Search

Seepage through an aquifer, the hydraulic conductivity of which varies vertically, is studied using the Dupuit-Forchheimer approximation (Girinskii’s potential) and numerically by FDM-MODFLOW and F...

ispartof: VADOSE ZONE JOURNAL vol:21 issue:1 status: published

Long-term use of recycled water (RW) for irrigation in arid and semiarid regions usually changes the soil solution composition and soil exchange characteristics, enhancing the risk for salinity and sodicity hazards in soils. This modelling study focuses on developing alternative management options that can reduce the potentially harmful impacts of RW use on the irrigation of wine grapes and almonds. The multicomponent UNSATCHEM add-on module for HYDRUS-1D was used to evaluate the impact of long-term (2018–2050) use of irrigation waters of different compositions: good-quality low-salinity (175 mg/L) water (GW), recycled water with 1200 mg/L salinity (RW), blended water of GW and RW in the 1:1 proportion (B), and monthly (Alt1) and half-yearly (Alt6) alternate use of GW and RW. The management options include different levels of annual gypsum applications (0, 1.7, 4.3, and 8.6 t/ha soil) to the calcareous (Cal) and hard red-brown (HRB) soils occurring in the Northern Adelaide Plain (NAP) region, South Australia. Additional management scenarios involve considering different leaching fractions (LF) (0.2, 0.3, 0.4, and 0.5) to reduce the salinity build-up in the soil. A new routine in UNSATCHEM to simulate annual gypsum applications was developed and tested for its applicability for ameliorating irrigation-induced soil sodicity. The 1970–2017 period with GW irrigation was used as a warmup period for the model. The water quality was switched from 2018 onwards to reflect different irrigation water qualities, gypsum applications, and LF levels. The data showed that the GW, B, Alt1, and Alt6 irrigation scenarios resulted in lower soil solution salinity (ECsw) than the RW irrigation scenario, which led to increased ECsw values (4.1–6.6 dS/m) in the soil. Annual gypsum applications of 1.7, 4.3, and 8.6 t/ha reduced pH, SAR, and ESP in both soils and reduced the adverse impacts of irrigation, especially in surface soils. A combination of water blending or cyclic water use with 3.8 t/ha annual gypsum applications showed promise for the SAR and ESP control. Additionally, irrigation with RW, a 0.2 LF, and annual gypsum applications limited the harmful salinity impacts in the soils. However, in the RW irrigation scenario, ECsw and ESP at the bottom of the crop root zone (90–120 cm depth) in the HRB soil were still higher than the wine grape and almond salinity thresholds. Thus, annual amendment applications, combined with the long-term use of blended water or cyclic use of RW and GW, represent a sustainable management option for crop production at the calcareous and hard red-brown soils.

Soil salinity increases when growers are forced to use higher salinity irrigation waters due to water shortages. It is necessary to estimate the impact of irrigation water on soil properties and conditions for crop growth to manage the effects of salinity on perennial crops. Therefore, in this study, we monitored root zone salinity in five almond and pistachio orchards in eastern and western San Joaquin Valley (SJV), California (CA). Volumetric soil water contents and bulk electrical conductivities were measured at four root-zone depths. Evapotranspiration was measured by eddy covariance along with three other types of data. The first is seasonal precipitation and irrigation patterns, including the temporal distribution of rains, irrigation events, and irrigation water salinity. The second is soil chemistry, including the initial sodium adsorption ratio (SAR) and soil solute electrical conductivity (ECe). The third type is the physical properties, including soil type, hydraulic conductivity, and bulk density. As expected, we found low salinity at the eastern sites and higher salinity at the western sites. The western sites have finer textured soils and lower quality irrigation water, measured actual ET was about 90% of modeled crop ET. Across the three western sites, the annual average apparent leaching fraction ranged from 11 to 28%. At the eastern sites, measured ET almost exactly matched modeled crop ET each year. Apparent leaching fractions in the eastern sites were approximately 20%.

International audience; Soil contains the largest terrestrial pool of organic matter, and the cycling of organic carbon in soils plays a crucial role in controlling atmospheric carbon dioxide (CO2) and global climate change. Although considerable progress has been made in previous modeling studies on the fate of soil organic matter (SOM), only a few models used a process-based approach for investigating these strongly coupled and complex soil systems, which involve SOM oxidation, transient water flow, and mass transport processes in aqueous and gaseous phases. Typically, physically based models for water flow, as well as solute and gas transport, are not coupled with state-of-the-art SOM degradation models. Reactive transport models (RTMs) provide a flexible framework for implementing different SOM degradation concepts and integrating biogeochemical processes with water flow and mass transport. Given the complex nature of carbon cycling in soils coupled with flow and mass transport, code intercomparison using well-defined benchmarks is in many cases the only practical method of model verification. The benchmark presented in this manuscript focuses on SOM oxidation under variably saturated flow conditions. The benchmark consists of three problems characterized by increasing complexity. The problems were solved using two different reactive transport codes, namely HP1 and MIN3P-THCm. The first supporting problem introduces a batch-type simulation to assess kinetic networks of SOM degradation. In the second supporting problem, transient water flow, solute transport, gas generation, and diffusive gas transport are considered. The principal problem combines the kinetic networks of SOM degradation with reactive transport under variably saturated flow conditions, including CO2 transport from soils to the atmosphere. Simulation results for the benchmark problems demonstrate an overall excellent agreement between the two codes, building confidence in the ability of RTMs to simulate complex C-cycling in dynamic environments.

Author(s): Kacimov, AR; Obnosov, YV; Simůnek, J | Abstract: Ovsinsky (1899, https://www.rulit.me/books/novaya-sistema-zemledeliya-read-193251-1.html) suggested and tested a water conserving soil no-till technology for rain-snow-fed field crops in a semiarid environment in southern Russia. We model Ovsynsky's unsaturated flow fragment, in which 1-D steady evaporation and evapotranspiration through a two-layered soil from a horizontal static water table to a dry soil surface takes place. Gardner's exponential and algebraic functions are used for the unsaturated hydraulic conductivity-suction head relations. The vertical evaporation flux depends on the dyads and triads (correspondingly) of the parameters of these functions, for example, the saturated hydraulic conductivity and the sorptive number of the two layers. The flux, as a function of the relative thickness of the upper stratum, is analytically found from the solution of one or two nonlinear equations. This relation can be nonmonotonic and exhibits either a minimum or maximum depending on whether this stratum is coarser or finer than the subjacent stratum fed from a horizontal isobar. HYDRUS-1D simulations confirm these extrema. This explains the experimental results from the literature on mulching/tillage/soil crusting-sealing, which can increase, decrease, or have no impact on evaporation from a shallow water table. Alterations of the soil's homogeneity to reduce evaporation losses can improve the hydrological balance of soil profiles.

Accurate knowledge of soil hydraulic properties (K-θ-h) for the entire range of crop available water is essential for the prediction of soil water movement and related processes by mechanistic models, including the partitioning of surface energy fluxes into transpiration and evaporation and the dynamics of root water uptake, mandatory processes for adjustments of crop water use efficiency. We implemented an experimental and numerical protocol to obtain K-θ-h of eleven soils with a broad spectrum of texture and land use. Measurements of the soil water content during evaporation experiments using gamma-ray beam attenuation, a non-invasive technique, were adopted as an alternative approach to conventional measurements of the soil water pressure head. Inverse parameter optimization was performed using Hydrus-1D. The optimized K-θ-h functions were interpreted with respect to crop available water, where results calculated by a proposed “dynamic” method were compared with those determined using the conventional “static” criteria with standardized pressure heads. The evaporation experiment protocol allowed the determination of the K-θ-h relationships by inverse modeling from near-saturation to the dry range (∼ −150 m) with satisfactory accuracy. Soil water retention curves of the fine-textured soils determined by the conventional method (pressure plates) deviated from those estimated by the inverse optimization near saturation and in the dry range, with the conventional method predicting larger water content values. In terms of crop available water, the “dynamic” method allowed incorporating system characteristics (atmospheric demand and crop properties) and K-θ-h in a process-based way, contrarily to the “static” method. Considering a specific scenario, for the fine-textured soils the “static” and “dynamic” approaches performed similarly, however, for the coarse-textured soils, they diverged significantly. No tendency could be revealed for crop water availability under different land uses, and, in general, crop available water for soils under forest use was very similar to their counterparts under agricultural use.

