separate UHCCs for domains of capillary water, film water, and water vapor. This requires parallel, noninteracting domains. A theoretical framework for aggregating domain conductivities to a bulk soil UHCC is presented to identify and possibly relax implicit assumptions about domain configuration. The paper develops arithmetic, harmonic, and geometric averages of the liquid‐water conductivities that can be arithmetically averaged with the vapor conductivity. However, current models for capillary and film conductivities are intrinsic, that is, valid within their respective domain. The vapor conductivity is a bulk conductivity, that is, it gives the conductivity of the gaseous domain as it manifests itself in the soil. Conversion relationships use the domain volume fractions as approximations of the as‐yet unknown weighting factors to convert between intrinsic and bulk conductivities. This facilitates consistent averaging of domain conductivities. Even with consistent averaging, a truly physically accurate model of the UHCC based on domain conductivities is fundamentally elusive. Nevertheless, models based on the three averages and the unweighted sum of the domain conductivities produce good fits to data for two soils but diverge in the dry range. The fitted curves for the capillary and film water depend on the averaging (or adding) method. Hence, they are not strictly characteristic of their respective domains. The true intrinsic domain conductivity functions may be impossible to determine.

Cover crop management systems improves soil quality and mitigate water erosion in tropical olive orchards

The production of olive trees in shallow soils in hillslopes requires adequate soil and water conservation systems. In this context, soil use and management besides vegetation cover contributes to better soil quality and the sustainability of the olive cultivation system. Thus, the objective was to determine the physical and chemical properties that are indicative of soil quality in areas of Dystrudepts, under different soil cover management systems in olive cultivation in tropical region. Olive tree culture field experiment was established in 2015, where soil was sampled over three years (2016, 2017 and 2021). The effect of five cover management systems were compared for each agricultural year, namely BS: bare soil in 2015/2016, 2016/2017 and 2017/2021; OBS: olive trees on bare soil in 2015/2016, 2016/2017 and 2017/2021; OSV: olive trees intercropped with mowed spontaneous vegetation in 2015/2016, 2016/2017 and 2017/2021; OJB: olive trees intercropped with jack beans (Canavalia ensiformis L.) in 2015/2016 and 2016/2017, and olive trees crowned intercropped with mowed spontaneous vegetation in 2017/2021; OMI: olive trees intercropped with millet (Pennisetum glaucum L.) in 2015/2016, olive trees intercropped with sunn hemp (Crotalaria juncea L.) in 2015/2017 and olive trees with spontaneous vegetations treated with herbicide (Roundup) in 2017/2021. The soil quality indices (SQI) proved to be sensitive to variations in different types of soil management from the second year of assessment, regarding water erosion. OSV and OJB showed the highest SQI, while OBS showed the lowest values. The SQI demonstrated an inverse correlation with soil and water losses starting from the second year of assessment. This highlights its efficacy in assessment the effects of adopted management on soil quality in the context of water erosion. Moreover, it reinforces the importance of vegetation cover in maintaining soil fertility, resulting in increase of soil organic matter and improving the structuring of Dystrudepts. The attributes that most correlated with the SQI were soil organic matter, effective cation exchange capacity, sum of bases, geometric mean diameter of aggregates, pH and unsaturated soil hydraulic conductivity. These attributes collectively provide valuable insights into soil health and water erosion susceptibility within the olive tree production system.

A modified model predicting the hydraulic properties of variably saturated soil accounting for film and capillary flow

Accurate knowledge of hydraulic properties of unsaturated soil is vital to modelling water and solute transport process and addressing soil salinisation problems. Due to the defect that the van Genuchten (VG) model cannot represent soil water characteristics (SWC) during the drying stage, we have introduced a modified model, which combines capillary flow with film flow models to describe the unsaturated hydraulic conductivity. The capillary SWC is obtained by assuming the specific water capacity function with lognormal distribution. The film SWC is modified using the logarithmic nonlinear expression by introducing a modification coefficient into the Campbell equation, and the film relative hydraulic conductivity (RHC) is obtained based on the logarithmic nonlinear relationship. The calculated modification coefficient values range from 0.99 to 2.49. Finally, the proposed model’s rationality and applicability are validated through root mean square error (RMSE) analysis with measured values and comparison with the VG model. While the calculation RMSEs of SWC in the two models are basically consistent, the RMSEs of RHC in the proposed model are around 1–10 times smaller than those of the VG model, indicating its superiority in calculating the hydraulic conductivities over the entire matric head.

