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Stony soils that have a considerable amount of rock fragments (RFs) are widespread around the world. However, experiments to determine the effective soil hydraulic properties (SHPs) of stony soils, i.e., the water retention curve (WRC) and hydraulic conductivity curve (HCC), are challenging. Installation of measurement devices and sensors in these soils is difficult, and the data are less reliable because of their high local heterogeneity. Therefore, effective properties of stony soils especially under unsaturated hydraulic conditions are still not well understood. An alternative approach to evaluate the SHPs of these systems with internal structural heterogeneity is numerical simulation. We used the Hydrus 2D/3D software to create virtual stony soils in 3D and simulate water flow for different volumetric fractions of RFs, f. Stony soils with different values of f from 11 % to 37 % were created by placing impermeable spheres as RFs in a sandy loam soil. Time series of local pressure heads at various depths, mean water contents, and fluxes across the upper boundary were generated in a virtual evaporation experiment. Additionally, a multistep unit-gradient simulation was applied to determine effective values of hydraulic conductivity near saturation up to pF=2. The generated data were evaluated by inverse modeling, assuming a homogeneous system, and the effective hydraulic properties were identified. The effective properties were compared with predictions from available scaling models of SHPs for different values of f. Our results showed that scaling the WRC of the background soil based on only the value of f gives acceptable results in the case of impermeable RFs. However, the reduction in conductivity could not be simply scaled by the value of f. Predictions were highly improved by applying the Novák, Maxwell, and GEM models to scale the HCC. The Maxwell model matched the numerically identified HCC best.

Landslide susceptibility and water balance in the soil, in the community of Lagoa Encantada, Recife Metropolitan Area, Brazil, were assessed using the computational models SINMAP and HYDRUS-1D. The SINMAP input parameters were the physical and hydrodynamic characteristics of the soil, evidence of landslides and the DEM; and for the HYDRUS-1D model, the hydraulic parameters of the soil. For both programs, simulations were also carried out, based on the rain recorded in the area. The soil was classified using the Unified Soil Classification System (USCS). To assess infiltration processes that cause landslides, HYDRUS-1D was used, under the same scenarios simulated by the SINMAP model and also in the evaluation of the infiltrated volume, in real landslides. The SINMAP results (susceptibility maps) show a 71% increase in the susceptible area (SI < 1; SI = stability index) between the two precipitation scenarios, and are consistent with evidence of landslides. The HYDRUS-1D results complement SINMAP results and suggest that infiltration values for simulated scenarios were similar to those of real landslides. It is concluded that it is possible to map areas of greater instability and to predict possible landslides in different precipitation scenarios, by quantitatively assessing the infiltrated volume that contributes to the destabilization of the soil.

In the current study, the temporal distribution of both soil water and soil NO3–N under several conservation agriculture (CA) practices during the wheat crop growth were characterized by HYDRUS-2D model. Treatments comprised of conventional tillage (CT), permanent broad beds (PBB), zero tillage (ZT), PBB with residue (PBB+R) and ZT with residue (ZT+R). Hydraulic inputs of the model, comprising the measured value of Kfs, α and n, obtained as the output of Rosetta Lite model were optimized through inverse modeling. Model predicted the daily change in soil water content (SWC) of the profile during the simulated period (62–91 DAS) with good accuracy (R2 = 0.75; root mean squared error (RMSE) = 0.038). In general, soil water balance simulated from the model showed 50% lower cumulative drainage, 50% higher cumulative transpiration along with higher soil water retention, in PBB+R than CT. Reported values of the first-order rate constants, signify nitrification of urea to NH4–N (μa) (day−1) nitrification of NH4–N to NO3–N (μn) (day−1) and the distribution coefficient of urea (Kd−in cm3 mg−1) were optimized through inverse modeling. Later they were used as solute transport reaction input parameters of the model, to predict the daily change in NO3–N of the profile with better accuracy (R2 = 0.83; RMSE = 4.62). Since NH4–N disappears fast, it could not be measured frequently. Therefore, not enough data could be generated for their use in the calibration and validation of the model. Results of simulation of daily NO3–N concentration indicated a higher concentration of NO3–N in the surface layer and its leaching losses beyond the root zone were relatively lesser in PBB+R, than CT, which resulted in less contamination of the belowground water. Thus, the study clearly recommended PBB+R to be adopted for wheat cultivation in maize–wheat cropping system, as it enhances the water and nitrogen availability in the root zone and reduce their losses beyond the root zone.

Determining the soil water content (SWC) in a soil profile is very important task for agriculture and also for a wider ecological context. The spatial and temporal variability of SWC is a elementary issue for agricultural practice, irrigation management, or landscape management globally. Various methods are used for obtaining the SWC data. Every method has some advantages and also disadvantages. Many of them are focused only on one dimension but modern precise agriculture needs the information about SWC in spatial scale. This study is focused on the spatial scale analysis of SWC in the Nitra river catchment for years 2013 and 2014. The HYDRUS 1D hydrological model and GIS tools were used for the creation maps of SWC. Combination of the measured and simulated data was used for the creation of the unique spatial maps of soil moisture in 0-30 and 30-60 cm soil horizons. Validation of our method shows trustworthy results. Soil water storage and fulfillment of maximum soil water storage were analysed with using the created maps.

Subsurface drip irrigation is one of the modern irrigation techniques that assist to control applied water by providing water to plant roots by drippers. Numerical simulation by using HYDRUS (2D/3D) was used to develop a formulas for estimating wetted area from subsurface drip irrigation together with water uptake by roots. In this study, two soil types, namely sand and sandy clay loam, were used with two types of crops, (tomatoes and onions). Different values of initial moisture content of soil, drip depth, and drip discharge were used in the simulation. The soil wetting patterns were analyzed each half an hour for three hours of irrigation time, and five initial soil moisture contents and different flow rates. To verify the results gained by applying HYDRUS (2D/3D) a field experiment was carried out to measure the wetted width and compare measured values with simulated values. Formulas for wetted width and depth were developed. The performance of the model was evaluated by comparing the predicted results with those obtained from field experiments. The modeling efficiency was greater than 98% and the root mean square error did not exceed 1.68 cm for both soils with good agreement.

Spatio‐temporal variations of nitrate‐nitrogen (NO3-‐N) leaching is driven by both soil hydrology and biogeochemistry. However, the widely used soil hydrology and biogeochemistry models have their weaknesses in simulating soil N cycling and soil water movement processes, respectively. In this study, we proposed an alternative approach by simply combining the HYDRUS‐3D and DNDC models to investigate the spatio‐temporal variations of NO3-‐N leaching on a representative tea garden hillslope in Taihu Lake Basin, China. Results showed that the soil hydrology and N cycle were well simulated by HYDRUS‐3D and DNDC models, respectively. Based on the leaching equation, the soil water flux simulated by HYDRUS‐3D and soil NO3-‐N content simulated by DNDC were combined to calculate the leachate NO3-‐N concentrations with good accuracy. The accumulative NO3-‐N leaching flux during the simulation year was 71.7 kg N ha⁻¹, with remarkable spatio‐temporal variations on this hillslope. Hot spots of NO3-‐N leaching were observed in blocks 24, 27, 31, 34, 37, and 40 with accumulative leaching fluxes > 82.0 kg N ha⁻¹ y⁻¹. The spatial variation of NO3-‐N leaching was mainly controlled by soil texture and soil hydraulic properties. Hot moments of NO3-‐N leaching were observed after the applications of spring fertilizer (16 March) and basal fertilizer (30 October). The temporal variation of NO3-‐N leaching was mainly controlled by precipitation and the spring fertilization. Methods and findings of this study will be benefit for the risk assessment of non‐point source N loss and the precise agricultural management.