Pecan [(Carya illinoinensis (Wangenh.) K. Koch] is an important specialty crop in New Mexico. This research quantifies soil water and soil nitrate-nitrogen (NO3-N) (mg L-1 of soil) variations with depth, root NO3-N (kg ha-1) uptake, and NO3-N (kg ha-1) balance for the 100-cm soil profile during two growing seasons in a flood-irrigated pecan orchard. Nitrate-nitrogen was determined six times during the growing seasons of 2015 and 2016. The HYDRUS-1D model was used to optimize the water flow parameters using measured volumetric soil water content (q). Model calibration and validation for NO3-N included the optimization of reaction parameters for nitrification and denitrification of each soil layer. The results showed that the model simulated q well (0.44 ≤ d [index of agreement] ≤ 0.73) at different depths during both calibration (2009) and validation (2010) periods. Generally, HYDRUS-1D simulated soil profile NO3-N concentrations that were correlated with measurements at all depths during both years. Total root NO3-N uptake showed a significant increase of 72% in 2016 compared with 2015. The NO3-N balance showed that ∼40% of applied NO3-N per year was denitrified, which was the main contributor to the NO3-N loss from the soil profile during both years. Nitrate-nitrogen leaching below the soil profile was 32 and 26% of applied NO3-N in 2015 and 2016, respectively. The fertigation rate was much higher than the plant demand during both years, and it should be decreased to reduce NO3-N losses.

The EU Nitrates Directive calls for urgent integration of process-oriented indicators of nitrate fate with map overlaying approaches for assessing nitrate vulnerable zones (NVZs). In the region of Campania (southern Italy) groundwater contamination represents a serious concern because of the presence of intensive agricultural practices and livestock farming. A protocol was proposed to assess the probability distribution of the following three indicators of nitrate transport across the vadose zone (obtained by using a physically-based model): i) an annual cumulative nitrate flux entering the shallow aquifer, ii) annual cumulative root nitrate uptake, and iii) nitrate transit time across the vadose zone. This method involves numerical simulations of soil water flow and solute transport using Hydrus-1D for a representative 10-m-thick soil profile beneath an irrigated maize plot located in a study area within the Sele plain, Campania. Two scenarios are built by running a set of one hundred (20-yr-long) simulations at a daily time resolution: i) 195 kg N ha-1 of nitrate fertilizer (urea) is applied annually to estimate the probability distributions of annual cumulative nitrate leaching and root nitrate uptake (Scenario 1), ii) 195 kg N ha-1 of nitrate fertilizer (urea) is applied once to estimate the nitrate transit time distribution across the soil profile (Scenario 2). In each Scenario, the simulations consider two agricultural practices with either one or three annual nitrate fertilizer applications subject to randomly generated climate forcing using a Monte Carlo approach. Variations in soil and rainfall properties are described by the Miller-Miller geometric similitude and the Poisson parameterization, respectively. In Scenario 1, roots absorb on average 80.3 kg N ha-1 every year (corresponding to 40% of applied nitrate), and the median annual cumulative nitrate flux across the soil profile bottom is 74.9 kg N ha-1 (representing about 38% of applied nitrate), when urea is applied in a single treatment. In contrast, when fertilizer is applied in three treatments, 112.4 kg N ha-1 (corresponding to almost 60% of applied nitrate) of nitrate is removed by root water uptake, and the median annual cumulative nitrate leaching is 52.4 kg N ha-1 (corresponding to about 27% of applied nitrate). In Scenario 2, mean transit time values are 2741 days, 2707 days, and 2650 days when urea is applied on April 1st, June 1st, and August 1st, respectively. Our model simulations provide useful indicators of nitrate transport and can be integrated with map overlaying procedures for delineating nitrate vulnerable zones.

22 Pags.- 9 Figs.- 5 Tabls. © 2020 The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited., Many different equations ranging from simple empirical to semi‐analytical solutions of the Richards equation have been proposed for quantitative description of water infiltration into variably saturated soils. The sorptivity, S, and the saturated hydraulic conductivity, Ks, in these equations are typically unknown and have to be estimated from measured data. In this paper, we use so‐called characteristic time (tchar) to design a new method, referred to as the characteristic time method (CTM) that estimates S, and Ks, from one‐dimensional (1D) cumulative infiltration data. We demonstrate the usefulness and power of the CTM by comparing it with a suite of existing methods using synthetic cumulative infiltration data simulated by HYDRUS‐1D for 12 synthetic soils reflecting different USDA textural classes, as well as experimental data selected from the Soil Water Infiltration Global (SWIG) database. Results demonstrate that the inferred values of S and Ks are in excellent agreement with their theoretical values used in the synthetically simulated infiltration experiments with Nash–Sutcliffe criterion close to unity and RMSE values of 0.04 cm h−1/2 and 0.05 cm h−1, respectively. The CTM also showed very high accuracy when applied on synthetic data with added measurement noise, as well as robustness when applied to experimental data. Unlike previously published methods, the CTM does not require knowledge of the time validity of the applied semi‐analytical solution for infiltration and, therefore, is applicable to infiltrations with durations from 5 min to several days. A script written in Python of the CTM method is provided in the supplemental material.

Quantitative analyses of empirical data requirements for hydrological simulations are rare. This study aims to analyze how a multi-objective optimization framework and information content computations aid in quantifying field-scale data worth in drainage studies. The results showed how a 1D numerical model and a differential evolution algorithm performed in describing the field water balance. The choice of the optimization target (subsurface drain discharge and surface runoff) impacted the simulation results more than parameter deviations. While the information content of surface runoff data was higher than that of drain discharge, drain discharge data contained more information on most of the soil parameters. Uncertainties related to groundwater outflow data, which were not used in the optimization, were higher than those of drain discharge and surface runoff. A central weighing optimization scheme with two data types produced the best but still incomplete description of the field hydrology. Despite the modest model performance, the results demonstrated how the choice of empirical data and optimization strategy can lead to uncertainties in drainage simulations and how the uncertainties can be assessed. Practically, a low amount of information and a parameter sensitivity analysis can lead to a biased description of uncertainty related to such hydrological variables which are not used in the optimization. Benefits of the modeling framework were shown when assessing (1) model structure adequacy with the Pareto front analysis, (2) information content of different data types regarding different parameters, and (3) uncertainties related to simulating hydrological variables based on optimization against a given data type. © 2020 Elsevier B.V.

An artificial capillary barrier (CB), which consists of two layers of gravel and coarse sand, was used to improve the soil water retention capacity of the root zone of sandy soil for the cultivation of Japanese spinach (Brassica rapa var. perviridis). The performance of a CB under specific conditions can be evaluated using numerical simulations. However, there have been relatively few numerical studies analyzing soil water dynamics in CB systems during crop growth. The objectives of this study were (i) to evaluate the performance of a CB during the cultivation of Japanese spinach irrigated at different rates and (ii) to investigate the effect of the irrigation schedule on root water uptake. Numerical analysis was performed using HYDRUS-1D after the soil hydraulic properties of the CB materials were determined. In most cases, the HYDRUS-1D results agreed well with the experimental soil water content data without any calibration when the dual-porosity model describing soil hydraulic properties was used for gravel and coarse sand. We found that the dual-porosity model was able to attenuate the unrealistically steep reduction in the unsaturated hydraulic conductivity predicted by the single-porosity model. The numerical simulations also showed that the CB played an important role in maintaining plant-available water in the root zone while maximizing the water use efficiency. The numerical simulations revealed that the irrigation frequency could be reduced by half during the early growth stage, and the water use efficiency could be greatly improved with the CB layer installed.

Water use and salinity dynamics in the soils are the crucial management factors influencing the productivity and long-term sustainability of almond and associated environment. In this study, HYDRUS-2D was calibrated and validated on measured spatial and temporal water contents and soil salinities (ECe) distributions under almond irrigated with different water qualities (ECiw) at different physiological stages. During two irrigation seasons (2014–15 and 2015–16), less saline irrigation water (average ECiw 0.78 dS/m) was substituted for recycled irrigation water (average ECiw 1.9 dS/m) in three phenologically different growth stages; pre-pit hardening, kernel growth, and post-harvest, along with no and full substitution during the entire season. Graphical and statistical comparisons (RMSE, MAE, ME, the Nash and Sutcliffe model efficiency, and the coefficient of determination) between measured and simulated values of water contents and ECe in the soil showed a close agreement in all treatments. The water balance data revealed that the seasonal crop evapotranspiration of almond (ETc) varied from 850 to 955 mm in different treatments over the two seasons which represented 68–79% of the water application. Trees irrigated with only less saline water through the two seasons (average ECiw 0.78 dS/m) showed 10% higher plant water uptake as compared to those irrigated with recycled water only (average ECiw 1.9 dS/m). Substituting less saline irrigation during the kernel growth phase, between pit-hardening and harvest, showed greater water uptake by almond and lower salinity buildup in the soil as compared to treatments that substituted less saline irrigation early or late in the season. For all treatments, the average daily root zone ECe (2.4–3.7 dS/m) remained above the level of the almond salinity tolerance threshold (ECe = 1.5 dS/m) throughout the period of investigation. Water use efficiency of almonds varied in a narrow range (0.21–0.25 kg m−3) for different treatments. Deep drainage below the root zone (2 m) varied from 22.4–31.1% of the total water application (Rainfall + Irrigation), which was episodic and insufficient to contain the salinity below the almond threshold. This study provided a greater understanding of soil water and salinity dynamics under almond irrigated with waters of varying qualities.