Hydraulic Characterization of Green Roof Substrates by Evaporation Experiments

Green roofs can be a valid solution for stormwater management in urban environments. The objective of this study was to develop a laboratory procedure for the hydraulic characterization of artificial substrates, used in the realization of green roofs, based on transient evaporation and steady-state unit hydraulic gradient (UHG) experiments. The retention, θ(h), and hydraulic conductivity, K(h), curves of two commercial substrates Terra Mediterranea® (TMT) and AgriTERRAM® (ATV) and a specifically developed substrate made by mixing peat, compost and sandy loam soil (MIX) were investigated. The unimodal van Genuchten–Mualem (VGM) hydraulic functions obtained by the direct evaporation method with different choices of the fitting parameters were compared with UHG measurements of K(h) conducted close to saturation. A numerical inversion of the transient evaporation experiments performed by Hydrus-1D software was also conducted, assuming that the hydraulic properties could be expressed either by unimodal or bimodal VGM models. The results indicated that an appropriate a priori choice of the residual water content parameter improved the estimation of the water retention curve. Moreover, the water retention data estimated from the direct evaporation method were not statistically different from those obtained with the inverse Hydrus-1D. The unsaturated hydraulic conductivity estimations obtained by the direct and inverse methods were highly correlated and the use of the bimodal VGM model improved the estimation of K(h) in the wet range. The numerical inversion of laboratory evaporation data with the hydraulic characteristics expressed by the bimodal VGM model proved to be a reliable and effective procedure for hydraulic characterization of artificial substrates, thus improving the reliability of simulated water fluxes in green roofs.

A Simple Model for Estimating the Hydraulic Conductivity of Unsaturated Soil

Describing the hydraulic conductivity of unsaturated soil is very important in predicting water transport. Most current models have complex forms and generally need to be calibrated by the measured unsaturated hydraulic conductivity curve. A simple model, by which it is possible to conveniently predict the unsaturated hydraulic conductivity, is proposed in this study. The soil–water characteristic curve and hydraulic conductivity curve are separated into three parts. The soil–water characteristic curve is represented by Fredlund and Xing’s equation. A simple model composed of three lines is proposed for estimating the hydraulic conductivity of unsaturated soil. The model parameters can be conveniently calibrated from the measured soil–water characteristic curve and saturated hydraulic conductivity. Finally, the proposed model is validated by the experimental data from different soils. The proposed model provides a simple approach to estimating the hydraulic conductivity of unsaturated soil, which is more convenient for practical application.

Numerical Determination of Unsaturated Hydraulic Conductivity From Time-Series Outflow Data

Numerical Determination of Unsaturated Hydraulic Conductivity From Time-Series Outflow Data

A new kinematic wave model that describes lateral subsurface flow and percolation in hillslopes

Kinematic wave (KW) models are commonly used for flood forecasting in large river basins, but have limitations in their ability to simulate percolation effects. Here, we suggest an extended KW model wherein the vertical pressure head is under non-hydrostatic conditions. The proposed model uses the Brooks Corey and Mualem models to estimate the water retention curve and unsaturated hydraulic conductivity and adopts the pressure head gradient as a new variable to calculate runoff based on changing water content distributions over time due to percolation. The increase in the pressure head gradient with rainfall infiltration is determined from the relationship between water storage and pressure head distribution, while the decrease in pressure head gradient due to percolation is modeled as exponential decay with time. A comparison of the proposed KW model and a numerical solution of the Richards equation shows that the proposed KW model can reproduce the storage effect caused by percolation, delaying runoff and reducing peak discharge. The agreement between the proposed KW model and the Richards equation is high for soils with high water retention. Conversely, the agreement becomes lower for soil with low water retention or deep soil layer thickness, where the complexity of water content distribution requires further refinement. The proposed model can easily be incorporated into distributed models while low computational cost with keeping the important percolation effects.