Subsurface drip irrigation is increasingly being used for sugarcane production in Southeast Brazil in attempts to conserve water, especially after extreme droughts in 2014 and 2015. Correct design of a subsurface drip system is essential to provide information about water and solutes dynamics in the subsurface, leading to possible water savings. While field investigations demand much time and financial resources, numerical models can also provide much information about expected water and solute distributions in the soil profile. The objective of this study was to use HYDRUS-2D for simulations of water and potassium movement in containers packed with a subsurface drip-irrigated tropical soil cultivated with sugarcane and comparing simulated and observed data through statistical parameters. Investigations were carried out in a greenhouse during 240 days after the tillering stage. Spatial and temporal distributions of water content and potassium concentrations were collected using Time Domain Reflectometry (TDR) to calibrate and validate HYDRUS-2D. Simulations were carried out using hydraulic properties fitted directly to measured retention date, as well as estimated using pedotransfer functions (Rosetta Lite and the class pedotransfer of Carsel and Parrish). RMSE and MAE indicated a favorable capacity of the model to simulate soil water content using with measured properties and a better performance than estimated properties by pedotransfer functions. For the potassium concentrations, a less than optimal performance was obtained with HYDRUS-2D using both the measured hydraulic properties and the pedotransfer functions. A better understanding and accurate determination of solute concentrations in soil, uptake parameters, the crop root growth and distribution should be necessary for improve the simulations and observed data. The inability of HYDRUS-2D to accurately estimate potassium concentrations was not necessarily a limitation of model, but rather a limitation of knowledge about the soil and plant parameters involved.

The soil hydrological process plays an important role in transporting and distributing water in soils. However, the correlation between water flow behaviors, soil physical properties, infiltration patterns of soil exhibiting different soil layers, and the variation patterns in water flow behavior in rubber-based agroforestry systems remain poorly understood. Here, we mainly used dye-tracer infiltration to classify water flow behavior and HYDRUS-3D to interpret variation patterns of water flow behaviors in a rubber-based agroforestry system in southwest China. The results showed that (1) the soil of forestry patches under Hevea brasiliensis (HB) and Citrus reticulata (CR) exhibited better soil physical properties than those with no vegetation (NV). Compared with these in the NV, the saturated soil water content and field capacity increased by 15% and 21% in CR, and by 2% and 12% in HB, respectively; while the saturated hydraulic conductivity enhanced by 584% (p HB > NV. Finally, (3) the infiltration flow in soil under HB and CR exhibited a faster downward wetting front and an obvious lateral flow. These infiltration patterns compensated for the insufficiency of soil water in NV and finally caused water redistribution to be more homogenized across the whole soil profile. Therefore, our findings indicated that the rubber-based agroforestry system is a successful approach for conserving water and reducing runoff in tropical regions.

In the subsurface irrigation management of extensively cropped vegetables, uniform crop growth requires the maintenance of uniform soil water suction at the root zone across a field. Moreover, a fixed value of suction that is suitable for crop growth should be maintained. However, accounting for the temporal and spatial changes in the suction is beyond human capability. Using HYDRUS-2D, this study modeled a spinach field in Tsukuba, Japan, which is irrigated by subsurface irrigation pipes. The subsurface pipes were located 55 cm below the soil surface. The pipes were placed 150 cm apart. Belt-shaped water shielding sheets were installed beneath the pipes. Irrigation was empirically managed. The measured physical soil properties of the spinach field were input into the model as initial values and then calibrated using the irrigation data and observed soil water suction across the field. The calibrated model was further verified by comparing the simulated and other observed suctions. After model verification, several scenarios were created by varying the given conditions: (1) the intervals of subsurface irrigation pipes, (2) the depths at which the irrigation pipes were located, (3) the existence of a water shielding sheet beneath the irrigation pipes, and (4) the shape of the water shielding sheet. These scenarios were compared, and the optimal scenario, which facilitates equal soil water suction that is close to the suction required for the growth of spinach, was selected.

Farmers along the main reach of the Zarqa River Basin (ZRB) commonly utilize treated wastewater for irrigation. Deep percolation is expected to occur as a result of irrigation, and it is expected that preferential flow pathways may facilitate the downward movement of irrigation water. Therefore, the aim of this research was to investigate the susceptibility of soils near Zarqa River to preferential flow, and the HYDRUS and Soil and Water Assessment Tool (SWAT) models were used. The methodology consisted of taking tension infiltrometer measurements along the Zarqa River to determine the main physical properties relevant to preferential flow, such as infiltration rate and macroscopic capillary length, followed by investigating the downward water movement using HYDRUS and SWAT. The HYDRUS simulations were conducted using single porosity (SP) and dual porosity (DP) constitutive functions pertaining to matrix and preferential flow, respectively. The in situ tension infiltrometer measurements were used to parameterize the surface layer of the HYDRUS DP model. HYDRUS simulations showed that preferential flow occurring in the surface layer of the soil profile controlled the vertical movement of soil water in excess of field capacity. The comparison between SWAT, SP and DP showed that both SWAT and DP were capable of simulating preferential flow in arid watersheds. However, SWAT simulations of lateral discharge and deep percolation resemble that of the DP only when the evaporation soil compensation factor (ESCO) was set to a value of 0.8 and the length of the soil slope was set to its maximum value. This research recommends using HYDRUS model to verify SWAT model predictions of soil water redistribution in the soil profile and to improve the parameterization of the SWAT model. The research also suggests an approach for the combined use of both models.

The HYDRUS-2D simulation software has been used for irrigation management. Its performance under realistic irrigation regimes requires evaluation with new methodologies that integrate larger soil volumes, because soil water content is highly variable in time, space and scale. We compare direct measurements in a sloping field environment under drip irrigation with simulation using HYDRUS-2D. An advanced mobile sensor technology is used to track the dynamics of soil water content, and thus of unsaturated flow, at 0.25 m and 0.50 m depth in a field plot (6 m × 3 m; 4° slope) beneath two parallel (0.5 m separation; 7 emitters per delivery tube) dripper arrays. We document an asynchronous sequence of wetting fronts driven by the sloping surface and capture the field results well using HYDRUS-2D, in the spatial (R2 = 0.935–0.963, p

A study to assess soil water redistribution under mobile drip irrigation (MDI), low-energy precision application (LEPA), and low-elevation spray application (LESA) was conducted under a cen...

Despite increasing use of pressurized irrigation methods, most irrigation projects worldwide still involve surface systems. Accurate estimation of the amount of infiltrating water and its spatial distribution in the soil is of great importance in the design and management of furrow irrigation systems. Moment analysis has previously been applied to describe the subsurface water distribution using input data from numerical simulations rather than field measured data, and assuming a constant ponding depth in the furrow. A field experiment was conducted in a blocked-end level furrow at Maricopa Agricultural Center, Arizona, USA, to study the effect of time-variable ponding depths on soil water distribution and the resulting wetting bulb under real conditions in the field using moment analysis. The simulated volumetric soil water contents run with variable and constant (average) ponding depths using HYDRUS 2D/3D were almost identical, and both compared favorably with the field data. Hence, only the simulated soil water contents with variable ponding depths were used to calculate the moments. It was concluded that the fluctuating flow depth had no significant influence on the resulting time-evolving ellipses. This was related to the negligible 10-cm variation in ponding depths compared to the high negative matric potential of the unsaturated soil.