Water and water related salinity risks to viticulture were assessed by running the HYDRUS-1D model with 100 ensembles of downscaled daily meteorological data obtained from the Global Climate Model (GCM) for 2020–2099. The modeling output was evaluated for seasonal irrigation requirements of viticulture (Ir), root zone soil salinity at the beginning of the new season (ECswi), and the average seasonal salinity (ECsw) for all 100 realizations for four 20-year periods centred on 2030 (2020–2039), 2050 (2040–2059), 2070 (2060–2079), and 2090 (2080–2099). The model showed a 4.2% increase in the mean seasonal Ir of viticulture during 2020–2039 as compared to Ir of 350.9 mm during 2004–2015. Similarly, the mean seasonal Ir increased by 7.5, 10.9, and 16.9% during 2040–2059, 2060–2079, and 2080–2099, respectively, as compared to 2004–2015. These projections indicate that viticulture can face significant deficit conditions, which may have a drastic impact on the sustainability and productivity of the grapevine. Likewise, the average median ECswi increased by 40% during 2020–2039 as compared to the 2004–2015 mean ECswi value of 1.63 dS/m, but remained below the threshold (ECsw = 4.2 dS/m) for viticulture. The median seasonal ECswi almost doubled (3.15 dS/m) during 2040–2059, varied from 1.73–8.15 dS/m during 2060–2079, and increased more than three times during 2080–2099 to surpass the threshold salinity for grapevines. Similarly, the seasonal average root zone salinity (ECsw) showed a 47% increase during 2020–2039 over the baseline salinity. It continued increasing at a growing pace during 2040–2059 (1.5–8.64 dS/m) and 2060–2079 (2.78–9.52 dS/m), and increased to almost three times (6.04 dS/m) during 2080–2099 compared to the corresponding baseline salinity (1.97 dS/m). The continued presence of high salt concentrations in the root zone can significantly affect the growth, yield, and wine quality. The modeling results indicate that soil salinity at the beginning of the vine season and the average seasonal salinity are crucial factors that may need special management to sustain the viticulture in this region.

Accurate estimation of the soil water balance of the soil-plant-atmosphere system is key to determining the availability of water resources and their optimal management. Evapotranspiration and leaching are the main sinks of water from the system affecting soil water status and hence crop yield. The accuracy of soil water content and evapotranspiration simulations affects crop yield simulations as well. DSSAT is a suite of field-scale, process-based crop models to simulate crop growth and development. A “tipping bucket” water balance approach is currently used in DSSAT for soil hydrologic and water redistribution processes. By comparison, HYDRUS-1D is a hydrological model to simulate water flow in soils using numerical solutions of the Richards equation, but its approach to crop-related process modeling is rather limited. Both DSSAT and HYDRUS-1D have been widely used and tested in their separate areas of use. The objectives of our study were: (1) to couple HYDRUS-1D with DSSAT to simulate soil water dynamics, crop growth and yield, (2) to evaluate the coupled model using field experimental datasets distributed with DSSAT for different environments, and (3) to compare HYDRUS-1D simulations with those of the tipping bucket approach using the same datasets. Modularity in the software design of both DSSAT and HYDRUS-1D made it easy to couple the two models. The pairing provided the DSSAT interface an ability to use both the tipping bucket and HYDRUS-1D simulation approaches. The two approaches were evaluated in terms of their ability to estimate the soil water balance, especially soil water contents and evapotranspiration rates. Values of thedindex for volumetric water contents were 0.9 and 0.8 for the original and coupled models, respectively. Comparisons of simulations for the pod mass for four soybean and four peanut treatments showed relatively highdindex values for both models (0.94–0.99).

California is increasingly experiencing drought conditions that restrict irrigation deliveries to perennial nut crops such as almonds and pistachios. During drought, poorer quality groundwater is often used to maintain these crops, but this use often results in secondary salinization that requires skilled management. Process-based models can help improve management guidelines under these challenging circumstances. The main objective of this work was to assess seasonal soil salinity and root water uptake as a function of irrigation water salinity and annual rain amounts. The manuscript presents a comparison of three-year experimental and numerically simulated root zone salinities in and below the root zone of almond and pistachio drip-irrigated orchards at multiple locations in the San Joaquin Valley (SJV), California, with different meteorological characteristics. The HYDRUS-1D numerical model was calibrated and validated using field measurements of soil water contents and soil solute bulk electrical conductivities at four root zone depths and measured soil hydraulic conductivities. The remaining soil hydraulic parameters were estimated inversely. Observations and simulations showed that the effects of rain on root zone salinity were higher in fields with initially low salinities than in fields with high salinities. The maximum reduction in simulated root water uptake (7%) occurred in response to initially high soil salinity conditions and saline irrigation water. The minimum reduction in simulated water uptake (2.5%) occurred in response to initially low soil salinity conditions and a wet rain year. Simulated water uptake reductions and leaching fractions varied at early and late times of the growing season, depending on irrigation water salinity. Root water uptake reduction was highly correlated with the cumulative effects of using saline waters in prior years, more than salt leaching during a particular season, even when rain was sufficient to leach salts during a wet year.

Accurate estimation of evapotranspiration ( ET ) and its partitioning into transpiration and evaporation is fundamental for improving water management practices in water-limited environments and under deficit irrigation conditions. This investigation was conducted to estimate the water balance and ET components of subsurface drip (SDI) irrigated Chardonnay wine grapes for two seasons (2010–2011 and 2011–2012) using a numerical model (HYDRUS-2D). Treatments involved the application of different volumes [51% ( I 1 ), 64% ( I 2 ), 77% ( I 3 ), and 92% ( I 4 ) of normal application] of water for irrigation. A modified version of the FAO-56 dual crop coefficient approach was used to generate daily transpiration and evaporation as inputs to the HYDRUS-2D model. The calibrated and validated model produced estimates of actual evapotranspiration ( ET Cact ), actual transpiration ( T pact ), and actual evaporation ( E sact ), and deep percolation under varied irrigation applications. The model-simulated values were then used to estimate actual crop coefficients ( K cact and K cbact ), and water productivity of wine grape under different deficit irrigation conditions. Seasonal ET Cact simulated by HYDRUS-2D for different treatments varied between 239 and 382 mm. However, seasonal evaporation accounted for 44–59% of seasonal ET Cact losses in different treatments. The modelled daily transpiration rate in I 4 treatment ( T p4act ) varied from 0.11–2.74 mm/day. Deep percolation accounted for 35–40% of the total water applied by rainfall and irrigation. The mean value of actual crop coefficient ( K cact ) estimated by HYDRUS-2D simulated ET C act over the two seasons was 0.27, which matched with other investigations. Similarly, values of K cbact for initial, mid and end stages were 0.13, 0.27 and 0.14, respectively. Monthly values of evaporation coefficient ( K e ) ranged from 0.1 to 0.32, with a mean value of 0.18. Water productivity with respect to ET losses ( WPET C ) ranged from 5.9 to 6.2 kg/m 3 of water use. However, water productivity for transpiration ( WPT C ) almost doubled as compared to WPET C in all treatments. The impact of deficit irrigation on berry juice composition (Brix, pH and titratable acidity) was lower than the inter-seasonal variability. These results can help develop better irrigation management strategies for SDI irrigated wine grapes under water scarce conditions.

Author(s): Xie, M; Simůnek, J; Zhang, Z; Zhang, P; Xu, J; Lin, Q | Abstract: Transport and losses of nitrate from sloped soils are closely linked to nitrogen fertilizer management. Previous studies have always focused on different types of fertilizer applications and rarely analysed various initial nitrate distributions as a result of nitrogen fertilizer applications. Under certain conditions, both subsurface lateral saturated flow and vertical leaching dominate nitrate losses. Soil tank experiments and HYDRUS-2D modelling were used to better understand the subsurface nitrate transport and losses through lateral saturated flow and vertical leaching under various initial nitrate distributions. Low (L: 180 mg L−1), normal (N: 350 mg L−1), and high (H: 500 mg L−1) nitrate concentrations were used in five different distributions (NNNN, NLLN, LHHL, LNLN, and HNHN) along the slope of the tank. The first two treatments (NNNN and NLLN) were analysed both experimentally and numerically. Experiments were conducted under 12 rainfall events at intervals of 3 days. The HYDRUS-2D model was calibrated and validated against the experimental data and demonstrated good model performance. The other three treatments (LHHL, LNLN, and HNHN) were investigated using the calibrated model. Nitrate concentrations in purple sloped soils declined exponentially with time under intermittent rainfalls, predominantly in the upper soil layers. Non-uniform initial nitrate distributions contributed to larger differences between four locations along the slope in deeper soil layers. The non-uniform nitrate distribution either enhanced or reduced decreases in nitrate concentrations in areas with higher or lower initial nitrate concentrations, respectively. Higher nitrate concentrations at the slope foot and along the slope were reduced mainly by lateral flow and vertical leaching, respectively. Increasing nitrogen application rates increased subsurface nitrate losses. Mean subsurface lateral nitrate fluxes were twice as large as mean vertical leaching nitrate fluxes. However, due to longer leaching durations, total nitrate losses due to vertical leaching were comparable with those due to lateral flow, which indicated comparable environmental risks to surface waters and groundwater.

