Shallow Saline Water Table Research Articles

Processes Controlling Formation of Salt Efflorescence in Coastal Salt Flats

AbstractSalt flats are bare soil surfaces with elevated salinity levels which inhibit vegetation. They are commonly found in areas of coastal wetlands where salt in surface soil accumulates due to evaporation from the shallow saline water table. The expansion of these vegetation‐free zones may severely affect the bio‐ecological function of these coastal wetland systems. In this study, sand flume experiments and numerical modeling were carried out to investigate the mechanisms underpinning the development of salt flats in the elevated areas of coastal wetlands. We found that salt precipitation occurred on the soil surface where water content is low, but the hydraulic connection to the saline groundwater table is maintained. This connection is required for evaporation to promote upward porewater flow and bring salt to the surface. However, the surface salinity level decreases with increasing surface saturation due to the density‐driven removal of salt. As a result, salt efflorescence is absent on the surface with higher water saturations, despite strong evaporation. Density‐driven flows can be triggered by the evaporation‐induced upward salinity gradient and transfer salt from the surface back to the water table. Numerical simulations confirmed this salt removal process and suggested the intensity of the density‐driven flow is mainly dictated by the soil permeability in the unsaturated zone. The findings from this study increase understanding of the processes involved in the formation and evolution of salt flats.

Impacts of a shallow saline water table on maize evapotranspiration and groundwater contribution using static water table lysimeters and the dual Kc water balance model SIMDualKc

The occurrence of shallow saline water tables in arid zones provides for groundwater-fed natural vegetation and for a substantial amount of irrigated crops’ water needs. This is the case of the Hetao plain, upper Yellow River Basin, Inner Mongolia, China, where one of the major irrigation systems of China and the World is installed. As reviewed, numerous irrigation and water management studies have been developed in Hetao and the upstream irrigated plain of Yinchuan, Ningxia. These studies have demonstrated the need for controlling salts through the autumn irrigation and the appropriate irrigation methods and scheduling. Moreover, studies evidenced the need for adopting irrigation schedules that consider groundwater contribution during the crop cycle but most of these studies were empirical, resulting difficult to transfer results. When models adopted were mechanistic, they are difficult to use for irrigation scheduling purposes comparatively with soil water balance (SWB) models. Thus, the current study used two sets of five static water table lysimeters cropped with maize and having water table depths (WTD) fixed between 0.85 and 2.25 m. It was therefore possible to observe the daily capillary rise fluxes from the water table, the dynamics of water and salts and to calibrate the SWB model SIMDualKc. Results show that the average electrical conductivity of the saturated extract of the soil ranged from 3.10 to 4.69 dS m−1 with the higher values observed when WTD was smaller, while the electrical conductivity of irrigation water ranged 1.73–1.87 dS m−1. Results also show that shallower WTD required less irrigation water but caused higher salinity impacts on crop growth and yields. Thus, the best WTD were around 1.75–2.00 m when basin irrigation was adopted in 2017 and 2018. In these crop seasons, the simulated groundwater contribution to actual crop evapotranspiration (ETc act) was up to 37% in the lysimeters having a shallow WTD (1.25 m), while in the lysimeters with deeper WTD (2.00–2.25 m) it was about 11% of the ETc act. Contrastingly, in 2019, when maize was not irrigated, the average groundwater contribution represented 73% and 49% of ETc act in the lysimeters with shallow and deep WTD, respectively. Results were obtained when a large leaching autumn irrigation (200 mm) was performed. Those experiments showed that, solutions for using basin flooding irrigation are ready but still require that irrigation scheduling is adjusted to provide for appropriate use of the saline groundwater contribution, which may be performed with the model SIMDualKc, as demonstrated by the high goodness-of-fit indicators used to evaluate the referred simulations.

