Agricultural water systems are increasingly exposed to climate-driven extremes, aging infrastructure, and intensifying cross-sectoral competition, requiring a transition toward more adaptive and resilient management. Here, we present a comparative analysis of agricultural water management pathways in California, USA, and South Korea—two regions facing similar hydroclimatic pressures but operating under contrasting governance systems. We show that California prioritizes decentralized, data-driven, and adaptive management, whereas South Korea emphasizes centralized coordination, infrastructure-based solutions, and national-scale planning. Despite these differences, both regions exhibit converging systemic challenges, including increasing vulnerability to droughts, floods, and heatwaves, inefficiencies in conventional water use, labor constraints, and growing trade-offs between agricultural production and ecosystem sustainability. Building on these findings, we identify four key pathways for advancing sustainable agricultural water management: (1) enhancing water supply resilience through diversification and optimized storage, (2) improving water-use efficiency via digital technologies and advanced irrigation systems, (3) integrating ecosystem-based approaches to sustain environmental functions, and (4) strengthening collaborative governance for equitable and adaptive water allocation. Our results demonstrate that sustainable agricultural water management depends not only on technological innovation, but also on institutional adaptability and governance integration. These findings provide transferable insights for regions facing similar water stress and highlight the need for hybrid management approaches that combine flexibility, coordination, and resilience under accelerating climate change.

Soil sodicity, salinity, clay dispersion, and clay soil cracking are significant issues for modern agriculture, especially in arid and semi-arid regions of the world. Sodium adsorption ratio (SAR) has traditionally been used to estimate potential changes in infiltration rates or hydraulic conductivity when sodium cations dominate irrigation water quality. Recent research indicates that the cation ratio of soil structural stability (CROSSf and CROSSopt) provides better predictive capabilities for soil structure and threshold electrolyte concentration than SAR, especially when water used for irrigation or aquifer recharge contains both potassium and sodium cations. In this study, soil columns filled with clay loam were used to assess the impact of recycled water reuse on soil structure stability and saturated hydraulic conductivity. Ten treatments were prepared using chloride solutions of sodium, potassium, calcium, and/or magnesium to create a broad range of synthetic recycled water qualities with varying SAR, CROSSf, and CROSSopt values. After a pre-saturation process, the columns were maintained to have a constant 1 cm head of treatment solutions with a salinity of 1.5 dS/m. The results showed that CROSSf had a stronger correlation with saturated hydraulic conductivity and soil aggregate stability in comparison to CROSSopt and SAR. The R2 for saturated hydraulic conductivity and soil structure were 0.90 and 0.94 for CROSSf, 0.41 and 0.60 for CROSSopt, and 0.75 and 0.78 for SAR, respectively. Notably, the treatments that received solutions with 0-SAR values but contained potassium had significantly more dispersible clay throughout the entire soil column than the treatment that received calcium chloride solution. It was concluded that the CROSSf model could offer enhanced accuracy and insight into predicting the impact of recycled water reuse for irrigation on soil infiltration rate and soil aggregate stability.

Surfactant molecules increase the infiltration rate into hydrophobic porous media by lowering the infiltrating water's surface tension and the interfacial tension between hydrophobic surfaces and water molecules. We investigated the relative effect of these rate-limiting processes on the infiltration rate of aqueous surfactant solution into hydrophobic porous media. Two surfactants at various concentrations were applied at a constant pressure head to 1D columns filled with hydrophobic soil, and water was applied at the same pressure head to columns filled with surfactant-pretreated hydrophobic soil. Based on the measured contact angle, surfactant pretreatment significantly reduced the hydrophobic soil's interfacial surface tension, which increased the infiltration rate compared to the direct aqueous surfactant application to the hydrophobic soil. The latter's slower infiltration rate was attributed to the depletion of surfactant molecules due to its adsorption to the hydrophobic molecules near the advancing wetting front, yielding an increase in the surface tension of the infiltrating solution. Surfactant pretreatment increased the opportunity time for surfactant adsorption to the hydrophobic molecules, resulting in interfacial tension reduction and infiltration rate increase. Diffusion-limited surfactant adsorption on the hydrophobic surfaces, leading to reduced interfacial tension between the surface and infiltrating liquid, had a greater impact on limiting infiltration into hydrophobic porous media compared to the reduction in surface tension of the infiltrating liquid due to surfactant presence.