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.

Soil compaction is a common consequence of forestry traffic traversing unprotected, moist soils; it decreases porosity and affects hydraulic conductivity even in coarse-textured soils. The aim here was to study root-zone hydrology and vegetation in three microsites (in, between, and beside wheel tracks) 4 to 5 yr after forwarder traffic, on stony and sandy till soils in two clearcuts in northern Sweden. Measurements of soil volumetric water content (VWC), vegetation indicators and one-dimensional hydrological modeling (Hydrus-1D) of wheel tracks and undisturbed soil were conducted. Soil VWC was monitored hourly during 2017 and 2018 in three or four plots along a slope on each site. Soil VWC was also measured once with a portable sensor in 117 plots along two slopes at each site, where the vegetation was recorded and analyzed using Ellenberg indicator indexes. Soil VWC was highest in wheel tracks and lowest between tracks; this was corroborated by the species composition in the wheel tracks (Ellenberg indicator for soil moisture). Bare soil was more frequent in wheel tracks and between tracks than in undisturbed soil. The model simulations indicated that the changed soil hydraulic properties influenced the VWC results in the wheel tracks. However, the differences in average pressure heads in the root zone were small between the microsites and only apparent during dry periods. In the wheel tracks, air-filled porosity was

Long-term evaluation of soil chemical changes in the soil is required to optimize irrigation of protected crops and to control associated environmental issues. In this study, the multi-component solute transport module UNSATCHEMof HYDRUS-1D was used to assess the effects of long-term (2018–2050) irrigation on salt build-up in the soil under unheated greenhouse conditions. Blended water (recycled water, artificially recharged groundwater and harvested rainwater) was used to irrigate tomato, cucumber, capsicum, and eggplant. Irrigation management included four leaching fractions (LF), i.e., accounting for 0, 15, 20, and 30% of applied excess water. The effects of four amounts of annual gypsum application, i.e. 0, 1.7, 2.6, and 3.4 t/ha, were also simulated.Model-simulated annual root water uptake by cucumber, tomato, capsicum, and eggplant was 303, 476, 642,and 649 mm, respectively, for an irrigation schedule based on outdoor temperature thresholds. Annual drainage was 4.1–6.1% of irrigation for these crops. Average salinity in the soil solution (ECsw) at the end of the simulation(year 2050) reached 6.5 dS/m for cucumber, 7.6 dS/m for tomato, 8.7 dS/m for capsicum, and 9.3 dS/mfor eggplant. Soil salinity was building up at a nearly constant rate over 33 years. Exchangeable sodium percentage(ESP) at the end of the simulation was 30.8% for tomato, 27.1% for capsicum, 33.2% for eggplant, and31.4% for cucumber. These results indicate that both salinity and sodicity will exceed critical threshold values and thus must be managed to maintain sustainability of irrigated horticulture. Modeling showed that higher irrigation (up to 15–20%) coupled with an annual addition of gypsum of 1.7 t/ha kept both salinity and sodicity (SAR, ESP) below critical thresholds while pH was reduced from 8.7 to 7.8, thus creating a favorable soil environment for long-term sustainable vegetable production under greenhouse conditions. The new gypsum application module implemented in the UNSATCHEM model has broad applicability in evaluating soil amendment scenarios to address sodicity hazards linked to long-term irrigation. Refereed/Peer-reviewed

Partitioning of evapotranspiration and estimating of irrigation contribution to evaporation play a crucial role in managing scarce water resources and help in increasing the water productivity of crops, especially of sparsely vegetated plants. In this study, the FAO-56 dual crop coefficient (DCC) approach for estimating evaporation from soil under cropped conditions is adapted for subsurface drip irrigation (SDI). This new approach involves one additional variable, the fraction of the irrigation depth contributing to evaporation (fI,Es), which was defined and integrated into the FAO-56 equations for estimating daily water balance from the evaporation layer (0–15 cm). Impacts of soil texture, heterogeneity, irrigation depth, design parameters of the irrigation system on fI,Es, and the fraction of the soil surface wetted by irrigation (fw) (and consequently the exposed and wetted fraction (few)), were evaluated through HYDRUS-2D simulations. The modified procedure was compared with the existing FAO-56 method for estimating components of annual ET for wine grape under SDI. The model simulations showed that the fI,Es fraction in a homogeneous, isotropic light-textured soil was minimal (0.04) when SDI was placed at a depth of 25 cm. However, in medium and heavy textured soils fI,Es was 4 times larger than in light-textured soils. The value of fw was slightly higher in fine-textured (0.09) than in medium-textured soils (0.07). In Duplex soils with two contrasting textural layers, fw (0.12–0.16) was higher due to the presence of a heavy-textured soil layer just below the drip line. Similarly, in Triplex soils (3 different textural layers), placing the drip line in the middle layer effectively reduced both fI,Es and fw close to zero. In contrast, fw (0.18–0.30) and fI,Es (0.28–0.42) both increased considerably in heterogeneous soils. Both fractions (fw and fI,Es) increased with an increase in irrigation depths, except for fI,Es in loamy sand. The fractions were slightly lower when a drip line was placed at a depth of 10 cm (an evaporation zone) than when it was placed on the soil surface. Applying the same amount of water with different discharge rates had little impact on fI,Es and fw fractions. An increase in the drip line spacing proportionally decreased the wetted fraction on the soil surface. Annual evaporation for SDI irrigated wine grapes at the field study site, estimated using the existing FAO-56 procedure, was overestimated by about 5–6% compared to using the modified procedure. However, this deviation between the two approaches increased (18%) for heavier soil textures. It is concluded that the existing FAO-56 procedure needs to be adjusted when used to estimate evaporation under subsurface drip irrigation. However, the impact of the proposed modification on evaporation needs further evaluation under other crops, soils, and climatic conditions.

The variably-saturated flow and multi-component transport module UNSATCHEM of HYDRUS-1D was used to evaluate the impact of the long-term (2018-2050) application of recycled water (RCW) for irrigating perennial horticulture (almonds, pistachios), viticulture (grapevines), annual horticulture (carrot, onion, and potato), and pasture crops in representative soils from the Northern Adelaide Plains (NAP), South Australia. The input parameters for soil hydraulic, soil solution, and cation exchange data were determined for 14 soil profiles from the NAP region. For a warm-up period from 1970 to 2017, the model used historical climate data and low-salinity irrigation water. In the subsequent period (2018-2050), irrigation continued with RCW and projected meteorological conditions were obtained by considering expected future climate change. The average soil water salinity (ECsw) at the end of the simulation period ranged from 2.9-10.5 dS/m across all soils and crops. Potential yields of salt-sensitive crops such as annual horticulture and almonds were reduced by 4-32% due to increased salinity in the soil. Similarly, the model predicted that the sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP) would increase above threshold values, typically considered as indicative of poor growing conditions for most crops. Relationships between SAR and ESP were developed for four representative soils, providing the threshold soil SAR that corresponds to a critical ESP (>6), which would lead to adverse soil health and crop growth impacts. Threshold SARs were derived for calcareous (SAR = 4), hard red-brown (SAR = 3.5), sand over clay (SAR = 6), and deep uniform to gradational (SAR = 3) soils. An increase in SAR and ESP in soils adversely affects soil structural stability and soil water movement, which can severely impact the sustainable crop production in the NAP region. Relationships such as those between SAR and ESP help in identifying critical soil constraints and assist in devising better guidelines for the sustainable use of recycled water for irrigated agriculture.

The occurrence of macropores in salt marsh sediments is a natural and ubiquitous phenomenon. Although they are widely assumed to affect pore-water flow in salt marshes significantly, the mechanisms involved and their extent are not well understood. We conducted laboratory experiments and numerical simulations to examine the effect of macropores on soil evaporation. Soil columns packed with either sand or clay and with or without macropores were set up with watertables in the columns set at different levels. A high potential evaporation rate was induced by infrared light and a fan. The results showed that in the soil with a low saturated hydraulic conductivity (and thus a low water transport capacity), the macropore behaved as a preferential flow path for groundwater to recharge the surrounding soil during evaporation. The evaporated water originated largely from the macropore rather than the soil matrix, maintaining a high evaporation rate in comparison with a homogeneous soil. This effect was more pronounced for sediments with lower hydraulic conductivities and shallower watertables. These results improve our understanding of water flow and evaporation in salt marshes with continuous macropores between the soil surface and groundwater.