Thermal Effects on the Soil Water Retention Curves and Hydraulic Properties of Benggang Soil in Southern China

Soil hydraulic properties significantly affect the occurrence and development of collapsing gully walls. The effect of temperature on the hydraulic properties of soil in collapsing gully walls remains unclear. In this study, the hydraulic properties of the red soil layer, the sandy soil layer and the detritus layer in a collapsing gully wall were investigated using the filter paper method, and the soil water retention curves of the different soil layers at 25 and 40 °C were determined. The aim of this study was to investigate the impact of temperature on the soil hydraulic properties of different soil layers in collapsing gully walls. The study found that when the water content in the red soil layer and sandy soil layer exceeded 20% and in the detritus layer exceeded 10%, the soil’s matric suction significantly decreased as the temperature increased from 25 to 40 °C. Additionally, the parameters of θs, α, n and m all exhibited a decreasing trend, and the soil water content in the detritus layer was primarily influenced by the temperature change, which resulted in a decrease of 38.10%. The unsaturated hydraulic conductivity of the detritus layer exhibited higher values than that of the sandy layer and red soil layer under identical temperature conditions. Moreover, the unsaturated hydraulic conductivity of the red soil layer, sandy soil layer and detritus layer increased with increasing temperature. It was observed that the unsaturated hydraulic conductivity of the detritus layer increased by 0.18 cm h−1 at a soil water content of 44%. This increase in conductivity was more pronounced than the corresponding changes in the red soil layer and sandy soil layer. An elevated temperature caused the water-holding capacity of the different soil layers of the collapsing gully wall to decrease and the unsaturated hydraulic conductivity to increase. However, the influence of the clay particle content within the soil of the collapsing gully wall rendered the temperature effect more distinct. Therefore, the destabilizing deformation of the soil in the collapsing gully wall during the summer under high temperatures and precipitation may have played a key role in its collapse.

SWRC interpretation of iron ore tailings blends focusing on saturation assessment of dry stacking

ABSTRACT The study addresses challenges in dry stacking of fine-grained materials by blending itabirite iron ore slime tailings with coarser flotation tailings. It focuses on flow dynamics, capillary saturation, and the necessity to prevent large, saturated volumes. Geotechnical tests were conducted on various blends, deriving unsaturated hydraulic conductivity functions using Fredlund and Xing’s methodology. The Soil-Water Retention Curve data, combined with transient 1D analysis, assesses capillary rise. Results show capillary rise up to 50 meters with over 80% saturation, and also influenced by weather conditions penetrating up to 20 meters. Integrating up to 30% slime content in flotation tailings mitigates saturation issues. Empirical and numerical findings enable inferring saturation tendencies in distinct iron ore tailings mixtures, establishing a procedural framework for practical field applications.

A Dimension-Reduced Line-Element Method to Model Unsaturated Seepage Flow in Porous Media

Contrary to the continuum hypothesis, which averages water flow across the entire domain, including both grains and pores, the line-element model concentrates unsaturated flow in the pore space in the intermediate region of horizontal and vertical channels. The flux equivalent principle is used to deduce the equivalent unsaturated hydraulic conductivity, the flow velocity and the continuity equations. It is found that the relative hydraulic conductivities derived from the line-element model and the continuum model are identical. The continuity equations in the two models are also similar, except that the coefficient in the water content term is half that in the line-element model. Thus, the unsaturated flow problem in porous media is transformed into a one-dimensional problem. A dimension-reduced finite line-element method is proposed that includes a complementary algorithm for Signorini’s-type boundary conditions involving the seepage-face boundary and the infiltration boundary. The validity of the proposed model is then proved by good agreement with analytical, experimental and simulated results for one-dimensional infiltration in a vertical soil column, unsaturated flow in a sand flume with drainage tunnels, and transient unsaturated flow water-table recharge in a soil slab, respectively. In general, the proposed method has good computational efficiency, especially for smaller mesh sizes and short time intervals.

Prediction of absolute unsaturated hydraulic conductivity – comparison of four different capillary bundle models