This study aimed to assess the impact of salinity in the root zone on crop yields and profitability in the Central Valley. A comprehensive biophysical model was developed by integrating soil variables, climate conditions, irrigation inputs, and economic data. The model considered four key crops (alfalfa, almonds, table grapes, and processing tomatoes), five levels of irrigation water salinity (ranging from 0.5 to 5.5 dS/m), and daily irrigation water amounts (ranging from 0 to 12 mm). The results indicated strong predictive capabilities of the model, with R2 values for predicted yields of 0.82, 0.77, 0.78, and 0.64 for alfalfa, almonds, grapes, and tomatoes, respectively. The corresponding RMSE values were 9%, 8%, 23%, and 11% for the same crops. Profit predictions showed an R2 value of 0.99 for alfalfa, almonds, and processing tomatoes, and 0.74 for grapes. The RMSE values were 48, 211, 2461, and 68 $/ha for alfalfa, almonds, grapes, and processing tomatoes, respectively. Furthermore, the model incorporated a spatial component, revealing variations in yield and profitability based on soil type and groundwater salinity across the Central Valley. Results indicated that at daily irrigation rates of 3 mm, no profits were predicted for any of the crops. However, a daily irrigation rate of 6 mm produced profits of up to $1000/ha for alfalfa and processing tomatoes, while almonds and grapes required more than 8 mm/day to achieve profitable outcomes. This integrated modeling framework provides valuable insights for policymakers to identify areas unsuitable for sustainable and profitable irrigated agriculture. It can help prioritize such areas for multi-benefit land repurposing, reducing agricultural water demand, and achieving groundwater sustainability. Additionally, the model serves as a decision-aid tool for growers in arid regions, enabling them to anticipate potential losses in crop yield and profitability due to irrigation water salinity.

Soil water repellency has a substantial effect on soil-water retention and flow. Typically, soils are denoted water repellent when they resist spontaneous wetting by water for more than five seconds. Soil water repellency reduces infiltration capacity, increases surface runoff, soil erosion, and induces uneven distribution of water content, including preferential flow pathways. We describe an in-situ study aiming to remediate these soils by surfactant application using a commercial drip system. The study was carried out on a commercial citrus orchard irrigated with secondary treated wastewater, which usage has been shown to induce soil water repellency over time. To relieve the adverse effects of soil water repellency, different concentrations of a nonionic surfactant were applied to the soil using a drip system for three years. The spatial variation of the soil's wettability was characterized by the sessile drop method (contact angle) and water drop penetration time (WDPT) test. The spatial soil-water content distributions and flow were monitored undisturbedly by electrical resistivity tomography (ERT) surveys. Spatial soil-agrochemical distributions along transects where the ERT surveys took place were determined by intensive soil sampling at two depths: 0-20 and 20-40 cm. The ERT results indicated that while the surfactant application via drippers improved the water repellent soil's wettability, it enhanced the development of preferential flow pathways. Although preferential flow pathways associated with treated wastewater irrigation existed in all soil profiles, they were exacerbated by the surfactant application. Additionally, increased leaching of mobile elements, like Cl, N, and EC, was measured for the surfactant-treated plots. Contrarily, P adsorption to the soil particles was increased in the surfactant plots compared to the untreated plots. While the contact angle along the soil surface showed no difference between the untreated and surfactant treated plots, the WDPT decreased in the latter. These findings indicate that aside from the foreknown causes of preferential flow in soils like earthworms, wet and dry cycles, aliphatic hydrocarbons, etc., localized surfactant application by drippers (point sources) for water repellent soils remediation enhances preferential flow and chemicals leaching. Therefore, a different method for surfactant application that remediates soil water repellency without enhancing agrochemicals leaching should be considered and examined.