Depth-Specific Soil Electrical Conductivity and NDVI Elucidate Salinity Effects on Crop Development in Reclaimed Marsh Soils

Agricultural management decision-making in salinization-prone environments requires efficient soil salinity monitoring methods. This is the case in the B-XII irrigation district in SW Spain, a heavy clay reclaimed marsh area where a shallow saline water table and intensively irrigated agriculture create a fragile balance between salt accumulation and leaching in the root zone, which might be disrupted by the introduction of new crops and increasing climate variability. We evaluated the potential of electromagnetic induction (EMI) tomography for field-scale soil salinity assessment in this hyper-conductive environment, using EMI and limited analytical soil data measured in 2017 and 2020 under a processing tomato–cotton–sugar beet crop rotation. Salinity effects on crop development were assessed by comparing Sentinel 2 NDVI imagery with inverted depth-specific electrical conductivity (EC). Average apparent electrical conductivity (ECa) for the 1-m depth signal was 20% smaller in 2020 than in 2017, although the spatial ECa pattern was similar for both years. Inverted depth-specific EC showed a strong correlation (R ≈ 0.90) with saturated paste extract EC (ECe), [Na+] and sodium absorption ratio (SAR), resulting in linear calibration equations with R2 ≈ 0.8 for both years and leave-one-out cross validation Nash–Sutcliffe Efficiency Coefficient, ranging from 0.57 to 0.74. Overall, the chemical parameter estimation improved with depth and soil wetness (2017), yielding 0.83 < R <0.98 at 0.9 m. The observed spatial EC distributions showed a steadily increasing inverse correlation with NDVI during the growing season, particularly for processing tomato and cotton, reaching R values of −0.71 and −0.85, respectively. These results confirm the potential of EMI tomography for mapping and monitoring soil salinity in the B-XII irrigation district, while it allows, in combination with NDVI imagery, a detailed spatial assessment of soil salinity impacts on crop development throughout the growing season. Contrary to the popular belief among farmers in the area, and despite non-saline topsoil conditions, spatial EC and subsoil salinity patterns were found to affect crop development negatively in the studied field.

SOIL SALINITY MONITORING UNDER DIFFERENT IRRIGATION TYPES, IN SINNURIS DISTRICT, FAYOUM GOVERNORATE, EGYPT

Soil salinity is one of the main factors limiting crop production in arid and semi-arid regions of the planet. Therefore, mapping and monitoring salinity concentrations is essential for land and water resources management and consequently for the improvement of agricultural production. The current study utilized the geostatistical Kriging method for soil data interpolation to generate soil salinity maps. In order to assess and monitor salinity changes in the study area under different irrigation types, the soil samples collected in 2018 and the soil salinity data available for 2009 were used. The results showed significant improvements in soil salinity levels, as the area of none saline soils (< 2 dS m-1) increased from 1.3 ha in 2009 to 9119 ha in 2018. These impressive results could be related to the construction of sub-surface drainage systems that started in 2007, consequently, demonstrate the effectiveness of water management policies in Sinnuris District. Moreover, soil salinity values showed a negative correlation with the elevation data, which could explain the increasing salinity levels around the Lake Qarun due to the shallow saline water table and the low efficiency of the drainage system.

A decadal multi-site study of the effects of frequency and season of harvest on biomass production from mallee eucalypts

Mallee eucalypts are hardy, woody perennials that are being developed as a short-rotation coppice crop in Australia for the production of eucalyptus oil, biofuels and other biomass products. The economic viability of this prospective crop is dependent on its ability to survive and regenerate following repeated harvesting of the above ground component. Here we report on survival and biomass yield of mallee belt plantings of Eucalyptus polybractea, E. loxophleba ssp lissophloia and E. kochii ssp plenissima, at 19 sites, under two harvest-frequencies (3–8 year cycles) and harvest seasons (autumn or spring) over a decade from 2006 to 2015. 16 sites had post-harvest mortality ranging from 1.0% to 12.2% while the remaining three sites with either shallow saline water tables or a silcrete hardpan failed. Average site dry biomass yield across treatments ranged from 2.2 to 32.8 Mg ha−1 yr−1. Higher yielding sites were generally characterised by pH between 3.8 and 8, ECe below 15.0 dS m−1 and high soil fertility. Lower yielding sites were generally near saline valley floors. After 7-years, biomass yield from unharvested treatments exceeded the average cumulative yield of harvest treatments at eight of the 16 sites, including all three E. kochii sites. For E. loxophleba, significant interactions were found between season and frequency of harvest with highest yields in long rotation spring treatments. There were also interactions between site and frequency of harvest, which were mainly driven by the variable performance of the uncut treatment. On average E. loxophleba yielded more biomass following spring harvests whereas E. kochii yielded more following autumn harvests. E. polybractea yield was unaffected by season or frequency of harvest; however, harvest treatments yielded more biomass than uncut treatments. After 10 years, at eight of the nine sites subjected to three 3-year cycles, no decline in biomass yield was observed. The site that declined in production was attributed to depletion of a sandplain aquifer by extensive mallee plantings. Overall, the results from this decadal study indicate that in warm-temperate semi-arid areas, such as the south-west of WA, mallees biomass can be harvested sustainably at most sites even in short (3-year) rotation cycles.