The development of the wet bulb under drip irrigation in stratified (sand covered soils) presents a different behavior from that observed under homogeneous soils. The presence of a very active crop as it happens in intensive greenhouses also imposes a series of variations that have not been fully characterized. The aim of this work is to present the data acquisition methodology to calibrate and validate the Hydrus-3D model to safely define the evolution of moisture in wet bulbs generated in stratified “sanded” soils characteristic of greenhouses with tomato and pepper crops grown intensively under drip irrigation.The procedure for collecting and processing moisture data in stratified soils has been defined. The soil and permeability curve has been adjusted experimentally for each material. It has been proved that the Hydrus-3D model can reproduce the behavior of a sand covered soils and it has been possible to verify that the predictions are adequate to what has been observed in the field.

The development of the wet bulb under drip irrigation in sand-covered soils presents a different behavior compared to the one observed in homogeneous soils. Moreover, the presence of a very active crop imposes a series of variations that have not been fully characterized. The aim of this work is to present the data acquisition methodology to calibrate and validate the Hydrus-3D model in order to safely define the evolution of moisture in wet bulbs generated in stratified “sanded” soils characteristic of greenhouses with intensive pepper crop under drip irrigation. The procedure for collecting and processing moisture data in stratified soils has been defined. Soil permeability, retention curve, texture, and bulk density have been measured experimentally for each material. It has been found that the inclusion of a previous day in the simulation improves model predictions of soil moisture distribution. In soils with less gravel, a lower average stress and a more homogeneous moisture distribution were observed. It has been proved that the Hydrus-3D model can reproduce the behavior of sand covered soils under intensive greenhouse growing conditions, and it has been possible to verify that the predictions are adequate to what has been observed in the field. In view of the results, the Hydrus-3D model could be used to establish future irrigation strategies or to locate the optimal placement point of tensiometers that control irrigation in sandy soils for intensive agriculture.

O objetivo deste trabalho é avaliar a capacidade de infiltração e determinar os parâmetros hidrodinâmicos de três superfícies (área de convivência, de recreação infantil e jardins) em um parque urbano na cidade de Recife/PE. A metodologia Beerkan foi utilizada para determinar os parâmetros da curva de retenção de água e da curva de condutividade hidráulica, a partir de 24 ensaios de infiltração; e o modelo Hydrus 1D para simular o balanço hídrico das superfícies, submetidas a 365 dias de precipitação pluviométrica. As áreas de jardins apresentaram maiores valores de taxas máximas de infiltração (553,58 mm.h-1), seguidas das áreas de recreação infantil (116,70 mm.h-1) e área de convivência (18,75 mm.h-1). As texturas predominantes das áreas não constataram correlação direta com a condutividade hidráulica saturada (Ks), apresentando valores entre 25,38 e 306,65 mm.h-1 para os solos franco-arenosos (jardins); 7,67 e 542,2 mm.h-1 para franco-argilo-arenosos (jardins e convivência); e 4,07 e 256,86 mm.h-1 para areia franca (recreação). A capacidade de retenção de água foi menor nos jardins e o comportamento oposto ocorreu nas áreas de convivência. As simulações no Hydrus resultaram em valores mais elevados de lâminas escoadas e de evaporação nos jardins, e que não há diferença de valores das lâminas infiltradas acumuladas entre as três áreas.

Greenhouse cultivation has proven to be an efficient solution to extra-early horticultural production, allowing the cycle of vegetable production to be closed throughout the year. This efficient solution depends on many factors, perhaps the main one being the localized irrigation system. On the other hand, the availability of water for irrigation will be one of the most limiting factors for the development of this agricultural practice. The permanent search for improving irrigation efficiency must be considered as one of the great challenges of sustainable agriculture and in the interest of environmental conservation. In this study, the distribution of the roots of the two main horticultural crops, tomato (Solanum lycopersicum L.) and peppers (Capsicum annuum L.), has been analyzed with the localized irrigation system. In addition, they have been studied for layered soils, which represent an advance in terms of resources, since they are artificial soils, where the natural soil does not allow a horticultural crop. It has been found for these stratified soils, that in pepper crop 90% of the root density is in the soil layer 0 to 9 cm. However, for tomato crops 90% of the root density is in the soil layer from 0 to 11 or 15.5 cm according to the type of soil, in other words filling almost all the added soil. The results obtained in this research allow the Hydrus 3D model for stratified soils to be calibrated. This work allows opening new perspectives in the efficient management of adding soils for new greenhouse construction and for localized irrigation of horticultural crops in general, tomato, and peppers in particular.

The possible impacts that climate change will have on soil water budget and specifically on deep percolation, runoff and soil water content have been investigated using HYDRUS, a methodology based on numerical modelling simulations of vertical water movement in a homogenous soil column on a flat surface. This study was carried out on four typical soil types occurring on the Kenyan coast and the adjacent hinterlands of up to an elevation of 200 m above sea level (m a.s.l.) covered by five weather stations (two dry and three wet stations). Results show that deep percolation and runoff are expected to be higher in 2100 for both Relative Concentration Pathways (RCPs) 2.6 and 8.5 scenarios than they were for the reference period (1986&ndash, 2005). The average deep percolation is expected to increase by 14% for RCP 2.6 and 10% for the RCP 8.5, while the average runoff is expected to increase by 188% and 284% for the same scenarios. Soil water content is expected to either increase marginally or reduce depend in the same scenarios. The average soil water content is also expected to increase by 1% in the RCP 2.6 scenario and to decrease by 2% in the RCP 8.5 scenario. Increase in deep percolation through clay soil is expected to be the largest (29% in both scenarios), while sandy and sandy clay soil are expected to be the least influenced with an average increase of only 2%. Climate change is expected to impact runoff mostly in sandy soils, whereas the least affected would be clay loam soils. These results further support the assertion that the change in climate is expected to impact the recharge of aquifers by triggering an increase in infiltration under both scenarios.

Arkansas uses a unique system for determining effluent loading rates for onsite wastewater systems based on wastewater storage in unsaturated soil above a seasonal water table. Evaluation of the soil volume available for storage relies on estimates of the slope of the effluent plume away from the trench, which has rarely been evaluated in the field. The objectives of this study were (i) to evaluate the simulated effluent slope for select soils in different hydraulic conductivity classes and with different seasonal water table depths, and (ii) to illustrate the utility of using model simulations to evaluate regulatory parameters established with limited measured data. The geometry of the effluent surface was evaluated by simulation of wastewater input and effluent movement with the HYDRUS (2D/3D) two-dimensional model. Nine soils mapped in Arkansas and in varying hydraulic conductivity classes were used. For each soil, initial seasonal water tables were established at target depths of ∼40, 60, and 100 cm. Limited lateral spread of effluent resulted in effluent slopes that increased proportionately to water-table depth. Averaged across water-table depths, the mean slope of the effluent surface was 16, 15, and 29% for soils in the high, moderate, and low hydraulic conductivity classes, respectively. Model-simulated slopes for soils in moderate and low conductivity classes were lower than those currently assumed for calculation of effluent storage volume. The differences were small, however, and regulatory storage volumes result in appropriately conservative loading rates that minimize the risk of failure due to effluent surfacing in the drainfield area.