Despite the known benefits of biochar application to soils, little is known about its effect on soil wettability and the consequences on soil water movement across the soil profile. Focusing on the latter, three types of commercial biochar derived from wheat, corn, and rice straw produced under low temperature (350–450 ℃) were mixed with a wettable sandy soil at rates of 0%, 2%, 5%, and 10% w/w. Soil water repellency (SWR) of the biochars and biochar–soil mixtures was determined by water drop penetration time (WDPT) test and sessile-drop contact angle (CA) measurement. The WDPT results (< 5 s) showed complete wettability for the biochar–soil mixtures, whereas CA results indicated some water repellency. The mean initial CA of the three biochars varied between 105.3° and 113.9°, with ∼ 30° for the pure sand, and between 56.8° and 75.7° for the biochar–soil mixtures. SWR increased with biochar-application rate, whereas biochar particle size (< 1 mm and > 1 mm) had no significant effects on SWR. A 2-D flow chamber experiment with point source water application at the surface was used to continuously monitor the flow pattern and soil water content (SWC) distribution across the soil profile during infiltration and redistribution periods. Biochar–soil mixtures (2% and 5% w/w) with the three biochar types were studied. Flow chamber results showed substantial differences in plumes shape and internal SWC distribution in the biochar–soil mixtures compared to the untreated sand during the wetting and drainage. The plumes' shape and nonmonotonic spatial SWC distribution suggested unstable flow in the biochar–soil mixtures. The internal fingers developed in the biochar treated sand indicate that SWR induced by biochar addition seemed to be physically induced via the blending of the biochar and soil particles, rather than chemically induced, via coating of the soil particles with amphiphilic molecules. Under field conditions, the primary and inner finger-like plumes may eventually form preferential flow paths that will affect the spatial distribution of water and fertilizer in soil profiles and their availability to plant roots.

The use of treated wastewater (TWW) has gained recognition as an alternative source for freshwater irrigation, and is steadily expanding worldwide. Despite the benefits of freshwater conservation and nutrient richness, there is mounting evidence of TWW adverse effects on soil, yield, and the environment. Irrigation using TWW has resulted in soil water repellency, in which preferential flow pathways and uneven soil water and chemical distribution occur. These increase deep water percolation and chemical leaching, which can lead to soil and groundwater pollution. This study was conducted in a commercial citrus orchard grown on sandy‐loam soil in central Israel and irrigated with TWW, with the aim of investigating the remediation of these adverse effects, by repeatedly spraying a nonionic surfactant on the soil surface. The surfactant application succeeded to turn the soil wettable, diminishing the preferential flow pathways, and rendering the soil water and dissolved chemicals uniformly distributed. The overall water content in the 0–40 cm layer increased, and deep percolation and chemical leaching substantially decreased. The grapefruit yield increase during the two‐year study period increased the water use efficiency. Electrical resistance tomography scans executed during and after irrigation events for two subsequent years revealed that a “soil memory” phenomenon has been developed for water repellent soils, where water flow takes place through previously developed preferential flow pathways in such soils. This study demonstrates that recurrent surfactant application enables a continuous use of TWW, while eliminating most of its prejudicial effects.