Abstract. To model water, solute, and energy transport in porous media, it is essential to have accurate information about the soil hydraulic properties (SHPs), i.e., the water retention curve (WRC) and the soil hydraulic conductivity curve (HCC). It is important to have reliable data to parameterize these models, but equally critical is the selection of appropriate SHP models. While various expressions for the WRC are frequently compared, the capillary conductivity model proposed by Mualem (1976a) is widely used but rarely compared to alternatives. The objective of this study was to compare four different capillary bundle models in terms of their ability to accurately predict the HCC without scaling the conductivity function by a measured conductivity value. The four capillary bundle models include two simple models proposed by Burdine (1953) and Alexander and Skaggs (1986), which assume a bundle of parallel capillaries with tortuous flow paths, and two more sophisticated models based on statistical cut-and-random-rejoin approaches, namely those proposed by Childs and Collis-George (1950) and the aforementioned model of Mualem (1976a). To examine how the choice of the WRC parameterization affects the adequacy of different capillary bundle models, we utilized four different capillary saturation models in combination with each of the conductivity prediction models, resulting in 16 SHP model schemes. All schemes were calibrated using 12 carefully selected data sets that provided water retention and hydraulic conductivity data over a wide saturation range. Subsequently, the calibrated models were tested and rated by their ability to predict the hydraulic conductivity of 23 independent data sets of soils with varying textures. The statistical cut-and-random-rejoin models, particularly the Mualem (1976a) model, outperformed the simpler capillary bundle models in terms of predictive accuracy. This was independent of the specific WRC model used. Our findings suggest that the widespread use of the Mualem model is justified.

Crop rotations influence soil hydraulic and physical quality under no-till on the Canadian prairies

Cropping system sustainability is dependent on the conservation of soil hydraulic and physical quality over time. This study examined the effects of crop rotations on soil hydraulic and physical quality on the Canadian prairies, emphasizing choices of crop species and sequence to preserve or improve soil quality under no-till management. Field experiments were initiated in spring 2018 at three sites: Lethbridge (Alberta), and Swift Current and Scott (Saskatchewan) to evaluate six crop rotations, consisting of (i) conventional (control), (ii) pulse/oilseed intensified, (iii) diversified, (iv) market-driven, (v) high-risk and high-reward, and (vi) soil health-enhanced. Undisturbed soil cores were collected from 5–10 and 15–20 cm soil depth increments in 2021 after crop harvest, to determine bulk density (BD), total (TP) and effective porosity (EP), pore size distribution, soil water retention, and unsaturated hydraulic conductivity. Results revealed that crop rotations did not significantly impact BD, TP, or EP in the 5–10 and 15–20 cm soil depth increments across the three sites. Depending on the site and soil layer, the pulse/oilseed intensified, diversified, high-risk and high-reward, and soil health-enhanced rotations improved macroporosity by 13−127% and mesoporosity by 1−36% compared to the conventional rotation, resulting in concomitant increases in large and medium unsaturated hydraulic conductivities. At Lethbridge, both conventional and high-risk and high-reward rotations resulted in increased water content at field capacity (FC) by 12–14%, permanent wilting point (PWP) by 7−12%, and plant available water capacity (PAWC) by 16−17%, accompanied by significant increases in microporosity (8%) and residual porosity (16%) in the 5−10 cm depth compared to the soil health-enhanced rotation. However, no significant differences were found at Swift Current or Scott in the 5−10 cm depth. The pulse/oilseed intensified rotation significantly improved FC by 22% and PAWC by 19% compared to the market-driven rotation. This rotation also showed an 18% increase in FC and a 32% increase in PWP when compared to the diversified rotation at Scott in the 15−20 cm depth, but did not differ significantly at Lethbridge or Swift Current. Overall, crop rotations with legumes and increased functional diversity have the potential to improve soil physical quality and plant available water but may require a period longer than the present study’s duration to become evident.

Characterizing uncertainty in process-based hydraulic modeling, exemplified in a semiarid Inner Mongolia steppe

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.

Study of the effect of the compaction level on the hydrodynamic properties of loamy sand soil in an agricultural context

Agricultural soil compaction adversely affects crop water use and yield performance and should be avoided or remediated through appropriate soil management strategies. The investigation of the impact of different levels of soil compaction on its hydrodynamic properties remains a crucial step in improving water use and crop yields. We examined five compaction levels of silty sand soil sampled from a potato field in the agricultural regions of northern Quebec (Canada). Soil hydraulic characteristics (saturated and unsaturated hydraulic conductivity, soil water retention capacity) were measured using the constant head method, the HYPROP device, and a WP4C dew point potentiometer. The sixteen hydraulic models integrated into the HYPROP software were fitted to the soil water retention curve (SWRC) data for the studied compaction levels. Statistical parameters such as the mean bias error, mean absolute error, correlation coefficient, and root mean square error were used to measure the performance of the models. The results show that saturated and unsaturated conductivity decreases with increasing soil compaction. The lowest saturated hydraulic conductivity (Ks) value is observed for the highest level of soil compaction, reflecting a solid medium with less pore space and connectivity. Among the hydraulic models, the Peters-Durner-Iden (PDI) variant of van Genuchten's unconstrained bimodal model (VGm-b-PDI) outperformed all other models for SWRC simulation of different soil compaction levels and was, accordingly, selected as the optimal model. This model was implemented in HYDRUS-1D to estimate the amount of irrigation for different compaction levels. We simulated irrigation scenarios with the dual-porosity model. The results indicated that soil compaction can strongly influence soil hydraulic properties and water differently. However, the amount of irrigation for the potato crop was optimal at a moderate level of soil compaction. Overall, combined HYPROP and HYDRUS 1D can provide helpful information on the soil hydraulics properties dynamics and a rigorous simulation for irrigation planning and management in potato fields.