Drywells are widely used as managed aquifer recharge devices to capture stormwater runoff and recharge groundwater, but little research has examined the role of subsurface heterogeneity in hydraulic properties on drywell recharge efficiency. Numerical experiments were therefore conducted on a 2D‐axisymmetric domain using the HYDRUS (2D/3D) software to systematically study the influence of various homogenous soil types and subsurface heterogeneity on recharge from drywells under constant head conditions. The mean cumulative infiltration (μI) and recharge (μR) volumes increased with an increase in the saturated hydraulic conductivity ( K s ) for various homogeneous soils. Subsurface heterogeneity was described by generating ten stochastic realizations of soil hydraulic properties with selected standard deviation (σ), and horizontal (X) and vertical (Z) correlation lengths. After 365 days, values of μI, μR, and the radius of the recharge area increased with σ and X but decreased with Z. The value of μR was always smaller for a homogeneous than a heterogeneous domain. This indicates that recharge for a heterogeneous profile cannot be estimated with an equivalent homogeneous profile. The value of μR was always smaller than μI and correlations were highly non-linear due to vadose zone storage. Knowledge of only infiltration volume can, therefore, lead to misinterpretation of recharge efficiency, especially at earlier times. The arrival time of the wetting front at the bottom boundary (60 m) ranged from 21 to 317 days, with earlier times occurring for increasing σ and Z. The corresponding first arrival location can be 0.1–44 m away from the bottom releasing point of a drywell in the horizontal direction, with greater distances occurring for increasing σ and X. This knowledge is important to accurately assess drywell recharged performance, water quantity, and water quality.

Subsurface drip irrigation is one of the most efficient systems for management of water. This study is aimed to analysis the wetted area for subsurface drip irrigation system. Several models are developed for predicting the wetted widths and the wetted depths which are very important for designing an optimal irrigation system. HYDRUS/2D is used for predicting the dimensions of wetting patterns numerically by using the two dimensional transient flow of water from a subsurface drip irrigation through sandy loam and loamy sand soils. The wetting patterns from a subsurface drip source are simulated by using the system of United States Department of Agriculture, USDA, the wetting patterns are simulated at different values of applied heads, different diameters of drip, and different values of initial volumetric soil water contents which selected as initial conditions. In this work, greater spreading occurs in loamy sand than sandy loam in vertical and horizontal directions. Moreover, the results showed that the empirical formulas which can be used for estimating the wetting dimensions of wetted width and wetted depth in terms of initial volumetric soil water contents, applied heads, diameters of the drip and times of operation, are good with an average relative error not exceed 3%, so it can be used to assist the designers in irrigation field.

Film hole irrigation is a relatively low cost and high efficiency irrigation method, which can significantly improve the efficiency of agricultural water use. In order to establish the quantitative model of film hole irrigation between cumulative infiltration and the wetting body and the irrigation volume model of crops, the infiltration process and wetting body characteristics of four different soils (Xi’an silt loam, silt, silt loam and loam) were studied in laboratory experiments and numerical HYDRUS simulation experiments. The relationship between cumulative infiltration and wetting body radius was established using a mathematical method, and a crop irrigation volume model was proposed based on the root distribution and the required water content of different crops. The experimental results showed that the shape of the wetting body of film hole irrigation is approximately half of the rotating ellipsoid, and the curve shape of the wetting front can be expressed using an elliptic equation. From the center of the film hole to the surface of the wetting front, the soil water content of the wetting body gradually decreases, and the change rate of water content gradually increases, reaching its maximum value near the wetting front. Furthermore, the distribution of water content in the wetting body can be accurately expressed using an elliptic curve equation. The cumulative infiltration of film hole irrigation is proportional to the third power of the equivalent radius of the wetting body, and the equivalent radius is equal to the geometric mean of the horizontal and vertical migration distances of the wetting front. In addition, based on the distribution of crop roots and the demand of crop roots on soil water content, the irrigation model of crops was established. This study provides a theoretical basis for the calculation of the irrigation volume for film hole irrigation under the condition of experiment, and has a guiding significance for the field experiment and application of film hole irrigation in different crops in future.

The “enarenado” (sand-covering soil) is a technique used in greenhouses located in the southeast of Spain that consists of placing a layer of soil between 20 and 40 cm above the original material, a thin layer of organic matter and above it a layer of sand of about 5 to 10 cm.It is necessary to know the shape of the wet bulb produced by the emitters for a correct design and management of the drip irrigation systems. In stratified soils, as in the case of “enarenado” soils, the distribution of water can change substantially with respect to the case of homogeneous soils. The objective of this work is to present the methodology of data acquisition and the actions carried out so far to obtain a model that precisely defines the evolution of humidity in wet bulbs generated in “enarenado” soils characteristic of intensive horticultural crops.The tests have been carried out at the facilities of the IFAPA Center La Mojonera, Almería, SE Spain. The textures of the added soils are sandy loam and clay loam, representative of the horticultural crops of Almeria. The crop was pepper , Mazo variety, planted on September 15, 2018 in the two selected greenhouses. The irrigation is automatic, with drippers of nominal flow Qn = 3 l / h, self-compensating, anti-drainage of Netafim. Irrigation control is carried out using classic tensiometers with built-in pressure transducer.The humidity has been measured at 10 points distributed around a dripper, 7 probes at 5 cm deep in the added soil layer and 3 probes at 18 cm depth, near the original soil layer. The sensor used is TE5 Decagon. The plantation frame coincides with that of the drippers, Sg = 50 cm and Sr = 120 cm, for this reason the probes were placed up to half of the plantation frame.The data collected show a small variation in humidity over time. That is, the added soil, with a clayey texture, quickly redistributes moisture and the probes register very small variations.Once the values specified in the methodology have been measured, the theoretical humidity retention curves of greenhouse soils have been calibrated. With the data collected, the system has been simulated by completing the fields that the Hydrus model needs. This operation has been specified in the definition of a simple, multi-layered 3D model. In general, the model predicts moisture behavior well in the conditions set.