Prototype and model of solar driven desalination plant in arid environment

Water shortage and salinity are crucial factors affecting plant growth in arid and semi-arid regions, where irrigation water shortage and capillary rise from shallow saline water tables are often encountered. The objectives of this study are to construct a prototype of solar driven desalination plant in an arid area of Jordan Rift Valley, to develop a mathematical model predicting thermal dynamics in the prototype, to calibrate model parameters with measured physical parameters, and to discuss the performance of the prototype as well as its applicability to other areas under different environment. Results of measurement and numerical simulation show that the model is capable to reproduce the thermal dynamics of the desalination plant and to predict dew yield. Overall, the developed model provides a sound basis for describing and explaining the mass and energy balance mechanisms in the developed desalination plant. This study offers also a useful tool for analysis and assessment of the dew yield and thermal dynamics of such a desalination plant in general. Using the constructed prototype, performance analysis based on crop cultivation is ongoing.

A paddy on sodic varved sediment and plant life constraints, NE Spain

In arid lands, irrigation is necessary for agriculture to be profitable. However, the nature of soils and parent materials is significant enough to trigger permanent management limitations and the loss of important investments, as happened in some areas of the Flumen irrigation district in the Central Ebro Basin, NE Spain. We studied the distinct soil characteristics of a salt-affected agricultural plot and its recurrent problems from the last 30 years. We describe and discuss the prominent features of this soil and their effects on plant life and agricultural management. The evidence of post-irrigation salt-related effects is documented together with the water and soil salinity monitoring records. The presence of varved Holocene sediments comprising alternating clays and carbonate-rich silt with high levels of salinity and sodicity, together with a shallow saline water table, were found to be the key unfavorable conditions. Despite a noticeable decrease in sodium adsorption ratio (SAR) from 1999 to 2015 and a reduction in soil salinity down to a steady state after rice paddy cultivation, SAR and alkalinity remained high enough to hamper irrigated agriculture. Only the native plant Puccinellia festuciformis thrives in the studied plot. The article presents and discusses chemical features―analytical data―and morphological features―pictures and descriptions―that are seldom reported and interpreted together in the scientific or technical literature about irrigation of sodic soils, often limited to chem data. The paddy field studied is deemed representative of the most unfavorable soils for agriculture in the irrigated districts of the Ebro valley.

Irrigation salinity hazard assessment and risk mapping in the lower Macintyre Valley, Australia

In the Murray–Darling Basin of Australia, secondary soil salinization occurs due to excessive deep drainage and the presence of shallow saline water tables. In order to understand the cause and best management, soil and vadose zone information is necessary. This type of information has been generated in the Toobeah district but owing to the state border an inconsistent methodology was used. This has led to much confusion from stakeholders who are unable to understand the ambiguity of the results in terms of final overall risk of salinization. In this research, a digital soil mapping method that employs various ancillary data is presented. Firstly, an electromagnetic induction survey using a Geonics EM34 and EM38 was used to characterise soil and vadose zone stratigraphy. From the apparent electrical conductivity (ECa) collected, soil sampling locations were selected and with laboratory analysis carried out to determine average (2–12m) clay and EC of a saturated soil-paste extract (ECe). EM34 ECa, land surface parameters derived from a digital elevation model and measured soil data were used to establish multiple linear regression models, which allowed for mapping of various hazard factors, including clay and ECe. EM38 ECa data were calibrated to deep drainage obtained from Salt and Leaching Fraction (SaLF) modelling of soil data. Expert knowledge and indicator kriging were used to determine critical values where the salinity hazard factors were likely to contribute to a shallow saline water table (i.e., clay ≤35%; ECe>2.5dS/m, and deep drainage >100mm/year). This information was combined to produce an overall salinity risk map for the Toobeah district using indicator kriging. The risk map shows potential salinization areas and where detailed information is required and where targeted research can be conducted to monitor soil conditions and water table heights and determine best management strategies.