The HYDRUS model can be used to evaluate the effects of different soil surface treatments at the bottom of the furrow, different initial nitrogen fertilizer locations, and different furrow irrigation rates on deep drainage and solute leaching in furrow irrigated systems. This paper extends our 2012 study, in which we considered only one irrigation cycle and ignored the effects of plants. As a result of considering only one irrigation cycle, a large amount of water was used to change the water storage in the transport domain and only limited deep drainage of water and leaching of fertilizer at the bottom of the domain occurred in most scenarios investigated. To obtain a more realistic and complete picture, we have in this study considered multiple irrigation cycles to reflect actual field practices better and accounted for root water and nitrogen uptake and plant transpiration. As in our previous study, soil surface treatments at the bottom of the furrow include untreated, compacted and an impermeable membrane, and fertilizer is initially placed at one of five different locations in the furrow or the ridge. We have also evaluated (1) the effectiveness of triggering irrigation based on a pre-set soil water pressure head at a specific location in the ridge compared with prescribed irrigation at a regular time interval to supply water and nitrogen, and (2) the effects of plant water and nitrogen uptake on the furrow water balance, infiltration, soil evaporation, deep drainage, transpiration and nitrogen leaching. Our simulations show that deep drainage and nitrogen leaching can be substantially reduced by using an impermeable membrane on the bottom of the furrow and that a substantial additional reduction in leaching can be achieved by triggering irrigation rather than using a fixed time schedule. We also show that the initial location of fertilizer has a substantial effect on nitrogen uptake and leaching.

This study presents a hybrid Finite Volume – Finite Element (FV-FE) model that describes the coupled surface-subsurface flow processes occurring during furrow irrigation and fertigation. The numerical approach combines a one-dimensional description of water flow and solute transport in an open channel with a two-dimensional description of water flow and solute transport in a subsurface soil domain, thus reducing the dimensionality of the problem and the computational cost. The modeling framework includes the widely used hydrological model, HYDRUS, which can simulate the movement of water and solutes, as well as root water and nutrient uptake in variably-saturated soils. The robustness of the proposed model was examined and confirmed by mesh and time step sensitivity analyses. The model was theoretically validated by comparison with simulations conducted with the well-established model WinSRFR and experimentally validated by comparison with field-measured data from a furrow fertigation experiment conducted in the US.

Canopies of forested and agricultural ecosystems can significantly alter rainfall patterns into separate stemflow and throughfall areas. These two areas often have also different organic matter contents and soil compaction properties, and hence also soil hydraulic properties, thus causing further differences in the local infiltration rates close to and away from trees. In this study we analyzed possible differences in the unsaturated soil hydraulic properties of the stemflow and throughfall areas below an oil palm tree. Tension disc infiltrometer experiments were carried out underneath the canopy and in the interspace area of an oil palm tree plantation at successive tensions of 5, 2, and 0 cm. Soil hydraulic properties were estimated inversely from the measured data using the HYDRUS-2D/3D software package. Four van Genuchten soil hydraulic parameters (i.e., the residual water content, θr, the shape factors α and n, and the saturated hydraulic conductivity, Ks) were optimized. Saturated water contents, θs, were fixed at their laboratory-measured values. Initial estimates of the optimized parameters were set according to Wooding's solution, which ensured rapid convergence of the inverse solution. The stemflow and throughfall regions exhibited contrasting hydraulic properties as indicated by the estimated hydraulic parameters. Values of θs, α, n and Ks for the stemflow area were all found to be higher as compared to those of the throughfall area. The inverse solution using tension disc infiltrometer data proved to be very useful for rapid characterization of hydraulic properties of soil under the oil palm trees.

Coal seam gas production in Australia generates large volumes of produced water that is generally high in total dissolved solids and has a high sodium absorption ratio (SAR) which may affect soil structure, hydraulic conductivity, and crop production if used untreated for irrigation. By coupling major ion soil chemistry and unsaturated flow and plant water uptake, this study incorporates effects of salt concentrations on soil hydraulic properties and on root water uptake for soils irrigated with produced water featuring different water qualities. Simulations provided detailed results regarding chemical indicators of soil and plant health, i.e. SAR, EC and sodium concentrations. Results from a base scenario indicated that the use of untreated produced water for irrigation would cause SAR and EC values to significantly exceed the soil quality guide values in Australia and New Zealand (ANZECC). The simulations provided further useful insights in the type of coupled processes that might occur, and what the potential impacts could be on soil hydrology and crop growth. Calculations showed that the use of untreated produced water resulted in a decrease in soil hydraulic conductivity due to clay swelling causing water stagnation, additional plant-water stress and a reduction in plant transpiration. In case the produced water was mixed with surface water in a 1:3 ratio prior to irrigation, the calculated soil SAR values were much lower and generally acceptable for sandy to sandy-loam soil. The use of reverse osmosis treated produced water yielded an acceptable salinity profile not exceeding guide values for SAR and EC; the plant water stress was limited as there was no additional salinity stress associated with the low level of salts. Results further illustrated that accounting for coupled geochemical, hydrological and plant water uptake processes resulted in more accurate water balance calculations compared to an approach where such interactions were not implemented. Coupling unsaturated flow modelling with major ion chemistry solute transport using HYDRUS provides quantitative evidence to determine suitable water quality requirements for sustainable irrigation using coal seam gas produced water.

Increases in Zn and Cu concentrations in soils amended with pig slurry (PS) can be described using numerical models. Our main objective was to validate that the HYDRUS-1D model is able to numerically describe profile concentrations and long-term vertical transport of Zn and Cu in a clay soil (Oxisol) cultivated under annual cropping in a no-till system and contaminated by successive doses of PS amendments. We first used a modeling approach that had previously been validated for an Alfisol. Then, we additionally also evaluated the effects of root growth and root water uptake on the transport of trace metals (TMs). Finally, we carried out 50-yr-long prospective simulations for different doses of PS amendments. Consideration of root growth and root water uptake processes in HYDRUS-1D simulations improved the description of measured field Zn concentrations. Although the correspondence between simulated and measured Cu concentrations was not as good as for Zn, we performed prospective simulations for both elements. Future scenarios that considered large PS doses showed large increases in concentrations of both TMs in the soil surface layer. The feasibility of using PS amendments on agricultural Oxisols will be limited by Cu because the soil Cu threshold concentration is exceeded in approximately 29 yr. Moreover, the total loads of both TMs allowed on agricultural soils are reached very fast when large rates are used, especially for Cu (19 yr), indicating that the long-term disposal of PS on agricultural soils should be done at low doses. These conclusions are probably conservative because our model did not consider potential leaching of TMs from the surface soil into deeper soil layers by dissolved organic C facilitated transport.

Saturated hydraulic conductivity (Ks) is a key input parameter for modeling water flow in soils. Well-established methods exist, but there is no methodological standard or benchmark. This paper presents a comparison of three well-established measurement methods, which we used in the specific conditions of extremely heterogeneous mountain podzols. The following devices were applied to undisturbed soil core samples (diameter of 5.6 cm). Ks was estimated for a shallow subsurface ash-gray layer. The geometric mean values for Ks measured using these three methods were: GP — 4.41 × 10 − 6 ms − 1 , SR — 3.20 × 10 − 6 ms − 1 , and LP — 7.09 × 10 − 6 ms − 1 . The mean values obtained using field methods were not statistically different. The laboratory permeameter yielded slightly higher values than the field methods. From the engineering perspective, all tested methods provided similar mean values.

Spreading of contaminants from land-applied animal slurry may create hazard for both soil and water environments. Both the leaching and persistence of the contaminants is controlled by the redistribution of the contaminants immediately after application, while the redistribution is influenced by site conditions (here different slurry dry matter content and soil texture). HYDRUS-2D was used to simulate the redistribution of water, chloride, mineral N, Salmonella Typhimurium Bacteriophage 28B (phage), Escherichia coli, and steroid hormone estrogens near the slurry injection slit over a 50-day period after slurry injection at two field sites (Silstrup and Estrup) in Denmark to estimate the controlling transport and reaction parameters based on field measurements of the contaminants. The calibrated model was thereafter used to predict the leaching potential into the subsoil. The simulations confirmed that the higher water contents measured in the slurry application slit were due to a change in the hydraulic parameters. Chloride was redistributed considerably beyond the sampled soil profile at Estrup, but not at Silstrup, which had lower hydraulic conductivities than Estrup. Average size of the microorganisms affected their mobility; the bigger the size, the higher was the effect of the site conditions. The sorption coefficient of estrogens for slurry-amended soil was remarkably lower than that for unamended soil. The study suggests that dissolved organic carbon retained in slurry can facilitate the transport of contaminants. E. coli, phage, and estrogens were vulnerable to leaching from the very first precipitation event after the slurry application, whereas mineral N started to leach when NO3-N accumulated. Model predictions suggest that there are potential risks of leaching of these contaminants from the top soil to the subsoil associated with the land-injected slurry. © 2013 Elsevier B.V.