Interaction of focused recharge and deep groundwater discharge near a wetland: A study in the Ordos Basin, China

Groundwater mounds and depressions induced by rainfall and evapotranspiration near wetlands/lakes have been widely observed, but their effects on groundwater flow field are poorly known. Here, a sandy hillslope near a wetland in the Ordos Plateau, China, which has a semi-arid climate, is selected for investigation. After identifying temporary groundwater mounds/depressions based on three water level observation wells, a HYDRUS-2D model is setup to obtain the highly transient daily flow field. The variable thickness of unsaturated zone near the wetland, which controls soil water content and unsaturated hydraulic conductivity, is found to be responsible for groundwater mounds resulting from focused recharge and groundwater depressions resulting from nonuniform evapotranspiration. On nonrainy days, evapotranspiration in the lowland is supported by flowpaths from regional groundwater discharge, and in the slope is supported by a flow cell from the upland to the upper part of the slope, which causes water table recession in the upland. On rainy days, focused recharge in the lowland leads to two temporary local flow cells, which break the regional groundwater discharge flowpaths into two temporary flow cells. The two temporary flow cells toward the upland contribute to water table rises in the uplandMoreover, we find focused recharge in rainy days does not change the overall direction of flowpaths controlled by regional groundwater discharge and strong evapotranspiration, but only increase the tortuosity of flowpaths. By coupling daily atmospheric conditions and regional groundwater discharge, this study has implications for groundwater recharge estimation and future groundwater modelling in arid regions.

Irrigation Salinity Affects Water Infiltration and Hydraulic Parameters of Red Soil

Unconventional water resources (e.g., saline water, etc.) for irrigation as a promising supplementary water source can alleviate the freshwater shortage in the agriculture of red soil areas in Southern China. It should be noted that the presence of soluble salt in this water source may have detrimental influences on soil water infiltration and crop growth. Understanding the effect of unconventional water irrigation (UWI) on water infiltration in red soil is important. Previous studies have shown that the salinity of UWI can alter soil hydraulic properties to change soil water movement in saline soils. However, the underlying mechanism and factors of water infiltration in red soil under UWI with different salinity levels remain limited. Therefore, a laboratory experiment (one-dimensional vertical infiltration experiment and centrifuge method) was conducted to evaluate the effect of UWI with different salinity levels [0 (the distilled water, CK), 1 (S1), 2 (S2), 3 (S3), 5 (S5), and 10 (S10) g L−1] on the soil water infiltration process, soil water characteristic curve (SWCC), soil water constants estimated using the SWCC, saturated and unsaturated hydraulic conductivity (KS and K) as well as the soil chemistry of soil profile [pH, electrical conductivity (EC), and Na+ and Cl− contents]. The primary factors of soil water infiltration were identified using stepwise regression and path analysis methods. The results showed that UWI salinity decreased water infiltration by 1.53–7.99% at the end of infiltration in red soil, following the order of CK > S1 > S5 > S2 > S3 > S10. Moreover, UWI could enhance soil water availability with an increase of 8.55–12.68% in available water capacity. In contrast, lower KS and K were observed in S1–S10, and there was a negative linear relationship between irrigation salinity and KS. UWI also produced the EC, Na+, and Cl− accumulations in the soil profile. As the salinity level of UWI increased, the accumulations aggravated. Soil acidification was found in S1–S5, while soil alkalization was observed in S10. Additionally, α, PWP, and KS were the primary factors influencing the water infiltration of red soil. This study can help optimize the soil infiltration model under UWI and establish a foundation for unconventional water management in the red soil regions of Southern China and other similar regions. In addition, the undisturbed red soil under agricultural unconventional water irrigation and the long-term effect of unconventional water application should be considered.