Understanding the rules of soil water movement under drip irrigation can provide data support and theoretical basis for developing precise drip irrigation strategies. In this study, a two-years-old Populus tomentosa plantation under surface drip irrigation on sandy loam soil was selected to measure the dynamics of soil water potential (ψs), wetting front and soil water content (θ) during irrigation and water redistribution periods were investigated in field experiments. Then, the observed data in the field were used to evaluate the accuracy and feasibility of the HYDRUS-2D/3D model for simulating the short-term soil water movement. Besides, the validated model was used to simulate the dynamics of wetting front under different initial soil water content (θi). During irrigation, the variation of ψs, horizontal and vertical movement distances of the wetting front, and θ within the wetting volume with irrigation duration could be described by the logistic function (R2 = 0.99), the logarithm function (R2 = 0.99), the power function (R2 = 0.82), and the polynomial function (R2 = 0.99), respectively. At the end of irrigation, the horizontal and vertical movement distances of the wetting front reached 22.9 cm and 37.3 cm, respectively. The ψs and θ within the soil wetting volume were 61.6% and 30.9% higher than those at the start of the irrigation, respectively, but the ψs decreased to its initial level about 120 hours later after the stop of irrigation. The average deviations of the horizontal and vertical wetting radius between the simulated and measured values were 1.3 and 4.5 cm, respectively. The mean RMSE and RMAE of HYDRUS-2D/3D for simulating θ at the end of irrigation and during water redistribution were 0.021 cm3∙cm-3 and 9.7%, respectively. The movement distances of wetting front in the experimental plantation under various soil drought degrees (soil water availabilities were 40%, 60%, 73% and 80%) were obtained through scenarios simulations using HYDRUS-2D/3D. And it was found that the wetting front could move further under higher θi, and the movement distance of the wetting front was always smaller in the horizontal direction than in the vertical direction under different θi conditions. Consequently, HYDRUS-2D/3D can be used to well simulate the short-term soil water movement in drip-irrigated young P. tomentosa plantations on sandy loam soil. In addition, the constructed figure (describes the variations of the horizontal and vertical soil wetting distances with the irrigation duration) can be used to determine the reasonable irrigation duration for the plantations of P. tomentosa and other tree species on sandy loam soil.

Successful field operations depend on the ability of the soil to provide traction and support for agricultural traffic and be workable in a desirable manner. This minimizes the risk of soil structural damage to ensure soil conservation and long-term crop yield. In the present study, the objective was to evaluate the performance of subsurface drainage in promoting soil strength for field operations in southern Manitoba. Data obtained from a field study and modeling exercise were used to achieve the objective. The field data include soil water content and watertable depth, which were measured in a potato field during the 2011 growing season. Soil samples were also collected from the field to determine the lower plastic limit (LPL) of the soil. Seventeen-year weather data were used to estimate the reference crop evapotranspiration. The soil strength of drained and undrained sandy-loam fields was compared to evaluate subsurface drainage in promoting soil strength for field operations. The subsurface tile drain was installed at 0.9-m depth and at 15-m spacing. A validated HYDRUS (2D/3D) model was used to extend the study by simulating soil water content dynamics due to different drain spacings (8 m, 10 m, 12 m, 15 m, 20 m, and 30 m) for different years and weather conditions. The soil strength to allow field operations was assessed based on soil water content corresponding to 90% of the LPL in the top 0.3-m depth of the soil, and soil water content corresponding to the LPL in the soil layer between 0.3-m to 0.5-m depth of the soil profile. The soil strength was sufficient to allow field operations when the two criteria were met. In the top 0.3-m depth, the soil strength was sufficient to allow field operations for all the years with or without drainage. Drainage impact was found to be more significant within the 0.3-m to 0.5-m depth of the soil profile throughout the years. Drain spacing less or equal to 12 m promoted soil strength to allow field operations without any significant impact on the number of field workable days during the growing season.

Models help to describe and predict complex processes and scenarios that are difficult to understand or measure in environmental management systems. Thus, model simulations were performed (i) to calibrate HYDRUS-2D for water and solute movement as a possible decision support system for Candler and Immokalee fine sand using data from microsprinkler and drip irrigation methods, (ii) to validate the performance of HYDRUS-2D using field data of microsprinkler and drip irrigation methods, and (iii) to investigate Br, NO, and water movement using annual or seasonal weather data and variable fertigation scenarios. The model showed reasonably good agreement between measured and simulated values for soil water content ( = 0.87-1.00), Br ( = 0.63-0.96), NO-N ( = 0.66-0.98), P ( = 0.25-0.78), and K ( = 0.44-0.99) movement. The model could be successfully used for scheduling irrigation and predicting nutrient leaching for both microsprinkler and drip irrigation systems on Florida's sandy soils.

Leaching experiments in soil under different saturations show inconsistent results regarding preferential flow, and therefore further investigations are needed. The comparative degree of non-equilibrium flow of chloride (Cl) was evaluated using replicated large intact columns taken from two alluvial (Rawal, Typic Hapludalfs and Kotli, Entic Haplusterts) and two loess (Guliana, Udic Haplustalfs and Mansehra, Typic Hapludalfs) soils that differed in structure below 20 cm depth. Lithium chloride (3.5 mM) was pulsed with constant flows generated by heads 10, −10, −40 mm water; Cl breakthroughs were fit into a physical non-equilibrium model with no sorption; and lithium (Li) breakthroughs (measured for the two loess soils) were fit into a physical and chemical non-equilibrium model using HYDRUS-1D. The Cl breakthrough curves were highly skewed, with immobile water contents in the range of 0.10 to 0.39 cm³ cm–³, indicating that physical nonequilibrium occurred under saturated flow as well as under unsaturated conditions. The nonparametric indicators (i.e., apparent dispersivity, the piston flow to Cl velocity ratio, the holdback factor, and the arrival time of the first 5% of Cl) indicated a greater strength of preferential flow in the Rawal and Guliana soils, which had more well-connected pores than the Kotli and Mansehra soils, which had fewer macropores and dense aggregates. Lithium breakthrough occurred under chemical non-equilibrium, which diminished with desaturation, especially in the Mansehra soil. There were two sources of preferential flow: (i) macropore flow under saturated conditions and (ii) bypass flow in the matrix due to regions of disconnected water under unsaturated conditions. The study results will help understand leaching potential of agro-chemicals in similar soils.

Soil water repellency affects soil water movement during infiltration significantly. The HYDRUS software has been popularly applied in soil water dynamics simulation for many years, but its performance in water-repellent (WR) soils has not been assessed thoroughly. Our objectives are to assess the performance of HYDRYUS-1D for cumulative infiltration (CI), wetting front (Zf), and volumetric soil water content (θv) during horizontal imbibition and vertical infiltration in wettable, slightly WR, and strongly WR soils. The key parameters of α and n in water retention curves were inversely estimated by RETension Curve software. The α and n were calibrated inversely until the observed data fitted the simulated values well enough. The α and n were then used for validation using three statistical parameters including relative root-mean-square error, R2, and Nash–Sutcliffe efficiency coefficient. The performances of calibration and validation for wettable, slightly, and strongly WR soils were good enough to be used for further simulations (RRMSE ≤20.2% for calibration and ≤21.1% for validation). Soil water movements for strongly WR soils of variable ponded depth during vertical infiltration were simulated. For Lou soil, as the ponded depth increased from 4 to 10 cm, the CI and Zfincreased 2.08 and 5.5 cm, respectively. The simulations for the other three soils also showed gradually increased CI and Zfvalues. In conclusion, the performances of HYDRUS-1D in four different soil types with changing WR levels were good, which confirmed the application of HYDRUS-1D in WR soils.