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

a b s t r a c t Adoption of high input irrigation management systems for South Australian horticultural crops seeks to provide greater control over timing of irrigation and fertilizer applications. The HYDRUS 2D/3D model was used to simulate water movement in the soil under an orange tree planted in a field lysimeter supplied with 68.6 mm of irrigation water over 29 days. Simulated volumetric water contents statistically matched those measured using a capacitance soil water probe. Statistical measures (MAE, RMSE, tcal) indicating the correspondence between measured and simulated moisture content were within the acceptable range. The modelling efficiency (E) and the relative efficiency (RE) were in the satisfactory range, except RE at day 19. Simulated daily and cumulative drainage fluxes also matched measured values well. Cumulative drainage flux was 48.9% of applied water, indicating large water losses even under controlled water applications. High drainage losses were due to light texture of the soil and high rainfall (70 mm) during the experimental period. Simulated root water uptake was 40% of applied water. The calibrated HYDRUS model was also used to evaluate several scenarios involving nitrate fertigation. The numerical analysis of NO3-N dynamics showed that 25.5% of applied fertilizer was taken up by the orange tree within 15 days of fertigation commencement. The rest of the applied NO3-N (74.5%) remained in the soil, available for uptake, but was also vulnerable to leaching later in the growing season. The seasonal simulation revealed that NO3-N leaching accounted for 50.2% of nitrogen applied as fertilizer, and plant N recovery amounted to 42.1%. The scenario analysis further revealed that timing of a nitrogen application in an irrigation event had little impact on its uptake by citrus in the lysimeter. However, slightly higher NO3-N uptake efficiency occurred when fertigation was applied late in the daily irrigation schedule, or was spread out across all irrigation pulses, rather than being applied early or in the middle. Modelling also revealed that pulsing of irrigation had little impact on nitrate leaching and plant uptake. Applying less irrigation (50% or 75% of ETC) resulted in higher nitrate uptake efficiency. This study showed that timing of water and fertilizer applications to an orange crop can be better regulated to enhance the efficiency of applied inputs under lysimeter conditions.

Mountainous soils usually contain a large number of rock fragments, particles with a diameter larger than 2 mm, which can influence soil hydraulic properties that are required to quantitatively describe soil water movement in stony soils. The objective of this study was to numerically estimate both the saturated hydraulic conductivity of a stony soil and its dependence on a relative content of rock fragments (stoniness), and the shape, position and distribution of rock fragments in a soil matrix. The assessment method was based on a numerical version of Darcy's classic experiment that involved steady-state flow through a porous material under a unit hydraulic gradient. Our experiments, involving hypothetical stony soils in this particular case, were simulated using mainly the two-dimensional (2D) numerical model, HYDRUS-2D. A limited number of simulations were carried out using a three-dimensional HYDRUS model. Three different shapes of hypothetical rock fragments were used in the study: a sphere, an ellipsoid with two different positions, and a pyramid, all represented by their 2D cross-sections (i.e., a circle, an ellipse, and a triangle, respectively). The mean relative effective saturated hydraulic conductivity ( K rs ) for the same stoniness was almost the same for all simulated scenarios and fine soil textures. A stoniness between 0.07 and 0.5 cm 3 cm − 3 can cause a decrease of K rs in the range of 0.17–0.70. Numerical experiments were divided into 3 scenarios. The largest and the smallest values of K rs were different for different shapes of RFs (scenario A), different orientations of the slab-sided elliptical RFs (scenario B), and regular or irregular distributions of spherical RFs (scenario C). The largest difference between K rs values (0.26) was found in scenario B when the slab-sided elliptical RFs were oriented either horizontally or vertically for stoniness of 0.24 or 0.31 cm 3 cm − 3 . Simulated K rs values were underestimated in all scenarios as compared to the Ravina and Magier (1984) function. The smallest differences (− 1.1%–2.5%) between numerically simulated and calculated (the Corring and Churchill (1961) method for a cylindrical shape of RFs) K rs values were found for scenario A with its 2D representation of spherical rock fragments. Calculated (the Corring and Churchill (1961) method for a spherical shape of RFs) K rs values corresponded well with those simulated using a 3D representation of spherical rock fragments. Numerical models provide a unique opportunity to evaluate the effects of different factors on the saturated hydraulic conductivity of stony soils that may be nearly impossible to measure in practice.

Published August 25, 2016 Original Research A Comprehensive Analysis of the Variably Saturated Hydraulic Behavior of a Green Roof in a Mediterranean Climate Giuseppe Brunetti,* Jirka Simůnek, and Patrizia Piro Core Ideas • A comprehensive numerical analysis of hydrological processes in a green roof was conducted. • The substrate of the green roof dem- onstrated bimodal behavior. • The validated model accurately describes the hydraulic behavior of the green roof. • The soil moisture governs the per- formance of the green roof during precipitation. Low-impact developments (LIDs), such as green roofs, have proven to be valuable alternatives for stormwater management and hydrological resto- ration. Mechanistic models are reliable and accurate tools for analysis of the hydrologic behavior of LIDs, yet only a few studies provide a compre- hensive numerical analysis of the hydrological processes involved and test their model predictions against field-scale data. Moreover, more research is needed to determine the unsaturated hydraulic properties of the substrates used in LIDs. For these reasons, the aim of this study was to provide a com- prehensive description of the hydrological behavior of an extensive green roof installed at the University of Calabria. The soil hydraulic properties were determined by using the simplified evaporation method. Both unimodal and bimodal soil hydraulic functions were used in the analysis. The estimated parameters were then used in the HYDRUS-3D model to simulate a 2-mo- long period. Precipitation, irrigation, evaporation, and root water uptake processes were included in the numerical analysis. The values of 0.74 and 0.8 of the Nash–Sutcliffe efficiency index for the model predictions using unimodal and bimodal functions, respectively, confirmed the good agree- ment between the modeled and measured outflows. The bimodal model was able to both accurately reproduce the hydrographs in both dry and wet periods and account for daily fluctuations of soil moisture. Finally, the validated model was used to carry out a hydrological analysis of the green roof and its hydrological performance during the entire simulated period as well as during single precipitation events. Abbreviations: AIC, Akaike information criterion; LID, low-impact development; NSE, Nash–Sutcliffe efficiency; RMSE, root mean square error; VGM, van Genuchten–Mualem. During the last few decades , the area of impervious surfaces in urban areas has G. Brunetti and P. Piro, Dep. of Civil Engineering, Univ. of Calabria, Rende, CS 87036, Italy; J. Simůnek, Dep. of Envi- ronmental Sciences, Univ. of California, Riverside, CA 92521. *Corresponding author (giuseppe.brunetti@unical.it). Vadose Zone J. doi:10.2136/vzj2016.04.0032 Received 19 April 2016. Accepted 14 June 2016. © Soil Science Society of America 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved. exponentially increased as a consequence of demographic growth. This long-term process has altered the natural hydrological cycle by reducing the infiltration and evaporation capacity of urban catchments, while increasing surface runoff and reducing groundwater recharge. Moreover, the frequency of extreme rainfall events, characterized by high inten- sity and short duration, is expected to increase in the near future as a consequence of global warming (Kundzewicz et al., 2006; Min et al., 2011). The combined effects of urbanization and climate change expose urban areas to an increasing risk of flooding. In this context, urban drainage systems play a fundamental role in improving the resilience of cities. In recent years, an innovative approach to land development known as low-impact development (LID) has gained increasing popularity. Low-impact development is a “green” approach to storm water management that seeks to mimic the natural hydrology of a site using decentralized microscale control measures (Coffman, 2002). Low-impact development practices consist of bioretention cells, infil- tration wells or trenches, stormwater wetlands, wet ponds, level spreaders, permeable pavements, swales, green roofs, vegetated filter and buffer strips, sand filters, smaller cul- verts, and water harvesting systems. Low-impact developments are able to reduce runoff Vadose Zone Journal | Advancing Critical Zone Science

Summary The objective of this study is to assess recharge rates and their timing under layered loessial deposits at the edge of arid zones. Particularly, this study is focused on the case of the coastal plain of Israel and Gaza. First, results of a large-scale field infiltration test were used to calibrate the van Genuchten parameters of hydraulic properties of the loessial sediments using HYDRUS (2D/3D). Second, optimized soil hydraulic parameters were used by HYDRUS-1D to simulate the water balance of the sandy-loess sediments during a 25-year period (1990–2015) for three environmental conditions: bare soil, and soil with both sparse and dense natural vegetation. The best inverse parameter optimization run fitted the infiltration test data with the RMSE of 0.27 d (with respect to a moisture front arrival) and R 2 of 96%. The calibrated model indicates that hydraulic conductivities of the two soil horizons, namely sandy loam and sandy clay loam, are 81 cm/d and 17.5 cm/d, respectively. These values are significantly lower than those previously reported, based on numerical simulations, for the same site. HYDRUS-1D simulation of natural recharge under bare soil resulted in recharge estimates (to the aquifer) in the range of 21–93 mm/yr, with an average recharge of 63 mm/yr. Annual precipitation in the same period varied between 100 and 300 mm/yr, with an average of 185 mm/yr. For semi-stabilized dunes, with 26% of the soil surface covered by local shrub ( Artemisia monosperma ), the mean annual recharge was 28 mm. For the stabilized landscape, with as much as 50% vegetation coverage, it was only 2–3 mm/yr. In other words, loessial sediments can either be a source of significant recharge, or of no recharge at all, depending on the degree of vegetative cover. Additionally, the time lag between specific rainy seasons and corresponding recharge events at a depth of 22 m, increased from 2.5 to 5 years, and to about 20 years, respectively, with an increasing vegetative cover. For this reason, and also likely due to a great depth of loessial sediments, no correlation was found between annual recharge and annual precipitations of the same year or subsequent years. Similarly, no differences were found between summer and winter recharge fluxes. Instead, numerical simulations indicated continuous year-round recharge of the aquifer. We conclude that the layered subsurface acts as a short-term (annual) and long-term (multi-annual) buffer to smooth sudden precipitation/infiltration events. Vegetation conditions can help in predicting long-term recharge rates (as percentage of annual precipitation), which in turn need to be considered when assigning recharge characteristics in regional assessments and models.

