Irrigation Induced Salinity and Sodicity Hazards on Soil and Groundwater: An Overview of Its Causes, Impacts and Mitigation Strategies

Salinity and sodicity have been a major environmental hazard of the past century since more than 25% of the total land and 33% of the irrigated land globally are affected by salinity and sodicity. Adverse effects of soil salinity and sodicity include inhibited crop growth, waterlogging issues, groundwater contamination, loss in soil fertility and other associated secondary impacts on dependent ecosystems. Salinity and sodicity also have an enormous impact on food security since a substantial portion of the world’s irrigated land is affected by them. While the intrinsic nature of the soil could cause soil salinity and sodicity, in developing countries, they are also primarily caused by unsustainable irrigation practices, such as using high volumes of fertilizers, irrigating with saline/sodic water and lack of adequate drainage facilities to drain surplus irrigated water. This has also caused irreversible groundwater contamination in many regions. Although several remediation techniques have been developed, comprehensive land reclamation still remains challenging and is often time and resource inefficient. Mitigating the risk of salinity and sodicity while continuing to irrigate the land, for example, by growing salt-resistant crops such as halophytes together with regular crops or creating artificial drainage appears to be the most practical solution as farmers cannot halt irrigation. The purpose of this review is to highlight the global prevalence of salinity and sodicity in irrigated areas, highlight their spatiotemporal variability and causes, document the effects of irrigation induced salinity and sodicity on physicochemical properties of soil and groundwater, and discuss practical, innovative, and feasible practices and solutions to mitigate the salinity and sodicity hazards on soil and groundwater.

Hysteresis in soil hydraulic conductivity as driven by salinity and sodicity – a modeling framework

Declining soil-saturated hydraulic conductivity (Ks) as a result of saline and sodic irrigation water is a major cause of soil degradation. While it is understood that the mechanisms that lead to degradation can cause irreversible changes in Ks, existing models do not account for hysteresis between the degradation and rehabilitation processes. We develop the first model for the effect of saline and sodic water on Ks that explicitly includes hysteresis. As such, the idea that a soil's history of degradation and rehabilitation determines its future Ks lies at the center of this model. By means of a “weight” function, the model accounts for soil-specific differences, such as clay content. The weight function also determines the form of the hysteresis curves, which are not restricted to a single shape, as in some existing models for irreversible soil processes. The concept of the weight function is used to develop a reversibility index, which allows for the quantitative comparison of different soils and their susceptibility to irreversible degradation. We discuss the experimental setup required to find a soil's weight function and show how the weight function determines the degree to which Ks is reversible for a given soil. We demonstrate the feasibility of this procedure by presenting experimental results showcasing the presence of hysteresis in soil Ks and using these results to calculate a weight function. Past experiments and models on the decline of Ks due to salinity and sodicity focus on degradation alone, ignoring any characterization of the degree to which declines in Ks are reversible. Our model and experimental results emphasize the need to measure “reversal curves”, which are obtained from rehabilitation measurements following mild declines in Ks. The developed model has the potential to significantly improve our ability to assess the risk of soil degradation by allowing for the consideration of how the accumulation of small degradation events can cause significant land degradation.

Solute movement through undisturbed calcareous and dry region soils under differing water flow velocities

<p>The use of low-quality irrigation water in arid regions ensures the reconstruction of diverse physical and chemical dynamics in the soil profile. The objective of this study was to examine the efficacy of two water flow velocities of tap and sodic water for characterizing ion exchange of colloidal particles. Undisturbed samples were taken into the plexiglas columns with 40 cm in height and 6.9 cm in diameter from the dry area of Konya, Turkey. Two different water sources with varying qualities, tap water and poor quality sodic water (ESP≈20, obtained by preparing solution from analytically pure NaHCO<sub>3</sub>), were applied to the top of the columns as leaching water in two water flow velocities; close to saturated hydraulic conductivity (Ks) (fast, saturated condition) and unsaturated condition (slow). The number of the columns with duplicated experiments was 8. In each leaching, a quarter pore volume (350 ml) of water was regularly applied and leachates were collected from the outlet of columns. The water flux in the soil column decreased faster in the fast leaching application than in slow leaching as the sodic irrigation water was applied. This shows to destructive effect of Na+ on inner surface of water flow channels in the soil. Gradual increases for the pH of the leachates in both water quality and velocity experiments were detected. The EC of the leachates dropped very fast at the beginning of leaching in both water quality applications, and then, became steady. No effect of tap water treatment on Ca<sup>+2</sup> contents of the leachates was observed. However, sharp decreases in Ca<sup>+2 </sup>concentration were detected at the beginning of sodic water application, and then remained constant. All sodic water applications caused an increase in Na+ concentration of leachates till the end of treatments. In slow leaching applications, the increase in Na concentration in the leachates was slower compared to those of the fast leaching. While Ca<sup>+2</sup> concentrations in the leachates remained constant with tap water applications, although the soils are calcareous. Ca<sup>+2</sup> was transported remarkable high at the beginning of the sodic water application. As the leaching progressed, transport of Ca<sup>+2</sup> from the soil continued constantly due to the Na-Ca exchange processes. The effects of different leaching treatments were clearly observed from the pH-EC, Ca<sup>+2</sup> and Na<sup>+</sup>transports. Consequently, sodic water application caused significant changes in the pH values of the soils with the effect of time, and this effect was expressively marked from the changes in the salt and sodium contents of the soils.</p><p>Keywords: flux, ion exchange, leaching, saturated and unsaturated leaching, solute transport, water flow velocity</p><p>Acknowledgement: This work was supported by the Scientific and Technological Research Council of Turkey [Project number: TUBİTAK-118Y343].</p>