Understanding dynamics of soil water content (SWC) and pore air relative humidity (RHpa), as influenced by wetting-drying cycles, is crucial for sustaining fragile ecosystems of desert lands across the world. However, to date, such an understanding is still incomplete. The objective of this study was to examine such dynamics at a typical desert site within the Horqin Sandy Land, located in Mongolian Plateau of north China. The results indicated that vaporization primarily occurred at a depth of around 10 cm below the ground surface. The diurnal variations of the SWC and RHpa in the top 10 cm soils were much larger than those in the soils at a deeper depth. For a non-rainy day, the SWC and RHpa were mainly determined by the relative magnitude of atmospheric temperature over soil temperature, whereas, for a rainy day, the SWC and RHpa were primarily controlled by the rainfall pattern and amount. The retardation role of the top dry soil layer, which is about 10 cm thick and exists most time at the study site, can effectively prevent the beneath moist soils from being further dried up, and thus is beneficial for sustaining the desert ecosystem.

Intense deforestation over large areas is an important component of global models which aim to quantify the transfer of terrestrial siliceous material from the continent to the coast. Hence, there is a need for improved understanding of land use impact on Si export. We present a model that simulates the kinetic dissolution of biogenic Si in a forest soil. A kinetic equation was calibrated based on leaching experiments of soil columns at constant water flux. The calibrated equation was then used to simulate the Si export from a forest soil under varying atmospheric conditions and provided realistic Si concentrations in soil water. The same model was used to simulate the impact of reduced evapotranspiration due to deforestation and consequently increased soil water fluxes on the Si export. Results showed that lower amounts of biogenic silicon dissolved and higher Si fluxes were released to the system once water flux increased. The use of the kinetic dissolution equation for biogenic Si improves our understanding and the modelling of the Si release from soils towards the hydrographic system.

Variably saturated flow models that simulate soil–water–plant interactions within the rhizosphere largely ignore the effect of plant health. This makes it difficult for them to effectively simulate root water uptake (RWU) and implement alternate management practices for diseased trees. This research was aimed at understanding the hydrological and plant controls on RWU simulations dominated by the health of the tree using experimental and numerical frameworks. Two research plots, one around a healthy mature and the other around a diseased mature (Phytophthora spp. affected) orange tree (Citrus reticulate Blanco), in the Vidarbha region of India were considered for our analysis. Three-dimensional electrical resistivity tomography (ERT) performed at the two locations revealed that the soil moisture profiles following irrigation are different between the two plots. A two-dimensional axisym-metric form of Richards’ equation was then solved using HYDRUS (2D/3D) by incorporating a root distribution function. A global sensitivity analysis was performed to identify the root distribution parameters that influence soil moisture simulations. These parameters were then optimized using a genetic algorithm for healthy and diseased conditions. We observed that the diseased orange tree had consumed less water, leaving high soil moisture in the rhizosphere, a condition favorable for the further growth of disease-causing fungi. Hence, managing irrigation water in accordance with RWU patterns is essential for diseased trees. To understand the error propagation in RWU estimation, we simulated RWU from a diseased tree with the optimal parameters derived for a healthy case. Results show that the error in estimating RWU from the model cells progressively increases with radial distance and soil depth. © Soil Science Society of America.

N2O emission has obvious water effect, but the current research is not deep enough. The soil wetting mode of drip irrigation technology is obviously different from that of conventional irrigation. Using the method of soil box indoor simulation, the N2O emission under different soil vertical water content was analyzed. Hydrus Software was used to simulate the soil wetting body under different drip irrigation technical parameters, the relationship between the combination of drip irrigation technical parameters and soil vertical water content was studied, and then the relationship between the N2O emission and the combination of drip irrigation technical parameters was proposed. The results showed that soil N2O emission flux increased with the increase of soil moisture, and the maximum emission flux was three times as much as the minimum emission flux. Under the condition of uniform distribution of soil moisture, soil N2O emission flux was smaller than that under non-uniform distribution of soil moisture. Hydrus software simulation results show that drip flow rate is 2.0 L/h, the irrigation period is 5 days, the irrigation quota is 12 mm, and the soil N2O emission flux is the largest. Adjusting the combination of technical parameters of drip irrigation can reduce soil N2O emission flux.

Agricultural Managed Aquifer Recharge (Ag-MAR) is an emerging MAR technique that uses agricultural fields as percolation basins to recharge the underlying aquifers. Ag-MAR can be a beneficial solution for storing excess surface water, however, if not managed properly it can potentially harm the soil and crops planted on the field at the time of recharge, ultimately leading to yield loss. Root zone residence time (RZRT), defined as the duration that the root-zone can remain saturated (or nearly saturated) during Ag-MAR without crop damage, is a key factor in Ag-MAR since extended periods of saturation in the root-zone can damage crops. Here we propose a simple RZRT model for estimating a safe Ag-MAR flooding duration based on hydraulic parameters deduced from soil texture, crop tolerance to saturation, effective root depth, and critical soil water content, which is the point where soil re-aeration occurs during drainage. We tested the model with different hydraulic parameter sets and compared the results to observed data and HYDRUS simulations. Using fitted and unfitted hydraulic parameters the average error of the predicted Ag-MAR flooding duration was less than 5 h, and up to a few days, respectively. Consequently, for crops with low flooding-tolerance, the model should be used with caution, but for more tolerant crops, the model provides reasonable predictions. The model also provides a first approximation of the possible amount of water that can be applied during an Ag-MAR event. Based on the RZRT model, we evaluated the Ag-MAR potential of various crops and effective root depths for each of the USDA soil texture classes. A spreadsheet containing the RZRT model including hydraulic parameters, and crop properties is publicly available and can be used as a learning tool or to estimate Ag-MAR flooding duration for different soils. The proposed model can be easily integrated into Ag-MAR assessment tools.

Soil properties are often assumed to be static over time in hydrological studies, especially in hydrological modelling. Although it is well appreciated that soil structure and its impact on hydraulic properties are time-variable, particularly on cultivated land, very few studies have focused on quantifying the influence of such changes on soil hydrology, especially at the short term (i.e. seasonal). This study explored the value of incorporating such short-term time-variable soil properties in hydrological models. It is based on soil hydraulic properties from temporal field data under no-till done by direct seeding and under conventional cultivation done by ploughing to 0.2 m and harrowing. It uses a controlled tillage experiment in Scotland, on a soil with very good structural stability that experiences gentle rainfall in a temperate oceanic climate (Koppen Cfb). Water retention data were collected from intact soil cores sampled at 0.025, 0.095 and 0.275 m depth at three times between April and August 2013; (i) immediately following tillage, (ii) at barley crop establishment 1 month later and (iii) after harvest. Soil structure varied over time, with no-till soils gaining porosity and ploughed soils losing porosity. We hypothesised that no-till soils would have less seasonal temporal variability, but found it to be comparable to ploughed soils, albeit with pore structure changes following different trends. These changes were reflected in Van Genuchten fitting parameters, which if accounted for in 1-D HYDRUS modelling, had a marked impact on modelled soil water content over time if contrasted to predictions assuming a static pore structure. Using data from multiple sampling events, as opposed to one sampling event, resulted in up to a 44 % difference in soil water content predictions and increased the temporal variability by a factor of 1.5. Hence, our results have demonstrated that it is important to account for short-term temporal variability in soil physical properties in soil water modelling studies, and should not be ignored as a default, particularly on cultivated agricultural soils.