© 2015, Springer-Verlag Berlin Heidelberg. Furrow irrigation and fertigation systems should be designed and managed to optimize the availability of water and fertilizer to plants and minimize their losses through evaporation, deep drainage and leaching. We developed a furrow irrigation submodule for HYDRUS (2D/3D) and used it to evaluate the effects of different furrow soil surface treatments and different timings of fertigation on root water and solute uptake, deep drainage and solute leaching in a loamy soil. Numerical simulations showed that more water was available for transpiration in the treatments with plastic placed at the furrow bottom compared to the control treatments. However, more water was lost due to evaporation and less water was drained from the soil profile for these treatments. The highest and lowest root solute uptake was achieved when fertigation was applied in the middle and at the beginning of the irrigation cycle, respectively. The least amount of solute was leached from the soil profile for treatments with the plastic bottom and when fertigation was applied at the end of the irrigation cycle. The scenarios with plastic and irrigation in alternate furrows showed a reduction in transpiration and yield, more water loss due to deep drainage, and less water lost due to evaporation. However, similar crop yields were obtained for this alternate furrow strategy as for the control furrow surface treatments. When only half the water was used for irrigation in this scenario, the reduction in yield was less than 20 % compared to the control treatments, producing higher water-use efficiency.

Inappropriate soil, water and fertilizer management in irrigated agriculture can result in environmental problems, including groundwater pollution with nitrates. Furrow irrigation is widely used around the world and is considered as a major source of nitrate leaching. Improved soil, water and fertilizer management practices are needed to improve the production and environmental performance of furrow irrigated agriculture. This paper describes results of a simulation study using HYDRUS-2D to assess opportunities to improve irrigation efficiency and reduce the risk of nitrate leaching from furrow irrigated systems. It focuses on the commonly used practice in Pakistan where irrigation water supply is turned off once the water level in the furrow has reached a pre-determined depth. The study involved analysing the impact of fertilizer placement on nitrate leaching from a loamy soil subjected to three different soil surface treatments. Fertilizer placements included placing the fertilizer on the bottom of the furrow ( P 1 ), sides of the furrow ( P 2 ), bottom and sides of the furrow ( P 3 ), on the sides of the furrow near to the ridge top ( P 4 ), and on the surface in the middle of the ridge top ( P 5 ). The soil surface management treatments included the original soil ( S o ), compacting the bottom of the furrow ( S c ) and placing a plastic sheet on the bottom of the furrow ( S p ). Results showed water savings varied with application rate and soil surface management, with soil surface management strategies S c and S p yielding water savings of 17% and 28% relative to S o for a water application rate of 1800 L h −1 for a 100 m long furrow. Leaching of nitrogen for this case was reduced from 33% for S o with fertilizer placement P 1 to 1% by compacting the bottom of the furrow ( S c ) and to zero loss by placing a plastic sheet on the bottom of the furrow ( S p ). By changing the fertilizer placement for S o from P 1 to P 2 , P 3 , P 4 , and P 5 , nitrogen leaching was reduced from 33% to 2%, 15%, 0%, and 0%, respectively. Results of this study demonstrate that placing nitrogen fertilizer on the sides of the furrow near the ridge top ( P 4 ) or on top of the furrow at the centre of the ridge ( P 5 ) maximize the retention of nitrogen fertilizer within the root zone. Results of this study also demonstrate that enhancements in irrigation efficiency, particularly in coarser soils with high infiltration rates can be achieved through compacting the bottom of the furrow or by placing a plastic sheet on the bottom of the furrow before applying irrigation.

The main objective of this study was to identify the main sources and processes that control SO4 2− groundwater concentrations in the Jinghuiqu irrigation district of China using isotope analysis. Lysimeter irrigation experiments and numerical modeling were used to assess the impact of long-term irrigation practices on sulfate transport, when different sources of irrigation water were used. SO4 2− concentrations in the groundwater of the entire irrigation area increased significantly from the years 1990 (a mean value was 4.8 mmol L−1) to 2009 (a mean value was 9.84 mmol L−1). The δ34S-SO4 2− values (ranging from +5.27 to +10.69 ‰) indicated that sulfates in groundwater were initially predominantly derived from dissolution of minerals. However, no soluble sulfate minerals (gypsum and/or mirabilite) were detected after 1990. To better understand this seeming anomaly, water content and SO4 2− data were collected before and after the field irrigation experiment and analyzed using the HYDRUS-1D and HP1 software packages. The experimental data were also used to assess sulfate leaching when different sources of irrigation water were used under current irrigation practices. The dissolved sulfate concentrations in the soil profile increased significantly when groundwater was used for infiltration compared to the use of surface water. Irrigation water sources had a great impact on the increase of sulfate concentrations in the shallow groundwater, especially when groundwater with elevated concentrations was used for irrigation.

The need for reducing irrigation water demand and non-point source pollution all across Europe has made sweet sorghum [ Sorghum bicolor (L.) Moench], due to its lower water and nutrient requirements, an interesting alternative to other traditional summer crops in European Mediterranean regions. HYDRUS-2D was used to model the fate of nitrogen in a plot planted with sweet sorghum grown under Mediterranean conditions between 2007 and 2010, while considering drip irrigation scenarios with different levels of nitrogen and salty waters. HYDRUS-2D simulated water contents, EC sw , and N NH 4 + and N NO 3 − concentrations continuously for the entire duration of the field experiment, while producing RMSE between simulated and measured data of 0.030 cm 3 cm −3 , 1.764 dS m −1 , 0.042 mmol c L −1 , and 3.078 mmol c L −1 , respectively. Estimates for sweet sorghum water requirements varied between 360 and 457 mm depending upon the crop season and the irrigation treatment. Sweet sorghum proved to be tolerant to saline waters if applied only during one crop season. However, the continuous use of saline waters for more than one crop season led to soil salinization, and to root water uptake reductions due to the increasing salinity stress. The relation found between N NO 3 − uptake and dry biomass yield ( R 2 = 0.71) showed that nitrogen needs were smaller than the uptakes estimated for the scenario with the highest levels of nitrogen application. The movement of N out of the root zone was dependent on the amount of water flowing through the root zone, the amount of N applied, the form of N in the fertilizer, and the timing and number of fertigation events. The simulations with HYDRUS-2D were useful to understand the best strategies toward increasing nutrient uptake and reducing nutrient leaching. In this sense, N NO 3 − uptakes were higher when fertigation events were more numerous and the amounts applied per event smaller.

Knowledge of the spatial and temporal distribution of pesticide concentrations is essential for pesticide registration. In field experiments performed during the registration procedure, suctions cups are widely used to monitor the evolution of pesticide leaching over time and to calculate the mean concentration for a given drainage period. Until now, there has been no detailed information regarding whether soil water sampling by suction cups is suitable for accurately predicting the field-scale leaching of pesticides in heterogeneous soils. To address this, we performed a numerical study to evaluate the uncertainties associated with suction cup sampling in heterogeneous soils under atmospheric boundary conditions using two pesticides with contrasting sorption and degradation properties. To address the two main operation modes of suction cup sampling, continuous and weekly sampling were analyzed. First, the variability of pesticide breakthrough concentrations was analyzed for a single pesticide application in a physically heterogeneous soil profile. Second, a 10-yr time series was used to analyze repeated pesticide applications, and estimate variability in the leached mass fraction (LMF) and mean concentrations. In both cases, pesticide breakthrough was compared to the breakthrough of an inert tracer. The results indicate that for a single pesticide application, pore water velocities varied only slightly for all operation sampling modes and compounds. On the other hand, the total extracted mass and LMF varied greatly, suggesting that the acceleration of the breakthrough sampled by suction cups plays an important role in terms of LMF and the mean concentration, especially for degradable substances.