Measurement of soil salinity using electromagnetic induction in a paddy with a densic pan and shallow water table

Rice (Oryza sativa L.) has become a monoculture in the saline lands of the Ebro Valley, Spain. The studied farm has produced rice since the 1970s; one exception was 1999, which enabled us to map the soil salinity. The farm had lateral salinity variations mirrored by the development of rye grass (Lolium multiflorum Lam.) planted in 1999. Our objective is to prove the value of a non-deterministic method using electromagnetic induction (EMI) to map the salinity of the rootable layer in the unfavorable circumstances of a paddy having shallow saline and quasi-artesian water table underneath a continuous densic layer. From our EMI readings and soil sampling, we draw a map of the electrical conductivity of saturated paste extracts (ECe) of the upper soil layer (0–40 cm), with ECe ranging from 1.6 to 20.8 dS m−1 and a mean of 7.9 dS m−1. A main achievement was the establishment of an easy procedure not requiring either: (i) knowledge regarding the salinity of the water table or the relationships between EMI readings and the deep soil composition; or (ii) a normal distribution of the EMI readings or of the ECe; or (iii) assumptions about the physical dimensions of the EMI readings. Our procedure will allow ECe to be mapped on other similar salt-affected paddies, helping to decide if a paddy can be planted with alternate crops for production, weed control, or soil structure improvement.

Impact of climate change on waterlogging and salinity distributions in Huai Khamrian subwatershed, NE Thailand

Regional climate models project significant changes in temperature and rainfall over the Greater Mekong Subregion over the twenty-first century. The potential impacts of climate change on areas affected by waterlogging and shallow saline groundwater in Northeast Thailand was investigated using the variable density groundwater model SEAWAT supported with recharge estimates derived from the hydrologic model HELP3. The focal area is the 154 km2 Huai Kamrian subwatershed. Changes in groundwater salinity and waterlogging areas at the middle and end of this century were predicted using the calibrated model. These predictions used the dynamically downscaled PRECIS regional climate change scenarios generated by ECHAM4 GCM A2 and B2 scenarios. Recharge rates are predicted to increase as a result of the higher intensity of rainfall. Shallow watertable areas are projected to increase by approximately 23 % from existing conditions during the middle of the century and up to 25 % by the end of this century. Although the precise rate and timing of climate change impacts are uncertain, all of the scenarios clearly point towards an extension in the area of waterlogging and area affected by shallow saline groundwater areas. Given that areas affected by shallow saline watertables are predicted to expand for both climate change scenarios as well as for the base case, it is concluded that climate change will have a significant impact on the area affected by salinity and waterlogging areas for both climate change scenarios. Evaluation of management options that explore the adaptation to saline environments and to means to reduce salt affected areas are required.

Organic Substrates in Bioremediation of Acidic Saline Drainage Waters by Sulfate-Reducing Bacteria

Deep drains used to manage shallow saline water tables in the Western Australian agricultural region discharge acidic, saline drainage water with high concentrations of metals. The activity of sulfate-reducing bacteria can treat these waters by generating alkalinity in the form of bicarbonate and by generating sulfide, which removes metals from solution as sulfide precipitates. Bacterial sulfate reduction was strongly influenced by the organic carbon substrate provided for bacterial consumption. Mixtures of lupin compost, wheat chaff, oil mallee distillate wastes, straw, ethanol, and sheep manure were compared to determine which substrate was most effective in promoting the activity of sulfate-reducing bacteria and the contribution of this to bioremediation of acidic saline drainage. Mesocosm treatment systems containing reactive mixtures and acidic saline drainage were operated for a 50-day establishment period and subsequent 27-day “batch flow” period. Effluent from the treatment systems was analyzed for pH, sulfate, metals, and nutrients over the period of operation. Effluents from all reactive mixtures showed increased pH (to 5.1–5.9) and decreased sulfate and metal concentrations compared with untreated drainage water. Straw with ethanol appeared to be the most effective substrate for treatment of low pH and high metal concentrations, followed equally by both lupin compost and wheat chaff. The latter are likely to be more suitable for use in a field scale low-maintenance bioreactor or composting wetland.