An adequate hydrological description of water flow in permeable pavement systems relies heavily on the knowledge of the unsaturated hydraulic properties of the construction materials. Although several modeling tools and many laboratory methods already exist in the literature to determine the hydraulic properties of soils, the importance of an accurate materials hydraulic description of the permeable pavement system, is increasingly recognized in the fields of urban hydrology. Thus, the aim of this study is to propose techniques/procedures on how to interpret water flow through the construction system using the HYDRUS model. The overall analysis includes experimental and mathematical procedures for model calibration and validation to assess the suitability of the HYDRUS-2D model to interpret the hydraulic behaviour of a lab-scale permeable pavement system. The system consists of three porous materials: a wear layer of porous concrete blocks, a bedding layers of fine gravel, and a sub-base layer of coarse gravel. The water regime in this system, i.e. outflow at the bottom and water contents in the middle of the bedding layer, was monitored during ten irrigation events of various durations and intensities. The hydraulic properties of porous concrete blocks and fine gravel described by the van Genuchten functions were measured using the clay tank and the multistep outflow experiments, respectively. Coarse gravel properties were set at literature values. In addition, some of the parameters (Ks of the concrete blocks layer, and α, n and Ks of the bedding layer) were optimized with the HYDRUS-2D model from water fluxes and soil water contents measured during irrigation events. The measured and modeled hydrographs were compared using the Nash-Sutcliffe efficiency (NSE) index (varied between 0.95 and 0.99) while the coefficient of determination R2 was used to assess the measured water content versus the modelled water content in the bedding layer ( R 2 = 0.81 ÷ 0.87 ) . The parameters were validated using the remaining sets of measurements resulting in NSE values greater than 0.90 ( 0.91 ÷ 0.99 ) and R2 between 0.63 and 0.91. Results have confirmed the applicability of HYDRUS-2D to describe correctly the hydraulic behaviour of the lab-scale system.

Soil hydraulic properties were mainly governed by soil structures especially when the structures is full of the connected soil macro-pores. Therefore, the good hydrological models need to be well documented for revealing the process of soil water movement affected by soil medium. The Hydrus-2D model with double domain was recommended in simulating water movement in a heterogeneous medium of soil. To evaluate the performance of the double domain Hydrus-2D model in loess soil, the dynamic of soil wetting front movement in differential loess soil columns under the constant water head were observed and the processes was simulated by Hydrus-2D model under conditions of different soil properties. The results indicated that the Hydrus-2D model was quite good in simulation of loess soil water movements, and the relative errors of simulation results are less than 15%, MRE less than 5%, and R 2 >0.9. The results provided the appropriate infiltration parameters of loess soil.

Three laboratory models were designed to simulate a field section of a clay sand liner. The laboratory models were designed to test 10 cm thick Al Qatif clay sand liners with clay content of 15%, 20% and 25% overlain by agricultural soil and underlain by granular sandy material. The percolation through the clayey layer was measured for repeated watering following variable drying periods. 30 tests were conducted for each clay content over a period of 3 to 4 months in a laboratory controlled environment. Temperature, moisture and electrical conductivity were recorded using 5TE sensors. The hydraulic conductivity and soil water characteristics of the material used in the liners were studied. It was found that the soil suction and drying are related to non-uniform performance of the liner on repeated drying and wetting. The results of a theoretical model using Hydrus 2D for a similar section subjected to different environmental conditions indicated that liners can significantly reduce percolating water. The laboratory model confirmed the findings. The temperature drop below the ambient laboratory value was found 1.0oC for the 15% clay and 0.6oC for 20% and 30% clay liners. The trends of moisture gain and drop were shown.

Although surface drip irrigation allows an efficient use of water in agriculture, the heterogeneous distribution of soil water complicates its optimal usage. Mathematical models can be used to simulate the dynamics of water in the soil below a dripper and promote: a better understanding, and optimization, of the design of drip irrigation systems, their improved management and their monitoring with soil moisture sensors. The aim of this paper was to find the most appropriate configuration of HYDRUS-3D for simulating the soil water dynamics in a drip-irrigated orchard. Special emphasis was placed on the source of the soil hydraulic parameters. Simulations parameterized using the Rosetta approach were therefore compared with others parameterized using that of HYPROP + WP4C. The simulations were validated on a seasonal scale, against measurements made using a neutron probe, and on the time course of several days, against tensiometers. The results showed that the best agreement with soil moisture measurements was achieved with simulations parameterized from HYPROP + WP4C. It further improved when the shape parameter n was empirically calibrated from a subset of neutron probe measurements. The fit of the simulations with measurements was best at positions near the dripper and worsened at positions outside its wetting pattern and at depths of 80 cm or more This research was supported by the National Institute for Agricultural and Food Research and Technology (INIA) [RTA 2013-00045-C04-01] of the Ministry of Economy and Competitiveness of the Spanish government, and by the European Social Fund

Simulation models are efficient tools to predict the fate of different solutes in agricultural soils. This work aimed to compare measured and predicted glyphosate and AMPA (aminomethyl phosphonic acid; its main metabolite) contents in a soil under no-tillage (NT), and conventional tillage (CT); and to compare the predictions considering constant and time-variable hydraulic properties. Additionally, we evaluated the ability of the model to predict glyphosate and AMPA accumulation during the crop cycle. Hydrus 1-D code was used to predict the glyphosate and AMPA dynamics, considering constant and time-variable hydraulic properties during the studied crop cycle. In general, the prediction of glyphosate and AMPA distribution along the soil profile using HYDRUS 1-D was satisfactory; however, an overestimation of both compounds was observed in the first 0.20 m of the soil probably because of the preferential flow. Additionally, the accumulation process of glyphosate and AMPA in the soil during the crop cycle was underestimated by HYDRUS 1-D, as compared with the observed field data. Simulated data show that higher values of K0 increase the risk of glyphosate and AMPA vertical transport. The inclusion of temporal variation of hydraulic properties in glyphosate and AMPA simulation did not improve the simulation performance, showing that the model is more sensitive to the parameters related to the solutes. From the obtained results, HYDRUS 1-D code allowed to predict glyphosate and AMPA dynamics reasonably well in agricultural soils of the Argentinean Pampas region and is a potential model to give support in the analysis of the environmental risk of leaching and soil contamination., Facultad de Ciencias Agrarias y Forestales