Micro-irrigation has become an optimal means for providing water and nutrients to crops. There is an ample space for improving fertilizer use efficiency with micro-irrigation, if the movement and reactions of fertilizers in the soil are well understood. However, the rhizosphere dynamics of nutrients is very complex, depending on many factors such as soil temperature, pH, water content, and soil and plant characteristics. Many factors cannot be easily accurately quantified. However, using state-of-the-art modelling techniques, useful and reliable information can be derived. An attempt was made to evaluate the reactive transport of urea in the root zone of a sugarcane crop under drip irrigation, and to quantify the fluxes of urea, ammonium, and nitrate into the crop roots, volatilization fluxes, and deep drainage using a numerical model. This quantification helped in designing an optimal fertigation schedule. Various parameters used in the model were taken from either the literature or the field study. A typical scenario, based on the recommended total quantity of urea for sugar cane crop under drip irrigation in India, was tested using HYDRUS-2D. The total amount of urea was divided into fortnightly doses, depending on the stage of crop growth. For this scenario, the modelled crop uptake was found to be 30% higher than the crop demand. Consequently, an optimal fertigation schedule was developed that reduced the use of urea by 30% while at the same time providing enough N for its assimilation at all stages of crop growth. This type of modelling study should be used before planning field experiments for designing optimal fertigation schedules.

Improving the sustainability of irrigation systems requires the optimization of operational parameters such as irrigation threshold and irrigation amount. Numerical modeling is a fast and accurate means to optimize such operational parameters. However, little work has been carried out to investigate the relationship between irrigation scheduling, irrigation threshold, and irrigation amount. Herein, we compare the results of HYDRUS 2D/3D simulations with experimental data from triggered drip irrigation, and optimize operational parameters. Two field experiments were conducted, one on loamy sand soil and one on sandy loam soil, to evaluate the overall effects of different potential transpiration rates and irrigation management strategies, on the triggered irrigation system. In both experiments, irrigation was controlled by a closed loop irrigation system linked to tensiometers. Collected experimental data were analyzed and compared with HYDRUS 2D/3D simulations. A system-dependant boundary condition, which initiates irrigation whenever the matric head at a predetermined location drops below a certain threshold, was implemented into the code. The experimental model was used to evaluate collected experimental data, and then to optimize the operational parameters for two hypothetical soils. The results show that HYDRUS 2D/3D predictions of irrigation events and matric heads are in good agreement with experimental data, and that the code can be used to optimize irrigation thresholds and water amounts applied in an irrigation episode to increase the efficiency of water use.

The spatiotemporal development of soil surface temperatures (SST) depends on water availability in the near-surface soil layer. Because the soil loses latent heat during evaporation and water available for evaporation depends on soil hydraulic properties (SHP), the temporal variability of SST should contain information about the near-surface SHP. The objective of this study was to investigate the uncertainties of SHP derived from SST. The HYDRUS-1D code coupled with a global optimizer (DREAM) was used to inversely estimate van Genuchten–Mualem parameters from infrared-measured SST and time domain reflectometry (TDR)-measured water contents. This approach was tested using synthetic and real data, collected during September 2008 from a harrowed silty loam field plot in Selhausen, Germany. The synthetic data illustrated that SHP can be derived from SST and that additional soil water content measurements reduce the uncertainty of the estimated SHP. Unlike for the synthetic experiment with a vertically homogeneous soil profile, a layered soil profile had to be assumed to derive SHP from the real data. Therefore, the uncertainty of SHP derived from real data was considerably larger. Water retention curves of undisturbed soil cores were similar to those estimated from SST and TDR data for the deeper undisturbed soil. The retention curves derived from SST and TDR data for the harrowed topsoil layer were typical for a coarse-textured soil and deviated considerably from the retention curves of soil cores, which were typical for a fine-textured soil and similar to those from the subsoil.

In this paper is presented the comparison of the selected hydrometeorological data from two experimental micro-scale catchments Modrava 1 (0.1 km2) and Modrava 2 (0.17 km2) in upper parts of Bohemian Forest. These catchments differ mainly in the vegetation cover – a dead forest with very young trees (Modrava 1) and primary forest clearings with 10 to 15-year old young forest (Modrava 2). For comparison were used the data monitored close to the catchments outlets during the hydrological year 2007. average hourly rainfall and runoff data were analysed. During the winter season, snow water equivalents were measured and the maximum value was added to the rainfall amount measured during the vegetation season for the estimation of total year precipitation on each catchment. The data of the air temperature and water conductivity measured in hourly time intervals were also compared. For the estimation of differences between the monitored data sets the cumulative values of the characteristics observed during whole year were computed. It follows from the comparison of the time series that the time rainfall distribution was similar during the year on both catchments with a higher total year precipitation and hour intensities on the catchment Modrava 2. The time distribution and total runoff depth were similar on both catchments. On Modrava 1 a faster recession of hydrographs could be seen which might relate to a lower retention capacity. The value of the water conductivity on the catchment Modrava 1 depended more on the changes of the runoff depth. The maximal values occurred during the peak discharges or in time of hydrographs rising. This fact can be the result of a lower stability of the soil profile in the catchment with dead forest cover.

Modeling fl ow in variably saturated porous media requires reliable estimates of the hydraulic parameters describing the soil water retention and hydraulic conductivity. Th ese soil hydraulic properties can be measured using a wide variety of laboratory and fi eld methods. Frequently, this proves to be an arduous task because of the high spatial and temporal variability of soil properties. In the last decade, researchers have shown a keen interest in developing a class of indirect approaches, called pedotransfer functions (PTFs), to overcome this problem. Pedotransfer functions predict soil hydraulic parameters using easily obtainable soil properties such as textural information, bulk density and/or few retention points. In this paper, we use a new methodology called Support Vector Machines (SVMs) to derive a new set of PTFs. Support vector machines represent a pattern recognition approach where the overall prediction error and complexity of the SVM structure are minimized simultaneously. We used the same database that was utilized to develop ROSETTA to generate the SVM-based PTFs. Th e performance of the SVM-based PTFs was analyzed using the coeffi cient of determination, root mean square error (RMSE) and mean error (ME). All soil hydraulic parameters estimated using the SVM-based PTFs showed improved confi dence in the estimates when compared with the ROSETTA PTF program. Estimates of water contents and saturated hydraulic conductivities using the hydraulic parameters predicted by the SVM-based PTFs mostly improved compared with those obtained using the artifi cial neural network (ANN)-based ROSETTA. Th e RMSE for water contents decreased from 0.062 to 0.034 as more predictors were used, while the RMSE for the saturated hydraulic conductivity decreased from 0.716 to 0.552 (dimensionless log 10 units). Similarly, the bias in the water contents estimated using the SVM-based PTF was reduced signifi cantly compared with ROSETTA. Abbreviations: ANN, Artifi cial neural networks; HYPRES, Database of hydraulic properties of European soils; ME, Mean Error; PTFs, Pedotransfer functions; RMSE, Root mean squared error; SLT, Statistical learning theory; SVMs, Support vector machines; UNSODA, Unsaturated soil hydraulic properties database; WISE, World inventory of soil emission potentials.

Solute displacement experiments with the anƟ bioƟ c sulfadiazine (SDZ) and its main transformaƟ on products in pig manure were performed to invesƟ gate the infl uence of manure on SDZ transport. Either pig manure containing 14 C-sulfadiazine (4-amino-N-2-pyrimidinyl-benzenesulfonamide), and its main transformaƟ on products 14 C-4-OH-SDZ and 14 C-N-Ac-SDZ, or a 14 C-SDZ soluƟ on was incorporated in the fi rst cenƟ meter of undisturbed and repacked soil columns, which were then irrigated. Breakthrough curves (BTCs) of 14 C, SDZ, 4-OH-SDZ, N-Ac-SDZ and 4-[2-iminopyrimidine-1(2H)-yl]-anilin were measured. The 14 C distribuƟ ons vs. depths were determined aŌ er the conclusion of the leaching experiments. An applicaƟ on of SDZ together with manure resulted in lower peak values of the 14 C BTCs and a slightly lower amount of eluted mass. In the experiments with manure, the 14 C concentraƟ ons in the uppermost layers of the soil columns were higher, probably due to the fi ltraƟ on of manure parƟ cles onto which SDZ or its transformaƟ on products were sorbed. The transformaƟ on products showed a relaƟ vely high leaching potenƟ al similar to SDZ. Cotransport with organic parƟ cles seemed to be of minor relevance for the eluted amounts of solutes. All BTCs were modeled using a numerical model that considered degradaƟ on chains from N-Ac-SDZ into SDZ and from SDZ into 4-OH-SDZ, as well as one reversible and one irreversible kineƟ c sorpƟ on site for each solute. The applied model fi Ʃ ed the BTCs of SDZ and its transformaƟ on products reasonably well. The fi ƫ ng process revealed a high mobility of both SDZ and its transformaƟ on products. While N-Ac-SDZ degradaƟ on into SDZ was fast and no extended tailing of N-AcSDZ was observed, the transport behavior of 4-OH-SDZ was similar to that of SDZ.