Environmental factors controlling the vegetation zonation patterns and distribution of vegetation types in the Olifants Estuary, South Africa

The Olifants Estuary is one of only three permanently open estuaries on the West Coast and is ranked third in terms of conservation importance of all estuaries in South Africa. It has the largest supratidal (143 ha) and floodplain (797.1 ha) salt marshes in the country. Intertidal salt marsh covers 91.94 ha, reeds and sedges 60.05 ha and the submerged macrophyte Zostera capensis 47.72 ha. Correspondence analysis revealed intertidal, supratidal, floodplain and terrestrial plant community types within the studied estuary. The species composition of these communities was the same for the lower, middle and upper reaches of the Olifants Estuary, with the exception of the supratidal community type in the upper reaches that consisted of halophytes with a lower salinity tolerance range rather than the typical dense monospecific stands of Sarcocornia pillansii. The environmental variables that had the greatest influence on the distribution of the dominant salt marsh species, S. pillansii, included soil moisture, distance from the estuary, elevation above mean sea level, and depth to the water table. The most important ecological driver for salt marsh vegetation, especially along the arid West Coast of southern Africa, is moisture. The low rainfall and irregular occurrence of advection sea fog increases the importance of a shallow (< 1.5 m) saline (< 35 psu) water table in the floodplain as a source of moisture during dry periods.

Salt crust development in paddy fields owing to soil evaporation and drainage: Contribution of chloride and deuterium profile analysis

Summary In Northeast Thailand lowlands with shallow saline watertable, rainfed paddy fields often present high salt concentration in the dry season, forming patches or spots of salt crusts on the soil surface. In this context, the mechanisms implied in salt concentration during dry season were studied by establishing salt budget with evaporation and drainage estimates inside and outside a saline patch. Drainage was estimated by Hydrus-1D modelling constrained by an hydrodynamic characterization and the profile of water contents at the end of dry season. Evaporation rates at the end of the dry season were computed by interpreting natural detailed profiles of deuterium (D) and chloride (Cl) contents. Because of the drastic diminution of hydraulic conductivity at saturation with depth and the decrease of groundwater level at the end of the cropping season, simulated hydrological balance with Hydrus-1D pointed out zero cumulated fluxes for depths of 39.5 cm (outside the saline patch) and 37.5 cm (inside the saline patch). Therefore, all the chloride accumulated in the very upper layers during dry season comes from the chloride that was present in the 0–39.5 cm layers before the beginning of the drying. Inside the saline patch, the tentative Cl budget is coherent with the hypothesis of saturation of the profile by aquifer saline water during the flooding. Evaporation rates computed from the diffusion of chloride and deuterium at the end of the drying season, when the aquifer level was 1.4 m deep, range between 0.121 and 0.378 mm d −1 . This does not sustain the assumption of a considerable salinity contribution from the aquifer during the dry season. Moreover, evaporation estimates based on Cl and D diffusion equilibrium showed depleted rates (38–63%) inside the saline patch due to salt accumulation in the first 12 cm of the soil. In the vapour transfer layer, estimated evaporation rate based on the vapour movement of D was in the same order of magnitude than computed rate assuming liquid Cl diffusion. This coincidence is attributed to the liquid fluxes that occurred during the expansion of the vapour transfer layer during the progression of the evaporation front.

Dry drainage: A sustainable solution to waterlogging and salinity problems in irrigation areas?