Agricultural use of pesticides may result in contamination of groundwater being used as a drinking water source. Additionally, the emission of these compounds via drainage into surface waters can adversely affect aquatic ecosystems. Pesticide risk assessment is applied to evaluate the potential for health and ecological effects of a pesticide and is commonly performed using mechanistic models. Pesticides currently used in agriculture are soluble in water. Hence, both pesticide transport and water flow through the soil must be studied together through an environmental risk assessment of pesticides. Water flow and pesticide transport can be described for field conditions as uniform or preferential. While uniform flow leads to stable wetting fronts parallel to the soil surface, preferential flow generates unstable wetting fronts, differences in water pressure and solute concentrations, and rapid flow through parts of the soil matrix. This Ph.D. research project focuses on one source of preferential flow; macropore flow. Macropore flow produces fast vertical water flow and pesticide transport in a small soil volume, bypassing the reactive soil matrix. One effect of this is that some of the applied pesticides cannot degrade in the soil and instead arrives in groundwater or surface waters, negatively affecting water quality. Therefore, mechanistic models must incorporate macropore flow in pesticide risk assessment to ensure accurate simulations. Macropores are originated mainly by biological activity, drying and wetting cycles, and shrinking clays, which results in natural variation of the number of macropores in time and space. Some macropores directly end within the soil matrix, referred to as ‘dead-end macropores.’ We have designated the spatial variation of macropores over depth as ‘heterogeneous macropore geometry.’ Dual-permeability models such as HYDRUS and SWAP are conventional mechanistic models utilized in pesticide risk assessment studies. The parametrization of these models for heterogeneous macropore geometries as produced by dead-end macropores is still a challenge. Two parameters commonly utilized for water flow and pesticide transport related to the description of heterogeneous macropore geometries in both models are the relative macroporosity and the effective aggregate width. We saw that the determination of both parameters under field conditions is poorly understood through an extensive literature review. Increasing the understanding of the parametrization of the relative macroporosity and the effective aggregate width for field conditions would be essential for HYDRUS and SWAP. To achieve this, the following objectives were proposed: (1) Understand the effect of dead-end macropores on water redistribution and outflow; (2) Simulate water flow with HYDRUS and SWAP in heterogeneous macropore geometries as produced by dead-end macropores; (3) Generate a new methodology for the determination of the relative macroporosity and the effective aggregate width under field conditions; (4) Compute the importance of the relative macroporosity and the effective aggregate width on different pesticide outputs of the SWAP-PEARL models. Chapter 2 reports the first two objectives, which were investigated utilizing two soil columns under controlled laboratory conditions with artificial macropores ending at different depths. We observed that dead-end macropores do not increase outflow proportionally to the increase in the relative macroporosity from the experimental results. The simulation results indicated that both HYDRUS-1D and SWAP performed well in the system with dead-end macropores. This is relevant for performing pesticide risk assessments at different scales because we can trust the accuracy of both model simulations. In Chapter 3, we present the results of Objective 3. Our methodology is based on Watson & Luxmoore (1986) but expands it beyond cylindrical macropore shapes by pore-scale modeling for rings, hexagons, bricks, and rectangular slabs macropore-matrix shapes using a transformation factor. We found that the actual relative macroporosity is underestimated, and the effective aggregate width is overestimated if always presuming cylindrical shapes for field conditions. The transformation factor obtained was constant for all the non-cylindrical shapes and equaled 1.5. We also introduce a mathematical relation between the relative macroporosity and the effective aggregate width for all the shapes analyzed. The methodology can be applied to former disk infiltrometer databases following only three conditions. We found that the physical assumptions performed in Chapter 3 to obtain the transformation factor tended to overestimate the water flow. Therefore, we improved the methodology by calibration with HYDRUS 2D/3D and presented those results in Chapter 4. The representation of heterogeneous macropore geometries in HYDRUS 2D/3D implies a greater number of parameters than for homogeneous macropore systems (Chapter 2). We tackled this issue by introducing a general meta-model which reduces the number of parameters required to represent heterogeneous macropore geometries. The meta-model parameters obtained, and macropore parameters from previous research were utilized to obtain a complete initial parametrization of HYDRUS 2D/3D, which then required some calibration to obtain a good match between observations and simulations. Subsequently, a dimensional reduction of HYDRUS 2D/3D parameters was utilized to parametrize HYDRUS 1D and SWAP. Therefore, HYDRUS 2D/3D can now be utilized as a transitional model for obtaining macropore parameters for HYDRUS 1D and SWAP utilizing disk infiltrometer measurements. Chapter 5 answers the last objective. A Morris screening and Sobol-Jansen sensitivity analysis were performed using the SWAP-PEARL model for the Andelst site, including complex hydrology. The seven most essential parameters selected through the Morris elementary effect were analyzed using the Sobol-Jansen method to quantify the parameter importance. The results indicated that parameters describing degradation and sorption of the pesticide are essential parameters for all output types and that for leaching to a depth of 1 m and below, the depth of the static macropores and the depth of the internal catchment were critical parameters. Therefore, we also found that the relative macroporosity and the effective aggregate width were not relevant parameters for pesticide outputs. This finding implies that a higher uncertainty in obtaining those parameters is acceptable in SWAP-PEARL models. The new equations and procedures generated are relevant for more realistic HYDRUS and SWAP parameterization in heterogenous macroporous systems. Our findings make an important contribution to accurate forecasting of potential contamination of groundwater and surface water by pesticide compounds or other agrochemicals, thus ensuring the availability of good quality water for current and future inhabitants of this planet.

Soils in arid and semi-arid environments are threatened by salinization. A cost-effective and efficient way to reclaim saline land is through leaching. This will be most effective in situations where direct human impact is the cause for salinity, e.g., in environments affected by industrial use or land rehabilitation following mining. Irrigation, which is the most common means of achieving salt leaching, is not feasible for the reclamation of mine sites&rsquo, salt-affected soils located in remote areas, and thus, land reclamation largely relies on natural climatic conditions. This study was conducted to assess the effect of different climatic conditions of semi-arid environments on spatio-temporal salt leaching from brine-affected soil, and investigate the efficacy of the reduction of soil bulk density as a reclamation technique for saline land experiencing water scarcity. Three regions (represented by the Australian cities of Roma, Mount Isa, and Quilpie) representing semi-arid environments of Australia were selected, and their climatic scenarios (23 years) were applied to a validated HYDRUS-1D model. A brine-affected soil typical to Queensland, Australia, was chosen for this study. The investigations established that a greater number of individual high rainfall events resulted in a greater reduction of salinity in Roma (96%) and Mount Isa (93.31%) compared with Quilpie (58.75%), in which the soil salinity approached a level (&lt, 2 dS m-1) that was suitable for sustaining plant growth. Soil salinity reduced to 8 dS m-1 under the climatic conditions of the Quilpie region. This study also demonstrated that the success of salt leaching from a brine-affected soil is a consequence of a sensitive response to the depth of individual rainfall events rather than rainfall distribution and the total amount of rainfall, and is controlled by the physical properties of the soil. Where climatic conditions cannot solely assist with salt leaching, reclamation may be successful by reducing soil bulk density.

Hydraulic conductivity is a key soil property governing agricultural production and is thus an important parameter in hydrologic modeling. The pH scaling factor for saturated hydraulic conductivity (Ks) reduction in the HYDRUS model was reviewed and evaluated for its ability to simulate Ks reduction. A limitation of the model is the generalization of Ks reduction at various levels of electrolyte concentration for different soil types, i.e., it is not soil specific. In this study, a new generalized linear regression model was developed to estimate Ks reduction for a larger set of Australian soils compared with three American soils. A nonlinear pedotransfer function was also produced, using the Levenberg–Marquardt optimization algorithm, by considering the pH and electrolyte concentration of the applied solution as well as the soil clay content. This approach improved the estimation of the pH scaling factor relating to Ks reduction for individual soils. The functions were based on Ks reduction in nine contrasting Australian soils using two sets of treatment solutions with Na adsorption ratios of 20 and 40; total electrolyte concentrations of 8, 15, 25, 50, 100, 250, and 500 mmolc L−1; and pH values of 6, 7, 8, and 9. A comparison of the experimental data and model outputs indicates that the models performed objectively well and successfully described the Ks reduction due to the pH. Further, a nonlinear function provided greater accuracy than the generalized function for the individual soils of Australia and California. This indicates that the nonlinear model provides an improved estimation of the pH scaling factor for Ks reduction in specific soils in the HYDRUS model and should therefore be considered in future HYDRUS developments and applications.