Hysteresis in soil hydraulic conductivity as driven by salinity and sodicity: a modeling framework

Declines in soil saturated hydraulic conductivity (Ks) as a result of saline and sodic irrigation water are a major cause of soil degradation. While it is understood that the mechanisms that lead to degradation can cause irreversible changes in Ks, existing models do not account for hysteresis between the degradation and rehabilitation processes. We develop the first model for the effect of saline and sodic water on Ks that explicitly includes hysteresis. As such, the idea that a soil's history of degradation and rehabilitation determines its future Ks lies at the center of our model. By means of a weight function, the model accounts for soil specific differences, such as clay content. The weight function also determines the form of the hysteresis curves, which are not restricted to a single shape, as in some existing models for irreversible soil processes. The concept of the weight function is used to develop a reversibility index, which allows for the quantitative comparison of different soils and their susceptibility to irreversible degradation. We discuss the experimental setup required to find a soil's weight function and show how the weight function determines the degree to which Ks is reversible, for a given soil. We demonstrate the feasibility of this procedure by presenting novel experimental results showcasing the presence of hysteresis in soil Ks, and using these results to calculate a weight function. Past experiments and models on the decline of Ks due to salinity and sodicity focus on degradation alone, ignoring any characterization of the degree to which declines in Ks are reversible. Our model and experimental results emphasize the need to measure reversal curves, obtained from rehabilitation measurements following mild declines in Ks. The developed model has the potential to significantly improve our ability to assess the risk of soil degradation, by allowing for the consideration of how the accumulation of small degradation events can cause significant land degradation.

Reclaimation of Sodic Bore Well Water for Irrigation through Gypsum Treatment at Anbil Dharmalingam Agricultural College and Research Institute, Trichirapalli District, Tamil Nadu

It is necessary to ascertain the quality of irrigation water at Anbil Dharmalingam Agricultural College and Research Institute farm in order to monitor the possible effects of the sodic irrigation water on the soil. Irrigation with sodic water enhances soil sodicity built up in soils of experimental farm which leads to adverse effects on soil physical, chemical and biological properties, not fitted for farming. In areas where ground water is sodic and where good quality surface water supplies are either inadequate or not available at all and the farmers are left with no option but to use sodic ground water for irrigation purposes, which pose grave risks for soil health and environment. The quality of sodic water can be improved by treating with gypsum. Due to gypsum dissolution calcium and sulphate ions come in soluble form in irrigation water. Research conducted at Anbil Dharmalingam Agricultural College and Research Institute Trichy for reclamation of sodic bore well water revealed that the sodic bore water samples collected from bore well 1 (AMP shed) having initial Residual Sodium Carbonate (RSC) of 8.0 meq /lit and bore well 6 (Boys hostel) having initial RSC of 6.2 meq /lit indicated the decrease in RSC upto - 0.6 meq / l and 1.2 meq / l respectively due to gypsum treatment with 0.1 per cent (12.50 tons/ha) and 0.35 per cent ( 43.75 tons /ha ) at the retention time of 1 hour to irrigate 1 ha paddy field throughout crop establishment stage. It was concluded that for lowest retention time higher doses of gypsum was required for sodic water reclamation. As we increased the retention time, the required gypsum quantity was also minimized as observed for bore well 1 (AMP shed 8 meq/l)) sodic water samples with gypsum dose of 0.15 per cent (18.75 tons /ha) with the retention time of 4 hours. These findings were very much helpful for the farmers of Manikandam block, Tiruchirappallii district having secondary sodicity built up in soils due to sodic water irrigation during summer.