Estimates of the global extent of irrigation-induced soil salinity vary, but there is widespread agreement that the twin menaces of waterlogging and salinisation represent serious threats to the sustainability of irrigated agriculture in many arid and semi-arid regions. In certain circumstances, the conventional drainage solution may be questionable due to economic and/or environmental limitations and “ dry drainage” has been postulated as an alternative. It involves the allocation of areas of fallow land, which operate as evaporative sinks drawing a stable flux of water and salt from irrigated areas. An evaluation of the merit of this approach requires answers to three key questions: (i) What is the limiting crop intensity? (ii) What is the limiting watertable depth? (iii) What is the long-term impact of salt accumulation in the drainage sink area? A simulation model was developed to investigate these questions for a dry-drainage system with a wheat–cotton cropping pattern using published data for the Lower Indus Basin in Pakistan, where shallow saline watertables, intensive irrigation, high evaporative demand and natural dry drainage exist. The simulation results showed that dry drainage could satisfy the necessary water and salt balance when the cropped area and sink area were approximately equal and watertable depth was around 1.5 m. The long-term impact of salt accumulation on the performance of the system was also considered.

Effect of watertable depth on evaporation and salt accumulation from saline groundwater

When the evaporative demand is greater than the ability of the soil to conduct water in the liquid phase, the soil profile above a watertable exhibits a liquid−vapour discontinuity, known as the evaporation front, that affects the depth of salinisation and the rate of evaporation. We conducted experiments on a sandy loam with shallow saline watertables under high isothermal evaporative demand (24 mm/day), monitoring rates of evaporation from the soil and upward movement of groundwater, and observing profiles of soil water and salinity over periods of up to 78 days. Three zones were distinguished in the soil profile: a zone of liquid flow above the watertable, a zone of vapour flow close to the surface, and an intermediate transition zone in which mixed liquid−vapour flow occurred. The vapour-flow zone above the evaporation front appeared after a few days and progressed downward to depths of 40, 60, and 120 mm, while eventual steady-state rates of evaporation were 1.3, 1.1, and 0.3 mm/day for watertable depths of 300, 450, and 700 mm, respectively. Salts mainly accumulated in the transition zone, suggesting that the depth of the evaporation front should be a criterion to locate and prevent salinisation as a result of capillary flow from a watertable in arid regions.

Airborne geophysics for natural resource management, Angas Bremer Plains, SA

Airborne electromagnetics (AEM), magnetics and radiometrics flown over the Angas-Bremer alluvial plain southeast of Adelaide, SA, provide information for natural resource management in an area of intense viticulture with a shallow saline water table, and a deeper fresh-water Tertiary aquifer at risk of salinisation. A specific aim of the surveys was to delineate shallow palaeochannels that could be pumped to lower shallow saline water tables. These are not apparent in the data, either due to absence, or inability to image such features due to lack of contrast in physical properties. The surveys give a new view of the landscape, geology and regolith framework of the area. There is no evidence for a fault (postulated from resistivity soundings 30 years ago) that has been modelled as a recharge conduit to the deep aquifer. However, several previously unrecognized faults have been interpreted from the data and drill information. These offset the Cenozoic aquifers by up to 80 m. AEM and drill data have helped to determine a new set of structure contours for the base of the aquifer system which will assist more robust groundwater modelling. AEM response in the aquifers correlates loosely with measured water salinity, but the relationship is not tight enough to allow imaging of high quality groundwater from the AEM. The DEMs constructed from the surveys give better accuracy to landscape modelling in the area, and the radiometrics have the potential to form the basis for upgraded soil maps. Ten broad land management units across the area have been defined by reference to geophysical properties and drill hole information.

If long fallow cropping is leaky then shallow groundwaters on the Liverpool Plains should be of recent origin

Previous groundwater studies have indicated that up to 195 000 ha of the Liverpool Plains catchment, south of Gunnedah, New South Wales, Australia, are at risk from shallow saline watertables. Replacement of hydraulically stable, native perennial grasslands with more ‘leaky’ annual cropping systems since the 1950s, particularly long fallow wheat–sorghum rotations, has been held responsible for an apparent increased frequency of shallow watertables and saline discharge. If so, then it follows that shallow groundwater in the alluvium will be recent (less than about 30 years old) and the solution to the problem is a straightforward reduction in deep drainage under farming systems via increased evapotranspiration. However, in this study, we have found levels of bomb pulse tritium in shallow groundwaters that indicate that about half of the shallow groundwaters in the Mooki subcatchment pre-date current agricultural practices. A hypothesis for this unexpected outcome suggests that the problem is complex and that solutions need to be site-specific.