Preferential flow pathways and uneven soil water and chemical distribution are intrinsic phenomena in water repellent soils. These uneven water and chemical distribution reduce water uptake by the plant roots on one hand and enhance deep percolation and chemical leaching, on the other hand, thereby enhancing soil and groundwater pollution. The results of attempts to remediate soil water repellency and heterogeneous spatial distribution of soil moisture and chemicals within the root zone by surfactant application will be addressed. This study was conducted in a commercial citrus orchard in central Israel that is irrigated with treated wastewater. Previous studies have revealed that prolonged irrigation using treated wastewater renders the soil water repellent with its associated adverse effects. The soil water distribution within the soil profile was monitored by frequent electrical resistance tomography (ERT) scans. The spatial distribution of different chemicals within the soil profile was obtained by chemical analysis of disturbed soil samples taken manually along a line transects. Two methods of surfactant application were used and compared: 1) on soil surface spraying (area source), 2) via drippers application (point source). Surfactant spraying onto the water repellent soil's surface succeeded in turning the soil wettable, diminishing the preferential flow pathways, and renders the soil water and dissolved chemicals uniformly distributed. In contrast, drip applied surfactant exacerbated the incidence of preferential flow pathways and the leaching of solutes from the soil. Moreover, the overall average water content in the 0-40 cm soil layer significantly increased with surfactant spraying than with drip application even though both were higher than the control plots. These results substantiate previous laboratory-scale studies in which surfactant was applied to water repellent soils packed in a transparent flow chamber by these two methods. Additionally, the yield from the on-surface surfactant sprayed plots show a slight continuous increase compared to the untreated plots.

Soil water repellency (SWR) has a substantial effect on soil water hydrology: it hinders infiltration, leading to enhanced surface runoff and soil erosion, and causes preferential flow in the soil profile beyond that from the soil's natural heterogeneity. SWR is associated with soil organic matter content, the latter added to the soil by vegetation exudates, litter and residues, forest fires, and replacement of fresh water by treated wastewater for irrigation. Surfactants are surface-active substances composed of organic molecules with hydrophobic tails and hydrophilic heads that can reduce the surface tension (gamma) of the aqueous solution, thereby reducing SWR, via adsorption to soil particles. Surfactants are commonly used to remediate water-repellent soils. We investigated the role of two surfactant-application methods on the efficacy of SWR remediation. Aqueous solutions of two commercial surfactants had a substantial effect on parameters used to characterize the persistence and severity of SWR. However, the efficacy of these surfactants in remediating sandy soils rendered water-repellent by irrigation with treated effluent was substantially affected by their application method. Whereas application of aqueous surfactant solution to the surface of water-repellent soil, the commonly used remediation method, formed finger-like plumes similar to those obtained for water application, bulbous-like plumes were formed when the soil was premixed with the aqueous surfactant solution prior to water application. These differences were attributed to the significant role of the rate-limited surfactant adsorption to the soil particles.

Soil water repellency is a common feature of dry soils under permanent vegetation and drought conditions. Soil-water hydrology is markedly affected by soil-water repellency as it hinders infiltration, leading to enhanced surface runoff and soil erosion. Although this phenomenon was primarily ascribed to sandy soils, it has been observed in loam, clay, and peat soils in dry and humid regions. One detrimental effect of soil water repellency on plants is the reduction of soil water availability that stems from the non-uniform water retention and flow in preferential pathways (gravity-induced fingers) with relatively dry soil volume among these paths. It was recently discovered that prolonged irrigation with treated wastewater, a widely used alternative in Israel and other Mediterranean countries due to the limited freshwater, triggers soil water repellency which invariably resulted in preferential flow development in the field. Due to climate change events, the use of treated wastewater for irrigation as a means of freshwater conservation is expected to widen, including in countries that are not considered dry. While a vast amount of research has been devoted to characterizing the preferential flow in water repellent soils, the effect of this flow regime on the spatial distribution of salt and fertilizers in the root zone was barely investigated. Results from a commercial citrus orchard irrigated with treated wastewater that includes the spatial and temporal distribution of preferential flow in the soil profile measured by ERT will be demonstrated. The associated spatial distribution of salinity, nitrate, phosphate, and SAR in the soil profile will be shown as well. We investigated the efficacy of two nonionic surfactants application to remediate hydrophobic sandy soils both in the laboratory and field. The effect of the surfactant application to the water repellent soils in the orchards on the spatial distribution of soil moisture and the associated agrochemicals will be presented and discussed.