METEORIZACIÓN E HIDROGEOQUÍMICA DE LOS RÍOS QUILISH Y PORCÓN EN LA CUENCA PORCÓN

METEORIZACIÓN E HIDROGEOQUÍMICA DE LOS RÍOS QUILISH Y PORCÓN EN LA CUENCA PORCÓN WHEATHERING AND HYDROGEOCHEMISTRY´S QUILISH AND PORCÓN RIVERS IN THE PORCÓN BASIN Carlos Malpica Sandoval, Hugo Rivera Mantilla, Sandra Rumay Villarreal y Víctor Vargas Rodríguez DOI: https://doi.org/10.33017/RevECIPeru2008.0004/ RESUMEN Con los resultados obtenidos, podemos señalar que la meteorización produjo reacciones de hidrólisis, oxidación, disolución de silicatos, sulfuros y azufre originando minerales secundarios, iones y coloides (arcillas, H4SiO4, SiO2, Fe2O3, FeOOH, Fe(OH)3, Al(OH)3, Ca2+, Mg2+, Al3+, Fe3+, Na+, K+,  2 4SO , Pb2+, H2AsO-4, Cu2+), parte de los productos de la meteorización entran al sistema hidrológico y otra parte permanece en el suelo debido a su baja movilidad o por intercambio catiónico o aniónico; estas reacciones están determinadas por la energía libre, Eh y pH. El análisis hidrogeoquímico se basa en la energía libre, constante de equilibrio, índice de saturación, diagramas Eh-pH, rNa/rCl y rCl/rHCO3-2, resultando agua de naturaleza cálcica-sódica, debido a la meteorización de los silicatos. Basándonos en los resultados obtenidos de los datos de energía libre determinamos que todas las reacciones están relacionadas con el índice de saturación, y basándonos en el diagrama Eh-pH, el hierro y aluminio reaccionan formando hidróxidos. Estudios petrológicos (30 muestras) y análisis hidrogeoquímico (9 muestras de agua), determinaron que los iones, coloides y moléculas originados por la meteorización de los silicatos y sulfuros que se encuentran en el río se deben a contaminación natural. Palabras claves: Energía libre, índice de saturación, diagrama Eh-pH, disolución, hidrogeoquímica. ABSTRACT With the results, we can point out that the wheathering produced reactions of hydrolyse, oxidation, silicate´s dissolution, sulphurs and sulphur reactions; originating secondary minerals (clays, H4SiO4, SiO2, Fe2O3, FeOOH, Fe(OH)3, Al(OH)3, Ca2+, Mg2+, Al3+, Fe3+, Na+, K+, SO42-, Pb2+, H2AsO-4, Cu2+), part of the weathering products going to the hydrologic system, and another part remains in the soil due to its low mobility, or for cationic or anionic interchange; these reactions are determined by the free energy, Eh and pH. The hydrochemistry analysis is based on the free energy, constant of balance, saturation index, graphs Eh-pH, rNa/rCl and rCl/rHCO3-2and, standing out to be calc-sodic water, due to the silicates weathering. Basing on the results obtained of the information of free energy, we determined that all the reactions are related to the saturation index and basing on the graph Eh-pH, the iron and aluminium react forming hydroxides. Petrologic studies (30 samples) and hydrogeochemistry analysis (9 water samples), determined that the ions, colloids and molecules that are in the river owe to natural pollution. Keywords: Free energy, saturation index, Eh-pH diagram, dissolution, hydrogechemistry.

Evaluating dispersive potential to identify the threshold electrolyte concentration in non-dispersive soils

Use of non-traditional and marginal quality saline sodic water will increase in water limited environments and methods to assess use suitability are required. The threshold electrolyte concentration (CTH) defines the soil solution concentration, for a given soil solution sodicity, at which an acceptable reduction in the soil hydraulic conductivity (10–25%) is maintained without further soil structural degradation. The traditional method of determining CTH is via leaching columns, which are laborious and often expensive. Dispersive potential (PDIS) is potentially a more rapid method with which to determine the CTH in a practical sense and make management recommendations for water quality use on a given soil. This work evaluated the PDIS method against known CTH data to determine the efficacy of use for non-dispersive soils irrigated with marginal quality saline sodic water. Results suggest that the PDIS approach to CTH did not reliably, or efficiently, determine the CTH in non-dispersive soils equilibrated with an irrigation solution. Using it to determine the aggregation and dispersion boundary for initially non-dispersive soil appeared to have merit, but only where the aggregates equilibrated with the irrigation solution were subject to rapid dilution with deionised water.