Growth and Chemical Composition of Pistachio Affected by Salinities and Depths of Water Table

Pistachio may be grown around the central desert of I.R. Iran with adverse conditions such as shallow saline water tables, which limit its growth and production. The effects of saline (13 dS m−1) and non-saline (0.5 dS m−1) shallow water table depths of 30, 60, 90, and 120 cm under irrigated and not irrigated conditions on growth and chemical composition of a local pistachio cultivar (Badami–Zarandi) were studied in a greenhouse experiment. The results indicated that appropriate growth of pistachio may occur at water table depth of 60 cm under irrigated condition. Only at this depth, the difference in plant growth between irrigated and not irrigated conditions were significant, and low plant growth was obtained at not irrigated condition. At saline water table (13 dS m−1) and not irrigated condition water table depth should be kept below 60 cm for normal pistachio production.

Modelling capillary rise and soil salinity for shallow saline water table under irrigated and non-irrigated conditions

Salinization of soil is a major problem in arid and semi-arid regions with saline shallow water table. This is influenced by climate, soil type, crop, irrigation water quality and management practice, depth to water table, and salinity of the water table. Modelling can be used for estimating capillary rise and salinity of soil profile with saline shallow water table. The objective of this study was to modify a transient state analytical model (TSAM) for estimating capillary rise and salinity of soil profile with different saline water table depths and salinities under irrigated and non-irrigated conditions in a micro-lysimeter. In the modified TSAM variable root depth, non-uniform water uptake pattern and a more complete water balance equation were included. Modified TSAM resulted in good agreement between measured and estimated cumulative and weekly capillary rise for wheat experiment. Furthermore, this modified model predicted the capillary rise and salinity of different soil layers for various water table depths (0.3–1.20 m) and salinity levels (0.5–13.0 dS m −1) under irrigated and non-irrigated conditions accurately. However, the prediction accuracy of capillary rise for a highly saline water table (13.0 dS m −1) and shallow water table depth (smaller than 0.6 m) was rather poor. This might has been occurred due to the effects of high soil salinity in the root zone on the roots water uptake reduction. Furthermore, the modified TSAM responded accurately to both irrigated and non-irrigated conditions. When the application of the numerical models to larger irrigation areas with varying soil types, depth to water table and agronomic practice may not be feasible, the modified TSAM may be suitable for estimating short-term mean rate of capillary rise, net long-term capillary rise and season soil salinities in different soil layers.

Simultaneous use of newly adopted simple sensors for continuous measurements of soil moisture and salinity

Methods available to measure salinity and moisture content in arid and semi-arid regions are limited because of the high salinities and very wide range of water contents (i.e. from saturation near the water table to air dry in the evaporation front). This paper is focused on the instrumentation employed in monitoring salt and moisture profiles in a column study which has wide applicability in salinity research. Experiments were conducted in a specially designed evaporation chamber which provided high evaporative demand as experienced in arid and semi-arid regions. Intensively instrumented soil columns with a constant shallow saline water table were used. Moisture content was measured by thermal conductivity and salinity by 4-electrode probe. In each case, instruments were manufactured specifically for the purpose in order to provide the desired degree of spatial resolution. Two soil types, sandy loam and clay loam, were used. Results indicated that thermal-conductivity probes measured water content over a wide range from saturation to 0.16 m3/m3 for clay loam and to 0.09 m3/m3 for sandy loam soil with great sensitivity (R2 &gt; 0.95) and were unaffected by salt accumulation. The 4-electrode probes provided reliable measurements (R2 &gt; 0.95) of the salinity of the soil solution for the range relevant to agricultural application. However, the accuracy of the probe decreased with the decreases in the water content after permanent wilting point.